Category Archives: weight loss

Fatness Is Strongly Influenced By Genetics, But How?

An image from twin studies featured in the talk by Jeffrey Friedman posted after the jump, or click on the image for the YouTube link

A reader e-mailed me a good question about weight loss that’s outside my area of academic expertise but within the realm of stuff I’ve read enough about that I can offer some speculations and references. I am continually amazed at how complicated nutrition is and how much disagreement there is even among people who study it for a living. The only thing I can say with complete confidence is that anyone who tells you weight loss is simple and anyone can do it is (A) lying, (B) misinformed, (C) trying to sell you something, or (D) all of the above.

Here’s the e-mail I got:

If you have the time to answer a question…

I recently came across these articles claiming, more or less, that metabolism does not account for why some people are fatter or thinner than others. 

Article 1 [BBC Health]

Article 2 [Mayo Clinic]

I remember your posts on Sour Salty Bitter Sweet about dieting not being an effective solution to weight loss [here], and it sounded like you thought someone’s weight had more to do with genetic factors than lifestyle factors. Do I have that right? Would you disagree with the articles? Or point to non-metabolic genetic factors?

-Anna Macdonald

simple! right? that's why everyone is precisely the weight they want to be! Image Credit: CDC.govBoth articles essentially argue that it’s a myth that fatter people have “slow metabolisms” and burn fewer calories than thinner people. Basal metabolic rates vary based on age, gender, and body composition (or maybe just body composition, but that tends to vary based on age and gender), but as far as researchers can tell, fat people have at least roughly the same metabolic rate as thin people. They just eat more.

I think they neglect or dismiss a few complications too easily—in both diet studies and over-feeding studies, subjects lose/gain less weight than they should based on caloric arithmetic, usually by a significant margin. That’s usually attributed to shifts in thermogenesis, or how much heat you generate, and unconscious motions like fidgeting. If you eat more than you’re used to, your body may respond by getting slightly warmer and engaging in more restless activity. Eat less, and your body may respond by getting cooler and engaging in less activity. There’s some evidence that even for the very rare individuals who lose weight and keep it off long-term, basal metabolic rate remains depressed compared to people with the same relevant characteristics (weight, age, gender, and body composition) who were not previously fat (see NYTimes “The Fat Trap”). Incidentally, there’s research from as early as 1980 suggesting that people who maintain weight loss long-term are frequently monomaniacal about food and exercise, engaging in behaviors that might be seen as evidence of an eating disorder in thinner people.

But in general, the articles seem pretty accurate up to the point where they claim that people can lose weight if they eat fewer calories and exercise. The BBC article even claims that “people not only manage to lose weight but are able to keep control of it in the long term,” which is technically true—a small percentage of the people who lose weight by dieting do—but certainly isn’t the norm. Both articles make an unsubstantiated leap from the idea that basal metabolic rate is at least relatively stable and consistent to the idea that therefore, anyone can be thin if they only eat as many calories as a thin person burns. The key question they fail to address is why fat people eat more calories than thin people in the first place.

I suspect that’s because most people think they know the answer: they assume fat people have less willpower, knowledge, or motivation than thin people and therefore make bad choices about what and how much they eat. There’s a widespread assumption that if fat people knew better or tried harder, they could be thin. Many people, whatever their weight, believe that they themselves would be probably thinner if they ate better and exercised more and would be fatter if they ate whatever they wanted all the time and exercised less (which is actually probably true, but only within a small range). A lot of people even have personal experiences with weight loss or gain that they may be able to attribute to conscious choices or lifestyle changes. However, for most people, those changes prove to be temporary and I think they overestimate how much control they actually have.

Fat people are not fat because they’re weak or lazy or unmotivated or unaware of the supposedly-dire medical consequences and actually-dire social consequences of being fat. Body size is strongly genetically determined and biologically-regulated. It may be sensitive to some environmental conditions, but that doesn’t mean it’s within individuals’ conscious control. If the tendency towards weight homeostasis doesn’t work by regulating how many calories people tend to burn, which I agree that it probably doesn’t, it must work by influencing how much people eat.

How Heritable Is Fatness? 

Also from the Friedman lecture below.Very. Perhaps less than eye color, but more than other conditions widely seen as having a significant genetic component, like schizophrenia or alcoholism. Based on twin studies, one of the classic ways of evaluating the genetic component of all kinds of conditions, weight consistently appears to be approximately as heritable as height—most studies conclude that just under 80% of variation in weight and height is attributable to genetics. Furthermore, genetic influence consistently trumps environmental effects by a wide margin. In adoption studies, another way of evaluating genetic influence, children’s weights are strongly correlated with their biological parents’ and not at all with their adoptive parents. 

In Stunkard et al 1986, which compared approximately 4000 sets of male twins, the “concordance rates for different degrees of overweight were twice as high for monozygotic twins as for dizygotic twins.” In other words, the “identical” twins who share nearly 100% of their genetic material were twice as likely to have similar body types than “fraternal” twins who share only 50% of the same genes. At age 20, comparisons of height, weight, and BMI for both sets of twins yielded heritability estimates of .80, .78, and .77, respectively (1.0 would be perfectly heritable, .00 would be not heritable at all). At a 25-year follow-up, the heritability estimates for the same traits were .80, .81, and .84.

In another Stunkard et al 1986, which divided a sample of 540 adult Danish adoptees into four weight classes: thin, median, overweight and obese, there were strong correlations between the weight class of the adoptees and their biological parents (p<.0001 for mothers, p<.02 for fathers). There was no correlation between the weight class of the adoptees and their adoptive parents.

