Things That Won't Kill You Volume 4: Saturated Fat, Part I

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Dec 14 2009

I know this is misleading because lard is mostly unsaturated, but it's been one of the major icons of "bad" fat and also, how graet is this image? from http://www.npnworldwide.com/lard

This is probably going to be an even harder sell than MSG, but I swear I'm not just trying to be contrary. It's true that all the major sources of public health and nutrition advice, including the Harvard School of Public Health, Mayo Clinic, CDC, and American Heart Association continue to refer to saturated fats as "bad fats" and suggest that people avoid them as much as possible, limit them to <7-8% of their total caloric intake, and replace them with "good," i.e. unsaturated fats, whenever possible. It's also true that there are a few studies that suggest that increased saturated fat consumption is correlated (albeit weakly) with cardiovascular disease (CVD).

However, many other studies have found no increase in CVD associated with saturated fat consumption. And several recent review articles have concluded that the evidence for a connection between saturated fat consumption and CVD is inconsistent, insufficient or nonexistent.

There are basically three things that have convinced me that saturated fat isn't independently responsible for heart disease or death:

1) groups of people who eat vastly more saturated fat than most Americans frequently have lower rates of CVD—or no apparent CVD at all

2) the study that first inspired many people to think saturated fat was a bad thing had a lot of obvious flaws and has been thoroughly discredited

3) there's no good evidence that the proposed mechanism actually works—briefly: saturated fat supposedly causes heart disease by raising serum cholesterol levels because cholesterol is what clogs arteries and causes heart attacks and strokes, but serum cholesterol turns out to be a really poor predictor of CVD 

1) The French (and Polynesian and Melanesian and Masai and Fulani and Sri Lankan) Paradox 

photo by Arun Ganesh http://en.wikipedia.org/wiki/User:PlaneMadThe most confounding phenomenon for the theory that saturated fat consumption causes heart disease (sometimes called the lipid hypothesis or lipid-heart hypothesis or diet-heart hypothesis) is the virtual non-existence of CVD in multiple populations that eat way more saturated fat than most Americans. This has primarily been documented in the Pacific islands where coconuts, which are very high in saturated fat, are a staple food. For example, before the 1970s, the inhabitants of the island Tokelau got an estimated 55% of their calories from saturated fat, but heart disease was virtually unknown (according to Gary Taubes and Stephen Guyenet; notably, since their diet has shifted to include less saturated fat but more sugars and refined carbohydrates, many health indicators have worsened).

Many proponents of "natural" foods have already embraced the coconut as a source of "healthy" fat, but the confounding phenomenon isn't unique to coconut-eaters. The Masai of Kenya and Tanzania and Fulani of Nigeria, whose traditional diet is composed primarily of cow's milk, meat, and blood and estimated to be 33% saturated fat, also had virtually no incidence of CVD—or didn't until they started eating refined carbohydrates. Red meat and dairy sources of saturated fat are about as classically "unhealthy" as you can get, and yet don't necessarily cause heart attacks and death.

The differences can't be attributed, at least entirely, to genetics, and not just because the phenomenon is consistent among so many far-flung populations. The Masai are known to be highly genetically diverse due to conflict/intermarriage, and all of the populations have experienced changes in their health as their diets have changed.

Nor are the changes likely due to higher activity levels, cyclical feast and famine, average lifespan, or the absence of other risk factors like cigarette use in these populations. A 1993 study of diet and health in Kitava, the Trobriand Islands, and Papua New Guinea found that Kitavans get an average of 17% of their calories from saturated fat (compared to about 10% for Americans or the <7% recommended by the AHA), tend to be about as active as moderately active Swedes, and have virtually no experience of food scarcity or shortage. Furthermore, 75% of the population smokes. Nonetheless, stroke and heart attack basically don't exist even among the elderly there, and their fasting insulin levels are significantly lower than Swedes' in every age group.  

Another potentially confounding fact that some low-carb proponents point to is the alleged decline in the average American's consumption of saturated fat. It's true that the consumption of some primary sources of saturated fat like butter and lard declined for most of the 20th Century; however, per capita red meat consumption grew until the 1970s, and according to the USDA, the proportion of saturated fat in the U.S. food supply has remained pretty steady for the last century. What is clear, at least, is that increasing rates of cardiovascular disease were not caused by increasing per capita consumption of saturated fats.

