Obesity rates in the United States began to climb sharply in the 1970s, and this trend has continued ever since. Many early explanations blamed individuals: they were told to eat less, move more, and summon more willpower. But that simplistic view doesn’t hold up under scrutiny. It’s not plausible that, almost overnight, Americans of every background — men, women, rich, poor, young and old — all collectively chose to eat more, move less, and lose control of their appetites. Something deeper changed: the food environment itself.
From the 1970s onward, three powerful forces emerged: the rise of ultra-processed foods, the explosion of snacking culture, and the convenience of takeaway and fast food. Together, these shifts fundamentally altered how and what people ate.
1. Ultra-Processed Foods Took Over
In the 1970s, food manufacturing changed. Advances in technology and supply chains allowed food companies to create cheap, shelf-stable, hyper-palatable products — often high in added sugars, refined grains, industrial fats, and salt. These “ultra-processed foods” were designed not just to satisfy hunger but to be moreish — to override natural satiety signals and keep people eating.
Studies have shown that people eating ultra-processed foods consume more calories without intending to. In one controlled trial by the National Institutes of Health, participants given ultra-processed meals ate about 500 more calories per day than when given whole, minimally processed food — despite being allowed to eat as much or as little as they wanted in both scenarios.
2. Snacking Became the Norm
Before the 1970s, Americans ate three meals a day with minimal snacking. By the 1980s, grazing had become common. Snack foods were aggressively marketed and increasingly available — in vending machines, convenience stores, petrol stations, and school lunchboxes. Portion sizes ballooned. Between-meal eating, once frowned upon, became part of the culture.
This constant availability of energy-dense snacks led to higher calorie intake, often without people noticing. Snacking contributes significantly to total daily energy intake, and research shows that people often underestimate how much they consume from snacks.
3. Takeaway and Fast Food Took Centre Stage
The 1970s saw the rise of the modern fast food industry. Drive-thrus, microwave dinners, pizza delivery, and chain restaurants offering cheap, calorie-dense meals meant fewer meals cooked at home. Eating out used to be an occasional treat; it became routine.
Research shows a strong link between frequent fast-food consumption and weight gain. Meals from restaurants — especially fast food — tend to be higher in calories, fat, and sodium and lower in fibre and nutrients than home-cooked meals.
In short, it wasn’t a mysterious collapse of willpower that caused the obesity epidemic. It was a radical shift in the way food was produced, marketed, and consumed. The environment changed — and our biology responded. When people are surrounded by irresistible, calorie-dense, heavily marketed foods, eaten in large portions at any time of day or night, it’s hardly surprising that waistlines expanded.
The answer isn’t to blame individuals. It’s to better understand the environment we’ve created — and begin reshaping it for better health.