In Stunkard et al 1990, the researchers used a Swedish database of twins separated early in life versus those reared together collected between 1886 and 1958. They ended up with 93 pairs of identical twins reared apart, 154 pairs of identical twins reared together, 218 pairs of fraternal twins reared apart, and 208 pairs of fraternal twins reared together. The mean age of comparison was 58.6 years old. The heritability estimates (shown in the chart below) are similar to those in the 1986 study. Notably, twins reared together were no more similar than twins reared apart.

"The fourth estimate of heritability, the intrapair correlation for the monozygotic twins reared apart, was the most direct and perhaps the best estimate of the heritability of the body-mass index. It was 0.70 for men and 0.66 for women."

A review study done in 1997 by Maes et al looked at the data from 25,000 twin pairs and 50,000 biological and adoptive family members, finding BMI correlations of .74 for monozygotic twins, .32 for dizygotic twins, .25 for siblings, .19 for parent-offspring pairs, .06 for adoptive relatives, and .12 for spouses.

Researchers have also been curious to see if the “obesity epidemic” has changed anything. Have environmental changes in the last few decades trumped genetic factors? Not really. In Wardle et al 2008, they evaluated 5092 sets of twins between the ages of 8 and 11 whose body measurements were taken in 2005. The heritability estimate for BMI was .77. In comparison, the shared-environment effect in the same study was estimated at .10.

As a 2008 review study of research on the heritability of fatness by Stephen O’Rahilly and I. Sadaf Farooqi concluded:

Hereditary influences on adiposity [fatness] are profound and continuing…. There is little serious doubt that the single most powerful determinant of inter-individual differences in adiposity is heredity.

Okay, But How Does It Work? Part I: Epigenetics

Genetics isn’t the whole story. We have known for a long time that children without access to adequate nutrition may have their growth "stunted," meaning they may never achieve the same height or weight as adults as they would have if they had been able to eat more as children. Dietary composition also seems to have an effect: populations with access to more protein (or calcium?) may grow taller or fatter than genetically-similar populations who consume less protein. The availability of highly-palatable, calorie dense, high-sugar and high-fat food in countries like the U.S. may create the conditions for some people (though clearly not all) to become fatter than they would in another environment. However, how fat they get in that environment  is still determined largely by genetics, just like how tall people get in the presence of ample protein is still largely determined by genetics.

There’s a lot of research being done right now on what are sometimes called "epigenetic" effects, which are factors that influence whether or not (and how) genes get expressed, without any changes happening in the genome itself. This is the idea that genes can get turned “on” or “off.”  Some epigenetic effects are trans-generational, meaning something that affects a particular individual or population may only show up in their offspring. So, for example, population that experienced a famine may have offspring who are more inclined to store fat when it’s available than a genetically similar population that didn’t live through a famine.

See: This Nature article or Herrera et al 2011

Okay, But How Does It Work? Part II: Leptin

Leptin-deficient child before and after leptin therapyThe expression of genes that affect body size probably involves changes in the endocrine system, and particularly the release or suppression of the hormones leptin and gherlin, which control appetite and satiety. Leptin in particular seems to be crucial to the regulation of body fat. It was only discovered in the mid-1990s, so scientists are still trying to understand how it works and what the implications are.

Some extremely fat children, like the kid pictured on the right, have been found to be deficient in leptin. They have seemingly insatiable appetites—when presented with meals in excess of 2,000 calories, they’ll eat the whole thing and still be hungry. After receiving leptin injections, they eat age-appropriate portion sizes and lose weight rapidly without dieting or engaging in any formal exercise program.

One of the major differences between people who’ve lost weight through dieting and people who weigh the same without having dieted is in their leptin levels. Most of what I know about leptin (and most of images in this post) are taken by the following talk by the biologist who discovered the hormone, Dr. Jeffrey Friedman:

In the very beginning of the talk, he makes some causal claims about high BMI/adiposity and mortality that I disagree with, because I’m not sure the correlations are actually caused by fatness, rather than social stigma, racism, poverty, lack of health insurance, etc. (all of which are also correlated with BMI). If fatness caused mortality, why would “overweight” people live longer on average than “normal” weight and “underweight” people and “obese” people who are active live longer than “normal” people who are sedentary? He also says that even modest weight loss is associated with significant health improvements, and I wonder if that claim isn’t based on studies where participants begin eating more vegetables and exercising, lose something like 5 pounds, and get healthier overall and researchers conclude that weight loss improves health when really the weight loss is totally meaningless. But once you get past that bit, he makes a pretty strong case for the genetic basis of body size and the role of leptin in the regulation of body fat.

Okay, But How Does it Work? Part III: Endocrine Disruptors

Just to complicate things even further, it turns out that a lot of the chemicals we’re exposed to can affect the endocrine system. Bisphenol A, the now-vilified chemical used primarily in plastics and also in the lining of aluminum cans, turns out to be an endocrine disruptor. Fluoride is also an endocrine disruptor. So are brominated fire retardants and many pesticides (even organic-certified ones, like copper sulfate).

