Category Archives: dieting

Diet Soda Follow-up: Are Diet Sodas Better For You Than Regular Soda?

Artificial sweeteners definitely pre-dated the "obesity epidemic." Saccharin was being used commercially in the early 20th C. and diet sodas were widely available by the 1960s For more on the history of artificial sweeteners, see Carolyn de la Pena's brilliant book _Empty Pleasures_

Soda cans from the 1970s from Found in Mom’s Basement

In response to the recent entry about the association between diet soda and fatness, Jim asked:

Has anyone proved that drinking Diet Soda is better for you than drinking Regular Soda? Does Diet Soda have the same impact on the body as drinking say a glass of water? I haven’t done any research on it and I don’t know if any is out there. I’d really like to see a study of what happens to obese people who stop drinking diet soda and switch to regular.

There’s a ton of research on artificial sweeteners, but I can’t find any studies in which obese people who habitually consume artificially sweetened-drinks were made to switch to sugar-sweetened drinks. That might partially due to ethical/IRB concerns—it’s possible that asking people to consume more sugar than they were previously would be considered a significant health risk. On the other hand, there are studies in which subjects are randomly assigned to consume either artificial or caloric sweeteners, so maybe consuming regular soda falls into the realm of acceptable risk with informed consent.

In those kinds of studies, both “overweight” and “healthy”* individuals who consume regular sweeteners (usually sucrose or high-fructose corn syrup, which are nutritionally equivalent as far as we know) end up eating more calories overall than people who consume “diet,” artificially sweetened foods and drinks. The sugar/hfcs groups also gain weight and fat mass and have negative health indicators like increased blood pressure. I don’t think fatness is bad or that being thin is better, but based on the current available evidence, regular soda appears to be both more likely to make you fat and also worse for your health than diet soda.

*Stupid current labels for BMI categories that don’t correspond at all to actual health outcomes.(1)

A Closer Look at the Studies

This is apparently what Diet Coke looks like in Denmark. Or did in 2009. Pretty! In a 2002 study from Denmark, 41 “overweight” men and women between 21 and 50 years old were assigned to two groups, matched for sex, age, weight, height, BMI, fat mass, fat-free mass and usual amount of physical activity. One group was given sucrose-sweetened dietary supplements (2 g/kg of body weight daily; 70% from drinks and 30% from solid foods) and the other was given artificially-sweetened dietary supplements (an equivalent amount of food and drink by weight sweetened with a combination of aspartame, acesulfame, cyclamate, and saccharin, collectively and individually far below intake levels generally regarded as safe). All the supplements were commercially-available foods and included soft drinks, flavored fruit juices, yogurt, marmalade, and stewed fruits. The researchers note that “great efforts were made before the intervention to find the most palatable artificially sweetened food products on the market for which a matching sucrose-containing product existed.” As some of the artificially-sweetened foods were also fat-reduced, subjects in the sweetener group were given additional butter or corn oil every week.

The study lasted 10 weeks. In addition to the supplements, subjects were free to consume whatever they wanted and as much as they wanted. The subjects visited the lab weekly to pick up the supplements and have urine samples taken (which were used to validate their dietary records). Their height, weight, and fat mass were measured every two weeks. They also kept food diaries that included ratings of their  hunger, fullness, the palatability of the food they ate, and their sense of well-being over the course of each day in the week before the study began, the fifth week, and the tenth week.

Results: The sucrose group ate more calories overall than the sweetener group and got more of their calories from carbohydrates (58% compared to 44%). Both groups decreased how many carbohydrates they were eating in addition to the supplements, but the sugar in the supplements more than made up for the decrease in the sucrose group. The sucrose group gained an average of 3.5 pounds—which was, interestingly, only about half the weight gain that would have been predicted based on how many more calories they were eating. Their activity levels didn’t increase, so the most likely explanation is thermogenesis—i.e. their metabolism changed in response to the increased caloric intake. The group eating artificial sweeteners lost an average of two pounds. In the sucrose group, systolic and diastolic blood pressure increased; in the sweetener group, it decreased. There were no differences in appetite sensations, hunger, or satiety.

