5.6: Cholesterol

Cholesterol (Figure 5.2) is found in all cell membranes in the body and helps adjust the membranes’ fluidity (“softness”). It’s flat, so it fits easily between the lecithins aligned in the cell membrane (Figure 9.1). Cholesterol also has other important functions, e.g., it’s used to make sex hormones and the bile acids used in digestion.

Cholesterol is in cell membranes of all animals, so all animal tissues have cholesterol. Plants have trivial amounts, if any. Plants have cell walls made mainly of the fiber, giving plants structural support—we have skeletons for this! Table 5-4 gives the cholesterol content of some foods. Note that cholesterol content is independent of total fat content (e.g., shrimp is high in cholesterol, but low in fat). When margarine, shortening, or salad oil is said to be cholesterol-free, don’t be fooled into thinking that cholesterol was removed. These products come from plants, so any cholesterol content is trivial at most.

Table 5-4: Cholesterol and Total Fat in Foods

Cholesterol isn’t needed in the diet because we can make what we need. When you eat cholesterol, your body can respond by making less (but it won’t completely shut down production). People respond differently to eating less cholesterol; some have a drop in blood-cholesterol but others do not.

Cholesterol is made entirely of carbon, hydrogen, and oxygen, but the body can’t break it down to carbon dioxide and water, as it does with triglycerides.* Thus, when blood-cholesterol, is excessively high, the excess can form plaques in the arteries and lead to heart disease (Chap. 8).

^{*We lack the enzymes needed to break down cholesterol; this means cholesterol is calorie-free. The amount in the diet is tiny (milligrams) compared to the amount of total fat (grams; 1 g = 1000 mg), so its calorie-free status doesn’t really change the 9 cal/g fat used to calculate a food’s calories.}