Is it possible to diet your way into shape? Last year, a study with the title, “Weight Loss With a Low-Carbohydrate, Mediterranean, or Low-Fat Diet,” published in the New England Journal of Medicine reported on the two-year effectiveness of these three types of diet for overweight people. The best results came from low-carbohydrate diets, and there were no signs of the health risks that opponents of these diets claimed would exist.

The results of this study are certainly encouraging. It looks like all we need to do is go on a low-carb diet and we’ll shed those excess pounds faster than with any other diet. Or is it? Unfortunately, there’s more to the story, and even the most effective diet ever won’t give you true fitness and health.

One major problem with basing your fitness plans on dieting is that diets don’t take into account this muscle loss. Effective diets may take fat off your frame, but they don’t help prevent this muscle loss, much less help you build additional muscle. It is an established scientific fact that starting at the age of 30 or so, we gradually begin losing muscle mass. Without taking steps to remedy this, a person will typically lose 5 to 10 pounds of muscle mass for every ten years they age. That’s a lot of muscle, and something that a diet won’t help you with.

Now this latest study didn’t specifically look at muscle mass (a search of the original report didn’t even turn up a mention of muscle) so it’s possible that one type of diet could have more of an effect on muscle mass than another. But going by the results of this study, there’s no reason to believe that any type of diet will do anything special to prevent the gradual muscle loss that comes with age. It’s going to be hard to build an awesome body when your youthful, sexy muscles are slowing fading away.

Second, the results cited in this study are pathetic. The participants were overweight men and women, or people with Type 2 diabetes. They were placed on one of three diet approaches. They were also given instructions and materials specific to the diet they were to follow. During the two-year study, each group of people had eighteen 90-minute meetings with a dietician who helped them stay with the plan. People who had trouble sticking to the plan got motivational phone calls as well.

So what were the detailed results of the study? When people stuck with the diet for the full two years, the low-fat diet gave the worst results, followed by the Mediterranean diet, with the low-carbohydrate diet giving the best weight loss results. In addition to weight loss, the diets also caused some welcome changes in blood chemistry, such as lower cholesterol levels. If you want actual numbers, the people on the low-carbohydrate diet lost just over 12 pounds during the two years of the study.

These results are very discouraging. Under more or less ideal conditions, and with some professional coaching, the best type of diet only resulted in the long-term loss of about a half a pound a month. There’s no denying that for an overweight person to lose 12 pounds safely is a good thing, but these results aren’t earthshaking. What about for you? Would losing 12 pounds in 24 months, while simultaneously losing muscle mass, make you happy?

A good diet is clearly an important piece of your health and fitness puzzle. And now we know that a low-carbohydrate diet is probably the best choice whether you want to drop some pounds or avoid getting fat in the first place. Unfortunately, it’s also clear that there’s more to getting and staying fit than diet alone. You’re going to have to invest in a complete fitness program, one that combines exercise and good nutrition.