I write about nutrition far more now than I used to. Part of that is because – as with health policy – as I’ve learned how little of what we say is based on data and evidence, the more irritated I become (see my Twitter avatar).
I recently came across a Viewpoint in JAMA that is illustrative of how things are changing in nutrition. It’s by Dariush Mozaffarian and David Ludwig, and it talks about the Dietary Guidelines Advisory Committee report. Here’s something I already wrote about at The Upshot:
In the new DGAC report, one widely noticed revision was the elimination of dietary cholesterol as a “nutrient of concern.” This surprised the public, but is concordant with more recent scientific evidence reporting no appreciable relationship between dietary cholesterol and serum cholesterol1 or clinical cardiovascular events in general populations.
But they want to focus on something else:
A less noticed, but more important, change was the absence of an upper limit on total fat consumption. The DGAC report neither listed total fat as a nutrient of concern nor proposed restricting its consumption. Rather, it concluded, “Reducing total fat (replacing total fat with overall carbohydrates) does not lower CVD [cardiovascular disease] risk.… Dietary advice should put the emphasis on optimizing types of dietary fat and not reducing total fat.” Limiting total fat was also not recommended for obesity prevention; instead, the focus was placed on healthful food-based diet patterns that include more vegetables, fruits, whole grains, seafood, legumes, and dairy products and include less meats, sugar-sweetened foods and drinks, and refined grains.
The complex lipid and lipoprotein effects of saturated fat are now recognized, including evidence for beneficial effects on high-density lipoprotein cholesterol and triglycerides and minimal effects on apolipoprotein B when compared with carbohydrate. These complexities explain why substitution of saturated fat with carbohydrate does not lower cardiovascular risk. Moreover, a global limit on total fat inevitably lowers intake of unsaturated fats, among which nuts, vegetable oils, and fish are particularly healthful. Most importantly, the policy focus on fat reduction did not account for the harms of highly processed carbohydrate (eg, refined grains, potato products, and added sugar)—consumption of which is inversely related to that of dietary fat.
As with other scientific fields from physics to clinical medicine, nutritional science has advanced substantially in recent decades. Randomized trials confirm that diets higher in healthful fats, replacing carbohydrate or protein and exceeding the current 35% fat limit, reduce the risk of cardiovascular disease. The 2015 DGAC report tacitly acknowledges the lack of convincing evidence to recommend low-fat–high-carbohydrate diets for the general public in the prevention or treatment of any major health outcome, including heart disease, stroke, cancer, diabetes, or obesity. This major advance allows nutrition policy to be refocused toward the major dietary drivers of chronic diseases.
As I’ve said repeatedly, I don’t know that the evidence is so clear that we should be making declarative statements telling anyone how to eat. But it’s amazing just how much the tide has turned not just against carbohydrates, but towards fat. I spent decades being told to reduce my fat intake, lower and lower and lower; that may have been the wrong thing to do.