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If you’ve ever managed to lose those last few pounds only to pile them all back on again, with added extras, you’ll be familiar with the standard explanations. Your body thinks it’s starving, ergo your metabolism slows down, ergo, by the time you reach your goal weight, you put on weight simply by standing in the vicinity of a chocolate digestive, right? And/or your poor watercress-weary being is so overcome by chocolatey goodness that you polish off the entire pack, of course. Well, according to new research, the real reason for the yoyo dieting effect could be something quite different. It’s all down to those friendly (or not-so-friendly) little gut bacteria we’ve been hearing so much about lately.
If you lambast yourself for your lack of self-control when one biscuit becomes two, then three and, seemingly before you know it, the relegation of your skinny jeans to the back of the wardrobe once more, you might be relieved to learn that you’re not alone. In fact, four years after reaching their goal weight, 40% of dieters weigh more than they did originally. It even happens to mice. Yes, mice. Rodents fed a high-fat diet become obese. When they start eating normally again, they lose weight. So far, so predictable. But put them back on the high-fat diet and they gain more weight than they did the first time.
Once the mice had lost weight, their appetites, metabolisms, cholesterol and blood sugar levels, insulin function and levels of physical activity returned to normal. But changes to their microbiomes (or bacterial communities) didn’t. Some species of bacteria had become more common, others less so. The exact balance differed from rodent to rodent, as did the magnitude of their ‘rebound’ weight gain. Incredibly the researchers were able to predict how much weight each mouse would regain with 72% accuracy, simply by analysing their gut bacteria.
But how, exactly, does bacteria make us fat? Our gut bacteria affect how we process and digest nutrients. They’re essential – but not always diet-friendly. More efficient gut bacteria actually extract more calories (as well as nutrients) from food. In this case, though, when the mice ate fatty food after dieting, their gut microbes were especially quick to break down flavonoids. Flavonoids are packed with antioxidant, anti-inflammatory and, crucially, fat-burning potential. Fewer flavonoids = less efficient fat-burning.
So is there anything you can do about it? Flavonoid supplements prevent the rebound effect in mice, although the researchers say it’s still too early to say whether this could also work for humans. That said, increasing your intake of flavonoid-rich foods (especially those containing flavonols and anthocyanidins) is unlikely to do you any harm. Good sources include onions, apples, pears, tomatoes, almonds, cabbage, quinoa, sweet potatoes, blueberries, bananas, strawberries, cherries, pears, plums, raspberries and cranberries.
There is another solution, of course: avoid high-fat foods. Not, necessarily, forever, but perhaps for, say, six months after reaching your goal weight. At least that’s how long it took for the mice’s microbiome communities to normalise. Researchers warn that the process could, potentially, take “years” in humans. However, they are confident that “there seems to be a point of no return in weight loss, beyond which subjects can keep their lost weight off”. And it’s all down to the individual, according to Liping Zhao of Shanghai Jiao Tong University, who says, “that point seems to be personalised”.