Obesity in its modern, mass form is surprisingly recent. In America, adult rates were fairly stable at around one in seven from the early 1960s to the late 1970s. Then something changed. From about 1980 the line turned sharply upward, and by 2000 roughly three in ten adults were obese. By 2022 an estimated 107 million American adults, 42.5% of the adult population, were obese, up from 34.7 million (19.3%) in 1990.
Britain followed the same curve about a decade behind. Data from the 1980 National Heights and Weights Survey put obesity in England at 6% of men and 9% of women. By 1993 it was 13% and 16%, and by 2019 it had reached 27% of men and 29% of women.
The most recent Health Survey for England found 30% of adults living with obesity in 2024, and 66% overweight or obese. Officialdom noticed slowly.
The timing is the most useful clue. Genes did not change in 1980. Willpower did not suddenly collapse across two nations. Something in the environment shifted, and the evidence points mostly at what we eat rather than how much we move.
The strongest candidate is cheap, abundant food. Food prices fell steadily relative to income, and per capita calorie supply in America rose by several hundred calories a day between the 1970s and 2000s. Much of that came as ultra-processed products engineered to be easy to eat in quantity.
A notable controlled trial at the US National Institutes of Health in 2019 found people ate about 500 more calories a day on an ultra-processed diet than on a minimally processed one, even when the meals were matched for sugar, fat and fibre. Larger portions, constant snacking, and more eating outside the home all pushed in the same direction.
Changing lives played a part. As more women entered paid work and time became costlier, home cooking gave way to convenience food. This is about rising prosperity and choice, not villainy, but the effect on waistlines was real.
Physical activity matters less than is commonly assumed. Desk jobs did replace manual labour, but most of that shift happened before 1980. Studies of energy expenditure suggest people today burn roughly what their ancestors did. You cannot easily outrun a bad diet, and populations did not try.
Several lesser factors probably contributed at the margin. The decline in smoking removed an appetite suppressant. Sleep shortened. Some widely prescribed medicines cause weight gain. The low-fat dietary advice that began with the US guidelines of 1977 may have nudged people toward refined carbohydrates.
Britain is a useful control group here. It saw the same rise without American farm subsidies and with very little high-fructose corn syrup, which weakens explanations that rest on those particular US policies. The common factor is the modern food environment itself.
The latest twist is pharmaceutical. Gallup surveys show the US obesity rate falling to 37% in 2025, after a record high of 39.9% in 2022, as more Americans turn to weight-loss drugs. Children have not yet shared in this, and US childhood and teen obesity rates have recently reached record highs. It seems the market created the problem by making food cheap and tempting, and is now selling the solution by the injection.
The evidence on dealing with it now points clearly in one direction. The most effective tool by far is pharmaceutical. Policies that change what food companies make come second. Campaigns that try to change what people know come a distant third.
The new appetite drugs work on a scale no earlier intervention came close to. Tirzepatide (Mounjaro) produced an average weight loss of 22.5% of starting body weight after 72 weeks at the maximum dose, and the higher 7.2 mg dose of Wegovy, approved in Britain in January 2026, gave an average loss of 20.7%. Diets and exercise programmes typically manage a few per cent, and most of that returns within a couple of years.
The main barrier is price and access, and both are shifting fast. In America, the Wegovy pill, approved in December 2025, and Lilly’s once-daily pill Foundayo, approved in April 2026, add lower-cost self-pay options. In early 2026 the White House’s direct-to-consumer site listed the Wegovy pill at $149 a month and Zepbound at $299. Pills are cheaper to make and easier to distribute than injections, which matters more than any price deal. Semaglutide patents are also expiring in several large markets, and generic competition will drive prices down further.
Britain is moving more slowly. An estimated 2.4 million people in the UK take weight-loss drugs, most of them buying privately from online providers or unregulated sellers. The practical lessons follow. Let competition and generics work. Widen pharmacy prescribing. Treat the drugs as a cheap preventive measure.
The British soft drinks levy is the best-studied food tax anywhere, and its design was clever. It taxed manufacturers rather than shoppers, and gave them two years to escape it by cutting sugar. Most did. Nearly every global soft drinks brand reduced sugar content and so avoided the levy, which cut intake by about 6,600 calories per year per UK resident, 80% of it from reformulation. That is a real achievement, but it works out at under 20 calories a day - about a quarter of an apple. The effect on obesity is measurable and modest. A levy changes recipes. It does not change appetites.
Information campaigns, calorie labels on menus, and advertising restrictions have weak track records. They cut purchases a little in the short term, and population weight barely moves. Exercise is excellent for health and poor for weight loss. Children are the hardest case. US childhood and teen obesity rates have recently reached record highs.
The drugs generally have to be taken indefinitely, since weight returns when they stop. Long-term effects beyond a few years are unknown, and some of the lost weight is muscle. Critics argue that medicating a population treats the symptom while leaving the food environment untouched, and that widespread state funding could become a huge open-ended cost.
Public health advocates argue that stronger regulation of ultra-processed food deserves more credit than the trial evidence yet gives it. Others reply that waiting for perfect evidence costs lives now. The likely outcome is that a problem caused by cheap calories will be solved by cheap chemistry.
Madsen Pirie