Some of these may only affect people if they’re exposed at a particular point in their development—in utero, pre-adolescence, etc.—or at a particular dosage. So if your mom ate a lot of highly-acidic canned foods while she was pregnant with you, that might affect your thyroid function from birth. Or if you spent a lot of time on a rug treated with flame retardant chemicals as an infant, that might affect you, but maybe if you’d been 5 or 6 years old, it wouldn’t. Those are just hypothetical scenarios, the actual effects and doses of endocrine disruptors are not yet well understood or documented. So I’m not saying you should stop getting fluoride treatments. I suspect (and hope) that in another decade or so, we’ll have a better sense of how chemical exposure affects weight gain.

For more on endocrine disruptors and obesity, see Julie Guthman, Weighing In especially Chapter 5.

When Metabolism Matters: The Evidence From Overfeeding

If body weight is genetic, it should probably be nearly as difficult to gain weight as it is to lose it. Although it does seem to be possible to gain weight deliberately—some athletes and actors do this—it takes a lot of work. The results of overfeeding studies suggest that people who deliberately eat more than they would normally have to suppress their desire to stop eating and lose any weight they gain very easily as soon as they stop “overeating.”

BBC made an hour-long documentary about one of these studies, called “Why Are Thin People Not Fat,” which I first saw posted on Tom Naughton’s blog FatHead:

If you don’t want to watch it (spoiler if you do): ten thin people were told to eat twice as much as they normally do (the target caloric intake for men was approximately 5000 kcal/day) and refrain from exercise for four weeks. There was a lot of variation in the results—some gained more weight than others, some gained more fat than others. One of the participants gained muscle. None of them gain as much weight as they “should” based on caloric arithmetic, meaning there must have been changes in their metabolism. Additionally, the subjects report feeling pretty miserable: the amount of food they have to eat makes them feel sick. At least one of them mentions throwing up some of what he ate. They all get tired of milkshakes and chocolate and pork pies. And month after the experiment was over, the participants had all lost most or all of the weight they gained during the experiment without engaging in any deliberate weight-loss strategies.

The documentary mentions another overfeeding study known as the Vermont Prison Experiment. Researchers at the University of Vermont led by Ethan Sims initially tried to use students as subjects. They were told to eat 2-3x their normal caloric intake, but even after 5 months, most had increased their weight by only 10-12%. Sims’ goal was 25%, so he turned to inmates at the Vermont State Prison, who he describes as “equally dedicated volunteers.” After 200 days of eating up to 9-10,000 kcal/day, some of the participants were still not able to gain 25% of their starting weight. For the few who were able to gain 25% or more, in order to maintain the goal weight for any length of time, they had to continue eating on average ten times the number of calories that should have been necessary based on simple caloric arithmetic. This is also explained by metabolic changes—whether through thermogenesis or unconscious activity, the men were burning vastly more calories than before despite being prevented from exercising. Again, after the study was over, the prisoners easily lost most or all of the weight they had gained.

In Conclusion

The genetic influence on weight seems to work primarily by affecting how much people eat, not how many calories they burn. Fat people burn more calories than thin people, but they also eat more than thin people. That doesn’t mean that fat people “overeat.” Most people, fat or thin, maintain a relatively stable weight over long periods of time. If fat people were eating more calories than they typically burn, presumably they would be constantly gaining weight. Appetite and satiety are governed by biology, not willpower. Most people seem to be capable of consciously and deliberately reducing or increasing their caloric intake temporarily, but that’s difficult and unpleasant and virtually impossible to maintain long-term.

Why Posting Calorie Counts Will Fail, Part III: Calorie-restriction dieting doesn’t work long-term for most people

Previously in this series: Intro, Part I, and Part II.

The article on "Making Weight Loss Stick" is by Bob Greene, the personal trainer and "fitness guru" Oprah first started consulting with in 1996. Sadly, I don't think that's *meant* to be ironic. Oprah 2005/2009

To test whether turning [fat people] into thin people actually improves their health, or is instead the equivalent of giving bald men hair implants, it would be necessary to take a statistically significant group of fat people, make them thin, and then keep them thin for long enough to see whether or not their overall health then mirrored that of people who were physiologically inclined to be thin. No one has ever successfully conducted such a study, for a very simple reason: No one knows how to turn fat people into thin people.
Paul Campos, The Obesity Myth (2004)

Diets do cause weight loss…in the short term

People who think calorie restriction dieting “works” haven’t necessarily been duped by the diet industry or seduced by the prevailing nutritional “common sense” that weight loss and gain are a simple matter of calories in vs. calories out. Many of them believe it because their personal experience seems to confirm it, often repeatedly. Of course, “repeatedly” is part of the problem. Weight cycling—losing and re-gaining 5% or more of one’s total body weight—isn’t what dieters or public health policy makers are shooting for. Even people dieting with a specific occasion in mind, like a wedding or a high school reunion, would generally prefer to achieve permanent weight-loss.

But almost a century of research has shown that dieting—which usually involves calorie restriction—is not the way to do that. Studies repeatedly find that while eating less causes weight-loss in the short term, a majority of participants in weight-loss interventions focused on diet gain most of the weight back within 1 year and the vast majority (90-95%) gain all of it back within 3-5 years. Approximately 30% gain back more than they initially lost, and there’s some evidence that people who’ve lost and regained weight have more health problems than people who weigh the same, but have never lost and regained a significant amount of weight.