So why the hell have the institutions we trust to tell us how our diets affect our health spent the last half-century trying to convince us that saturated fat clogs your arteries, causes heart attacks, and might kill you?

2) It All Began With Some Falsified Data January 13, 1961 cover of Time magazine

I know, I sound like a climate change skeptic, but this is way more blatant than some sketchy e-mails.

The research that first convinced many Americans and public health institutions like the AHA that saturated fats cause heart disease was the Seven Countries Study led by Ancel Keys. Keys and his colleagues carried out surveys of men (only men because the rate of CVD in women was considered too low to merit attention) in eighteen rural regions in Italy, the Greek Islands, Yugoslavia, the Netherlands, Finland, Japan, and the U.S. The regions were supposedly chosen because they were areas with stable and widely-contrasting diets. The researchers asked the men about their eating habits, performed chemical analysis on meals prepared by randomly-selected families, and compared their findings to the rate of disease and death in the different populations, with special attention given to CVD and "risk factors" like serum cholesterol levels. They concluded that higher levels of dietary saturated fat cause elevated serum cholesterol and heart disease. The especially low rates of CVD in Crete, despite relatively high proportions of dietary fat, were a large part of the impetus behind the "Mediterranean Diet" and the idea that olive oil is nutritionally sacrosanct.

However, as many people later pointed out, it seems more than coincidental that Keys only included regions where both saturated fat consumption and heart disease were high or where they were both low. Apparently, data was available for a number of other countries (anywhere between 15 and 27, according to various critics), perhaps most notably France, which would have been just as easy to study as Finland and Japan. Keys seemingly ignored, or systematically excluded, all confounding data from his analysis.  

Even for the countries that were included, according to statistician Russell H. Smith:

The dietary assessment methodology was highly inconsistent across cohorts and thoroughly suspect. In addition, careful examination of the death rates and associations between diet and death rates reveal a massive set of inconsistencies and contradictions…. It is almost inconceivable that the Seven Countries study was performed with such scientific abandon. It is also dumbfounding how the NHLBI/AHA alliance ignored such sloppiness in their many "rave reviews" of the study…. In summary, the diet-CHD relationship reported for the Seven Countries study cannot be taken seriously by the objective and critical scientist.

The problem seems to be that Keys had already decided that saturated fat was the problem. According to the Time magazine cover article (click the picture to read it), Keys had treated a heart disease patient with large knobs of what turned out to be cholesterol under his skin and very high serum cholesterol. When he put that patient on a low-fat diet, his cholesterol went down. Since cholesterol is what clogs arteries and causes heart attacks, and foods high in saturated fat are often also high in cholesterol, Keys concluded that the high rates of heart disease in American men were caused by the saturated fat and cholesterol content of their diets. In the Seven Countries study, he set out to prove that theory (as opposed to testing it).

Fifty years of subsequent research have not found a consistent or reliable correlation between saturated fat consumption and heart disease or death. This entry got a little out of hand, so I split it into a couple of parts. More coming soon on dietary cholesterol and the dreaded LARD, neither of which, it turns out, are likely to kill you or even probably hurt you a little bit. Also, an epilogue of sorts on trans-fats, which might actually kill you.

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Good Stuff. The telling of

Good Stuff. The telling of the Ancel Keys/saturated fat/heart disease story was one of the things that I found really fascinating in the Gary Taubes book. It's just so bizarre to me that such bad science can last so long.

I sympathize with you over trying to convince people about this: I've mentioned it to some of my coworkers (usually when they were joking about the heart attacks we're going to get from the giant omelets/bacon we get across the street from our office) and mostly got some strange looks in response. I've pretty much given up, just to avoid sounding like a broken record.

Looking forward to hearing about trans-fats, because the little I've heard about them has not given me a very clear picture.

