WHY WE ARE OVERWEIGHT?

Hamburg - For some, just a small piece of cake with coffee is a setback in the battle of the bulge, while not even a couple of cream puffs can tip the scales in other people’s disfavour.

Genes affect weight more than environment and upbringing or so it seems to many people, especially if they are fat.

In a pioneering study of more than 500 adopted children in the 1980s, United States psychiatrist Albert Stunkard found that their weight correllated largely to that of their biological, not adoptive, parents.

Earlier this year, a University of St Louis team headed by James Romeis presented results of a long-term study of male twins, identical and fraternal, who served in the US military during the Vietnam War. The team concluded that about 50 percent of the men’s weight change was genetic.

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Genetic tests may help guide eating
Clearly, our genes fat-storing capacity has been selected by evolution for physically active people facing periods of going without food. So office workers who constantly snack are often overweight.

But genes’ influence on weight, though considerable, is not total, said Professor Volker Pudel, a nutritional psychologist from the University of Gottingen.

“Environmental factors are also important. And people can shape their environment to a degree.”

But why are there slim office workers who neither exercise nor diet? Again, part of the answer is genetic predisposition.

“The rate at which food is metabolised depends on one’s genetic make-up,” explained Annette Schurmann, a pharmacologist at the German Institute of Nutrition Research in Potsdam.

‘You can eat more intelligently when you know what your personal risks are’
The chemical basis of obesity is known to some extent. Some overweight people have a defective melanocortin-4 receptor, which means their brains receive messages from leptin, the appetite-blunting hormone, poorly or not at all. Other overweight people, though very few, have a defective gene for leptin.

Released by the body’s fat cells, leptin plays a major role in obesity in any case, Schurmann said. The more fat cells a person has, the more leptin the cells release. But the body develops resistance to the excessive amounts of the hormone, and does not react normally to it.

“For example, the hormone doesn’t bind to the receptor as well, or the message is passed on in a weakened form,” she said. So the urge to eat is not curbed - a vicious circle that is hard to break.

The trick is to monitor one’s weight early, and adjust eating habits before the scale shows 20 kilogrammes too many. The more out of balance the various chemical messengers are, the harder it is to establish the balance, Schurmann said.

Genes not only affect metabolism and appetite, but also taste. People with a certain gene type, for instance, have an aversion to cabbage and spinach.

As Professor Wolfgang Meyerhof from the Institute of Nutrition Research discovered, such people are especially sensitive to the bitter constituents of those foods.

On the other hand, people who do not taste the bitterness at all, tend to eat more fat and be overweight.