High cholesterol in anorexia nervosa

One of the (many) paradoxes of anorexia is that the excessive weight loss that accompanies the disorder often results in high cholesterol levels. This seems to go against what many doctors and researchers say about cholesterol: decreasing food and fat intake as well as increasing exercise should decrease cholesterol levels, not raise them.

It turns out that this high cholesterol (formally known as hypercholesterolemia) also happens to starving people, and is a well-known side effect of malnutrition. The question that remains, then, is why? Why this paradoxical effect?

Let me back up a bit and explain what cholesterol is and what it does. Cholesterol "is a lipidic, waxy alcohol found in the cell membranes and transported in the blood plasma of all animals. It is an essential component of mammalian cell membranes where it is required to establish proper membrane permeability and fluidity." Cholesterol is hydrophobic, meaning it doesn't dissolve in water or blood, so it is transported in the body by lipoproteins. Your total cholesterol count is a combination of triglycerides, low-density lipoproteins (LDLs, aka "bad" cholesterol) and high-density lipoproteins (HDLs, aka "good" cholesterol). Both LDLs and HDLs transport fats along with cholesterol. The lipid hypothesis holds that there is a causal link between high intake of saturated fats, hypercholesterolemia, and heart disease, promulgated by none other than Ancel Keys, he of the Minnesota Starvation Study.

So. What does this all mean?

Besides just having unusually high levels of total cholesterol, patients with anorexia were found to have unusually high levels of an enzyme called cholesterylester transfer protein (CETP), which swaps cholesterol and fat molecules between the different lipoproteins. The researchers speculated that low levels of thyroid hormones and low breakdown of existing cholesterol contributed to high cholesterol levels, and that "CETP activity increases cholesterol turnover as an adaptation to its low intake." The highest levels were seen amongst AN patients who also binged and purged. In severely malnourished AN patients, however, cholesterol levels and CETP activities drop dramatically.

Other studies have suggested that starvation results in the increased synthesis of lipoproteins. It could also be that these lipoproteins are transporting fats in the body, which the body is relying on as fuel due to insufficient food intake. If the body is going to rely on fat as fuel, it needs some way to mobilize those fat molecules and get them to a location where they can be broken down effectively. This could perhaps explain the abnormal rise in cholesterol levels. As body fat is essentially depleted in the severely malnourished AN patients, the body may rely more and more on breaking down organ and muscle tissue, thus decreasing the need for abundant lipoproteins.

Regardless of the reasons for hypercholesterolemia during anorexia, it is NOT an indication that the sufferer needs a low-fat or low-cholesterol diet. With sufficient foot (and fat!) intake, cholesterol levels typically right themselves rather rapidly.

(cross-posted at ED Bites)