Nov. 18, 1998 ATLANTA -- Cool weather, holiday parties and big family dinners: it all adds up to more chances to overeat. But genetics have a much stronger influence in pulling us to the table than do weather or social situations, says Georgia State University Psychologist John de Castro, whose research shows that heredity may have more to do with what, when and how much we eat than any other factor.
A few years ago, de Castro published research showing that people tend to eat more as the weather cools and they spend more time feasting in larger groups. Now he's zeroed in on why: it's genetic. He studied adult twins who kept diaries on their food intake for several months, finding that the amount, type and frequency of their eating was indeed influenced by everything from change of season, the number of other people present and Circadian rhythms, but that no single factor influenced people's eating patterns more than genetic makeup.
Heredity probably influences how we respond to environmental changes like cooling weather and large-group social situations in the first place, de Castro says.
"We find that identical twins, even if they live in completely different environments, tend to eat about the same amount of food, " de Castro says. The amount of carbohydrates, fats and proteins they ate were also similar, the study showed. They even ate at similar times. "It's all influenced by genes."
A behavioral psychologist, de Castro used computer modeling to study the diet-diary reports of more than 250 pairs of adult fraternal and identical twins who lived and ate apart from each other in an effort to determine how genetics affected what they ate; the results indicated overwhelmingly that genetics affect all aspects of eating behavior.
Think about all the factors that can influence what you eat during the course of a day. One day you're invited to a banquet and surrounded by a huge amount of food; the next day you go to dinner with a large group of friends and overeat; the next day a hectic schedule forces you to skip a meal. De Castro wanted to know how we regulate food intake when it's obviously influenced by so many different things.
"That's what's so intriguing -- heredity indicates how this can occur. Genes dictate not only the amount of body fat a person has but also how much they want to be in a particular social situation, and how much they eat while they're there," de Castro says. "So genes are not only influencing behavior, but they also seem to be indirectly influencing the environment."
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