PROTEIN SOURCE & RECOVERY FROM RESISTANCE EXERCISE: THE ADVANTAGES OF MILK

Studies have examined the effect of the source of dietary protein, specifically milk, on muscle protein balance and muscle accretion after resistance exercise (1,40-42). An early investigation in young adults showed that milk consumption following resistance exercise resulted in the uptake of the amino acids, phenylalanine and threonine, by the exercised leg, which is representative of net muscle protein synthesis (40).

More recently, an investigation in eight young men who regularly participated in weight lifting activities found that consuming fat-free milk after a single or acute bout of resistance exercise (i.e., lower body leg workout such as leg press, hamstring curl, knee extension) resulted in a greater net muscle protein balance and 34% more muscle protein synthesis over the three hours following exercise compared to intake of a soy protein beverage (41). The beverages were equal in protein, carbohydrate, fat, and calorie content. Because the protein (amino acid) content of the two beverages was similar, the researchers hypothesized that the differences in net muscle protein balance and muscle protein synthesis were likely due to differences in the delivery of and patterns of change in amino acids (41). Specifically, the slower digestion of milk protein (which contains an ~1:4 ratio of whey [fast] to casein [“slow”] proteins) than soy protein (which contains “fast” proteins) can be expected to result in a more gradual and sustained release of amino acids into the bloodstream that are available to muscle over time (43,44). Thus, consuming milk following resistance exercise may lead to a greater increase in muscle mass over time than intake of a soy protein beverage. The researchers speculated that milk consumption following resistance exercise may be particularly valuable for persons with compromised muscle mass, such as older adults (41).

To determine if the short-term benefits of consuming milk following resistance exercise shown in the study previously described (41) translate into superior gains in lean body mass over the long-term, researchers conducted a randomized controlled trial in 56 healthy young men who were moderately active, but not participating in any weight lifting activities (42). During the 12-week study, the men participated in a resistance exercise program five days/week and were randomly assigned to consume two cups of one of the following three beverages immediately and then again one hour after exercise: fat-free milk; a fat-free soy protein drink (calories, nitrogen content, and proportion of macronutrients matched to milk); or a flavored carbohydrate drink (calories matched to other study drinks). Skeletal muscle, body composition, and strength were measured before and after the 12-week program (42).

According to a new study, young men who consistently drank fat-free milk following resistance training improved their body composition, gaining more muscle mass and losing more body fat over time, than when they consumed a soy protein or carbohydrate only beverage.

Results showed that muscle mass increased in all groups throughout the training period, with the greatest increase seen in the milk group. Participants in the milk group gained nearly 40% more muscle mass than the soy protein beverage drinkers and over 60% more muscle mass than the carbohydrate only beverage drinkers (42). Also, those in the milk group lost significantly more body fat (2.9 pounds) than those in the carbohydrate drink group (1.1 pounds) or the soy drink group (0.4 pounds). The researchers (42) speculated that the milk group’s higher overall calcium intake (~700 mg/day greater) and/or properties of milk proteins themselves (e.g., relatively high leucine content) may explain the greater loss of body fat observed in the milk group (39,45-47).