This is not controversial. Virtually every study of weight-loss dieting that has followed participants for longer than 6 months has found that the majority of dieters regain all the weight they lose initially, if not more. In other words, Oprah’s high-profile weight fluctuations are not the unfortunate exception to most dieters’ experience, they are the rule. A gallery of pictures of Oprah through the years illustrates the most frequent and reliable outcome of dieting:

Oprah in The Color Purple Screen shot of the infamous "fat wagon" episode first aired in the fall of 1988, when Oprah strode on set in what she proudly declared were size 10 Calvin Klein jeans after an Optifast diet, wheeling a Red Flyer wagon full of lard representing how much weight she'd lost  At the Emmy Awards, holding her third for "Outstanding Talk/Service Show Host"  Holding yet another Emmy at the end of that impressively-muscled arm, shaped with the help of trainer Bob Greene

             1985                           1988                             1992                             1996

 At the party celebrating the first anniversary of O Magazine  At the Academy Awards, wearing Vera Wang Presenting at the Emmy Awards presenting at the 2010 Oscars, possibly on the way back down again?

              2001                            2005                          2008                            2010        

I am not concerned (in this entry) with why calorie restriction diets fail—there are competing theories and perhaps I’ll try to tackle them some other time. However, when it comes to evaluating public health policies aimed at the general population, like posting calorie counts on menus, it doesn’t really matter why the kind of behavior it’s designed to encourage fails, especially when it fails so spectacularly. Whether the problem is that 90-95% of people don’t have the willpower to stick to calorie-restricted diets or that most peoples’ metabolic rates eventually adjust or both or something else entirely, continuing to prescribe calorie restriction to individuals seeking to lose weight is futile at best. Given the health problems associated with weight cycling and psychological distress caused by diet “failure,” it’s probably also dangerous and cruel. More on that another day, too.

The goal of this entry is to provide a condensed-but-comprehensive overview of the evidence that convinced me that weight-loss dieting—and particularly calorie-restriction dieting or eating less—does not “work” for most people. By “work” I mean lead to significant weight loss—at least 10% of starting body weight—that lasts for more than 3 years (in keeping with the clinical definition of “weight loss success” proposed by the 1998 National Heart, Lung, and Blood Institute [NHLBI] Obesity Education Initiative Expert Panel proposed). I honestly tried to keep this as short as possible and bolded the “highlights” if you want to skim. However, if brevity is what you’re looking for, see this 2007 Slate article.

A Meta-Review of the Literature

Of course, I’m not the first person to try to figure out what kind of picture decades of weight-loss research was painting. I found 14 reviews of weight-loss research in peer-reviewed journals (Mann et al 2007, Jeffrey et al 2000, Perri & Fuller 1995, Garner & Wooley 1991, Jeffrey 1987, Bennett 1986, Brownell & Wadden 1986, Brownell 1982, Foreyt et al 1981, Wilson & Brownell 1980, Stunkard & Penick 1979, Wooley et al 1979, Foreyt 1977, Stunkard & Mahoney 1976). And they all say basically the same thing: calorie-restriction diets don’t work long-term. Here’s how three of the most recent ones came to that conclusion, and one meta-analysis that claims to challenge the consensus, although it turns out that all they’ve really done is redefine “success.” 

Diets Don’t Work—Mann et al 2007 (free full text): This review of 31 weight-loss studies by a team of UCLA researchers was aimed at developing recommendations for Medicare regarding obesity prevention and treatment. They were only able to find 7 studies of weight-loss dieting that randomly assigned participants to diet or control groups and followed them for at least two years (the “gold standard” required to make causal claims about the effects of dieting). And the “gold standard” studies did not support the claim that dieting promotes significant or long-term weight loss:

Across these studies, there is not strong evidence for the efficacy of diets in leading to long-term weight loss. In two of the studies, there was not a significant difference between the amount of weight loss maintained by participants assigned to the diet conditions and those assigned to the control conditions. In the three studies that did find significant differences, the differences were quite small. The amount of weight loss maintained in the diet conditions of these studies averaged 1.1 kg (2.4 lb), ranging from a 4.7-kg (10.4-lb) loss to a 1.6-kg (3.5-lb) gain. (223)

They also examined 14 studies with long-term follow-ups that didn’t involve control groups. The average initial weight loss in those studies was 14 kg (30.8 lb), but in the long-term follow-ups, participants typically gained back all but 3 kg (6.6 lb). Of the eight studies that tracked how many participants weighed more at the follow-up than before they went on the diet, the average was 41% with a range of 29%-64%, and in every case was higher than the percentage of participants who maintained weight loss. In other words, participants were more likely to regain more weight than they initially lost than they were to maintain their initial weight loss. Although Mann et al note several problems with these studies, like low participation rates in the long-term follow-ups, heavy reliance on self-reporting as the primary or only measure of weight, and failure to control for the likelihood that some of participants were already dieting again at the follow-up, those factors should have biased the results in the direction of showing greater weight-loss and better long-term maintenance, not less.

Finally, they looked at 10 long-term studies that didn’t assign participants to “diet” or “non diet” conditions randomly. In general, these were observational studies that assessed dieting behavior and weight at a baseline time and then followed up with participants to measure changes in behavior and weight over time. Of those studies, only 1 found that that dieting at the baseline led to weight loss over time, 2 showed no relationship between dieting at the baseline and weight gain, and 7 showed that dieting at the baseline led to weight gain.

