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The Truth About Carbs: How Low Should You Go?
Fall is traditionally the time of year for x-c skiers to up their training intensity and do some serious calorie burning workouts. Ironically, it’s also the time of year I get deluged by email from athletes wanting to lose weight, but still get in shape for the upcoming ski season.
That’s when carbohydrate recommendations really get confusing. High carb or high pro? What’s the right diet for an endurance athlete? 
Carbohydrate: The Maximum Requirements
Let’s start by looking at the maximum carbohydrate requirements that an individual could need. Our best information about the upper limit of carbohydrate requirements comes from cyclists who race in the Tour de France. Unlike runners, these athletes can eat a fair amount of food while racing, and indeed, those that win have mastered the art of grazing without missing a pedal stroke.
Just in case you’re not familiar with the Tour, here’s the low down on the event specifics: the race lasts 22 days, course is 4000 kilometers, has 30 mountain passages, and only 1 rest day is scheduled. Obviously, I’m not talking about doing a 10-k; these upper limits are for extreme, intense events. Typically, the average Tour participant is eating 6000-7600 calories per day.
In a controlled study which simulated the Tour de France over 2 days of exhaustive exercise, the effects of providing a high glucose polymer sports drink during exercise was studied in terms of what happened to endurance and protein balance. The results showed that athletes consumed 80% of their calories from carbohydate, with 30% of the carb calories coming from the liquid sports drink, averaging about 8 g carb/pound of body weight. They were able to maintain protein balance, which means they did not break down muscle for energy despite doing exhaustive exercise. Their protein intake was between 1.5 to 1.8 g/kg (.7 g/pound).
A comparison group of cyclists who were given a 50% fructose sports supplement, which is a sweeter tasting, higher osmolarity carb source, were not able to take in as much of the supplement due to tolerance problems. This comparison group was not able to maintain their weight, nor did they stay in protein balance, despite eating the same amount of protein as the high carb group. In fact, they continued to show signs of protein breakdown for the next 36 hours following exercise.
So what does this research tell us? First, if you’re doing back-to-back days of exhausting exercise, carb intake must be at least 8 grams/pound of body weight in order to prevent muscle breakdown. The ingestion of a high glucose polymer sports drinks during exercise is probably necessary in order to meet total caloric requirements and prevent protein from being used for energy. Protein requirements for this type of exercise are about double the RDA for the general population, falling in the range of 1.5 to 1.8 g/kg body weight. For a 150 male, this is roughly 102 – 122 g/day. Most athletes will be able to eat this amount of protein without the use of supplements, however, there is some new research that suggests that the timing of supplements is critical. Following the first 40 minutes after exercise, ingesting a sports drink containing protein in a 4:1 ratio of carbohydrate to protein can speed glycogen repletion for faster recovery.
Carbohydrate Minimum: How Low Can You Go To Lose Weight?
Now let’s look at the other extreme: high protein weight loss diets. I have had a lot of sheepish email from citizen class athletes who are going with the low carb/hi pro approach for weight loss. Not surprising, many of them have been successful. But is this the best approach?
The bottom line is that in order to lose weight, you have to eat fewer calories than you burn off. Calories count. And no matter what diet you choose, all weight loss will be a combination of some fat and some muscle. For an endurance athlete, timing when you try and lose weight is an important consideration. Based on what we’ve learned from the Tour cyclists, intense exercise will promote loss of muscle if energy balance (ie weight maintenance) is isn’t achieved. Clearly, during intense exercise, adequate carb is necessary to prevent muscle from being used for fuel.
Studies on endurance athletes performing low to moderate exercise (45% - 50% VO2 max) tell us a different picture. When exercising at low intensity, given an equal level of calories, endurance trained athletes will burn greater amounts of fat if they are consuming a high protein (1.2 g pro/lb) diet than a moderate protein diet of .45 g/lb. (slightly above the RDA). This increased reliance on fat may possibly reduce the amount of fatigue an active person feels while dieting, because glycogen stores would not become as depleted. For an athlete willing to keep their exercise at a low intensity level, a moderately high protein diet, moderate carb, low fat diet may be a good approach.
What happens if athletes severely limit their carbohydrate intake? Not surprising, it becomes difficult to exercise due to glycogen depletion and feelings of fatigue. Limiting carb to 100-300 g/day may lead to muscle wasting particularly when exercise is performed at higher intensities.
The reality is that most of us will never compete in the Tour de France. We will, however, face weight problems from time to time. Tempting as quick weight loss diets are, experience with training has taught most of us that there are no quick fixes but patience and persistent will eventually pay off.
So how much carbohydrate should you eat? As much as you need. During pre-season training where moderate to heavy workouts are done, carb should be approximately 3.2 – 5.5 g/lb. For high intensity, sustained endurance exercise carbohydrate requirements can be as high as 4.5 – 5.5 g/lb. If you need to reduce body fat, concentrate on a performing easy-to-moderate exercise combined with a balance of protein, carbohydrate and low fat intake. Flexibility in dietary intake, plus recognition of the changes in carbohydrate requirement are essential for success.
All slow and no carb is not the magic formula for weight loss.
Be successful in weight control and in competition. Plan ahead, and adjust diet needs to match training. That’s the right diet for an endurance athlete.
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