Effects of milk protein supplementation in older adults

A meta-analysis of Randomized Controlled Trials

Protein plays a role in the building and maintenance of muscle mass. The effects of milk protein supplementation on body composition in older adults, when combined with resistance exercise, were examined in several recent randomized controlled trials. Meta-analysis of these studies shows that milk protein supplementation in combination with resistance training has a positive effect on fat-free mass in older adults.

Summary | This meta-analysis of 10 Randomized Controlled Trials shows that supplementation of milk protein in combination with resistance training is effective in increasing fat-free mass in adults aged 60 years and older. Exercise and a varied diet which includes an adequate amount of protein contributes to the maintenance of muscle mass.

Gradual changes in body composition occur as part of the natural aging process which result in the percentage of fat mass increasing and fat free mass decreasing. A healthy lifestyle which includes physical activity and a varied diet with sufficient amounts of protein can slow down the rate of these body composition changes.

Milk protein

Proteins consist of chains of amino acids which are classified as essential amino acids (n=9) and non-essential amino acids (n=11). The body cannot synthesise the essential amino acids itself and therefore these need to be obtained through food. The essential amino acids are: phenylalanine, histidine, isoleucine, leucine, lysine, methionine, threonine, tryptophan and valine. Milk protein has a high digestibility score and contains all nine essential amino acids in high amounts. Next to that milk proteins are widely available and relatively inexpensive. Read more on the quality of milk protein.

Study characteristics

Effects of milk protein supplementation in older adultsResearchers Hidayat et al (2018) performed a meta-analysis of Randomized Controlled Trials (RCTs) to examine the effect of milk protein supplementation, in combination with resistance training, on body weight and composition in adults aged 60 years or older. The meta-analysis includes 10 RCTs and a total of 574 participants with a mean age range between 60 to 80.8 years. Four studies were performed in the Netherlands, three in the United States, one in Australia, one in Italy and one in Canada.

Protein supplementation

The amount, timing and protein source differed between the 10 RCTs in the meta-analysis. The researchers provide an overview of all the study characteristics described under the Methods section of the original publication. Participants in the intervention group received a protein supplement, consisting of milk-based beverages, a combination of whey protein, casein and egg albumin, whey protein concentrate, casein hydrolysate, milk fortified with calcium and vitamin D3, milk protein concentrate, or whey protein. In seven studies the participants in the treatment group received this supplement on a daily basis, whereas in the other three studies participants received a protein supplement on training days only. The placebo group performed exercise training but did not receive a protein supplement.

Exercise training

The type, duration, intensity and frequency of resistance training varied between the 10 RCTs. An overview of the training characteristics is depicted in this table:

TABLE Characteristics of resistance training

Duration 12 – 72 weeks
Frequency 3 workouts / week (range: 2 – 5 workouts / week)
Type Whole body training (9 studies)

Lower-body training (1 study)

Intensity 79% of 1 repetition maximum (range: 70-85%)

Results

The researchers observed a positive effect of milk protein supplementation when combined with resistance training on fat-free mass in the elderly. Participants who received resistance training and a protein supplement gained on average 740 gram fat-free mass (95% CI: 0.30-1.17 kg), which was a significant difference compared to the placebo group. The gain in fat-free mass was even bigger among those who experienced age-related loss of muscle mass, frailty and loss of mobility. The older adults receiving exercise training and a protein supplement, gained on average 1600 gram fat-free mass (95% CI: 0.92-2.28 kg). Studies using whey protein resulted in a greater gain of fat-free mass, compared with other milk protein supplements. The researchers gave various explanations for this effect: whey protein is digested and absorbed rapidly and whey protein contains relatively high amounts of the essential amino acids in particular leucine. Overall, there was no effect of milk protein supplementation combined with resistance training on total fat mass or body weight.

Conclusion

Hidayat et al (2018) concluded that supplementation of milk protein in combination with resistance training can increase the fat-free mass in adults aged 60 years and older. Exercise and a varied diet including sufficient amounts of protein contribute to the maintenance of muscle mass in older adults.

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