What protects muscle better when dieting: whey, soy or carbs?

Short-term restriction of calories causes the body to be less responsive to the ingestion of protein. Thus, over time this may lead to greater loss of muscle mass. Very little research has examined whether this negative effect of weight loss on responsiveness to protein can be prevented. 

In one recent study, obese subjects were all randomized to 3 groups and put on a short-term restricted diet (-750 kcal/day) for 14 days. They consumed supplements containing similar calories of whey (27g), soy (26g) or carbohydrate (25g) twice per day. The rate of muscle protein synthesis in response to ingestion of the supplements was tested before and after weight loss. After 2 weeks, all groups lost weight, body fat and muscle mass.

Before the weight loss intervention, the rate of muscle protein synthesis was significantly greater after the ingestion of whey, compared to soy and carbohydrate. As expected, after 2 weeks of weight loss, the rate of muscle protein synthesis decreased for all groups. However, the decline in rate of muscle protein synthesis was less severe in the whey group (-9%) compared to the soy (-28%) and carbohydrate (-31%) groups. The researchers also measured the rate of fat breakdown after ingestion of the supplements and showed the carbohydrate group inhibited the breakdown of fat the most.

Although this was just a short-term study lasting only 2 weeks, the results support a positive effect of whey protein on protecting rates of muscle protein synthesis without suppressing fat breakdown. Such responses would be predicted to translate into better preservation of muscle and body composition during long-term weight loss.


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