Another popular myth about the low carb diet...
One of the most common criticisms of a low carb diet is that it can harm your
performance in the gym. However, what's not so well known is that
overweight people burn less carbohydrate and more fat when they
exercise.
In fact, a recent trial shows that during 60 minutes of exercise, overweight
men burn almost 50% less carbohydrate than lean men. While a low carb
diet might not be the best way for athletes to maximize their performance, it's
a perfectly acceptable way to eat if you want to lose fat — even if you're
exercising regularly.
Low carb diet
There are many different variations of the low carb diet, ranging from an extremely
low carb diet (such as the
induction phase of The Atkins Diet) to a moderately low carb diet
(such as The Zone). What all types of the low carb diet have in common is the
fact they reduce the amount of carbohydrate your body stores.
Carbohydrate is stored in the form of glycogen (pronounced gly-ka-jun) in your
liver and muscles. Glycogen molecules are linked together like a chain of sausages.
They can range in size from a few hundred to several thousand glucose molecules.
In total, your body can hold 400-500 grams of glycogen (the equivalent of 1600-2000
calories). That's the same amount of carbohydrate found in 25 slices of bread.
Of course, this does vary from person to person. The more muscle you have, the
more glycogen you can store.
Your body has a remarkable ability to adapt to what you eat. Follow a low carb
diet for just a few days, and your body adapts by producing more of the enzymes
that convert stored fat into energy. Not only that, the fuel your body uses
during exercise also depends on how fat you are. Some evidence for this comes
from a trial published in Obesity Research.
Exercise
Seven obese and seven lean middle-aged men with a similar level of aerobic
fitness exercised on a bike for 60 minutes. Results showed that the overweight
men burned almost 40% more fat calories than the lean men. The amount of glycogen
used was also 50% lower in the obese men.
There are anecdotal reports of people performing better on a low carb diet.
However, most trials show that exercise performance is enhanced when your glycogen
stores are higher rather than lower. The confusion in this area often stems
from the misleading comparison between absolute and relative carbohydrate
intake.
• Absolute carbohydrate intake is usually described in grams relative
to bodyweight.
• Relative carbohydrate intake is usually described as a percentage
of total calorie intake.
For example, if you were to consume 5,000 calories, with 1600 of those calories
coming from carbohydrate, then your diet derives 32% of its calories from carbohydrate.
That's an example of carbohydrate intake expressed in relative terms.
If someone weighing 200 pounds ate two grams of carbohydrate per pound of bodyweight,
they would also be consuming 400 grams of carbohydrate. This time, however,
carbohydrate intake is expressed in absolute terms.
For many people, 400 grams of carbohydrate would be enough to keep their glycogen
stores topped up — despite the fact that the diet appears to be
low in carbohydrate when expressed in relative terms. The difference between
absolute and relative nutrient intake is one reason why you'll see conflicting
reports about the effect of carbohydrate on exercise performance.
The bottom line is that for people who want to lose fat, keeping glycogen stores
topped up is less important than for someone aiming to improve athletic
performance.
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Reference
Goodpaster, B.H., Wolfe, R.R., & Kelley, D.E. (2002). Effects
of obesity on substrate utilization during exercise. Obesity
Research, 10, 575-584
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