Q: I have read that runners and other athletes often restrict dietary fat. Is this true? What are trans fatty acids and are they bad for you? What are the recommendations for athletes regarding fat intake and the types of fat?
A: You are correct, research studies suggest that some athletes consume diets very low in fat (e.g. 10-15% total calories from fat) and often low in calories. Insufficient consumption of either carbohydrates or fats can result in muscle fatigue and impair performance. Although limited research exists, dietary fat, like carbohydrates may be important during long duration physical activity for optimal muscle metabolism. However, it should be noted that extremely high fat diets (e.g. 60-70% fat), which are typically very low in dietary carbohydrates, are associated with reduced performance during endurance exercise. It is recommended that a healthy diet consist of 20% of total calories as protein, 50% as carbohydrate, and 30% as dietary fat.
Types of Dietary Fats:
Polyunsaturated fatty acids are found in vegetable oils (e.g. soybean, safflower, corn oil, and sunflower), nuts, and grain products. The essential fats, linoleic and linolenic acid, are polyunsaturated fatty acids and are necessary to consume. They may be protective against heart disease, and play a role in immune function.
Saturated fatty acids are the fats found in animal products such as meats and dairy products. It is recommended to limit your intake of saturated fatty acids because their consumption can raise the level of LDL-cholesterol in the blood, which is associated with coronary artery disease.
Monounsaturated fatty acids are found in olive oil and avocados. These are vegetable fats that may protect against heart disease.
Trans fatty acids are derived from the partial hydrogenation of vegetable oils to make them solid at room temperature. Products that contain trans fatty acids include margarines, crackers, cookies, snack foods, and other foods made with partially hydrogenated oils. Trans fatty acids also increase the LDL-cholesterol, but they have an added effect on reducing the HDL-cholesterol, which is the good cholesterol in the blood.
Omega-3 fatty acids are the long-chain fats found in fish oils. These fats may be protective against heart disease and inflammation.
Trans fatty acids have received more press recently due to their demonstrated effect in increasing the risk of heart disease. It is recommended that we limit our intake of these types of fat and consume polyunsaturated, monounsaturated, and omega-3 fats instead of trans and saturated fats. In the 1995 Dietary Guidelines for Americans it is acknowledged that trans fatty acids raise blood LDL-cholesterol, albeit not the same extent as saturated fat. The Food and Drug Administration has proposed that food labels contain information about trans fatty acid content of products. As a final note, adequate research does not exist to suggest which types of fats may be more or less beneficial for exercise performance.
Rebecca L. Persinger, RD, CNSD, PhD
Rebecca is active in the Seattle running and cycling communities and enjoys other outdoor activities including: snowshoeing, skiing, mountain biking, and hiking.
