Research shows higher-protein diets increase lean muscle mass

A new study shows that higher protein diets are better for promoting lean muscle mass and improving fat loss.

This study, out of Iran, specifically focuses on normal-weight obese women. While “normal-weight obese” may be a new term for some, it simply refers to individuals whose weight and body mass index fall in the “normal” range — but they still have greater than 30% body fat.

In conducting this study, 47 women were randomly prescribed a high-protein or low-protein diet, each with equal calories. The study’s high-protein diet consisted of 1.2 to 1.4 grams of protein per kilo of body weight, which averaged 25% of participants’ total calories. The remainder of the diet was 30% of energy from fat and 45% from carbs.

(Based on our definitions at Diet Doctor, this would be a moderate-protein diet. You can learn more in our guide on how much protein we should eat.)

The study’s low-protein diet was 0.8 to 1.0 grams of protein per kilo of body weight per day, which averaged 15% of their total calories. The remainder consisted of 30% energy from fat and 55% from carbs.

After 12 weeks, there was no difference in perceived appetite or overall body weight between the groups (both groups only lost about 1 kilo). However, the high-protein diet group saw significant improvements with a 1.5-kilo greater gain in lean body mass, 1.1-kilo greater decline in fat mass and 1.4-cm greater decline in waist circumference.

It was a bit surprising that appetite did not differ between the groups. Many other studies show that higher-protein meals tend to be more filling, but this trial did not confirm that finding.

We must keep in mind that the diets were matched for equal caloric intake. Why? Because in a “real-world” trial, subjects would likely adjust their caloric intake on their own.

For the purposes of this study, it made sense to isolate the effect of protein on outcomes. Otherwise, a difference in caloric intake could have acted as a confounding variable, thus potentially skewing the results. But, matching calorie intake between groups may have also limited the study’s ability to predict “real world” outcomes.

Additionally, we should note that neither diet was low carb. These were high-carb diets with varying degrees of carb and protein intake. Would a low-carb diet have fared better? Again, many studies suggest it would, but this trial did not assess that.

You can read more about protein and low-carb diets in our evidence based guide.

The main takeaway from this study is a reminder that the protein level set by the Recommended Dietary Allowance (RDA) of 0.8 grams of protein per kilo of body weight per day is the minimum requirement when trying to prevent nutritional deficiencies. This study shows that the target amount for improved health and strength is significantly higher, above 1.2 grams per kilo of body weight per day.

At Diet Doctor, we agree and that is why we recommend a moderate protein diet with 1.2 to 1.7 grams per kilo of reference body weight (notice this is reference body weight and not total body weight. You can see more about this in our chart here). And we have hundreds of recipes that match this protein level and are delicious too!

Thanks for reading,
Bret Scher, MD FACC

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