Back in October 2018, Public Health England announced that childhood overweight and obesity had increased to their highest recorded levels, prompting talk of an obesity crisis and lamentation on the inadequacy of current strategy. Then, just yesterday, the House of Commons Environmental Audit Committee presented a compelling report arguing that hunger among British families was was a “significant and growing” problem, and calling for the appointment of a minister for hunger, to tackle this neglected emergency. This has led many people to wonder: what on earth is going on? Hunger is not having enough food. Obesity is having too much. How can you have a crisis of both types going on at the same time?

This question seems particularly acute since the groups affected by the two crises are one and the same—families on low incomes and in deprived areas. It’s not that those at the top of the social ladder are suffering from surfeit and those at the bottom suffering from want. Those left behind are bearing the burden of both crises.

The truth is, though, that you can have a hunger crisis and obesity crisis at the same time; indeed the two may be intimately connected. Social scientists have understood this for several decades. It’s known as the “hunger-obesity paradox” and it is not, in fact, a paradox at all.

Obesity arises when the average energy content of your diet, over a prolonged period, exceeds average energy expenditure. Thus, hunger is about the mean or central tendency of caloric input over time. Hunger arises when you have a short term fluctuation in your food intake — say going without for a day or two. Thus, hunger is about the fluctuations rather than the average. This makes it perfectly easy for people to be both obese and suffer terribly from hunger.

Consider the following example: A person gets paid Universal Credit once a month. For the first couple of weeks, there is still cash in their wallet. They stock up using the cheapest, easiest available ways to satiate themselves. Unfortunately these are things like sugar-sweetened drinks and calorie dense foods. Sugary, junk foods give you by far greater caloric bang for the penny than more nutritious foods, and this cost gulf has in fact widened in recent years. Then in the final week of the month, the money runs out, and the person has to do without. A week of awful hunger follows. Under pay day when, of course, the cycle begins again. What would you do if you had been experiencing privation for a week? You would go out and satiate yourself in the most comforting and rapid way possible, of course. Thus, within the very same person, it’s possible for the calories consumed over the whole month to exceed those expended; and at the same time for the month to have very significant hunger in it. The feast part and the famine part may be causally connected. What greater motivator is there to save energy and eat plenty than the memory that recently there was none, and the prospect that this may be true again in a few days’ time?

My colleagues and I recently reviewed the evidence that hunger can not only coexist with obesity, but is actually a risk factor for it. We synthesised 125 studies, showing that being food insecure (which roughly equates to experiencing periodic hunger) substantially increases the odds of obesity for women, but not for men. Of course, correlation does not demonstrate causation, but it does show how the two crises co-reside. In fact we think that the causation lies in economic factors: the inability, in a country that is richer than it has even been, for a substantial group of the population to access enough nutritious food every day of the month is  grotesque, and, in the long run, unsustainable. After all, countries as diverse as Japan and Switzerland manage to have relatively low obesity rates. What these very different countries have in common is not their national diets, but the fact that the poor people within them are not as poor or insecure as the poor people in the UK or USA.

Understanding the hunger-obesity (non-)paradox helps you to think differently about obesity. Instead of thinking about trying to make people restrict themselves to less, we should be designing an economic system that makes sure everyone always has access to enough: enough nutritious, high-quality food, not some of the time, but every single day.