To Your Health

Q. I have heard about a "thrifty gene" that makes it easy to gain weight. Is it real? How would a person know if they carried this thrifty gene, and what could be done to keep from gaining weight if they do?

A. The evidence for such a gene in mice and rats is convincing, and it is not much of a stretch to believe that a similar gene exists in humans. Eating behavior is influenced by a multitude of factors, many of them psychological, but there are internal influences. Certain messenger chemicals such as Neurotransmitter Y, among about a dozen others, have predictable effects on how much we eat. Other neurotransmitters influence our food choices, when we start eating, how long we eat, how fast we eat, when we stop eating, and how long the interval between meals will last. Each of these chemical influences will be mediated through a receptor in the brain that originally received its instructions from our genes.

The street is not one way. The food we eat, specifically the type and amount of fat, carbohydrate, and protein, also influences the expression of various genes. Probably the best clue to your genetic legacy is to observe the response of your parents and grandparents to their environment. This was easier in earlier times, when people seldom strayed more than 30 miles from their birthplace. Today's multiethnic society makes it very difficult to judge which of our ancestors' genes will affix to us.

The best evidence for a "thrifty gene" in humans comes from the Pima Indians. About 500 years ago, some of this tribe moved into central Mexico while some remained in Arizona. Those in Mexico eat a diet similar to the diet of their ancestors and still do hard physical labor. They remain healthy. Those in Arizona have adopted the white man's ways, eating more fat and refined carbohydrate and expending much less physical energy. More than half of this group suffers from obesity and diabetes. The proposed explanation is a thrifty gene in most of these people, which in the past increased the chance of survival during times of famine.

Because it appears that all human populations share this genetic susceptibility to some degree, as worldwide standard of living rises there will likely be an increase in obesity and other "diseases of civilization."

Fat cells are more than simple storage sites. Fat cells tell the rest of the body when their calorie stores are low and apparently send out a call for more calories by releasing leptin, one of the medium-sized proteins that cells use to communicate with one another. Thus far the search for a way to stifle leptin production in humans has been disappointing, but not for lack of effort. A safe and painless remedy for obesity will make the discoverer wealthy.

The production of leptin depends to some extent on the number of fat cells. Fat cells in adults usually just inflate in size when we overeat rather than increase in number. But at two stages of childhood development, toddler stage and puberty, the number of fat cells can easily increase. So children who are not overweight at these two stages of life generally find it easier to maintain proper weight all through life.

If you suspect you do have "thrifty genes," don't fall for the "Darwin made me do it" excuse. Find a lifestyle (exercise and eating behavior) that you can live with for the rest of your life, which will result in gradual weight loss and work better than the quick fix.