Similarly, in a 1990 study done at the Monnell Chemical Sense Center, a group of 30 subjects gained weight during a three-week period when they were given regular soda (sweetened with HFCS) and lost or maintained their weight during the two three-week periods when they were given diet soda (aspartame-sweetened) or no soda. In the regular and diet soda periods of the experiment, they were given 40 oz. of soda to drink every day. In the no soda period, they were told they could consume any beverages as they normally would. They also kept detailed dietary records for the duration of the experiment. The order of the 3-week periods was counterbalanced so some of them got regular soda first, some of them got the artificial stuff first, some of them had no soda for the first three weeks, etc. Here’s what the aggregate changes in their body weight looked like: 

Tordoff and Alleva 1990 in the American Journal of Clinical Nutrition 51: 963-9 (graph appears on 965)

During both the regular and diet soda weeks, they decreased their dietary sugar consumption by an average of 33% (i.e. aside from the sugar in the soda).

Studies like these also point to what I suspect is the more likely explanation why there’s never been a study like the one Jim describes: there’s just not much debate about whether consuming calorically-sweetened drinks leads to weight gain and possible health risks (which shouldn’t be conflated—weight gain is primarily an aesthetic issue, and high levels of sugar consumption may lead to negative health outcomes whether or not they make you fat). What is up for debate is whether artificial sweeteners are a good substitute and likely to promote weight loss or also bad and contributing somehow to weight gain. And if they’re contributing to weight gain, how and how much?

There appear to be three types of theories about why artificial sweeteners might cause weight gain and/or other undesirable outcomes.

Theory #1: Artificial sweeteners might have direct metabolic effects

I don't know what this has to do with anything, I just thought the entry needed more picturesIt’s possible that although they have no caloric value, artificial sweeteners could affect blood sugar or insulin in ways that cause the body to store fat. This is the theory being tested in the study described in the previous entry in which mice consuming aspartame in amounts comparable to an average-sized woman drinking 20 oz of aspartame-sweetened soda per day had higher fasting glucose levels than mice on the same diet minus the aspartame. The effect could be chemical, but seems more likely to be an effect of the sweet taste—i.e. the perception of sweetness might affect the hormones that govern appetite and metabolic rate.

Evidence for this is still extremely scant. Not only is it unclear whether or not the effect is reliable, biologically significant, or occurs in humans; it’s also unclear if it’s specific to aspartame or an effect of all artificial sweeteners, if it scales such that a small amount of aspartame causes a smaller increase in fasting glucose or only occurs at a certain critical level of aspartame consumption, if it only occurs after regular daily consumption over a long period of time or after a single dose, if it affects all people in the same way or only “overweight” people, if it interacts with other dietary conditions (i.e. does it only happen in conjunction with diets high in corn oil, like the ones the mice in the study were fed?), etc.

There are studies involving rats that suggest some kind of metabolic effect of artificial sweeteners might promote weight gain. Rats fed artificially-sweetened yogurt consume more calories than those fed sugar-sweetened yogurt.

However, it seems like it might not work the same in people—or at least that the effect might be smaller. Note that in both of the studies described above, subjects given artificial sweeteners decreased both their overall carbohydrate and dietary sugar intake. Additionally, in a 2001 study done at the Pennington Biomedical Research Center in Baton Rouge, 31 subjects (19 lean, 12 obese) were given sucrose (493 kcal), aspartame (290 kcal), or stevia-sweetened (290 kcal) "preloads" before lunch and dinner on three separate days. Their food intake, satiety (how full they felt), and postprandial (after-meal) glucose and insulin levels were measured. When they had the lower-calorie, artificially-sweetened preloads, they did not compensate by eating more at either the subsequent meals and reported similar levels of satiety as they did on the day they consumed the higher-calorie, sucrose preload.

Theory #2: Artificial sweeteners might have a psychological effect.

