It is claimed that cholesterol in the diet is a causative agent of rises in cholesterol in the plasma. This hypothesis, sometimes called the lipid theory of cardiovascular disease also claims that the cholesterol in the plasma is the cause of atherosclerosis. However, the scientific literature does not support this contention. One case in point are the Masai, a group of nomadic herdsmen that live in parts of Kenya and Tanzania. The Masai have a diet that is very high in cholesterol (and saturated fat) and yet do not have elevated levels of plasma cholesterol. Many explanation have been used to dismiss this observation, including that the Masai are protected from high levels of plasma cholesterol through exercise or genetic factors. However, these explanations are ad hoc hypotheses, and they should not be used to dismiss and observation that falsifies a hypothesis. Clearly cholesterol is not the causative factor in raised levels of plasma cholesterol, other factors must be involved. It is also not established that plasma cholesterol causes cardiovascular disease.
Because of their unique diet and good health, researchers have extensively studied subjects from the Masai. The result of this researcher has produced some interesting studies. For example, in one study1, researchers investigated the effects of large intakes of milk on plasma cholesterol levels. To do this they used two treatments. One of the treatment was milk supplemented with tween (10 mg tween per 20 grams of fat in the milk). Tween is a surfactant and it has been hypothesised that surfactants can increase cholesterol absorption because they increase the formation of lipid micelles in the gut, and this may facilitate the absorption of lipids to the enterocytes. The tween milk also contained olive oil. The other treatment was composed of milk only with olive oil. Olive oil was used to equalise the fat content of both milk treatments. The researchers had hypothesised that the milk treatments would increase plasma levels of cholesterol, particularly the tween containing treatment.
However, when the plasma cholesterol levels of the Masai subjects was measured, the researchers discovered that the cholesterol of both groups decreased. This was despite the fact that the subjects all gained weight on the extra milk that they were drinking. Based on the results of the study, the researchers concluded that milk must contain some anti-cholesterolaemic properties. This data is interesting as milk contains both cholesterol and saturated fat and it would be expected, based on the lipid theory of cardiovascular disease, to increase cholesterol levels in the blood. Milk does not have this effect in Masai, and other studies have shown that it does not have this effect in genetically diverse groups. In fact, observations from nutritional studies show that milk has weight loss properties and may be protective of cardiovascular disease. Those who are lactose intolerant of course cannot drink milk in large quantities, but for other individuals milk appears a healthy food that can supplement a high quality diet.
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