Protein sparing effect
I recently received a letter from a reader that asked about the protein-sparing effect of carbs. He sent me the address of a bodybuilding website he had been reading and wanted to know if what the guy who wrote the material said was true.
The basic premise of the piece is that in order to keep from losing muscle during dieting, one has to eat carbs. If no carbs are eaten, then muscle vanishes, or so he would have us believe. Is this true, the reader wanted to know. Let’s take a look.
Here are the pertinent paragraphs from the website:
The first thing you may think of is protein. Protein builds muscle. You learned that in the high school weight room. Protein in excess, however, can be used as energy or converted to body fat. Using protein as energy means less body fat is being used as energy. So, having the right amount of protein plus a little extra “just to be sure” you have enough is optimal, but gross overages of protein isn’t going to help you build muscle or retain it.
Believe it or not, carbs are key to retaining muscle. Carbohydrates and insulin have been targeted as the deadly duo in obesity and weight loss for very good reasons. However, even though excess carbs will make you gain fat fast, the silver lining is that you gain and retain muscle through the same mechanism.
Even when dieting with a lower than normal carb intake, your carbs can be targeted to help you retain muscle, maintain energy levels, and keep your metabolic rate high.
The anabolic effects of carbohydrates have been well documented since a 1940’s study showed them to be “protein sparing.” Compared to a fasting group, those with carbs (still no protein) lost only half as much muscle as those without carbs. Throw protein in and you get the same effect just at a higher level. Those with less carbs lose more muscle. Protein is certainly still king in the body’s anti-catabolism campaign, but carbohydrates are just as important.
Reading these paragraphs gives meaning to the old saying: “A little learning is a dangerous thing.”
Let’s look at what we know for sure about biochemistry and see where our bodybuilder went wrong.
What do we need to maintain life? We need a source of energy to keep our bodily functions humming along. We need blood sugar to feed our central nervous systems, red blood cells, and a few other tissues. And we need water.
Let’s assume we’ve got plenty of water, but we have no food to eat. How do we survive? Where do we get our energy and our blood sugar if we don’t eat?
We get our energy from the breakdown and release of stored fat. The fat we store away as adipose tissue is our energy reservoir, and that’s where we go when we need energy for all our cellular processes. Most of us, even those of us who are not overweight, have plenty of stored fat to last us a long time. Somewhere in one of our books I made the calculation that the amount of fat stored on the body of a 150 pound man was enough to allow him to walk from St. Louis to Miami (at least, I think those were the cities) without eating.
During starvation we get our blood sugar primarily from our muscles. Just as adipose tissue is the reservoir for energy, muscle is the reservoir for blood sugar. We get some sugar from the breakdown of fat, but not much. Triglycerides, i.e., stored fat, are made of three fatty acids attached to a glycerol backbone. When the fatty acids that we are burning for energy are stripped away from the glycerol, the liver converts these left-over glycerol molecules into glucose. Most of our sugar, however, comes from the breakdown of muscle tissue. The liver converts certain amino acids that make up muscle into sugar in a process called gluconeogenesis.
If we starve, our fat stores gradually ‘melt’ away as we use the stored fat for energy and our muscle mass diminishes as we breakdown muscle tissue to provide sugar.
Let’s say that during our period of starvation we find a bag of sugar. If we eat that sugar in amounts small enough to provide sugar to all the cells that need it, we won’t have to break down muscle tissue. We’ll be getting our energy from the fat we’re breaking down and we’ll get our sugar from the sugar, so we’ll retain, or spare, our muscle tissue. From this fact of biochemistry has arisen the notion that carbohydrates are muscle or protein sparing, which they indeed are under starvation conditions.
But what about when we eat? What happens under non-starvation conditions? Let’s say we’re dieting to lose weight. We create a caloric deficit and we burn our stored body fat for energy. If we’re on a low-calorie, high-carbohydrate diet we use the carbohydrate to provide the blood sugar we need, but at the expense of driving up insulin levels and stimulating the fat-storage process. If we’re on a low-carbohydrate diet, however, where do we get the sugar we need to maintain our muscle mass? From the protein we eat.
It’s important to eat plenty of protein while on a low-carbohydrate diet so that the dietary protein can be converted into blood sugar as needed. The author of the bodybuilding piece cautions against consuming too much protein because he believes any excess protein will be converted to fat, which is really stretching the biochemistry. Nature has designed our biochemistry to be efficient. The conversion of protein to fat, although possible, is extremely inefficient, and any excess energy from the excess protein would likely be more than used up in the conversion. As a consequence, dietary protein turning to fat is not something we really need to worry about. Dietary protein will convert to sugar, however, so that dietary protein, like dietary carbohydrate, is protein sparing.
The best way to lose excess stored fat and maintain (or even build) muscle is to eat plenty of protein to provide the building blocks for new muscle and to convert to blood sugar as needed while keeping overall calories low enough so that fat is burned to make up the energy deficit. The best diet to follow in order to accomplish all this easily is a whole-food low-carb diet. Protein is high, calories are low, and the limited carbohydrate insures that insulin levels remain low so that the fat easily flows from the fat cells and makes its way to the cellular furnaces for burning. (Click here for an earlier post disussing the low-calorie nature of low-carb diets.)