杏吧原创

Earlier this month, the UK brought in a new tax on sugary drinks, following a few other countries, including France, Mexico and Finland. As a result, a can of Coke, for instance, now costs 8 pence more, although many brands, such as Ribena, Irn-Bru and Lucozade, have replaced some of their sugar with sweeteners, to a chorus of internet outrage.

But the official crusade against the white stuff isn鈥檛 stopping there. Now, a group of doctors says we need to start taxing sweet foods, like chocolate, confectionary, cakes and biscuits.

The team used data on the shopping habits of more than 30,000 British households to study what happens when the prices of sweet snacks and sugary drinks rise. In both cases, a price hike of 10 per cent reduces purchases by around 7 per cent. Because snacks contribute twice as much sugar to our diets as drinks do, a tax on the former should lead to a bigger fall in consumption, argue of the London School of Hygiene and Tropical Medicine and his colleagues.

Yet it is not clear that taxing sugar will achieve our true goal 鈥� controlling our ever-expanding waistlines. Almost two-thirds of UK adults are now overweight or obese, with figures being similar in most Western countries. But we don鈥檛 actually know why.

Too much sugar in our diets isn鈥檛 the only possible cause of this widespread weight gain 鈥� other causes might be excess of fat, processed food, overall calories and our sedentary lives. We might be focusing on the wrong thing by singling out one particular food group for taxes and bans. Perhaps we would do better to put more effort into teaching children to cook, encouraging more sport participation or changing our cities to help people get around by cycling and walking. No one knows.

Sweet talking

The desire of governments to nudge us into healthy eating habits has parallels with anti-smoking measures, but our understanding of these problems is not at the same level. While the evidence linking tobacco with cancer and heart disease is solid, the science of nutrition stands on shakier ground.

Most nutrition research consists of 鈥渙bservational鈥� studies, which, rather than randomising people to different diets, just record what they choose to eat, and are notoriously open to bias. It is unsurprising then that dietary advice has undergone some changes over the years.

For decades, the line was that the root of all dietary evil was fat, particularly saturated fat from red meat and dairy products. As part of this narrative, we demonised cholesterol, a fatty substance also found in animal products; eggs were almost verboten. Now we know that dietary cholesterol has little bearing on levels in our blood. Come back eggs, all is forgiven.

Similarly, we have long been told to replace butter with vegetable oil. But, for decades, vegetable oil-based spreads and processed foods like biscuits were based on trans-fats, which we now think are even worse for our arteries than saturated fats. Most such foods have been reformulated to cut their trans-fats, but it makes you wonder if we鈥檇 have been better sticking to butter all along.

Sugar now seems to have taken over from fat as public health enemy number one, but in the light of previous U-turns, perhaps governments should be a little more cautious about trying to remodel our eating habits, when the science is still uncertain. At the least, we should wait to assess the results of the first sugar tax before broadening its scope.