The Nurses Health Study is probably one of the more interesting long-term studies around. Started in 1976, it is still ongoing, and the data from it are being analyzed pretty much continuously by scientists from the whole range of disciplines.
Perhaps most famously, Gary Taubes, in Good Calories, Bad Calories, cites this study frequently as evidence of both the theory that easily digestible carbohydrates may be harmful to our health, and the fact that the results of studies are often misinterpreted, willfully or not, to fit a preconceived notion of what they should be.
In a recent article in Science Daily, The Nurses Health Study pops up again. Citing materials provided by The Harvard School of Public Health, the article examines the link between carbohydrate intake and fat intake and Coronary Heart Disease (CHD).
A brief summary of the findings:
1: There is no link between low-carbohydrate diets and an increased risk of CHD.
2: Higher dietary glycemic load was associated with increased risk of CHD. (Briefly, if you eat 150 grams carbohydrate from sugar and “healthy whole grains” a day, your dietary glycemic load will be higher than if you eat 150 grams carbohydrate from vegetables.)
3: A low-carbohydrate diet where the fat and protein comes mainly from vegetable sources instead of animal sources is associated with a lower risk of CHD.
Anyone who reads what I write here or at our gym’s blogs will know that I consider #1 and #2 to be no-brainers. The “confusing” part for me is number three, because I am an advocate of a high-animal-fat diet. I advocate this because animals are better sources than plants for complete proteins, fat-soluble vitamins, and pretty much everything our bodies need for upkeep.
So what about #3? Some things to keep in mind: The Nurses Health Study is epidemiological study, and therefore is incapable of proving anything. It can only find associations, and associations alone should not be treated as dietary guidelines. This is because these kinds of studies are not controlled and there are many variables affecting the outcomes. For instance, many people who become vegetarians do so for health reasons. These same people are more likely to be non-smokers. Smoking is a major risk factor for CHD, probably as important as diet. Left uncontrolled, as it is here, this factor can and will make it impossible to claim that the lower CHD is a result of the lower animal product intake.
On the flip side, vegetable fat sources consist mainly of polyunsaturated fats, usually in the form of seed oils. Not a natural part of our diet before the agricultural revolution, seed oils have been shown to be associated with cancer and other health issues, especially in conjunction with easily digested carbohydrates. This brings me to my second thing to “keep in mind”, that the Nurses Health Study article is not discussing all-cause mortality. Avoiding CHD is nice unless, as a result of it, you end up with breast or liver cancer, or a stroke, or… well, dead is dead, either way, and if your chances of dying increase it’s a bad deal. The article doesn’t even mention all-cause mortality, and it irks me that the data have not been made available. But that is pretty typical.
I look forward to hearing more about this, preferably from someone who is willing to share the data with us, but as always I will be taking the conclusions with a grain of salt.
Goat
