Preventive Medicine Column
Dr. David L. Katz
No, it is not suddenly good to eat more saturated fat- and the new study grabbing headlines this past week showed no such thing. The new study, a meta-analysis the Annals of Internal Medicine, really shows the following two things: (1) there is more than one way to eat badly; and (2) you cannot get a good answer to a bad question.
The questions posed in this paper were: what are the differences in rates of coronary heart disease in observational studies when the top third of intake is compared to the bottom third of intake for some particular class of fatty acid?; and, what are the differences in coronary disease rates in intervention trials between groups when one group is given some kind of fatty acid supplement?
For the observational studies, representing over 500,000 people, the investigators found more coronary heart disease in the highest intake of trans fat compared to the lowest; and less heart disease in the highest intake of omega-3 fat compared to the lowest. There was a hint of benefit for higher monounsaturated fat intake. And then the part spawning the predictably exaggerated headlines: there was no appreciable difference in coronary heart disease rates seen comparing the top to bottom third of saturated fat intake, although there was in fact a suggestion of more heart disease with more saturated fat consumption. There was no difference when comparing the top to bottom third of omega-6 fat intake either.
For the most part, the intervention studies, which included over 100,000 people, administered some omega-3 supplement. A smaller batch of studies administered some other kind of polyunsaturated fat. You may recall we had already heard the news that omega-3 supplements, all other things being equal, did not appreciably reduce rates of coronary disease, so it should come as no surprise that this study found the same. In fact, while not statistically significant, there was a trend toward benefit seen with all of the polyunsaturated fat supplements, including omega-6 fat. For long-chain omega-3 fat, or so-called “fish oil,” the apparent benefit was very close to statistically significant.
Now, consider for a moment some of the leading arguments about diet and health swirling around us. Are they all about dietary fat? Not remotely. Much of our collective attention over recent years has been focused on sugar, starches, carbohydrates in general, meat in general, processed meats, and grains. I searched the new paper for the word “sugar,” and could find no mention of it. None.
People eating less saturated fat don’t simply stop eating a nutrient and leave a big hole in their diets. They eat less of A, and make up for it by eating more of B. The most obvious of questions, yet one to which this study was totally inattentive, is: what is B?
We know those trends at the level of the general population. When we started cutting back on saturated fat, we started eating more refined starch and added sugar. We also know that excess intake of sugar, starch, and calories is associated with obesity, diabetes, and coronary disease. So if eating less saturated fat means eating more sugar, it would at best be a lateral move in terms of health- and probably worse than that. The study simply ignored this consideration.
Does this indicate, as the titillating headlines suggest, that saturated fat is unrelated to coronary disease? No, however we might wish it to be so. It merely shows there is more than one way to eat badly- and from my perspective, our culture seems committed to exploring them all.
Basically, this study showed that if you vary your intake of saturated fat or omega-6 fat without altering the overall quality of your diet, you are not likely to alter your health much either. There was no suggestion at all here of any health benefits of saturated fat. There were suggestions of favorable effects of the usual suspects, omega-3 fat and monounsaturated fat.
Dietary guidance must be about the whole diet, and should be directed at foods rather than nutrients. If we get the foods right, the nutrients take care of themselves. A diet that is made up mostly of vegetables, fruits, beans, lentils, nuts, seeds, and whole grains, with or without fish, seafood, lean meats, eggs and dairy simply has less room for saturated fat, let alone trans fat. Such a diet is natively high in omega-3 and monounsaturated fat, and balanced in terms of polyunsaturates. Just as important, such a diet is relatively low in refined starch and added sugar, and natively rich in fiber, vitamins, minerals, and antioxidants.
My advice is as it ever was. Chew carefully on headlines before choosing to swallow the hyperbole, and eat a diet of wholesome foods reliably associated with good health across a vast and stunningly consistent literature. Do that, and let the fatty acids and other nutrients sort it out for themselves.
Dr. David L. Katz