Sports nutrition: the importance of body fat for the endurance athlete

How much fat should an endurance athlete consume in their diet?

Recently, six endurance athletes at the State University of New York at Buffalo increased their fat consumption by about 60 per cent for a week - and boosted their performances by over 30 per cent!

It wasn't a seven-day pizza party which turned the trick, or even a prolonged sojourn at the local ice cream parlour. The athletes' blubbery diets and prosperous performances were part of an investigation carried out by a team of researchers at SUNY-Buffalo's School of Medicine.

The focus on fat's ability to promote endurance wasn't exactly new. After all, the first North-Pole explorers needed a 60-per cent-fat diet to sledge-dog their way to the top of the world, and various scientific studies have linked high-fat diets with heightened perseverance during prolonged exercise. In addition, some sports nutritionists have contended that high-fat diets 'teach' muscles to metabolize fat during exercise, conserving precious glycogen and giving muscles greater access to the most bountiful source of energy in the body.

In the SUNY-Buffalo inquiry, the six accomplished athletes, all of whom were training more than six hours per week, consumed their normal diets for one week, a high-fat diet for the subsequent week, and a high-carbohydrate diet for one final week. At the end of each week, the athletes participated in an endurance test, which consisted of running as long as possible on a treadmill at an intensity of 75-85% V02max (85-92 per cent of maximal heart rate).

The normal diet consumed during the first week contained only 2800 daily calories, about 700 calories less than the athletes really needed, according to the Buffalopian scientists. The normal diet was composed of about 61-per cent carbohydrate, 25-per cent fat, and 14-per cent protein.

During the following week, the high-fat diet crammed about 3500 daily calories into the athletes' bodies, with a composition of just 50 per cent carbohydrate, 38 per cent fat, and 12 per cent protein. Finally, the high-carbohydrate eating also provided 3500 calories per day, with 73 per cent coming from carbos, 15 per cent from fat, and 12 per cent from protein.

We all know that the lofty carbo eating produced the best performances, right? Well, carbo consumption was definitely better than 'normal' eating; the athletes stayed on the treadmills for 76 minutes after a week of carbohydrates, compared to just 69 minutes with their normal fare. However, the best dietary plan of all turned out to be the high-fat protocol ! After a week of increased fat consumption, the athletes ran for over 91 minutes on their treadmills, a 20-per cent advance beyond the carbo plan and a huge 30-per cent improvement over regular eating.

The Buffalo scientists theorised that a fattier diet fostered better performances by increasing the amount of fat stored inside the athletes' leg muscles. These intramuscular bubbles of fat supposedly provided a rich source of fuel during exercise - helping the athletes to run for a more extended period of time. At long last, it appears that sports-active people can savour bountiful bowls of guilt-free ice cream and other high-fat foods - and then set new PBs in their races!


Actually, don't start stoking in the high-fat sweets just yet, because it' s likely that other factors were responsible for the fatty-diet advantage. For one thing, the Buffalo athletes had to complete an overnight fast prior to all three of their endurance tests. Without even a whisper of breakfast, the athletes also had to finish a maximum treadmill exercise test before they even started their endurance runs. During this maximal test, the grade of the treadmill increased every three minutes until the athletes were simply too exhausted to continue.

The athletes rested for 30 minutes between the maximum exertion and the actual endurance run (again without ingesting a single morsel of food), but they then faced additional hardship during the first 30 minutes of their endurance effort: the scientists jacked up the treadmills so that the athletes were forced to work at 85% V02max (90-95 per cent of maximal heart rate) - an intensity which forced the athletes' muscles to rely primarily on carbohydrate, not fat, for energy.

After those tough 30 minutes, the treadmill grade was lowered so that the poor fellows could run at a more moderate 75-80% V02max, but by then the athletes' leg muscles were probably extremely glycogen-depleted. An overnight fast, abstinence from breakfast, a maximal exercise test, and a 30-minute 'carbo-burner' at 85% V02max will tend to remove most of the glycogen from anyone's leg muscles!

The bottom line is that the cards were stacked against the athletes after their week of eating carbohydrate. During the high-carbohydrate week, their leg muscles had grown accustomed to utilizing carbohydrate as a preferred fuel, but - due to the design of the study - carbohydrate levels were greatly reduced inside their muscles after the first 30 minutes of the endurance test. That threw the advantage over to the fat-eating plan. After a week-long fat orgy, the athletes' muscles were well attuned to the idea of using fat for fuel, so their quads and calves naturally and easily relied on fat when carbo levels dropped, helping the athletes stay on the treadmills longer. The high-fat strategy probably socked more fat away inside the athletes' muscles and converted their blood into a literal river of fat, so the fat-eaters simply had a greater supply of alternative fuel (fat) available when their carbohydrate tanks were drained.

I'd put money on the notion that things would have been far different if the carbohydrate-eaters had taken breakfast on the morning of the endurance tests, avoided the maximal treadmill effort, and started the endurance test at a more moderate pace to avoid carbohydrate flame-out. If the carbo-consumers had also sipped a little sports drink during the endurance test, they probably would have run rings around the fat-eating people, even if the fat-eaters had wolfed down a high-fat breakfast and forced fat into their bodies intravenously.

Let's be realistic. The circumstances which confronted the Buffalo athletes are not the ones you'll face before and during your own competitions. After all, how many competitions force you to fast for 12-16 hours before the race, or participate in a maximal test before the race begins, or start the race far too fast?

