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Updated 27 December 2013

Eating too much? Blame your genes

Recent research reveals that our genes not only affect the type of foods we choose to eat, but also how much, and how often.

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There is a relatively new area of genetic study that is causing waves in the world of nutrition. It’s called nutrigenomics, and can best be described as the study of the interplay between genetics, diet and lifestyle, and how this affects individuals in their quest to achieve and maintain a so-called healthy weight.

“In the same way that our eye and hair colour are determined by our genes, so too is our individual response to food,” says Yael Joffe, a dietician and leading specialist in the field of nutrigenomics, and director at DNAlysis Biotechnology.

DNAlysis, which opened in South Africa in 2007, is a pioneer in the development of nutritional and lifestyle advice, which is personalised according to an individual’s genetic makeup. This field of study is essentially corroborating what many people who have struggled with weight loss have been saying for years: “I can’t help it, it’s my genes.”

“To a certain extent, this is exactly true,” says Joffe, but she cautions that it’s not as simple as inheriting a ‘fat’ gene, or a ‘thin’ one.

“We now believe that the genetics of weight is governed by over 300 genes,” says Joffe. These gene sets include the most obvious ones, such as those that govern metabolic rates, fat absorption and exercise responsiveness; but also some less obvious and newly-discovered gene sets, such as those that govern taste, hunger and satiety.

Taste is indeed individual

“We assume that everyone tastes food in the same way, but that’s just not true,” says Joffe. For starters, Joffe explains, some people are what she terms ‘high tasters’ while others are ‘low tasters’.

“High tasters experience food flavours very strongly, while low tasters don’t – it’s almost as if the flavours are duller. Because high tasters experience the full flavour of food, they tend to eat less than low tasters do in order to reach the same level of satisfaction. The research has shown that low tasters tend to have a higher body weight,” says Joffe.

Taste sensitivity is largely determined by differences in taste papillae density, which is widely believed to be genetic, although the individual gene governing this density has yet to be discovered.

In addition, within each taste sensation (there are five recognised by humans: sweet, bitter, sour, salty and umami), there are genes that change the way in which individuals experience these taste sensations.

“For example, some people have an enhanced perception of bitter taste, while others have an enhanced perception of sweet,” says Joffe. The logical result is that those who have an enhanced perception of the bitter taste tend to avoid bitter foods (largely vegetables) and often end up replacing them with more energy dense foods – thereby unbalancing their diet and tending them towards a higher body weight. 

Portion sizes

By comparison, those with an enhanced perception of sweet tend to avoid foodstuffs that are too sweet – leaving them in the enviable position of not over-indulging in sweet foods, or even ‘craving’ sweet foods.

“How you taste changes your individual eating experience, which in turn impacts on food choice and thus caloric intake – ultimately affecting weight,” states Joffe.

In the same way that people believe we taste in the same way, they also tend to believe that we experience hunger and satiety in the same way. And again, we’re learning that this is absolutely not true, says Joffe.

She explains that people with a number of specific gene variations are simply hungrier than others, at a physiological level. “In the past, dieticians believed that hunger was behaviourial and environmental – we now know that it is definitely also genetic.”

Satiety, or how people experience being ‘full’, is also largely governed by our genes. “Some people simply feel fuller on smaller portions of food,” says Joffe. “Others require larger food portions to achieve the same level of satiety.”

Genes have also been linked to a propensity towards binge eating and snacking, and even an increased carbohydrate intake.

Don’t blame your parents

Joffe cautions, however, that not all weight problems can be explained by genetics – of course socioeconomics and learned behaviour, as well as physiological and environmental factors play a critical role in the way in which we consume food.

“Nutrigenomics has simply allowed us to understand weight more holistically, and paved the way for dieticians to create diets that are individually personalised according to a patient’s individual genetic make-up.

“A diet that is designed not only around a patient’s lifestyle but also his or her genetic propensities simply has a better chance at success,” Joffe concludes.
 
DNAlysis Biotechnology press release

 
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