I've always just made mayo in

I've always just made mayo in the cuisinart. I like being able to adjust the seasoning (mustard, lemon juice, which oils I use to make the mayo) as well as the consistency to suit my purpose. I only whip up a batch when I'm making something that uses a considerable amount of it like potato or chicken salad, or when I'm using it as a sauce.
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I think it all just comes

I think it all just comes down to variety. I don't remember Michael Pollan's specific stance on saturated fats, but I do remember his stressing that other, healthier cuisines around the world include a much more varied diet. Too much saturated fat, of course, would probably be something to avoid, but as part of a balanced diet? Just fine, I would expect. I think Gary Paul Nabhan might have touched on this, too, in "When Some Like It Hot." I CERTAINLY wouldn't be able to do without it in my own cuisine, although I suspect I could cut back a bit. ;)

not sure variety is actually the key

many of the populations that don't seem to suffer from "lifestyle" diseases like heart disease, cancer, and dementia don't actually have varied diets, particularly in comparison to many people in industrialized countries; nor is it clear what "too much" saturated fat would be or what the goal of cutting back would be if it, alone, doesn't cause disease or death. i'm not sure there is such a thing as an optimal, "balanced" diet.

the things i've been reading instead seem to indicate that it may the combination of saturated fat with refined carbohydrates that doesn't work so well. so, diets high in carbohydrates but low in saturated fat and total fat--seemingly okay; diets extremely high in saturated fat but low in carbohydrates, especially sugar--also okay. but lots of saturated fat + lots of refined carbohydrates= oxidation of carbohydrates and CVD.

It's worth acknowledging that

It's worth acknowledging that fats are calorie-dense foods (which is why you can power a car burning used fry oil). A pound of butter is almost twice the calories of a pound of sugar.

But I agree--calorie for calorie, substituting high glycemic index carbs in place of fats is likely worse for you.

This relates to one of my pet peeves: The growing fraction of the population being prescribed statin drugs to reduce blood cholesterol. I'm not convinced there's any proven benefit, unless you are in the sub-population with other known risk factors (family history of heart disease, high blood pressure). Perhaps there's a similar issue with saturated fat: A sub-population who are already prone to heart disease might be harmed by it. Epidemiology which looks at the whole population might show a small, but misleading effect.

I'd be afraid to figure out the fraction of my dietary calories that comes from cheddar cheese.

mmmm cheddar cheese

Sorry for the slow reply--I somehow missed this. It's true that fats are calorie-dense, which is why people attempting to lose weight by reducing their caloric intake so often reduce their fat consumption (which works very well in the short term but very poorly long-term--90% of people who lose weight that way usually gain all of it back and a large number gain back more than they initially lose).

Fats also have very high satiety ratings--and there's some indication that saturated fats are actually better than unsaturated on that front, i.e. that eating butter will make you feel full faster and stay full longer than an equal amount of olive oil. The same is likely true of cheddar cheese--you may eat fewer total calories because of the cheese than you would if you avoided cheese and replaced it with less calorie-dense and less satisfying food. Not necessarily in the same meal, but you might get hungrier faster, snack more, etc.

You're right about the statin business re:cholesterol, but I haven't found anything yet to suggest that there's a sub-population with saturated fat sensitivity. The inconsistent effects in the studies on saturated fat and heart disease could be entirely explained by trans-fats and refined carbohydrate consumption, and interactions between the latter and un-saturated fats. I'm hoping to get to that in the follow-up entries to this one...

Trans fat and Study Revision

I remember reading a study a couple years ago showing when researchers controlled for trans fat intake on a lot of old saturated fat studies, they found that saturated fat only raised cardiovascular disease risk by some 2% (insignificant) while the trans fat in the participants' diets raised it by almost 100%. The conclusion, I believe, was that because trans fats often show up in foods that are rich in saturated fats (like partially hydrogenated oils), and because trans fats were ignored for so long, saturated fats ended up taking the blame for the unhealthy effects of trans fats. Unfortunately, I can't seem to find the study on Google. Maybe you've read it?

the Framingham study

Saturated fat intake appeared to be correlated with heart disease until they controlled for trans-fat consumption by separating the butter-eaters from the margarine-eaters.

There was a link in the entry on trans-fats:
http://www.ncbi.nlm.nih.gov/pubmed/9229205?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_SingleItemSupl.Pubmed_Discovery_RA&linkpos=3&log$=relatedarticles&logdbfrom=pubmed

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