"You are what you eat" is a frequently used saying to establish the importance of diet in all facets of living. But if the theory proposed by a company called Interleukin Genetics Inc. is right, that saying will change a bit.

People will now say, "You are, so here's what you eat."

The saying will change because Interleukin Genetics does gene testing to determine what sort of diet works best with your DNA. While many in the medical profession are skeptical about the need for such a measure, independent research performed at Stanford University on the efficacy of gene testing for diet was impressive.

Subjects in the study on a diet thataccording to Interleukin Genetic's DNA testing"matched" them lost more than four times the average amount of weight than those who were intentionally given a diet that didn't suit their DNA.

So would I recommend the test, along with its $149 price tag, to a loyal reader who needs to lose a bit of weight?

No, but that doesn't mean that I doubt the validity of the Stanford research. It's simply because there's another way to gain the same sort of insight, it seems to me, without any expense.

And it's something I've written about beforegoing all the way back to the late 1980s.

All you need to know is your body type, which generally reveals your muscle type. Both bits of are extremely valuable in creating not only an enjoyable and injury-free exercise regiment but also an effective diet.

Years ago, William Sheldon, an American psychologist and social anthropologist, believed that there was more to the jolly-fat-guy stereotype. He also believed heavy people were very social and loved comfort, thin people tended to be introverts and had better emotional restraint, and muscular people tended to be loud, aggressive, and bold. As a result, he proposed that your personality was to some degree predicated by your somatotype or body type.

His idea was later discredited, but his system for determining body types endured.

To use his system, you need to take photographs of yourself from all angles (preferably naked) and score yourself from a range of one to seven on three aspects: endomorphy, mesomorphy, and ectomorphy. Endomorphy is the tendency to be soft and rounded; mesomorphy, the tendency to be strong and muscular; and ectomorphy, the tendency to be thin and narrow-boned, especially at the joints.

After objectively judging your photographs, give yourself a from 1 to 7 in all three areas, with 7 being the highest.

To see how the numbering works, let's use Ryan Howard, the Philadelphia Phillies' first baseman as our example.

Although Howard is very muscular, he is also thick-waisted; therefore, he probably could get chubby if he didn't work out and watch what he eats. Let's give him a 4, a middle score for endomorphy, the

Just how muscular is Howard? It's possible that a thin and petite teenage girl reading this has a waist that measures about 20 inches. Howard's arms around his biceps are probably pretty close but not quite that size.

Howard has to be at least a 6 for mesomorphy, the tendency to be strong and muscular.

Howard really shares few qualities with ectomorphs, except that his muscle attachments, especially in the forearms, seem to be close to the joints. This keeps him from having those massive Popeye forearms common on many home run hitters. Give him a 2 here.

So in Sheldon's system Howard's somatotype is a 4-6-2, which suggests that he has more quick-twitch muscle fiber than the typical personvaluable information when creating a workout plan and a diet.

Knowing your somatotype can guide your diet because those who tend toward endomorphy tend to have a slower basal metabolic rate, the speed at calories are burned during normal activities, than an ectomorph.

Because of this as well as the way their internal systems handle blood sugar, high-carb diets often spell doom. Generally, endomorphs do better on high-protein diets, particularly for weight loss.

Since increasing the basal metabolic rate is a key to weight control and an endomorphs is usually low, the best exercise for them is the type that builds muscle while burning calories. An exercise like walking or cycling or aerobic dance generally isn't as effective as weightlifting or stationary rowing or rock climbing.

Mesomorphs, naturally muscular people, often gain unwanted weight as they age and become less active. The best diet to counteract that depends on the total somatotype score.

Mesomorphs who tend toward endomorphy, like Ryan Howard, would do better on a lower-carb diet, but mesomorphs who tend toward ectomorphy, such as Jayson Werth, could consume a higher percentage of carbs and still lose weight.

Ectomorphs, naturally skinny people like Chase Utley, often want to put on muscle but not fat. They need a high-carb diet, to lift weights, and to reduce or avoid aerobic exercise.