Their recommendation to Medicare:

In the studies reviewed here, dieters were not able to maintain their weight losses in the long term, and there was not consistent evidence that the diets resulted in significant improvements in their health. In the few cases in which health benefits were shown, it could not be demonstrated that they resulted from dieting, rather than exercise, medication use, or other lifestyle changes. It appears that dieters who manage to sustain a weight loss are the rare exception, rather than the rule. Dieters who gain back more weight than they lost may very well be the norm, rather than an unlucky minority. If Medicare is to fund an obesity treatment, it must lead to sustained improvements in weight and health for the majority of individuals. It seems clear to us that dieting does not. (230)

Long-term Maintenance of Weight Loss: Current Status—Jeffrey et al 2000 (free abstract or full text with umich login): A review of 20 years of long-term weight loss studies that describes the weight loss and regain among patients who participate in behavioral treatments for obesity as “remarkably consistent” (7) which is visually represented by lots of graphs of different studies on the long-term results of weight loss studies that all pretty much look the same:

Very low calorie diets vs. Low calorie diets (Wadden et al 1993)  Fat restriction vs. calorie restriction (Jeffrey et al 1995)

Diet only vs. Diet + exercise (Sikand et al 1988) People who were paid $25/wk for successful weight loss vs. people who weren't paid (Jeffrey et al 1993)

Basically no matter what researchers do, most dieters achieve their maximum weight loss at 6 months and then gradually regain all or almost all of the initial weight lost within 3-5 years, if not faster. They conclude:

The experience of people trying to control their weight is a continuing source of fascination and frustration for behavioral researchers. Overweight people readily initiate weight control efforts and, with professional assistance, are quite
able to persist, and lose weight, for several months. They also experience positive outcomes in medical, psychological, and social domains (NHLBI Obesity Education Initiative Expert Panel, 1998). Nevertheless, they almost always fail to maintain the behavior changes that brought them these positive results. Moreover, as we hope we have shown, efforts to date to change this weight loss-regain scenario have not been very successful.

Confronting the Failure of Behavioral and Dietary Treatments for Obesity—Garner and Wooley 1991 (free abstract or full text with umich login): Like Mann et al, Garner and Wooley were seeking to translate the available evidence about weight-loss dieting into recommendations for treatment—in this case, best practices for mental health practitioners seeking to counsel and treat overweight and obese patients. They note that short-term behavioral studies consistently show that modifications in eating and exercise behaviors lead to weight-loss, but that as the duration of studies increases, “over and over again the initial encouraging findings are eroded with time” (734).

The authors are particularly perturbed that poor results are often presented by study authors as positive. For example, an 1981 study comparing standard behavioral therapy with a weight-loss drug, or the therapy and drug combined found that all of the treatment groups lost a significant amount of weight in the first 6 months, and then all of the treatment groups showed significant re-gain by the end of the 18 month follow-up.the consistency in the curves is really eerie after a while...the 6 month nadir, the gradual incline; also, it is completely baffling to me how someone could look at this graph and think the most notable part is the gap between the three treatments at 18 months

Instead of concluding that all of the treatments had failed to produce lasting weight loss, the authors conclude that these results provide hope for behavioral therapy, because that group showed the slowest rate of weight re-gain:

This most recent study provides grounds for optimism as to the future of behavioral treatment of obesity . over the long run, behavior therapy clearly outperformed the most potent alternative treatment with which it has yet been compared. (734 in Garner and Wooley, 135 in the original)

This pattern is nearly as consistent as the finding that weight is gradually regained and many individuals eventually weigh more than they did at the start of the treatment. After four years, nearly all participants in nearly all studies gain back nearly all the weight they initially lost: Adams, Grady, Lund, Mukaida, & Wolk, 1983; Dubbert & Wilson,1984; Kirschenbaum, Stalonas, Zastowny, & Tomarken, 1985; Murphy, Bruce, & Williamson, 1985; Rosenthal, Allen, & Winter, 1980, Bjorvell & Rossner, 1985; Graham, Taylor, Hovell, & Siegel, 1983; Jordan, Canavan, & Steer, 1985; Kramer, Jeffery, Forster, & Snell, 1989; Murphy et al. 1985; Stalonas, Perri, & Kerzner, 1984; Stunkard & Penick, 1979. And yet, the authors of those studies insist that the diet interventions are “effective,” sometimes claiming that if the subjects had not dieted they would weigh even more. They almost never admit that the treatments completely failed to do what they set out to do, which is produce a clinically significant weight loss that can be maintained long-term. When they do admit that the results are “disappointing,” they frequently call for more “aggressive” treatments like very low calorie diets (VLCD or <800 kcal/day) or supervised fasting (which is no longer approved because of the risk of mortality).

Garner and Wooley also evaluate studies that used VLCD, some of which involved Optifast, the protein shake that Oprah used to achieve her 67 lb weight loss in 1988. Just like with other calorie-restriction diets, people on VLCD generally lose weight initially, although drop-out rates are much higher than in other weight loss studies (50% or more). Participants who stick to the diet typically maintain the weight loss for about a year, but regain most if not all of the weight they lost within three years and many gain more than they initially lost (Swanson and Dinello, 1970, Sohar and Sneh, 1973, Stunkard and Penick, 1979, Johnson and Drenick 1977, Drenick SC Johnson, 1980, Wadden et al., 1983, Wadden, Stunkard, & Liebschutz 1988, Hovel et al., 1988). Based on all of those studies, they conclude:

Although the rate and magnitude of weight loss have been the basis for recommending the VLCD, its most remarkable feature is the speed of weight regain following treatment. (740)

