Is your DNA to blame for weight gain?

It sounds like the most monumental excuse: ‘I’m overweight not because I stuff my face with doughnuts, but because of my genes’. But if you’re hitting the gym, pounding the pavement or cycling like a whirling dervish and still carrying that last few pounds, it could be your DNA to blame.

Scientists have already identified fat DNA. They have found variations in two important genes that are associated with obesity. Having a specific type of ‘fat mass and obesity’ (FTO) gene and the 'Brain-derived neurotrophic factor' (BDNF) gene increases a person’s likelihood of being overweight.

A study published by the American Journal of Clinical Nutrition has discovered a possible reason why. They observed that those people with the fat versions of the FTO and BDNF genes tended to eat more. The study also found that it wasn’t just the increased volume of food in terms of more meals and snacks these people ate, but the type of food. The FTO and BDNF people were drawn to high-fat, high-sugar foods.

So could your DNA propel you towards the chocolate aisle in the supermarket? The answer increasingly appears to be: yes. A different group of scientists are studying a variation of another gene called DRD2. This is the gene that codes for the number of receptors in your brain for a naturally occurring hormone we all make called dopamine.

Dopamine has lots of functions, but it’s important for food and weight because low dopamine is associated with compulsive behaviours, such as drug and alcohol abuse and over-eating.

Having the low DRD2 gene seems to make people vulnerable to anything that can stimulate feelings of pleasure and just as drugs and alcohol stimulate dopamine receptors, high-fat and high-sugar foods light them up like a Christmas tree.

This may account for why some people can eat one biscuit and put the packet back, while others finish the packet. The one biscuit people could have the ‘normal’ DRD2 gene, while the whole packet group have the low DRD2.

What is worse is that as with any over-stimulation of receptors in the brain, a sort of resistance begins to occur. If you are a low DRD2 person, after you have the first yummy cookie, the next doesn’t have quite the same effect, so you keep eating to chase the same sugar ‘high’, without success. Chronic overstimulation can lead to dopamine depletion which further fuels sugar cravings. Those people who have to be craned out of their bedrooms to have gastric bypasses are not just greedy, they could be DRD2 dopamine deprived.

There are other hormones involved in appetite, notably serotonin, and other genes. Indeed, the interplay between DNA and weight is a complex area that we are just starting to understand. It is a case of lots of bits of a puzzle that we are finding and trying to put together.

Other researchers have discovered something they have named ‘Thrifty Gene Syndrome’. This gives those with this genetic variation the ability to store more of their food as fat; fantastic in an age of food scarcity, but not so great with a Tesco Express on every corner.

Yet more research is being done into gut flora and weight, with experts discovering variations in the amount and type of flora we carry in our guys. We know that microflora helps us digest our food. The theory is that differences in the type and amount of flora, not only affect digestion but how that food goes on to be used. Some of us have friendly bacteria that allow us to be lean, others have less friendly bacteria that decree a moment on the lips is a lifetime on the hips.

All of this could lead you to think: ‘Why bother? If I’m genetically programmed to be fat, I might as well eat my body weight in chocolate fudge ice cream. But, as Jeanine M. McCaffery, who led the research into the FTO and BDNF genes says: ‘Genetic traits alone do not mean obesity is inevitable. Our lifestyle choices are critical when it comes to determining how thin or heavy we are.'

And that is the bottom line. Understanding DNA is useful in deciding whether you’re not mad or weak, you just have rubbish fat genes.

However, it should not be a cause for defeatism. There is a lot you can do. Here are our top tips for overcoming fat DNA:

• Build your genetic profile. Look at parents, siblings, aunts and uncles. Are you part of an overweight family, or are you the only one who gains weight? If the former, you may have fat DNA.
• Keep your blood sugar stable. Stable blood sugar means more stable moods which also balances out hormones such as dopamine and serotonin. Eat little and often and avoid highly processed, sugary foods.
• Exercise - this is the single most important thing you can do. Exercise has been shown to overcome Thrifty Gene Syndrome, it burns calories, improves mood and stimulates endorphins in the brain which give you ‘runners high’.