Nutritional Pharmacology
For the Enlightened Athlete
Food as a drug…and drugs that affect nutrient disposition
By Brian Petty
Dietary Fat and VO2 Max
Forget the fat people, doctors, and talking heads and their carb vs. fat debate. Your nutritional requirements as an athlete bear little resemblance to theirs. There is one compelling reason to add fat to your diet: increasing dietary fat has been shown to increase endurance capacity in athletes. Most studies show maximum oxygen utilization (VO2 max) to increase in as little as five days when consuming 30-50% of calories as fat. There it is: eat more fat, increase your respiratory capacity.
Muoio and colleagues found that after only seven days on a diet of 38% fat, elite runners were able to increase their time to exhaustion and VO2 max. Changing fat intake from 15% to 38% increased subjects' maximum oxygen uptake by 11.4%! It is crucial to note that these were not novices but Division I middle distance runners logging 50+ miles per week. The conclusions: "…our data indicate that endurance performance may be optimized by a fat-rich diet…severe restriction of dietary fat may be detrimental to endurance performance."
Why would large amounts of dietary fat improve endurance and enhance the training effect? In order to understand this it is necessary to sketch some of the adaptations to endurance exercise. Fat intake reinforces some of these changes in skeletal muscle.
During long duration endurance training you tax your body's energy production systems. As you adapt to this stress you become able to exert the same effort for longer periods or perform higher intensity work or both. This is measured as VO2 max, which describes the maximum amount of oxygen you are able to utilize at any given point.
VO2 has much more to do with cellular energy production than lung capacity or the ability of the blood to transport and deliver oxygen! In fact what matters is whether the oxygen can be used to burn fuel for energy. As Holloszy and Coyle noted in 1984,"…increased endurance in the trained state might in large part be due to metabolic consequences of biochemical adaptation in muscles rather than to improved delivery of O2." The specific adaptations they refer to are increases in the ability to transport and use fatty acids and ketones (breakdown products of fatty acid metabolism) for energy. Fat utilization spares blood glucose and muscle glycogen, delaying fatigue.
Where does dietary fat figure in this equation? The answer lies in a phenomenon known as fuel homeostasis, which simply means that the body attempts to balance intake and use of various forms of stored energy so that a major deficit does not occur. As a result, what your body burns depends more on what you eat than whether you exercise. Cycling won't do it--in order to burn more fat, you must eat more fat. In the words of Roy and colleagues, "fuel oxidation shifts both acutely and chronically to approximate the macronutrient composition of the diet…whereas prior athletic training had no effect on substrate oxidation".
How does your body adapt to changes in diet in the short and long term, and how do these adaptations influence your endurance? As dietary fat increases and carbohydrate intake decreases, enzymes in muscle responsible for energy production change activity level.
There are acute and chronic reasons to increase the amount of free fatty acids and ketones used for energy. The acute response of the body is beneficial to endurance. Long term exposure to high fat diets creates adaptations in energy systems that enable virtually all energy needs to be met by fat oxidation, at least at rest.
Your body burns what it gets. The greater the percentage of fat in your diet, the more energy you will derive from fat at rest and during exercise. Enzymes throughout the body but most especially in skeletal muscle change in response to this fuel mix. The point is not to burn more fat as in lose body fat, but burn more fat at any given intensity because this increases endurance. Eating a high fat diet trains the muscles to do what aerobic conditioning does. The pattern of change is remarkably similar. Endurance athletes store more and use more intramuscular triglyceride for energy.
Summary
• A major adaptation to endurance training is to increase the use of fat as fuel at a given intensity.
• The mechanism of this adaptation is alterations in muscle enzyme activity.
• When athletes eat a high fat diet they burn more fat at rest and when exercising.
• The mechanism of adaptation to a high dietary fat intake is very similar to the effects of endurance exercise.
• There is evidence that the diet-induced changes in fat burning capacity are additive to the training effect.
• Endurance athletes can increase VO2 max by eating 35-85% calories as fat.
• Certain types of fatty acids (polyunsaturated and monounsaturated) have other beneficial effects on health and performance, so they should be used to increase the percentage of dietary fat as carbohydrate is removed.
• Consumption of a high amount of dietary carbohydrate reduces the utilization of fat as fuel and may impair the response to training.
©2003 by Brian Petty
References
1. Brown RC, Cox CM, Goulding A. High-carbohydrate versus high-fat diets: effect on body composition in trained cyclists. Med Sci Sports Exerc 2000; 32: 690-694.
2. Hawley JA, Myburg KH, Noakes TD, Dennis SC. Training techniques to improve fatigue resistance and enhance endurance performance. J Sports Sci 1997; 15: 325-333.
3. Helge JW, Wulff B, Kiens B. Impact of a fat-rich diet on endurance performance: role of the dietary period. Med Sci Sports Exerc 1998; 30: 456-461.
4. Hickson RC, Rennie MJ, Conlee RK, Winder WW, Holloszy JO. Effects of increased plasma free fatty acids on glycogen utilization and endurance. J Appl Physiol 1977; 43: 829-33.
5. Holloszy, JO. Coyle EF. Adaptations of skeletal muscle to endurance exercise and their metabolic consequences. J Appl Physiol 1984; 56: 831-838.
6. Hurley BF, Nemeth PM, Martin WH, Hagberg JM, Dalsky GP, Holloszy JO. Muscle triglyceride utilization during exercise: effect of training. J Appl Physiol 1986; 60(2): 562-567.
7. Lambert EV, Hawley JA, Goedecke J, Noakes TD, Dennis SC. Nutritional strategies for promoting fat utilization and delaying the onset of fatigue during prolonged exercise. J Sports Sci 1997; 15: 315-324.
8. Lambert EV, Speechly DP, Dennis SC, Noakes TD. Enhanced endurance in trained cyclists during moderate intensity exercise following two weeks adaptation to a high fat diet. Eur J Appl Physiol 1994; 69: 287-93.
9. Langfort J, Pilis W, Zarcenzny R, NazarK, Kaciuba-Uscilko H. Effects of low-carbohydrate diet on metabolic and hormonal responses to graded exercise in men. J Physiol Pharmacol 1996; 47(2):361-371.
10. Muoio DM, Leddy JL, Horvath PJ, Awad AB, Pendergast DR, et al. Effect of dietary fat on metabolic adjustments to maximal VO2 and endurance in runners. Med Sci Sports Exerc 1994; 26: 81-88.
11. Okano G, Sato Y, Murata Y. Effect of elevated blood FFA levels on endurance performance after a single fat meal ingestion. Med Sci Sports Exerc 1998; 30(5): 763-768.
12. Phinney SD, Bistrian BR, Evans WJ, Gervino E, Blackburn GL. The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metabolism 1983; 8: 769-76.
13. Pitsiladis YP, Smith I, Maughan RJ. Increased fat availability enhances the capacity of trained individuals to perform prolonged exercise. Med Sci Sports Exerc 1999; 31: 1570-1579.
14. Saltin B, Astrand PO. Free fatty acids and exercise. Am J Clin Nutr 1993; 57 (supplement): 752S-758S.
15. Stepto NK, et al. Effect of short-term fat adaptation on high-intensity training. Med Sci Sports Exerc 2002; 34: 449-455.
16. Venkatraman JT, Leddy J, Pendergast D. Dietary fats and immune status in athletes: clinical implications. Med Sci Sports Exerc 2000; 32: S389-S395.