Weight of evidence

Study reveals why some people gain weight more easily than others — and it’s not genetics.

Factors other than genetics may explain why one twin can get away with eating biscuits daily while the other can’t even look at them without putting on kilos.

If you blame your propensity for being lardy on your genes, the latest scientific findings may come as a blow. At last month’s American Society for Nutrition conference in Baltimore researchers revealed that while we can hold our parents responsible for many things in life, piling on the kilograms isn’t likely to be one of them.

The results of a trial carried out by Tim Spector, professor of genetic epidemiology at King’s College London, in collaboration with experts from Massachusetts General Hospital, suggest that genetic make-up has little influence on the way our bodies metabolise food.

Factors such as when we eat, our exercise habits and sleep patterns have a larger bearing on why we may feel unfathomably fat.

For the Predict study Spector and his colleagues recruited 1100 people from Britain and US — including 700 identical twins — who were asked to consume set meals and log every mouthful of food or drink across two weeks.

Throughout the trial blood tests to measure levels of glucose, triglycerides and the hormone insulin were taken, as were samples of gut bacteria. The aim was to monitor individual nutritional responses to normal meals to predict personalised food responses.

Subjects also were asked to record their sleep patterns, hunger and physical activity.

No two bodies alike

The results showed that body responses to different foods, measured by levels of glucose, fats and hormones in the blood, were widely different, even for the identical twins. No two people processed fats and carbohydrates in the same way and less than half of the variation in their biochemical reaction to the food could be attributed to genetic influences.

It was eye-opening even to Spector. “I had expected there would be some differences, maybe twofold, but in some cases the extent of variation between people in response to identical meals was eightfold,” he says.

“Only about 30 per cent of the glucose response that occurs after a meal was genetic according to our latest estimate and virtually zero, or at least less than 5 per cent, for fat. That is a real surprise.”

Genes don’t fit

Follow-up studies are planned, with the next phase of research being conducted in the US, but they are findings that could revolutionise the way we eat and diet. In recent years there has been a move towards personalised nutrition, driven by companies selling DNA-testing kits that promise to tailor your diet to your genetic prefer­ences for certain food types.

Spector says his results prove they are a waste of money. “As a geneticist, in the past I would have said that your propensity for weight gain was mostly down to genetics,” he says. “But we now know that there is a whole other area of human biology that we haven’t really thought about.”

It explains, he says, “why some people will lose weight on one diet while others won’t”. If you’ve always wondered why a sibling can get away with eating biscuits daily while you can’t even look at them without gaining centimetres, this could be the reason.

Yet if it’s not our DNA that determines our dieting success, what is it? Spector says there is a range of factors that correlate with one another. Levels of gut bacteria are influential, not because of the microbes but because of the chemicals they produce that affect appetite and brain responses. Hours of sleep and exercise also are considerations.

Body clock

So is our body clock. “We are starting to see that things we didn’t previously consider important — like changes in the order you have meals — might have an impact,” Spector says.

“We gave some people the same meal at breakfast and the next day at lunch, and they had twice the response to the carbohydrates and fats when they ate it for lunch.

“It wasn’t consistent, but it suggests we might all have a different circadian rhythm and that is why some people can easily skip breakfast while others feel dreadful if they do.”

Guidelines in doubt

The ramifications of such findings are huge. Standardised government healthy eating advice could become a thing of the past, Spector says.

“It is outrageous that (government health guidelines) don’t keep up with science, they never change composition — and they are extremely boring guidelines,” Spector says.

His message is that we should start experimenting with our eating habits to find out what works best. “Don’t just say, ‘I must eat a good breakfast,’ because that’s the official advice, but experiment without it,” he says.

“Play around with the timing and composition of your meals, and experiment with time-restricted eating where you have a specified eating window each day.”

Variety of foods is key, if only to make sure you limit foods that could prove your undoing.

“For 10 years I ate the same tuna and sweetcorn sandwich from the hospital cafe every day,” Spector says. “I now know it is the worst lunch for me as I react poorly to bread. If I had eaten a pasta salad or a baked potato with a tuna filling, I could have saved myself from gaining a kilo a year in weight.”

Personalised nutrition

It may seem like a minefield of information to digest, but personalised nutrition is in the ascent and we can expect a slew of companies promising to guide us towards an optimally tailored plan.

A start-up operation, co-founded by Spector and called Zoe (the Greek word for life), is using data from the Predict trials to develop an app that will inform users about their personal nutritional res­ponses and help them to choose foods that optimise their metabolism and aid weight loss.

Users will be provided with a glucose tester and food log and will have access to tests, the results of which will predict their reaction to foods. Input a choice of foods into the app — a ham sandwich, for example — and it will inform you which is more suitable.

“Already, with our data and testing, we can predict with 73 per cent accuracy which foods are best suited to a person, but our results are evolving and improving as more people get on board and more data is produced,” Spector says.

“Compare that with a genetic test that gives you 5 per cent accuracy at most, and there is a huge difference.”

It should launch early next year.

In the meantime, Spector’s advice is to remain open-minded.

“Counting calories and reading food labels is really not the way to go,” he says.

“Current (British) guidelines state we should have strictly 30 per cent fat and mainly starchy carbs, tell you exactly what proportions of foods you should be eating and that we should eat low-fat dairy that is highly processed — and they are ridiculous rules.

“They are no longer valid and we should move towards more personalised eating.”

The Times