If you want to lose weight, it's worthwhile cutting out quickly absorbed carbohydrates like those in soft drinks, sweets and white bread, and restricting your diet to slowly absorbed carbohydrates. In 2007 nutritionists at Tufts University published the results of a study which shows that this kind of diet saves muscle mass.
The kind of diet the researchers were studying was a low glycaemic load diet. That meant that the subjects in the experimental group [LG] not only ate slow carbs, but also made sure they didn't eat too many carbohydrates in total. Their energy was derived for 30 percent from proteins, 30 percent from fat and 40 percent from – slow – carbohydrates.
The people in the control group [HG] were given a diet made up in energy terms of 20 percent proteins, 20 percent fat and 60 percent slow and fast carbs.
The test subjects had an average BMI of 35, putting them in the obese bracket. They dieted for a year, eating 30 percent fewer calories than they burned. Not all the subjects were able to stick to the diet.
At first glance both diets seemed to be equally effective in terms of energy burning. But when the researchers removed the data from a couple of subjects who had obviously not stuck to the diet – they'd lost less than five percent of their bodyweight – they noticed that the subjects in the LG group had lost weight in a better way: they'd lost more fat and less muscle than the subjects in the HG group.
A couple of days ago we wrote about an animal study in which mice became more muscular when given low-glyc feed. In that study the animals started to exercise more of their own accord. The researchers suspected that this was why the mice built up more muscle.
Open Nutr J. 2007 Apr 1;85(4):1023-1030.