Carbohydrate and weight loss: How low should you go?Researchers from University Hospital Geneva tracked a group of 68 overweight men and women for three months [2]. The goal of this study was to compare the effects of two low-calorie diets differing in carbohydrate content (25% and 45%). Most studies compare high-carbohydrate (50-60% of total calories) with low-carbohydrate (30-40% of total calories). What's interesting about this study is that it compares a moderate-carbohydrate diet with a low-carbohydrate diet. Here's what each diet looked like.
In other words, this was a little like comparing the second phase of the Atkins Diet (Ongoing Weight Loss) with the Zone Diet. And the results? The 25% carbohydrate group lost more weight than the 45% carbohydrate group (22.4 pounds versus 18.9 pounds). However, the loss of fat was a lot closer between the two groups — 17.6 pounds for the 25% carbohydrate group versus 15.8 pounds for the 45% carbohydrate group. Both groups also finished the study with less muscle than when they started. The 25% carbohydrate group lost 4.8 pounds of lean mass, with the 45% carbohydrate group losing 3.1 pounds. Unfortunately, the researchers weren't able to distinguish between protein and water loss, so we don't know if this loss came from muscle protein, or water stored in the muscle. Most probably it's a combination of the two. The loss of muscle could have been reduced with the addition of a 3-day per week weight training program and more protein in the diet (0.8-1.0 grams per pound of weight). Participants in the study were only eating between 5.8 and 6.6 calories per pound of bodyweight daily, which is very restrictive. This explains why both groups lost muscle. Research carried in the American Journal of Clinical Nutrition also shows greater fat loss with a diet containing more protein and less carbohydrate [1]. The high-protein diet contained meat, poultry, and dairy foods (27% of energy as protein, 44% as carbohydrate, and 29% as fat). The standard-protein diet provided 16% of energy as protein, 57% as carbohydrate, and 27% as fat. After 12 weeks on the diet, followed by four weeks of energy balance, here's what happened.
As you can see, weight loss was greatest in both the men and women on the high-protein diet. However, the men in this group also lost a considerable amount of muscle. Why? Firstly, even though the diet was described as being high in protein, it still contained little more than 100 grams of protein per day, which is the equivalent of roughly 0.5 grams per pound of bodyweight. With the kind of severely restrictive diet the men were following (6.5 calories per pound of bodyweight), you'd need a lot more protein to preserve lean mass — at least 1 gram per pound of bodyweight, preferably a little more. The research team address this in their discussion of the results: "Proteolysis was not measured in the current study, but the reported protein intake in the HP diet group was 1.1 g/kg ideal body weight for the men and 1.4 g/kg ideal body weight for the women. Presumably, there was sufficient dietary protein to suppress proteolysis and preserve lean mass in the women, but the lower protein intake was not adequate for the men."
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