This is how exercise and protein reinforce each other's effect on fat percentage and muscle
If you want to tone up you'll have to a. get more exercise (preferably resistance training) and b. eat more protein. Nearly everyone who goes to a gym can tell you that these two factors have a mutually reinforcing effect on each other, but only recently have scientists started to discover this. American nutritionists published a study in the Journal of the Academy of Nutrition and Dietetics which shows exactly how much effect protein consumption and physical exercise have.
The researchers analysed data on 8,298 women aged 50-79. They knew how much exercise the women got each week, and how many grams of protein they consumed daily. The researchers divided the women into five equal-sized groups – quintiles – based on both their protein intake and their exercise.
The quintiles for protein intake are shown below.
We were unable to work out how much exercise the women in each quintile got as that information is not in the article.
The more protein the women consumed, the lower their fat percentage and the higher their lean body mass. The researchers discovered a similar relationship for exercise. They also discovered that protein intake and exercise strengthen each other's effect on body composition.
The positive effects of protein only become noticeable when about 2 g protein per kg bodyweight are consumed daily.
"While it is known that protein supplementation increases muscle mass in the presence of exercise (particularly resistance training) or physical activity, this is the first study to demonstrate a cross-sectional association between habitual activity levels on lean mass in postmenopausal women within a range of usual dietary protein intakes," the researchers wrote. "Protein's positive association with lean mass, as well as the additive effect of physical activity, was observed regardless of BMI category."
"These results suggest that dietary protein's association with lean body mass is maximized when combined with physical activity at or above the minimum American Heart Association recommendations."
"Future research should consider physical activity level as a modifier when relating dietary protein intake to body composition and health outcomes."
J Acad Nutr Diet. 2017 Feb;117(2):192-203.e1.
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