Garner and Wooley found only two studies of weight-loss dieting that reported better long-term results, and both had extremely low rates of participation in the follow-up and relied on self-reported weights. For example, Grinker et al (1985) reported that 55% of the participants in a residential treatment program had maintained a 5-kg weight loss based on the responses of only 38% of the original participants. They suggest that it seems far more likely that the low participation in the follow-up biased the results than that those studies are right and all the other ones or wrong and conclude:

It is only the rate of weight regain, not the fact of weight regain, that appears open to debate. While this may be discouraging to the individual intent on weight loss, it should also provide some solace to the many individuals who have failed at dieting and have attributed the failure to a personal lack of will power. (740)

It is difficult to find any scientific justification for the continued use of dietary treatments of obesity. Regardless of the specific techniques used, most participants regain the weight lost. (767)

They make the following recommendation to mental health practitioners:

We suggest that at the least, if weight loss is offered, it should be done with full disclosure of the lack of long-term efficacy and of the possible health risks [which, as they explain, include physical and psychological risks correlated with weight fluctuation]. It is further recommended that alternative nondieting approaches aimed at improving the physical and psychological well-being of the obese individual be given priority over dietary treatments as a subject of research and that such treatments be offered on an experimental basis. (767)

Long-term weight-loss maintenance: a meta-analysis of US studies—Anderson et al 2001 (free full text): As the title suggests, this is a meta-analysis rather than a review article, meaning rather than summarizing and evaluating what other studies found, they lumped together the data from 29 different studies. 13 of the studies involved “very low energy diets” (VELDs), 14 involved “hypoenergetic balanced diets” (HBDs) and 2 involved both—in other words, they were all calorie-restriction diets, and about half of them required participants to eat less than 800 kcal/day. The authors claim that no long-term randomized, controlled studies were available, and it’s unclear why they didn’t think studies like Jeffrey and Wing 1995 (discussed below) should count.

They don’t provide details for any of the studies individually, but do disclose that the number of participants ranged from 6 to 504, the length of treatment ranged from 8 to 30 weeks, average initial weight loss ranged from 3.5 to 37.9 kg for women and 6.2 to 44.2 kg for men, and follow-up participation rates ranged from 50% to 100% with a median of 82%. In other words, these were very different studies. Here are the results of their aggregation of the data:

again, what they're focusing on is the relatively small loss maintained by year 5 rather than, say, the precipitous drop from year 1 to year 2

The average weight loss at 5 years for both VELDs and HBDs was 3.0 kg, or ~3.2% of the participants’ starting weight and 23.4% of their initial weight loss. Anderson et al conclude:

These average values are higher than those reported in earlier studies and indicate that most individuals who participate in structured weight-loss programs in the United States of the type reported in the literature do not regain all of the weight lost at 5 y. of follow-up.

Sure, not all of the weight, only 76.6% of it. It still seems to me like a perversion of the idea of “success” to claim that these results show that calorie-restriction diets are “effective.” The average initial weight loss was 14 kg. If you lost almost 31 lbs and then regained 25 lbs, would you consider your diet a long-term success? Mann et al wouldn’t. In the 14 long-term studies without control groups that Mann et al evaluated, they also note an average maintenance of ~3 kg. They just don’t think that’s very impressive:

It is hard to call these obesity treatments effective when participants maintain such a small weight loss. Clearly, these participants remain obese. (Mann et al 223)

Interpretation/equivocation aside, there’s still some discrepancies between their analysis and the consensus in the other reviews which I wish I could explain. It’s not like this was a study of a new treatment—they relied exclusively on existing studies, at least some of which were also included in the reviews of the literature discussed above. However, some of the studies they included must have reported (possibly significantly) better results to bring up the average. Since they didn’t evaluate the studies individually, it’s impossible to tell from their write-up whether those studies involved some sort of strategy that made calorie restriction dieting “work” (and somehow didn’t attract widespread attention) or whether the results in those studies were biased by low participation rates in follow-ups, self-reporting, or some other factor(s).

A Closer Look at the Studies Themselves

I have not read every single study referenced in the review articles, although I have at least glanced at many of them. The ones I chose to explore in further depth here either 1) meet the “gold standard” of randomized assignment to diet/non-diet conditions and at least 2 years of follow-up or 2) are too recent to be included in the review articles.

Long-term Effects of Interventions for Weight Loss—Jeffrey and Wing 1995 (free abstract or full text with umich login): This is one of the seven studies included in the first part of the Mann review. 202 participants between the ages of 25 and 45 who were between 14-32 kg above the MetLife standards for the “ideal weight” for their height were randomly assigned to one of five experimental groups:

  • a control group which received no intervention
  • a standard behavioral therapy group (SBT) that received instruction on diet (including advice on how to follow a 1000-1500 calorie/day diet), exercise (including the recommendation to walk or bike 5 days/wk with an initial goal of burning 250 kcal/wk and gradually increasing that to 1000 kcal/wk), and behavior modification (including keeping food and exercise diaries. This advice was given in weekly counseling sessions for the first 20 weeks and monthly sessions thereafter for a period of 18 months.
  • a SBT + food group, which received the same counseling along with premeasured and prepackaged breakfasts and dinners for 5 days/week for 18 months
  • a SBT + $ incentive group, which received the same counseling along with up to $25/week  for achieving and maintaining weight loss
  • a SBT + food + $ incentive group, which got the counseling, meals, and money

In addition to the 18 months of the study, the participants were contacted at 30 months (a full year after the study ended) for an additional follow-up, which was completed by 177 (88%) of the original participants. Here are the results:

 is this shape getting familiar? 

