Everybody knows that when you go on a diet, consuming a bit more protein will help you hold on to hard earned muscle. The reason for this is that, skeletal muscle is your body’s main “store” of protein and when food is scarce the body uses this protein for glucose (sugar) production. You can blame your brain for this. You see, your brain and central nervous system rely almost entirely on glucose for energy, fat is out of the question. In order not to slip into a hypoglycemic stupor, or even worse, a coma, the body has set up a system that goes around breaking down muscle tissue in order to feed its glucose manufacturing centers in the liver. A necessary evil I guess.
So does the type of protein you eat make any difference in how much muscle you save during a diet? Apparently it does. In a recent study in the Annals of Nutrition and Metabolism, they compared the effects of a moderate diet, high-protein diet and resistance training, using two different protein supplements, or the diet alone on body compositional changes in overweight police officers (1). It was a randomized 12-week study. One group was placed on a hypocaloric diet alone (80% of maintenance). A second group was placed on the hypocaloric diet plus resistance exercise plus a high-protein intake (1.5 g/kg/day) using a casein protein hydrolysate. In the third group treatment was identical to the second, except for the use of a whey protein hydrolysate. They found no difference in total weight loss between groups (about 5.5 lbs. for all groups). Mean percent body fat with diet alone decreased from 27 to about 25% at 12 weeks. With diet, exercise and casein the decrease was from 26 to about 18%, and with diet, exercise and whey protein the decrease was from 27 to about 23%. So the mean fat loss was 2.5 (no protein supplement), 7.0 (casein supplement) and 4.2 kg (whey supplement) in the three groups. Lean mass gains in the three groups did not change for diet alone, versus gains of about 4 kg in the casein group and 2 kg in the whey group. Mean increase in strength for chest, shoulder and legs was 59% for casein versus 29% for whey, a statistically significant difference.
I will admit I was really surprised to see such dramatic differences between the casein and whey groups. It should be noted that the dietary habits of these police officers were pretty bad before this study even began. Many weren’t eating enough protein, and most were bingeing on carbs late in the day having not had the time to eat earlier in the day. Just by improving their baseline diet probably had an impact on their muscle mass gains. Still, this brings up the “Fast vs. Slow Protein” study that has gotten so much attention recently (2).
Obviously, whey and casein, although both milk proteins, behave differently and have different physiological effects. There is a lot to discuss about these recent findings. Further research is needed to explain just what peptides in casein are responsible for the anticatabolic effect, or, as Boirie et al demonstrated, whether it is simply a matter of absorption rates. Not only that, but what effect do other nutrients like carbs and fat have on these two protein supplements during a diet? There’s more to come I’m sure…
1. Robert H. Demling, Leslie DeSanti. Effect of a Hypocaloric Diet, Increased Protein Intake and Resistance Training on Lean Mass Gains and Fat Mass Loss in Overweight Police Officers. Annals of Nutrition & Metabolism 44:1:2000, 21-29.
2. Boirie Y, Dangin M, Gachon P, Vasson MP, Maubois JL, Beaufrere B Slow and fast dietary proteins differently modulate postprandial protein accretion. Proc Natl Acad Sci 1997 Dec 23;94(26):14930-5