Two of them — cholesterol and triglycerides — can be reduced by eating walnuts

Q: I would appreciate your explanation of the differences between lipids, fats, oils, cholesterol and triglycerides. Along with this, I would like to know if I began eating a serving of walnuts regularly to lower my blood cholesterol level, would that have any effect on my blood triglycerides?

A.R., Del Mar

A: “Lipid” is an umbrella term for a group of chemicals that share one characteristic — namely, that they do not dissolve in water, but will dissolve in organic solvents such as mineral spirits or cleaning fluid. The lipid food items of note include fats, oils, fatty acids, triglycerides and cholesterol.

Fats and oils are similarly built, and the terms are often used interchangeably, especially in the kitchen. The main difference between the two is that fats are solid while oils are liquid at room temperature (77 degrees F, 25 degrees C).

The basic unit of fats or oils is the fatty acid, which is a long chain of carbon atoms with an acid group at the end. The number of hydrogen atoms attached to the carbons in the chain determines whether the fatty acid is saturated or unsaturated, and this defines the nature of the fatty acid. Oleic acid, for example, is the main fatty acid in olive oil. It is 18 carbons long and it has one point of unsaturation. It is referred to as a monounsaturated fatty acid.

Triglycerides are the form in which fats and oils are carried and stored in the foods and in the body. A triglyceride can be visualized as a letter “E” where the three horizontal lines are three fatty acids and the vertical line is glycerol.

As examples, butter is called a fat because it’s solid at room temperature, and olive oil is an oil because it’s liquid at room temperature. Both exist in the form of triglycerides, and each is made up of different combinations of saturated and unsaturated fatty acids.

The final lipid on your list is cholesterol, which is built with a fused ring arrangement known as a steroid. This same structure is present in a number of the body’s hormones, but cholesterol is not a hormone. (If you want additional information on lipids, along with some pictures of their structures, check out

Now, about walnuts. A study in the March 2010 issue of the European Journal of Clinical Nutrition used diets in which 12 percent of the day’s calories came from walnuts (between one ounce and 2.2 ounces of walnuts a day). For the first six months, half of the subjects ate the walnuts and the other half did not; this was reversed during the following six months. The study reported that those who ate the walnuts experienced significant reductions in total cholesterol and triglycerides.

An earlier meta-analysis in the July 2009 issue of the American Journal of Clinical Nutrition provided similar positive information for walnuts on blood lipid levels (cholesterol and triglycerides).

The message here is that walnuts are an excellent food. Understand that the same can also be said for other nuts, including almonds, peanuts and pistachios, and remember that nuts are a high-fat food. The key is to eat them regularly, but in moderation — and not in addition to lots of other high-fat foods.
