Hold on tight — the nutrition pendulum is still swinging — there is yet another report about the dangers of diet. You thought dietary fat had acquired a clean (OK, cleaner) bill of health compared to dietary sugars, but we seem to still have some anti-fat folks out there. Should we worry? Probably not, and here's why.
The report, recently published in the BMJ, is another compilation of observations from the Nurses' Health Study (73,147 women) and the Health Professionals Follow Up Study (42,635 men). These, as we've explained before, are longitudinal, observational studies that are based on self-reported food intakes. As such, they're subject to any and all errors in food recall, which would certainly lead to errors in assessing the effects of individual fatty acids on the risk of coronary heart disease (CHD), which was the goal of the investigation.
Led by Dr. Geng Zong from the Harvard TH Chan School of Public Health, the investigators quantified the intake of various saturated fats (including lauric, palmitic, myristic and stearic acids) and assessed whether their intake was associated with an increased risk of CHD. This connection makes sense since saturated fatty acids are implicated in raising the levels of blood cholesterol. They found that the consumption of these individual fatty acids was associated with a 7 to 18 percent increased risk of CHD; when the intakes of all four were combined, there was an increased risk of 18 percent. All of these measurements were comparisons of the highest to the lowest levels of intake of the individual and combined fatty acids.
The investigators then calculated that if one percent of the most abundant saturated fatty acid (palmitic acid) were replaced with monounsaturated fat (e.g. oleic acid) it would reduce the risk of CHD by 10 percent. But note, this isn't an actual replacement in an experimental setting — it's a "what if" calculation.
The upshot is that if one's own healthcare provider/nutrition expert suggests changing your intake of saturated fats, it's likely advisable to do so. But otherwise, stick to a balanced diet that doesn't overemphasize the consumption of any particular nutrient, and don't get carried away by the results of observational studies like this one.