Same Calories, Different Bodies: How Protein Changes Weight Loss

We are frequently told that if you cut calories, you will lose weight. While this is true, we should ask what type of weight are we losing? Is it fat mass, muscle tissue, water, inflammation? I recently heard Dr. Don Layman give a synopsis of a study his lab conducted back in 2005 about this question. Dr. Layman is a professor and researcher at the University of Illinois that has spent decades studying how protein, carbohydrates, and amino acids regulate metabolism and muscle maintenance. The study is titled, “Dietary Protein and Exercise Have Additive Effects on Body Composition during Weight Loss in Adult Women”. Let’s take a look at the study design.

This was a 4-month study that compared four groups: high protein/low carb + no exercise, high protein/low carb + exercise, high carb/low protein + no exercise, and high carb/low protein + exercise. The exercise groups were prescribed a minimum of 30 minutes of walking 5 days per week and 30 minutes of resistance training 2 days per week. The protein groups were prescribed 0.7 grams of protein per pound of bodyweight consuming on average 106 grams protein, 134 grams carbohydrate, and 49 grams fat per day. The carbohydrate groups were prescribed 0.36 grams of protein per pound of bodyweight consuming on average 57 grams protein, 200 grams carbohydrate, and 38 grams fat per day. The calories were the same in both groups at 1700 calories per day.

Let’s look at the results.

The high protein + exercise group reported significantly greater outcomes than the other groups. This group lost 19.4 lbs. of fat and only 0.9 lbs. of muscle. In comparison by weight, the protein only group lost a similar amount of weight (19.2 lbs.), but only 13 lbs. of fat and 4.4 lbs. of muscle. The high carb + no exercise group had the worst outcomes where they only lost 11 lbs. of fat and 6 lbs. of muscle. A reminder here that all groups were on the same 1700 calories per day but different compositions of protein, fat, and carbohydrate.

Lesson of the story? Don’t simply chase weight-loss. Target fat loss and muscle preservation by prioritizing daily protein intake.