Fat Loading and Endurance Athletes

Fat Loading and Endurance Athletes
Written by Linda Kees

Endurance Athletes, should you fat load?
As an endurance athlete, you want to take advantage of any “edge” you can get right?

Fatigue and impaired endurance performance can be caused by depletion of the body’s carb stores (muscle and liver glycogen and blood glucose), therefore, it makes sense to consume a carb-rich meal before exercise and continue to provide the body with carbs during exercise to improve performance. But……what if we could train the body to use fat stores instead of carbs?
Each pound of fat supplies 3,500 calories, while the total amount of glycogen stores in the liver and muscle only amount to 2,000 calories. If we could train our body to use the abundant fat stores and save our glycogen stores, in theory, we could delay fatigue, which, in turn, may improve our performance.

In order to burn more fat during exercise, we need to increase epinephrine and decrease insulin, which is naturally what happens when you exercise below 65 percent of your VO2 max. Once you hit above 85 percent of your VO2 max, your body prefers to use carbohydrate as the fuel source. Why, you ask? It’s very simple, your body can’t keep up with the energy demand and can convert stored carbs (glycogen) to energy much faster than it can fat.

The metabolism of most endurance athletes have an increased ability to use a higher percentage of fat during exercise as compared to a sedentary person. This allows the athlete to exercise longer and delay fatigue and glycogen depletion. In theory, fat adaptation should provide the greatest benefits for ultra-endurance athletes since they compete at lower VO2 max levels (about 65%) and durations over 4 hours. Since trained athletes can efficiently use stored fat, should they “fat load” and skip the “carbo load”?
Long-term Fat Loading: Several studies examined a high-fat diet (67-85%) vs. a high-carb diet (66-74%) for a time period of 2 weeks to 28 days and did find that the body used more fat to supply energy, but overall, did not improve performance except when VO2 max was <60% (most endurance athletes exercise at levels way above this). Long-term fat loading can also be detrimental to those athletes predisposed to high cholesterol levels and heart disease.

Short-term Fat Loading: Many studies have looked at the results of a five-day fat loading period (60-70% energy from fat) followed by one day of carb loading (10gm carb/kg) in trained athletes and performance. Although these studies showed that fat burning was significantly increased, it failed to show any benefit towards enhancing performance. In fact, one of the studies showed that fat adaptation may actually impair utilization of carbs when needs are high (higher VO2 max).

Endurance and ultra-endurance athletes can still gain an “edge”, but unfortunately, it will not be from fat-loading. Competitive moves at high intensities such as “breaking away”, pushing during an uphill stage and sprinting, all are fueled by carbohydrate, no matter how hard you train your body or what you eat. Fat loading and adaption appears to interfere with the ability to quickly convert carbs to energy and does not enhance endurance performance, therefore, there is no reason to use this strategy unless you are unable to give up your bacon, lard and pork rind habits.

Bottom line: stick with a high carbohydrate training diet to provide quick, accessible energy and healthy foods to fuel your ride!