Joe Proietto
Professor of Medicine at Melbourne University

Obesity is a significant health problem in Australia, with over 50 per cent of women overweight or obese, according to research in the Medical Journal of Australia. The main reasons are changes in lifestyle (think technical advances) and the availability of energy-dense foods. But how much is caused by genes and how much by the modern environment? The main evidence comes from twin and adoption studies, which demonstrate genes play a bigger role than environment in determining body weight. Research published in the New England Journal of Medicine, which studied more than 670 twins, found identical twins reared apart had the same high correlation in body weight with their twin, irrespective of being raised together or not. Adopted people resemble their biological parents in body weight but have little resemblance to their adoptive parents who’ve fed them their whole lives. What’s more, body weight is physiologically defended at a preset point (the weight range our body fights to maintain), found another study in the New England Journal of Medicine.

Most cases of obesity can be explained by the phenomenon of epigenetics, in which genes are altered permanently by an environmental factor, such as nutrition during pregnancy or what children are fed after birth. In future, we’ll need to focus our efforts on preventing children from becoming obese by discovering the environmental factors that are epigenetically imprinting children to become obese in the first place.”


Amelia Burton
Health and fitness coach

There’s no question that many people who diet put the weight back on, but to blame our genes isn’t accurate. Of course genes play a key role in our physiological make-up, but recent findings from the University of San Francisco, US, found lifestyle and environmental factors (diet, physical activity and stress) influence the way our genes express themselves. Until recently, we believed we’re born with a set number of fat cells (determined by DNA), and throughout our lives these fat cells grow or shrink. British researcher Professor David Barker found when a child becomes obese, their genetic expression shifts, and they’ll grow more fat cells that’ll stay with them for life. Similar research from Baylor College of Medicine, US, found if a pregnant woman is obese, the chance of her child becoming overweight is increased significantly. However, if this same woman, with the same genes, reduced her weight to a healthy level before she fell pregnant, her child’s risk of obesity falls. This is because we now know that certain genes can be switched ‘on’ or ‘off’ based on lifestyle choices.

We can’t blame genes alone for rising obesity levels. Many other factors affect our weight, such as reduced incidental activity, daily kilojoule intake, high fat, low nutrient food (nutritionally poor, kJ-dense fast food), as well as junk food advertising. In short, we can control the destiny of our waistline.”

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