”…low carbohydrate diet sets the stage for a significant loss of lean tissue as the body recruits amino acids from muscle to maintain blood glucose via gluconeogenesis.”
Exercise Physiology, Mcardle, Katch & Katch 2007
There is one aspect of human metabolism that is too often overlooked in the discussion of human nutrition and exercise metabolism. It is the simple fact that there are two energy sources for our cells. Energy from the food we eat and energy from energy stores in our body (glycogen and fat).
I am often met with the claim that muscles cannot hypertrophy if you are in a negative energy balance. I am willing to agree that the claim does seem plausible, but it is misunderstood. It is misunderstood because we have to view the energy situation from the muscles point of view.
The muscles do seem to require a positive energy balance to grow, but they require a local positive energy balance, not a whole body positive energy balance. Simply put, the muscles may have surplus energy even though we consume less energy than we expend, provided the energy stores give out enough energy.
Local cellular energy availability does not necessarily reflect whole body energy availability. This means that we can loose weight as fat while gaining muscle mass even if our body is in a negative energy balance.
Loss of muscle mass or lean body mass is common in weight reduction studies. The number is often as high as or higher than 30% of total weight lost. This is counterintuitive. The point of loosing weight when you are overweight is to lose fat not muscles.
It seems that in studies of low calorie diets that the muscles often lack the energy to maintain their size. In a recent study by Wycherley et al, 59 overweight persons with diabetes did calorie restricted diets combined with supervised resistance exercise 3 days a week. You would expect to see an increase in muscle mass from all this resistance exercise, but after 16 weeks the participants had lost on average 2kg of fat free mass.
To be fair, several studies have shown maintenance of fat free mass with weight loss from calorie restriction when combined with resistance exercise. But calorie restriction may not be the best way to tap into the body’s energy stores.
A low carbohydrate diet will increase the availability of the energy stored as fat. In addition, ketone bodies prevent a large use of proteins for glucose production. Contrary to what the quote at the start of this post claims.
In 2002 Volek et al put overweight men on a 6 week diet with only 8% carbohydrate. The study caused an obvious decrease in fat mass, but in combination with a significant increase in lean body mass, without a resistance exercise intervention.
Willy et al put six overweight adolescents on a ketogenic diet and observed an average weight loss of 15.5kg in combination with 1,4kg increase in lean body mass. All in eight weeks.
Individual results in studies show that it is possible to markedly increase muscle mass while reducing fat mass. I’ve personally seen large reductions in fat mass in combination with more large increases in lean body mass from a combination of carbohydrate restriction and resistance exercise.
My point is that if muscles require a positive energy balance to hypertrophy, carbohydrate restricted diets offers an effective way of giving muscles the energy they need while reducing fat mass. Future studies will hopefully elucidate further.