The main reason we're gaining weight at a pace unprecedented in human history is because our eating habits have fundamentally changed and our ability to feel full has been severely compromised. My father grew up in a Swiss mountain village where he cooked from scratch and ate fresh, whole foods cooked that day. But in his 30 years between his childhood and mine in suburban London, the nature of food has changed across the Western world. He was appalled to see that almost everything I ate was reheated and heavily processed. It's clear that the foods my father grew up eating are ones that make you feel full quickly. But the type of food I grew up eating, much of it made in factories and often using artificial chemicals, left me feeling empty, like a pit in my stomach. A recent study on what American children eat found that ultra-processed foods make up 67% of his daily diet. This kind of food makes me want to eat more and more. Feelings of satiety are delayed, if at all.
One scientific experiment — which I named Cheesecake Park — seemed to me to embody this effect. Paul Kenny, a neuroscientist at New York's Mount Sinai Hospital, grew up in Ireland. When he immigrated to the United States in his 20s in 2000, he gained 30 pounds in two years. He began to wonder if the American diet was having some strange effect on our brains and desires, and designed an experiment to test it. He and his colleague Paul Johnson raised groups of rats in cages and enriched them with healthy, balanced rat chow made from the types of foods that rats had long eaten. I gave it. The rats eat it when they're hungry, but it seems they stop when they feel full. They didn't gain weight.
But then Dr. Kenney and his colleagues fed the rats an American diet of fried bacon, Snickers bars, cheesecake, and other treats. They fell in love with it. The mice threw themselves into the cheesecake and munched it until they came out with their faces and beards all covered in cheesecake. They quickly lost almost all interest in healthy foods and any self-control they had shown toward them disappeared. Within six weeks, their obesity rates soared.
After this change, Dr. Kenny and his colleagues tweaked the experiment again (in a way that seemed cruel to me, a former KFC addict). They took away all the processed foods and fed the rats an old-fashioned, healthy diet. Dr. Kenny was convinced that processed foods expanded their appetites and they would eat more. But something strange happened. It was as if the rats no longer recognized the healthy food as food at all, and they ate very little of it. Only when they were starving did they reluctantly begin to take it again.
Although Dr. Kenny's research was in rats, this form of behavior can be seen everywhere. We all live in Cheesecake Park. And it's clear that the unsatiating effects of industrially assembled foods create the need for these drugs. A drug like Ozempic works precisely by giving a feeling of fullness. Scientist Karel Le Roux, whose research was critical to the development of these drugs, says these drugs enhance what he and others once called the “satiety hormone.”