High-fat diets might be helpful prior to occasions when you know you'll have to run in a glycogen-depleted state. However, since carbos promote a higher intensity of exercise, compared to fat, competitive athletes should always stack up as much carbohydrate in their muscles as possible - and then keep carbohydrates cascading toward their muscles to prevent glycogen depletion (by taking five to six swallows of sports drink every 15 minutes during an endurance race, for example). Such a strategy will always keep you moving toward the finish line at a faster pace, compared to a plan which forces your muscles to rely primarily on fat. It's also more efficient. Bear in mind that for each litre of oxygen that you consume, carbohydrate yields 7 per cent more energy than fat.

However, that doesn't mean the Buffalo study should be ignored. The fact that the Buffalo athletes' muscles adapted to fat burning after just a week of corpulent eating raises an interesting possibility. What if you could eat in a way that would stimulate your muscles to burn fat efficiently - but also squirrel away lots of carbohydrate? In that case, you'd have the best of both worlds; you would use the abundant carbohydrate to move more quickly and mix just the right amount of fat into your carbohydrate flame, slowing down the carbohydrate-depletion process. There'd be less worry about ingesting the right quantity of carbohydrate during a race and fewer problems if a stomach upset prevented you from consuming a sports drink.

Miller and Lapachet

Enter Wayne Miller, a researcher at Indiana University, and Richard Lapachet, his graduate student. Together they've come up with a neat dietary plan which may super-saturate leg muscles with glycogen and also promote efficient fat utilization.

In the ingenious Miller-Lapachet research, 48 male rats trained on treadmills for eight weeks. 12 rats consumed a high-carbohydrate diet throughout the entire research period (we'll call these rodents the CC group), 12 rats ingested mainly carbohydrates but switched over to a high-fat diet for the final three days of the study (the CF group), 12 rats feasted on fat throughout the eight-week period (FF), and 12 rodents started out with fat but finished with three days of carbohydrate (FC). At the end of eight weeks, Miller and Lapachet tested the rats for both glycogen storage and endurance capacity.

The clear winners in the glycogen-storage race were the FC rats. Consuming fat for eight weeks and then suddenly switching to carbohydrate for three days produced supramaximal leg-muscle concentrations of carbohydrate. In fact, FC rats had 25-30 per cent more muscle glycogen, compared to CC and FF rodents, and 136 per cent more glycogen than the CF group. Why were CF rats so bad at glycogen storage, even though they had binged on carbohydrate for almost eight weeks? Apparently, the prolonged period of carbo-eating had slanted their muscles toward carbohydrate utilization. Taking the carbohydrate away - even for only three days - caused their sinews to rapidly use up their glycogen stores, especially since they weren't accustomed to processing fat.

Better endurance

In terms of endurance, the FC rats again won hands down, hustling along on their treadmills for 467 minutes at just-under marathon intensity (85% V02max). No other exercise group lasted for more than 356 minutes.

Not surprisingly, Miller and Lapachet contend that rat endurance times are optimized when rats adapt to a high-fat diet and then ingest substantial amounts of carbohydrate for a short period of time. Would the same strategy work for humans? 'Human runners who follow a 30-per cent fat diet for several weeks and then switch over to carbohydrates shortly before an important competition should do very well,' says Miller. The idea is that such runners will be great 'fat burners' and will also have ample supplies of high-octane carbohydrate. However, please bear three things in mind:

  1. If the 'high-fat-followed-by-carbo-loading' strategy works, it should only be effective for races longer than an hour or so. In shorter races, the intensity is so high that fat plays only a small role in metabolism, and the race is so brief that glycogen depletion shouldn't be a big problem.
  2. The high-fat diet should be adhered to for only a short period of time (no more than a few weeks). Over longer periods, there would be a risk of gaining unwanted body fat or shifting blood-fat profiles toward an abundance of 'nasty fats' - the LDLs.
  3. In the Miller-Lapachet research, the rodents didn't toss down Ratade (or some other carbohydrate-containing substance) during their competitive efforts. If they had sipped sports drinks, the results might have been different (the CC rodents may have done considerably better). If you take part in long-duration competitions, your best strategy is still to consume lots of carbohydrate during the days before the race, eat a high-carbohydrate breakfast on the morning of the event, and imbibe a sports drink during the competition itself.

So what's the final word? It's not possible to recommend a doughnuts and ice cream diet - if only for a few weeks - just yet. Even though the Miller-Lapachet rats ran best after the fat-followed-by-carbos scheme, things probably work differently in humans, so a well-controlled study with actual male and female athletes is necessary before we can go out on a limb.

If you usually eat lots of carbohydrate and you're convinced that eating more fat might help you, be very wary of regressing to a higher-fat diet for a few days, especially prior to an important competition or a rigorous workout. If you don't follow a fat splurge with at least three days on your usual carbohydrate regimen, the Miller-Lapachet research suggests that you could dramatically increase your risk of glycogen depletion and fatigue.

For now, taking a 'middle ground' on fat intake is advisable. There's no solid evidence that a few weeks of higher fat intake will help you set new PBs, but you shouldn't try to totally eliminate fat from your diet, either. Fat is necessary for the absorption of many vitamins, and a moderate intake of fat can help some endurance athletes who have a tendency to burn far more calories than they ingest.

To increase your chances of performing at your highest level, PP continues to recommend a carbohydrate intake of about four grams per pound of body weight per day during vigorous training, with a significant amount of the carbohydrate ingested during the two hours after a workout - when your leg-muscles' carbohydrate 'doors' are open to their fullest extent.

Owen Anderson

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