How dietary carbohydrates cause weight gain

Part 5: Low-fat diets cause muscle loss

There is more to the question about which is the better way to lose weight than mere weight loss. I asked earlier what it was you wanted to lose, and suggested that it was fat. All weight loss diets will reduce your weight, but not all of them do it by reducing fat.

With all low-fat, calorie controlled diets, weight is lost from muscles. This is because, deprived of its necessary supply from carbs and conditioned to using glucose as a fuel, the calorie-controlled dieter's body uses an alternative source to produce glucose: proteins from lean muscle tissue are cannibalised and that weakens you.

So this is another area where low-carb diets win over the low-calorie ones: by changing the dieter's body to using fats, they preserve muscle mass and favour fat loss. This effect was ably demonstrated in the small study done by Dr Charlotte Young in the early 1970s.[1]

Her overweight patients all consumed 1800 kcal per day and they all consumed 115g of protein per day. Only the fat and carb content was varied. Those eating the most fat (133 g/day) and least carb (30 g) lost more body fat and less muscle mass than those getting less fat (103 g/day) and more carb (104 g/day) .

When we are talking of obesity, these findings are tremendously important. Muscles use more energy than fat. This means that, if muscle mass is lost, this lowers the rate at which your body uses energy. Weight loss that involves a significant loss of muscle mass is much more likely to result in rebound weight gain. So that's another good reason to lower your intake of carbs, not fats.

References

1.Young C. Weight Loss on 1800 kcal Diets varying in Carbohydrate Content. Am J Clin Nutr 1971; 290-6.