“Britain needs to go on a diet,” said the Chief Executive of Public Health England, Duncan Selbie, in 2018. “Children and adults routinely eat too many calories, and it’s why so many are overweight or obese.” Public Health England is no more and Selbie grew a moustache and flew off to Saudi Arabia, but his idea of putting Britain on a diet lives on. Public Health England’s successor, the Office for Health Improvement and Disparities, continues to “work with” the food industry to take sugar, fat and calories out of the food supply. A target of removing 20 per cent of calories from a vast range of packaged foods was set in 2018. The target date was supposed to be 2024, but it has been pushed back to 2025. Either way, it has no chance of being met. Taking calories out of food is easier said than done — and it is not even easy to say with a straight face.

The idea behind food reformulation is that people will lose weight without trying if the food companies subtly cut the calorie content — which, in practice, usually means shrinking the product. The UK scheme is currently voluntary. The pointless quango Nesta recently said it should be mandatory, with retailers heavily fined if they don’t somehow take the sugar out of cakes. The new health secretary Wes Streeting seems keen on the idea and has told the food companies that they either get on board his “steamroller” or they go under it.

Before Mr Streeting gets too carried away, we should consider an obvious unintended consequence of this policy. From the perspective of body weight, it may be true that most people consume too many calories. Most adults are overweight or obese. But what about those who are not? Around 4 per cent of 4-5 year old children and around 7 per cent of 10-11 year old children are underweight. Many other children are skinny enough to be on the brink of underweight. For kids, being underweight is associated with more health problems than being overweight. What will happen to them if, as the Public Health England plan intended, food reformulation makes everyone eat less?

Surely, I hear you say, Public Health England would have considered the consequences of playing God with the food supply?

That is the question I sought to answer in a new report for the IEA co-authored by the health experts Gavin Sandercock and Alex Scott-Bayfield. We modelled various different scenarios, but reformulation led to a major increase in underweight children in all of them. Even in the best case scenario, two children would become underweight for every child who stopped being obese. 

The reason for this is that the weight distribution of children is skewed. As shown by the blue lines in the graph below, there is a long tail to the right — those are the obese kids — and a bit of a cliff edge on the left. Those are the skinny and underweight kids:

Under the Public Health England scheme, children would eat between 59 and 87 fewer calories a day (depending on age and gender). That would make the entire distribution shift to the left, as shown below, and would be enough to prevent some cases of obesity. But because there are more children bunched up on the edge of underweight, it would cause far more children to become malnourished. And the kids who are already underweight would get even thinner. (The black line is “before”; the grey line is “after”.)

We did not model the effect on adults (1.8 per cent of whom are underweight), but the result is likely to be very similar for the same reason. It is far from certain, to put it mildly, that this would be a net win for public health. For millions of people, a reduction in daily calorie intake would not be beneficial, and for many it would be harmful. For some it would be life-threatening.

Surely, I hear you say, Public Health England would have considered the consequences of playing God with the food supply? Not really. When they set out their plans in 2018, they said that since the scheme was “aimed at moving energy intakes of the general population more towards current UK dietary recommendations” it was “anticipated that the intended approach to calorie reduction would present a low risk of significant undernutrition in the general population” In the world of modern public health, intentions are more important than outcomes and so, when they modelled the impact of nationwide calorie reduction, they simply excluded people who are underweight or normal weight.

Outcomes were derived only for those aged 4 to 79 years who are overweight, obese or morbidly obese at the outset. It was assumed that reductions in calorie intake are likely to have minimal impact on the health of healthy weight and underweight people and these groups were therefore excluded.

A slight oversight? I think so.

The good news is that none of this is likely to happen because it is a public health policy and therefore won’t work. The sugar reduction scheme was a flop and the food industry is getting nowhere with the calorie reduction scheme. Even if it did succeed in removing 20 per cent of calories out of the most popular food products, it is likely that people would just buy more food to fill them up. That would have the negative consequence of hiking people’s grocery bills up and would be particularly bad news for the poorest households (where a disproportionately high number of underweight children can be found), but at least it wouldn’t lead to an epidemic of malnourishment. It wouldn’t lead to a reduction in obesity either, so the whole thing is a bit of a silly waste of time, isn’t it?