Ontario: People who regularly do resistance exercises may get stronger and build more lean muscle mass when they add more protein to their diet, a recent study suggests.


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Researchers examined data from 49 previously published studies with a total of 1,863 people who did muscle-building workouts like weightlifting. Participants who boosted their protein intake - whether from foods or from supplements like bars, powders and shakes - added more lean muscle mass and got stronger muscles than exercisers who didn’t add extra protein to their diets.


However, increasing daily protein consumption beyond more than 1.6 grams for every kilogram (2.2 pounds) of body weight didn’t appear to have any added benefit.


“Performing resistance exercise is an effective way to maintain or increase lean muscle mass,” said lead study author Robert Morton of McMaster University in Hamilton, Ontario.


“Protein supplementation is sufficient and necessary to augment increases in muscle mass and strength during periods of resistance training,” Morton said by email.


Added protein didn’t help older adults as much as younger people, however.


Also, the benefits of extra protein were more pronounced for newer exercisers than for people with lots of previous experience with resistance training.


All of the studies included in the research review had healthy adults performing resistance exercises at least twice a week. For each study, participants were randomly selected to stick to their usual diets or add extra protein.


Across all these studies, people adding protein to their diets consumed an extra 4 grams to 106 grams daily. Overall, the most common source of added protein was whey protein supplements, followed by supplement blends.


Ten studies gave people added protein with milk, and another seven examined adding protein with whole foods like beef and yogurt.


One limitation of the study is that researchers didn’t have enough data on older adults to determine how much added protein might help these individuals build lean muscle mass, which typically declines with age. Researchers also didn’t look at what happens when dieters get added protein.


“It has been difficult to cultivate one simple message, quantifying how much protein, what types of protein and whether messages should differ among different populations of people,” said Kelsey Mangano, a nutrition researcher at the University of Massachusetts in Lowell who wasn’t involved in the study.


Still, the findings offer fresh insight into the amount of protein some people might add to their diets to get additional benefits from muscle-building workouts, Mangano said by email.


The results might not apply to people who don’t do resistance training at least twice a week, said Dr. Mingyang Song of Massachusetts General Hospital and Harvard Medical School in Boston.


Adding protein also isn’t risk-free, Song said by email. It can lead to digestive problems and damage the kidneys, and there’s also some concern that it may increase the risk of cardiovascular disease.


“It may result in an imbalanced diet,” Song said. “Thus, a healthy, whole-food based diet should be consumed.”