Matt Ridley from the UK: The exoneration of dietary fat

Britain’s obesity tsar, Susan Jebb, says that it is not fair to blame fat people for their failure to lose weight. Genetically predisposed, many people cannot realistically lose weight by eating less, especially when the food industry tempts them with snacks. Meanwhile, George Osborne is slapping a tax on sugar to tackle obesity.

The new obsession with sugar definitely makes more sense than the low-fat sermons we have heard for decades. And the prevailing idea in the public-health industry that you get fat simply by eating more calories than you burn is misleading to say the least. While of course that’s true, it says nothing about what causes appetite to exceed need by the tiny amount each day that can turn you obese.

The crucial thing is satiety. If some foods make you feel full quicker or for longer, then they will prevent you over-eating. Moreover it is easily possible, indeed likely, that people are less satiated when they eat carbohydrate than fat.

As I argued two years ago in respect of heart disease, scientists are performing a screeching U-turn on dietary advice, away from demonising fats and towards demonising carbohydrates. In the case of obesity, they cannot quite bring themselves to admit it. They want to tell us not to eat sugars, yet they won’t exonerate fat.

This is typical in science. When paradigms break, you rarely hear scientists say: “We were wrong.” They tiptoe away from their previous position. Yet this has been a costly mistake. “Getting the wrong answer on such a huge and tragic scale borders on the inexcusable,” the writer and diet critic Gary Taubes has written.

Taubes and the investigative journalist Nina Teicholz have catalogued not just the emptiness of the evidence linking dietary fat with health problems, but the politicking and jealousy that has kept heretic researchers off the key committees in the world of dietary advice. They are still treated as pariahs, even as more and more scientists quietly adopt their position. This month, Teicholz was disinvited at the insistence of fellow speakers from a slot speaking at America’s National Food Policy conference. They don’t want her argument heard that too many scientific findings are being systematically ignored in the US Dietary Guidelines, which still recommend replacing fat with carbohydrates.

In the science behind food advice it is mad simply to put both sugar and fat in the “bad” category. Telling people to eat less sugar and refined carbohydrates, while still telling them to eat less fat, is not going to work. You cannot eat less of both without eating too much protein, which is not affordable, practical — or healthy. The shelves of supermarkets are still groaning with low-fat foods; the websites of diet preachers are still calling for people to eat less saturated fat as well as less sugar. Fast food, so hated by the kale-and-quinoa crowd, is often described as full of “fat and sugar”.

Yet the science is now crystal clear that eating lots of fat is actually less likely to make you fat than eating lots of carbohydrates. Around 1980 much of Britain, following America, started to cut saturated fat out of the diet — and a few years later, obesity, far from declining, suddenly began increasing. There is a good physiological reason for this. The pancreas reacts to high levels of glucose in the blood by secreting more insulin to regulate the blood glucose level. Insulin encourages the body to burn sugar rather than fat for energy. But insulin also orders fat cells to accumulate fat (made from sugar in the liver) for later use. So the more sugar you eat, the more fat gets laid down and the less gets burnt off.

Eventually, having too much fat reduces the sensitivity of the body to insulin. The body reacts by making more insulin. High insulin levels for longer mean more fat being laid down and eventually type 2 diabetes. As Gary Taubes has argued, we knew all this in the 1930s — or at least German-speaking scientists did — and saw obesity as a consequence of hormonal defects. The idea that it was just about eating too much came later. Yet to this day the World Health Organisation opines: “The fundamental cause of obesity and overweight is an energy imbalance between calories consumed and calories expended.”

We probably know enough to justify discouraging the consumption of sugar through the tax system. That should be accompanied by re-encouraging fat eating. We must also take care not to declare premature certainty about sugar. A bit of humility would not come amiss.

Let’s face it: we do not know for certain why some people are obese and others not. The easy availability of plentiful food, especially sugars, is part of the story, as is less exercise. Yet we all know people who stay thin whatever they eat or do. The rise of high-fructose corn syrup as a sweetener coincides well with the upsurge of obesity in the 1980s, and fructose is digested in the liver, where it possibly interferes with insulin sensitivity even more than glucose. Do we know for sure that fructose is especially bad? No.

There could be all sorts of reasons why some people are more susceptible to obesity than others. Consider an extraordinary experiment conducted at Washington University in St Louis a few years ago. A pair of genetically identical twins, one of whom was obese and one of was not, donated samples of their gut contents to some genetically clonal mice whose guts had been stripped of all bacteria. The mice that received the fat twin’s gut flora grew fatter than the ones that received the thin twin’s gut flora. Perhaps some people have a mixture of gut bacteria that alters their appetite or their insulin reactions, and perhaps something about our lifestyles or the medicines we take has altered our gut flora.

Whether obesity is caused by unbalanced gut flora, or susceptible genetics, or the effects of fructose, or something else, there is every chance that Susan Jebb is right that we should not blame lack of willpower. Meanwhile it is worth remembering that obesity is nothing like as bad as it was forecast to be by now, and is not currently getting worse. The prevalence of obesity in Britain doubled in the 1990s. For the past ten years, in defiance of predictions, it has remained about the same — roughly a quarter of adults are obese.