By Coach Steve

Optimal fueling for our bodies during endurance sports is a complicated topic. We all need some fat in our diets for our bodies to function properly, but as endurance athletes we also need it to fuel our training and racing. Fat is necessary for our bodies to synthesize hormones, chemical messengers that activate various bodily functions.

Most nutritional counselors recommend that sedentary individuals consume no more than 15% of their total calories as fat. Many exercise physiologists differ on this opinion, recommending anywhere from 15% up to 30%. The higher values may be necessary for endurance athletes given the amount of energy we need to fuel training and racing in addition to our everyday activities. During aerobic endurance training we burn some proportion of fat simultaneously with glycogen (the stored form of carbohydrates). The ratio of fat to carbohydrate we use is entirely speed dependent. At moderate speeds we utilize a higher proportions of fat to glycogen. As we go faster, the mix becomes progressively more biased toward glycogen usage.

This makes sense when we consider the example of the IronMan distance athlete's metabolism. Physiologists know that well-trained athletes can store only about 2000 (glycogen) calories within their muscle tissue and liver. This is enough to get you through about 2.5 hours of very intense racing. Athletes can't digest carbohydrates fast enough to keep up with the caloric demands of a high quality IronMan effort on glycogen stores alone. My relatively lean (~7% fat) body has approximately 32,000 calories of stored energy as fat (I can't safely use all the calories, but I won't need to). If I keep a reasonable pace, I have several times the caloric energy (with the help of stored fat) that I need to complete an IronMan. If I'm daring (or foolish) and go very (too) fast, I'll burn too high a proportion of carbs and only a little fat. This is the scenario where athletes bonk and "lose it" before the finish. Meanwhile, if I cruise along at a relatively comfortable pace, I can cover 140.6 miles in a day!

Consumption of some dietary fat is important for endurance athletes. Training and racing for Olympic distance athletes probably doesn't require a higher level of fat intake for optimal performance, but that may change for IronMan training and racing. Generally, keep fat intake lower during the off-season's lower volume of training, but a little higher during heavy in-season training.

The ratio of fat, carbohydrates, and protein we consume on a daily basis is important, but even more critical are the types of fat. Saturated fat is the bad stuff; you can check any food label to find out if it's there and in what proportion. Unsaturated fats are the healthier ones to eat, and these can be mono- and poly- unsaturated fats, or omega oils from nuts, seeds, or fish. The fats from animal sources (excluding most fish) are saturated. Animal sources include all meat and dairy products. Poultry is a little better than red meat due to its lower overall fat content. The tropical oils (e.g., palm kernel, coconut, and cottonseed) should be avoided. These are cheap for food manufacturers, and are used in many processed foods like cookies and other baked goods. Most other vegetable oils are not as bad, except hydrogenated and partially hydrogenated vegetable oils, which should be avoided. These are also known as trans-fats because hydrogen is added and the molecule becomes stiffer as its molecular shape changes from 'cis' to 'trans'. Hydrogenated fats give processed foods a longer shelf life; fresh foods are always better for you. Olive oil and canola oil (Canadian flaxseed) are definitely the best to consume in processed foods and use in cooking. Canola is great because it has virtually no taste, while olive oil does.

Try to be selective about which fats you consume. Stay away from saturated and hydrogenated fats by choosing foods with predominantly unsaturated fats. Also, avoid heavily processed foods that have to sit on the shelf for a long time before they get to you.

Here's a brief explanation of fat (lipid) blood values. There are two major tests that doctors can perform to assess whether you're consuming too much saturated fat. The better known is the cholesterol test. This simply measures the amount of serum cholesterol you have, and generally should not exceed 200 mg/dL (all of our bodies produce and need some cholesterol, but too much is bad). The more important test value is your ratio of high-density lipoproteins (HDLs) to low- and very-low density lipoproteins (LDLs and VLDLs). HDLs are good and allegedly can even scavenge plaque off vessel walls. VLDLs and LDLs are bad and contribute to blood vessel occlusion. Therefore, a ratio where HDL is high relative to LDL is what we want to achieve. The good news is endurance athletes seem to have slightly higher levels of HDLs simply because of their training. Your eating habits can enhance endurance performance as-well-as help you live longer!