All the treatment groups lost weight during the intervention, achieving their maximum results at 6 months. However, by 12 months—even though they were all still receiving the treatment, they were beginning to regain weight. By 30 months, there was no significant difference between any of the treatment groups and the control group. The authors wheedle a bit, claiming the difference “approaches levels of statistical significance” (.08), but are honest enough to admit in the end:

The overall results of this evaluation reemphasize the important point that maintaining weight loss in obese patients is a difficult and persistent problem.

Preventing Weight Gain in Adults: The Pound of Prevention Study—Jeffrey & French 1999 (free full text): This more of a “failure of low-cost educational interventions designed to encourage weight loss” than a failure of weight loss dieting per se, but it’s still relevant because 1) the experimental group “got the message” communicated in the educational intervention but gained the same amount of weight over 3 years as the control group and 2) calorie labeling is essentially a large-scale, low-cost educational intervention. The idea that education will make people thinner relies on the assumption that people would not be (as) obese if they only knew they were gaining weight, that they should eat more fruits and vegetables, that they should reduce their consumption of high-fat foods, and/or that they should get more exercise.

But most people do know all those things. In this study, 228 men and 594 women employed by the University of Minnesota and 404 low-income women, all between the ages of 20-45, were recruited to participate in a 3-year study. Half of the participants were assigned randomly to a control group and the other half were assigned to the “intervention” group, which received a 2-4 pg monthly newsletter called Pound of Prevention. The newsletter emphasized five themes:

1) weighing yourself regularly (at least once a week)
2) eating at least 2 servings of fruit per day
3) eating at least 3 servings of vegetables per day
4) reducing the consumption of high-fat foods
5) increasing exercise, especially walking

In other words, “common sense” nutritional advice, although not explicitly calorie reduction. The newsletter included recipes, suggested particular areas/routes in the local areas for walking, and included a return-addressed, stamped postcard asking participants to report their current weight and also answer whether they had walked for 20 minutes or more, eaten 2 servings of fruit, eaten 3 servings of vegetables, or weighed themselves in the last 24 hours. Intervention participants were also invited to take part in a variety of activities during the three years, including 4-session weight control classes, aerobic dance classes, free 1-month memberships to community exercise facilities, walking groups, and a walking competition. Additionally, half of the “intervention” group was assigned randomly to an “incentive” group who were eligible for a monthly $100 lottery drawing for members who returned the postcards.

All participants were evaluated in annual physicals where they were weighed, their height was measured, their dietary intake evaluated using a standard 60-item Food Frequency Questionnaire, and they were asked about behaviors like exercising, eating fruits and vegetables, decreasing fat intake, using “unhealthy diet practices” like laxatives and diet pills or liquid diet supplements, weighing themselves, and smoking. At some point in the study, a questionnaire was administered to test “message recognition.”

Participation in the “intervention” group was high—68% of postcards were returned, 80% of the participants reported having read most or all of the newsletters at their annual visits, and 25% participated in one or more of the extra activities. The “message recognition” test was somewhat successful—the intervention group was significantly more likely to identify the 5 targeted treatment messages as being among the best ways to prevent weight gain; however, even 66% of the control group endorsed the treatment messages. The intervention groups were slightly-but-significantly more likely to weigh themselves and more likely to continue practicing “health weight loss practices” as measured by a 23-item questionnaire. However, changes in BMI, energy intake, percent of calories from fat, and rates of physical activity were not significantly different between the control and intervention groups. All participants gained an average of 3.5 lbs over the course of the 3 years.

In short, the intervention was a failure. The authors conclude:

It is easier to teach people what to do than to persuade them to actually do it…. The overall impact on weight itself…was very weak, indicating that stronger educational strategies are needed or, alternatively education alone is insufficient to deal effectively with this important problem.

Weight Maintenance, Behaviors and Barriers—Befort et al 2007 (free abstract or full text with umich login): Based on the abstract, this study sounds like a success, but under closer examination, not so much. The data was collected at a university weight loss clinic where participants were recruited to follow low-calorie or very low-calorie (500 kcal/day) weight-loss diets followed by a maintenance program. The “weight-loss” phase lasted for 3 months during which participants consumed prepackaged meals and/or shakes. The maintenance programs ranged from 6 to 21 months and consisted of weekly or bi-weekly meetings at the clinic during which participants were counseled to follow a structured diet plan with a daily calorie goal and exercise 150-300 minutes per week. In 3 out of 4 trials, the participants were also encouraged to continue consuming the shakes/prepackaged meals.

Out of 461 participants who started treatment, 44 dropped out during the 3-month weight loss phase and 211 dropped out during the maintenance phase. They sent follow-up surveys to everyone who completed the 3-month weight loss phase (n=417), and got 179 back (46.6.%). The more recently participants had been part of one of the studies, the more likely they were to respond to the follow-up survey. Responders had only been out of treatment for an average of 14 months.

Their claim that a “majority” of the participants maintained their initial weight loss is based on them lumping together respondents who had only been out of treatment for 6 months with people who had been out of treatment for 24 months or more, despite the fact that—just like in every other study of calorie-restriction weight loss—the results showed that most participants gradually regain weight. As they admit:

Compared to participants who were out from treatment for 24 months or longer, those who were out for less than 6 months (P<0.05) or for 6–12 months (P<0.01) had significantly greater weight loss maintenance, both in terms of kg and percent of baseline weight.

