I’m not one to let one study overthrow conventional wisdom, since conventional scientific wisdom is usually made out of many decades of study. However, a meta-analysis is a pretty powerful argument. So, hopefully here’s where someone with some expertise can come in and explain this all.
Not dairy fat for most of our evolutionary history. Only since some time in the neolithic. And although we evolved eating meat (including the fat) I believe that meat is thought to be a much smaller proportion of a hunter-gatherer diet than it is for a modern first-worlder.
Also, just because we evolved under certain conditions doesn’t mean those conditions are optimal for us. We may have evolved in an environment where there was a nonzero chance of getting eaten by a sabre-toothed tiger; it does not follow that releasing sabre-toothed tigers into Manhattan would increase human life expectancies.
Most of our ancestors pretty much ate anything they could get their hands on; their first priority was to avoid starvation. Most of us have the luxury of not worrying about starvation, so we can be more concerned with taste and nutrition.
I have yet to read the article, so don’t know if what I’m about to say was addressed in it.
When people decrease their intake of saturated fat (which comes mostly from animals with a few exceptions), they often offset it by increasing their intake of so-called polyunsaturated fats. Indeed, this was the recommendation of many of health-promoting organizations in the 60’s through 90’s (appx).
However, while it is true that decreasing saturated fat intake and increasing polyunsaturated fat intake will lower your LDL (“bad” cholesterol), it also will lower the HDL (“good” cholesterol). Basically, the ratio between them will remain unchanged. The net effect to cardiac health would be expected to be zero.
Bottom line of what I’m getting at, is that the reason saturated fat intake seemed neutral in the cited study may be that it was (inversely) linked to polyunsaturate intake in the populations studied in the original articles on which the meta-analysis was based. Such a link would neutralize the effect of reducing dietary saturated fat.
ETA: BTW, the authors of the study are members of what is arguably the “best” group in the world for this type and topic of research (i.e. epidemiology of heart disease).
Yes, it’s true. And the supporters of conventional wisdom are going to be feeling pretty stupid in a few years as eveidence continues to indicate they are dangerously wrong. I’m very excited to see this study getting so much attention.
I’ve spent a lot of time over the past two years researching nutritional science and epidemiology. I’ve been of the opinion for some time that not only is saturated fat not bad for you, it is the ideal fuel for the human body. I now get around 75% of my daily calories from animal fat. I feel great and blood tests are good (I’m young and I’ve always had a nice lipid panel, but now my HDL is going up, LDL down.).
It’s also my opinion that conventional wisdom in the matter of nutrition is largely responsible for the ever-increasing incidence of ‘metabolic syndrome’ in any population that eats a modern diet, AKA the standard American diet (very high in carbs, many processed foods with wheat flour, sugar/corn syrup, soy products, and polyunsaturated vegetable oils providing most calories) - a predictable grouping of health conditions including vastly increased fat mass especially in the abdomen, high triglycerides and low HDL, insulin resistance leading to diabetes, hypertension, and a high incidence of heart/vascular disease and stroke.
This is hardly the only study which finds no link between saturated fat consumption and heart disease. I recommend this review of 25 important studies by Stephan Guyanet:
This is discussed at length in Michael Pollan’s In Defense of Food. Comments that fat is not a “bad thing” as it is a critical element of our diet, and that animal fat is - at least - no worse for you and arguably better than some of the processed hydrogenated alternatives.
Doesn’t it intrigue you, though, that all they could ‘get their hands on’ for most of our history was meat, animal fat, animal organs, fish, shellfish, root vegetables, greens, and wild fruits?
If I had to think of the opposite of this diet - probably it would be the sub-standard diet of most American dogs and cats (one brand of processed fortified corn pellets, for life). But a close second would be what many people I know eat - a steady diet of bleached white flour and sugar, with occasional skim milk and cheese, and small amounts of meat and non-fructose-laden vegetables (most people I know don’t even eat meat daily).
For an in-depth history of nutritional science in American, including the rise of the theory of saturated fat contributing to heart disease, please read Good Calories, Bad Calories by Gary Taubes. It’s appalling how little real science coventional dietary wisdom is based on.
It’s not like our bodies take animal fat and deposit it from our stomachs into our arteries. Our bodies make cholesterol when our blood sugar rises. Maybe an over simplification but that’s why diabetics have increased coronary artery disease. This is the type of thing that makes me question medical science. It seems so obvious.
I have had a chance now to very quickly look at the article cited in the OP. One of the major caveats the authors discuss (and actually mention in the abstract which I missed earlier) was that the lack of association of saturated fat intake with heart disease may well depend on the nature of what replaced the saturated fat in the diet of those individuals with low saturated fat intake. Replacement of saturated fat calories by carbohydrate, polyunsaturated fat, or monounsaturated fats may lead to widely varying risks of heart disease.
At the risk of overstepping my welcome in this thread, and even of sounding patronizing, it really must be emphasized that epidemiological* studies, such as the ones on which the article under discussion is based, cannot determine causation, only association. (And, as an aside, a meta-analysis, the method used in the current study, is no better than the studies which it analyses. “Garbage in, garbage out”)
It behooves anyone who a lot of faith in epidemiologic data to consider both the vitamin E and postmenopausal estrogen replacement debacles. In both cases, the epidemiologic evidence for their use was consistent, compelling, indicative of substantial effect, and supported by underlying physiologic mechanisms (some proven, some theoretical). In a nutshell, when proper randomized blinded controlled studies were done, however, not only were vitamin E and estrogen replacement found to be of no benefit, but, at least for estrogen, of some harm (in fact, there is now also evidence - from RCTs - to show that vitamin E is also harmful). (references available on request)
So, the study in the OP, based on epidemiologic data and all its inherent liabilities does not, and in my opinion cannot, prove that high levels of saturated fat consumption protect, promote, or have no effect on heart disease. At best, it is hypothesis generating.
*epidemiology is the study of disease in populations
I wouldn’t be surprised by anything. Back when I was a biochem major and teaching a computer lab for seniors in food science/nutrition, I was appalled to learn that only two or three of the people in the class understand that correlation does not equal causation and none of them understood statistical analysis of data.
We had people about to graduate with a 4-year degree from a respected university who were writing papers that were on the level of: “Japanese drink more green tea; Japanese have lower rates of heart attacks; therefore, green tea prevents heart attacks.” That paper got an A.
Dr. Melik: This morning for breakfast he requested something called “wheat germ, organic honey and tiger’s milk.” Dr. Aragon: [chuckling] Oh, yes. Those are the charmed substances that some years ago were thought to contain life-preserving properties. Dr. Melik: You mean there was no deep fat? No steak or cream pies or… hot fudge? Dr. Aragon: Those were thought to be unhealthy… precisely the opposite of what we now know to be true. Dr. Melik: Incredible.
I posted this quotation in the “What if everything we knew is wrong” thread yesterday, but this also seems like an appropriate place for it.
I’m always suspicious of meta-analyses in general, regardless of the field or result. It’s just too easy to get a non-representative sample of studies, or to give undue weight to groups which publish basically the same results many times, or to let in work which was just plain shoddily done. The authors of a single, original study just have to worry about their own experimental design (which they have control over), but the authors of a meta-study have to worry about the experimental design of everyone whose work they use (and over which they have no direct control).