Ancel Keys and the Lipid Hypothesis
Lately, almost all new information about eggs has been positive. This week the Egg Nutrition Center presented new research that highlights the role high protein eggs play in increased satiety and reduced hunger hormones. There has been new appreciation of the value of low glycemic foods for diabetics, the importance of nutrients like choline lutein and xeazanthin.
Perhaps more exciting is that a lot of the old theories about eggs have been reassessed or outright de-bunked. Today the New York Times wrote an article about a recent study that looked at the idea that people inherit any of a wide variety of genetic variations that determine how much HDL cholesterol they produce.
For 40 years or longer, eggs were a dietary pariah, a dangerous or unhealthy food. The medical consensus was a simple equation:
- There is saturated fats in eggs
- Dietary saturated fat from food becomes cholesterol (lipids)in the body
- Raised levels of cholesterol lead to higher incidence of heart attacks and strokes
- On top of that, fat makes you fat, too
- Simply: eggs = high cholesterol
There is now a broader appreciation and understanding of the role of fats in the diet and fats and cholesterol in the body. Very generally speaking, certain types of fats, ‘good fats,’ are now better recognized as having a healthy role. Additionally, the understanding of the mechanics of the body in transforming dietary fat to cholesterol has been radically revised and the previous models which cast the saturated fat as a contributor to higher levels of dangerous low density lipo-proteins (LDL) have been thrown out.
Eggs are now being recommended by health professionals when not ten years ago it would have been considered irresponsible. And yet it remains so entrenched that most people still believe the simple proposition that consuming fats is invariably bad for you and many dietary guidelines still tell you to avoid fats indiscriminately.
How did we get there? It starts with a guy named Ancel Keys. If he looks like the mad scientist in a horror film, well, he had tendencies. He did military research during WWI to see how long a person could go without eating and the minimum calories soldiers could function on. Out of that research came the K ration, named after him and the bane of a generation of soldiers.
Keys believed that there was a relationship between fat consumption, hypercholesterolemia (increased serum cholesterol) and CVD (coronary vascular disease). This was based on some very preliminary studies from the 1920s so after the Korean War he undertook what became known as the Seven Countries study.
Keys conducted a lengthy study of diet, lifestyle and heart disease in the populations of industrialized countries. Keys showed that in seven countries, the US included, there was a correlation between a high consumption of dietary fat and CVD. Compellingly, the data seemed to demonstrate that as nations become wealthier and began to consume more meat and eggs, heart disease and strokes increased.
His theory came to be known as the lipid hypothesis and became very widely accepted in the medical and nutrition disciplines after the mid-1960s. Health officials in the government accepted the theory and in trying to improve public health, developed policies and education that moved people away from fats. Beef, pork and poultry became increasingly lean and cuts of meat were change to avoid fat. This was harder for eggs. Because of this and the many uses of eggs as an ingredient, the public was directed to minimize or avoid eggs altogether.
The first food pyramid came out of this consensus and in order to make for the lost calories from protein sources there was much more emphasis put on carbohydrates in the form of grains and cereals. By the 80s, the food pyramid recommended the consumption up to 12 servings of grains a day. You can see why people started to be shaped like grazing animals
Much of this was enacted without further confirmation; major studies undertaken to confirm the theory were inconclusive and to some extent contradictory. But the lack of confirmation didn’t matter because the lipid hypothesis showed some very promising initial results. During the 60s and 70s, incidence in heart attacks and strokes in the US did drop and fairly significantly. It leveled off thereafter but cemented the consensus. The only large scale study using a low fat diet to show success (reduction of CVD) involved the use of statins (drugs like Lipitor) so the promotion of the lipid hypothesis became attractive to drug companies producing statins.
Yet, as Americans have moved away from fat, our incidence of obesity and diabetes has exploded and many experts attribute this to the over consumption of carbohydrates. There is some doubt that in the absence of drugs like statins and the trend away from smoking, the overall incidence of heart attacks and strokes would have changed all that much. In fact, the initial success of the reduction of CVD in the US is also strongly correlated with the policies, education and prohibitions against smoking.