In today’s blog post, I will briefly review a fascinating study that was first published in 2005, and that should inform our approach to losing weight and improving our fitness and metabolic health.
A group of researchers led by Dr. Donald Layman (a famous nutrition researcher) at the University of Illinois enrolled a group of overweight women and split them into four groups:
Group 1 was given a diet that accorded with the “food pyramid”, e.g. lots of whole grains, fruits, and vegetables, with moderate amounts of low fat dairy and lean meat. They consumed 0.8 grams of protein per kilogram of body weight (that’s about 0.3 grams per pound), which is the current recommended dietary allowance (RDA). They were not given any exercise to do, but they were kept in a small caloric deficit so as to induce weight loss.
Group 2 was given the exact same diet as group one, but in addition told to follow an exercise program that consisted of light weight lifting for 30 minutes twice per week, and 30 minutes of walking on the other five days.
Group 3 was given the same diet as groups 1 and 2, except that their percentage of calories from protein was doubled to 1.6 grams per kilogram of body weight (about 0.75 grams per pound), and their carbohydrates were cut back a bit to ensure that they stayed on the same number of total calories as the first two groups. Just like group 1, they were not given any exercise to do.
Group 4 got the same higher protein diet as group 3, and the same exercise program as group 2.
All four groups got the same exact number of total calories, and all four groups got the same number of calories from fat. Thus, the only variables being changed between the groups were how much of their calories came from carbohydrates versus protein, and whether or not they exercised. This is crucial to understanding the results, so before going any further, let me re-summarize the four groups one more time in shorthand:
Group 1 – normal diet, no exercise
Group 2 – normal diet, with exercise
Group 3 – higher protein diet, no exercise
Group 4 – higher protein diet, with exercise
The results were fascinating. All four groups lost weight, which is not surprising, since they were all eating at the same small caloric deficit. However, at the end of four months when the researchers evaluated the groups not just by the scale but by body composition, they learned the following about the weight loss:
Group 1 – lost 65% fat and 35% muscle
Group 2 – lost 75% fat and 25% muscle
Group 3 – also lost about 75% fat and 25% muscle
Group 4 – lost 94% fat and just 6% muscle
Take a look at those numbers again, and you will see a few key points emerge.
First, the group that did by far the best was the group that consumed extra protein AND exercised.
Secondly, the higher protein group that didn’t exercise did just as well as the lower protein group that did exercise. In other words, eating more protein was about the equivalent of exercising for 30 minutes per day.
Third, the first group lost weight, but a large percentage of that weight was from muscle, not fat, and therefore it is debatable as to whether that weight loss really did much to improve their health. In fact, each of the first three groups lost more muscle than desirable.
And fourth, it didn’t take that much exercise to see big improvements in body composition. Both of the exercise groups (group 2 and group 4) outperformed their “diet peers” (groups 1 and 3) just by doing light exercise for 30 minutes per day.
One more point that this study highlights is that the scale is only a blunt and imprecise tool for measuring body composition and metabolic health. All four of the above groups lost approximately the same amount of weight, and so by the scale their outcomes appeared to be similar. But once they were evaluated with a body composition scanner, it became clear that the higher protein diets really were superior, and that while exercise did not lead to additional weight loss, it did help to ensure that more of the lost weight came from fat versus muscle.
To be clear, maintaining muscle isn’t just about looking better at the beach. Lean body mass and improved strength are linked to better metabolic health, lower risk for diabetes, and even to having a lower risk for dementia. Preserving muscle tissue during a weight loss phase also reduces the chance of weight regain once the diet is over.
Bottom line: if you want to lose weight, keep it off, and improve your health, a great place to start is by increasing the percentage of your diet that comes from protein and incorporating at least a little bit of resistance exercise into your life. If you are just eating less calories and doing lots of cardio, the science suggests you won’t get nearly as much benefit. Which is NOT the same thing as saying that eating fewer calories and doing cardio aren’t beneficial – they are. But they shouldn’t be the exclusive focus of your efforts.
