If you follow the high-carb mantra touted by the American Heart Association, the realization eventually hits your cortex that it really isn’t the best diet after all. That’s true for most people. In fact, head-to-head comparisons of high- and low-carb diets typically show that low-carb diets are better or no different for improving body composition.
Limited data exist in terms of the responses of men vs. women, so scientists sought to address that with a 12-month randomized clinical trial with four months of weight loss and eight months of weight maintenance.1 Overweight middle-aged men and women were randomly assigned to energy-restricted diets—a deficit of about 500 calories a day—providing protein at 1.6 grams per kilogram of bodyweight per day or 0.8 grams per kilogram of bodyweight per day, which is the silly recommendation of many clinical dietitians. What happened?
When expressed as a percentage change from baseline, males and females lost similar amounts of weight at 12 months, about 10 to 11 percent, as did the subjects on both diets, about 10 percent each, with no respect to gender. A similar pattern emerged for fat and lean mass. On the other hand, bodyfat was significantly influenced by both sex (men lost 18 percent while women lost about 7.3 percent) and diet (the high-protein subjects lost 14.3 percent, while the high-carb subjects lost about 9.3 percent). So when it comes to reducing bodyfat, the higher-protein diet was more effective than the high carb over the 12-month cycle of weight loss and maintenance. Men lost bodyfat and trunk fat more effectively than women. Yes, it isn’t fair that it’s easier for me—but life’s not fair.
In another intriguing study, the battle of soy vs. whey raged on, and once again, whey won the round, at least in older individuals.2 Thirty elderly men, aged 71, completed a bout of single-leg knee-extensor resistance exercise prior to taking in no protein or either 20 grams or 40 grams of soy protein isolate. The scientists compared those responses to previous responses from similar-aged men who had taken 20 grams and 40 grams of whey protein isolate. Here’s the lowdown.
Whole-body leucine oxidation increased with protein intake and was significantly greater for those who got 20 grams of soy than those who had gotten 20 grams of whey. So soy protein tends to be used as fuel more than whey. Rates of muscle protein synthesis for the 20-grams-of-soy subjects were less than what the 20-grams-of-whey subjects had shown and not different from what those who got no soy experienced in both exercised and nonexercised leg muscles. That’s odd, as it suggests that soy is basically no different from zero protein. Apparently, if you do use soy, you need at least 40 grams of it.
Muscle protein synthesis was also lower in those who got 40 grams of soy compared with 40 grams of whey under both rested and postexercise conditions, but it was greater in the soy subjects than in those who got none under postexercise conditions.
Thus, the type of protein matters—whey is likely better than soy for muscle protein synthesis. Also, the dosing matters. If you take soy alone, you’ll need to get more to elicit the same effect as you’d get with whey. That’s likely due to higher rates of oxidation for soy and its lower levels of the amino acid leucine.
—Jose Antonio, Ph.D.
Editor’s note: Jose Antonio, Ph.D., is an assistant professor at Nova Southeastern University in sunny South Florida.
1 Evans, E.M., et al. (2012). Effects of protein intake and gender on body composition changes: a randomized clinical weight loss trial. Nutr Metab (Lond). 9:55.
2 Yang, Y., et al. (2012). Myofibrillar protein synthesis following ingestion of soy protein isolate at rest and after resistance exercise in elderly men. Nutr Metab (Lond). 9:57.