THE G.I. FACTOR: WHY DO PEOPLE BECOME OVERWEIGHT?
‘It must be in my genes.’ Before we talk more about food, let’s look at the role genetics plays in weight control. There are many overweight people who tell us resignedly, that:
• ‘well my mother’s/father’s the same’,
• ‘I’ve always been overweight’,
Research shows us that this comment has much truth behind it A child born to overweight parents is much more likely to be overweight than one whose parents were not overweight. It may sound like an excuse, but there is a lot of evidence to back the idea that our body weight and shape is at least partially determined by our genes.
Much of our knowledge in this area comes from studies in twins. Identical twins tend to be similar in body weight even if they are raised apart. Even twins adopted out as infants show the body-fat profile of their true parents rather than that of their adoptive parents. These findings suggest that our genes are a stronger determinant of weight than our environment (which includes the food we eat).
It seems that information stored in our genes governs our tendency to store kilojoules as either fat or as lean muscle tissue. Overfeeding a large group of identical twins confirmed that within each pair, weight gain was similar, however the amount of weight gained between sets of identical twins varied greatly. From this, researchers concluded that our genes control the way our bodies respond to overeating. Some sets of twins gained a lot of weight while others gained only a little, even though all were overconsuming an equivalent amount of kilojoules.
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