Fat was targeted for years as a principal cause of obesity and heart disease. The diet-heart hypothesis attributed cardiovascular disease to dietary fat, and the 1977 Dietary Guidelines promoted reducing it — which necessarily permitted an increase in carbohydrate.
What replaced the fat
The shift away from natural foods containing animal products and fats did not leave a gap. It was filled by refined carbohydrate and industrial seed oil. Processed foods labelled low fat are therefore worth avoiding on principle: the fat was removed and something had to make the product palatable again.
What the saturated fat evidence shows
Reducing dietary saturated fat does not reduce cardiovascular events or death. Improvements in cardiovascular outcomes appear independent of direct cholesterol lowering. In cohort data, saturated fat intake was not associated with all-cause mortality, cardiovascular mortality, total coronary heart disease, ischemic stroke or type 2 diabetes.
Source matters more than the category. Diets with cheese and meat as the primary sources of saturated fatty acids produce higher HDL cholesterol and apolipoprotein A-1, and on that basis appear less atherogenic than the label would suggest.
The Women’s Health Initiative
One of the largest randomised controlled diet trials ever conducted enrolled 48,835 post-menopausal women with a mean follow-up of 8.1 years, randomised to either a standard western diet or a low-fat, calorie-reduced diet with increased exercise. The hypothesis was that the low-fat arm would reduce cardiovascular disease.
The intervention achieved an 8.2% reduction in energy from total fat and a 2.9% reduction from saturated fat. It did not reduce the risk of coronary heart disease or stroke.
Full-fat dairy
A 2014 study concluded that participants in the highest tertile of whole-fat dairy intake — milk, cheese, yogurt — had significantly lower odds of being obese. Real fat from real food does not appear to make people fat.
Fat is satiating, and metabolically quiet
Fat induces satiation, and compared with protein and carbohydrate it has the least impact on blood glucose and insulin production. Demonising it because it carries more calories per gram ignores the information that matters: what the food does hormonally after it is eaten.
What people believe
A 2015 global survey found 90% believed fat consumption could lead to cardiovascular problems and 87% believed it could lead to obesity. Among professionals, 54% of doctors and 40% of nutritionists thought dietary cholesterol was a significant driver of blood cholesterol. Belief and evidence have diverged here for a long time, and the belief is not confined to patients.
The subsidy
Real-food saturated fat is not subsidised. Industrial seed oils are. That asymmetry shapes relative price, which shapes what is in the food supply, which shapes what people eat.