Another possibility is that drinking “diet” soda might make people believe that they can afford to eat more or nutritionally worse foods. This is similar to the “health halo” research being done by Brian Wansink and others, which has shown that people are more likely to underestimate the caloric content of foods they perceive as “healthy,” like a turkey sandwich from Subway, than they are with foods they perceive as unhealthy, like a Big Mac. They’re also more likely to order sides with the “healthy” choice that ultimately push the calorie content of the meals higher. Organic and “trans-fat free” labels or even just having calorie counts posted on a menu can have similar effects—triggering people’s dietary conscientiousness seems to cause many people to “treat” themselves to something extra.

However, it’s not clear that the “halo” affect actually influences total or long-term consumption. Thinking they’re getting the “healthier” sandwich may make people more likely to eat a bag of chips at that meal than they would have if they’d eaten a burger, but if that means they’re less likely to have an afternoon snack or they eat less at dinner, it might not affect their weight. I can’t find any studies that measure that.

Theory #3: Artificial sweeteners might change people’s palates

Artificial sweeteners might make people more accustomed to sweetness, which might cause them to eat more sweet things or sweeter things than they would otherwise. Since sweet things and the taste for them are seen as a kind of indulgence and not liking or eating sweet things is often constructed as proof of maturity, masculinity, or self-control, this is often described in morally judgmental terms like “infantilizing our taste sense” or “corrupting the palate.” But it’s not a theory entirely confined to blowhards. In an opinion piece in JAMA published in 2009, David S. Ludwig writes:

Individuals who habitually consume artificial sweeteners may find more satiating but less intensely sweet foods (eg, fruit) less appealing and unsweet foods (eg, vegetables, legumes) less palatable, reducing overall diet quality in ways that might contribute to excessive weight gain.

However, he admits that there’s no research showing this to be true. On the contrary, at least one study has found that people who consume artificial sweeteners regularly are more likely to eat foods generally considered to be healthy and less likely to consume foods generally considered to be fattening. According to a 2006 study done by the American Cancer Society as part of a larger project involving 1-2 million men and women who weigh 40% or more above average for their age and height, those who reported using artificial sweeteners also ate chicken, fish and vegetables significantly more often than non-users and consumed beef, butter, white bread, potatoes, ice cream and chocolate significantly less often. That study also found that artificial sweeteners were associated with weight gain. Given that their diets were apparently “healthier,” the authors conclude: “our weight change results are not explicable by differences in food consumption patterns,” perhaps implying that artificial sweetener might indeed be the culprit.

I think their data suggest something different entirely: people who drink diet soda are more likely to be dieters. They’re eating more of the stuff everyone tells them they ought to be eating to lose weight, and less of the stuff they’re supposed to avoid. It’s not working, and they’re getting fatter anyway, but that doesn’t mean diet soda makes you fat, it could simply mean that dieting doesn’t work.

Not Implausible, Just Not Supported By the Evidence

My suspicion is that if diet soda has any affect on weight, it’s a small one. I think it might be possible that in large amounts (probably 16 oz or more of diet soda per day), some artificial sweeteners might affect the metabolism slightly and lead to people being slightly fatter than they would be if they consumed less or no artificial sweeteners at all. However, I don’t think you’d see the results you see in studies like the ones from Denmark or the Monnell Chemical Sense Center if artificial sweeteners really have a dramatic, immediate effect on weight gain or fat storage.

Of course, that doesn’t mean artificial sweeteners are healthy, just that they probably don’t make you fat. Jury’s still out on the relationships between aspartame and cancer, sucralose (Splenda) and intestinal bacteria, saccharine and neurological function (especially in children), and stevia & its derivatives and DNA mutation. But for what it’s worth, most of the review articles I came across and Ludwig’s JAMA article claimed that concerns about cancer have basically been put to rest.

Of course, there’s still the problem of how they all taste

(1) Broken record footnote: Weight is a poor indicator of health. People in the BMI categories labeled “overweight” and “obese” people are often as healthy or healthier than people in the “healthy” or “normal” BMI category. People in the “overweight” category live longer on average than people in the “normal” or “healthy” category. People who are “overweight” or “obese” who engage in regular physical activity are healthier on basically every measure than sedentary “normal” or “healthy” weight people. The people who are really (statistically) screwed are the “underweight.”

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.