Dietary fats

Fat is a family of molecules, not one ingredient that is either virtuous or dangerous. Most of the fat in food and in the body is triglyceride: three fatty acids attached to a glycerol backbone. Phospholipids, which also carry fatty acids, are structural parts of cell membranes. Steroids, including cholesterol, are a different shape and do different jobs, from cell membranes to hormone synthesis. Putting all of those in one “fat is bad” sentence is how clients end up afraid of olive oil and confused about eggs.

Fatty acids worth naming

Fatty acids differ by length and by how many double bonds they have. Saturated fatty acids have none. Unsaturated fatty acids have one or more. The essential fatty acids are the ones the body cannot make in the amount it needs: linoleic acid in the omega-6 family and alpha-linolenic acid in the omega-3 family. They are essential the way essential amino acids are essential. That fact does not mean a supplement is required. It means a diet with no food sources of them, for long enough, fails a basic requirement. Fish, some plant oils, nuts, and seeds are the ordinary sources. A trainer can name those foods. A trainer should not assign high-dose fish oil to treat a disease.

Digestion and the trip through the blood

Fat does not dissolve in the watery contents of the intestine. Bile breaks large droplets into smaller ones so enzymes can reach them. The products of digestion are absorbed into the cells of the small intestine and packaged, because the blood is also watery. Those packages are lipoproteins. Chylomicrons carry fat from a meal through the lymph and then the blood. Other lipoproteins move cholesterol and triglyceride between the liver and the rest of the body. This is the “transport of lipids” the course lists. It is why a blood test reports several cholesterol numbers rather than one. Explaining that a number is a passenger inside a particle is more accurate than telling a client that a food “clogs arteries” on contact.

Fat is energy-dense: about 9 calories per gram, which is why small portions move the day’s total quickly. It also carries fat-soluble vitamins and slows gastric emptying, which is one reason a meal with some fat keeps a client full longer than a meal of only starch. Cutting fat to near zero to “get lean” often cuts calories, and it often makes the diet impossible to stay on. The calorie side of that trade is in calories and the energy nutrients.

For a client with high blood lipids or heart disease, the eating pattern is a clinical question. You can support the training plan their clinician already approved. You should not replace that plan with a list from a magazine.

These ideas are taught in more detail in The Science of Nutrition, a 5-hour continuing-education course for fitness professionals. To enroll, call customer service.