What they don’t say is that the percentage of respondents who report maintaining their initial weight loss drops off precipitously after 24 months.

no graph; perhaps it would have been too damning?

Of the 31 respondents who’d been out of treatment for 24+ months, only 25.8% had maintained a weight loss of 10% of their body weight or more and 48.4% had maintained a weight loss of 5% or more. That means out of the original pool of 417 who completed the 3-month diet, only 8 had proven capable of maintaining weight loss equal to 10% of their body weight for more than 2 years and only 15 had proven capable of maintaining a weight loss equal to 5% of their body weight. Other participants might be able to maintain their initial weight loss—that data isn’t available, but the trajectory certainly doesn’t look good. And that’s based on the half of the participants who participated in the follow-up—as Garner and Wooley note, the higher the rate of participation and the longer the follow up, the less weight loss on average is maintained.

What About the National Weight Loss Control Registry?

Several of the studies and at least one person who commented on one of the earlier posts in this series mentioned the National Weight Loss Control Registry (NWCR) as evidence that people can indeed lose weight and keep it off. I’ve never disputed that. Even in the studies that show the least hope for long-term maintenance, there are exceptions to the general trend. But that’s what they are: exceptions.

According to the NWCR website, they have over 5,000 members, all of whom have lost at least 30 lbs and kept it off for at least 1 year; however, most of them have done far better—registry members have lost an average of 66 lbs and kept it off for an average of 5.5 years. As the research above suggests, that’s not remotely “representative” of people who attempt to lose weight. On the contrary, the entire raison d’être of the registry is to figure out what’s different about the 5-10% of dieters who lose significant amounts of weight and keep it off. The goal is to identify strategies that might help other dieters, but as the researchers who run the registry admitted in a 2005 article (free abstract):

Because this is not a random sample of those who attempt weight loss, the results have limited generalizability to the entire population of overweight and obese individuals.

Indeed, the kinds of things the registry members do are generally the same things the participants in most weight loss studies are counseled to do (or, in clinical settings, forced to do): most of them follow a low calorie, low fat diet, eat breakfast every day, weigh themselves at least once a week, watch less than 10 hrs of TV per week, and engage in very high levels of activity—420 minutes per week on average. The NWCR has yet to figure out what makes those things work for them and/or makes them capable of sustaining those behaviors when for most people, they don’t/can’t.

Collecting 5,000 success stories does not prove that dieting “works” for most people let alone that it’s the norm. Somewhere between 45 million and 90 million Americans diet to lose weight every year, most of them by attempting to reduce their caloric intake. According to a survey conducted in April 2010 by a private consumer research firm on behalf of Nutrisystem, 30% of Americans have dieted repeatedly—an average of 20 times. Unsurprisingly, weight loss attempts are more common among overweight and obese people. If calorie-restriction dieting “worked,” America would be a nation of thin people.

Conclusion: Putting the burden of proof back where it belongs

Traditionally, researchers assume that a treatment is not effective until they have evidence that proves otherwise. The reverse is true in regard to weight-loss dieting: most people assume dieting is effective for long-term weight loss and challenge anyone who believes otherwise to prove that it doesn’t—not that that’s difficult, given the consistent failure of most weight-loss interventions to produce lasting results. I have not been able to find one long-term, randomized, controlled study that shows that dieting works (i.e. a statistically significant group of people following a calorie-reduction diet losing a clinically significant amount of weight and keeping it off for more than 3 years). Instead, what all the research to date shows is that the most reliable outcome of calorie-restriction dieting is short-term weight loss followed by weight regain.

I suspect the stubborn persistence in prescribing calorie-restriction dieting as a weight loss strategy in spite of the available evidence probably has a lot to do with dominant and deeply-engrained attitudes about fatness, meritocracy, virtue, and effort. People exhibit remarkable cognitive dissonance when it comes to the research on weight loss—they hold up exceptions as the rule and claim that the 90-95% of people for whom calorie restriction dieting does not produce weight loss must simply not be trying hard enough. 

Imagine this scenario playing out with any other condition—imagine that instead of weight, we were talking about some kind of rash that was widely considered unattractive and thought to be correlated with a variety of other health problems. There’s a treatment that showed promise in short-term trials. In virtually every study, most of the people who get the treatment experience significant improvement in their symptoms, with peak results around six months. However, in longer-term studies, there’s a reversal. Just as consistently, the vast majority of sufferers—at least 75% and usually closer to 90 or 95%—experience a gradual return of their symptoms. For approximately 30-40% of participants, their symptoms actually get worse than before they started the treatment. Only 5-10% show lasting improvement. Of course you would want to do more research to figure out why the treatment works for that 5-10%, but in the meantime, would you keep prescribing it to everyone with the same skin condition?

Even if the problem is that only 5-10% of them fail to use the treatment as instructed—say, it’s a topical cream that only works if you apply it every hour on the hour and people get fatigued, especially by trying to wake up at night to put it on. If 90% of the affected population can’t use the treatment effectively, the results are the same as if the treatment never worked in the first place. Well, except for that part where 30-40% of them end up worse off than before they started the treatment…

So even if the calorie counts on menus were accurate, and people could accurately and reliably estimate how many calories they burn, and they did choose lower-calorie options at least some of the time, and they didn’t compensate by eating more on other occasions…in other words, even if the calorie counts worked the way they were intended to, the best you could hope for would be short-term weight loss. There’s no reason to believe the policy—even under ideal conditions—would have a lasting effect on most Americans’ weight or health.