Some people talk of their metabolism like they might talk of the performance of a motor car – slow or fast. Many people carrying excess weight might like to attribute it to their slow metabolism, but there’s no evidence that it works that way. In fact, there is evidence that metabolism is neither slow nor fast, but varies across a gradient both within and between populations. A small number of people are at the upper end of this gradient and are much less likely to gain excess weight than the small number of people who are at the lower end. There are also some people who do have genuinely very slow metabolism, but this is usually down to them having an endocrine or metabolic disorder. But driving on life’s metabolic freeway, most people are neither crawling in the slow lane nor cruising in the fast lane, but changing lanes according to circumstance. Like freeway driving, metabolism is dynamic, flexible, and adaptable.

I have met few adults who are happy with their own bodies, at least in Western societies. But even in non-Western societies, many people are unhappy with their bodies. The exact nature of this unhappiness varies, but what overwhelmingly dominates is the thought, whether objectively true or not, that they carry too much weight, and following that, the thought that they really should lose weight. I have met very few people who actively want to put on weight, and they have almost all been of athletic disposition, and the weight gain sought is usually (but not always) in terms of muscle. Some people are entirely ‘fat-phobic’ and not persuaded that some types of body fat might actually be good, healthy even. Many people don’t know that there are different types of fat deposit, and that some deposits of fatness carry limited or no negative health consequences – around the buttocks, hips and thighs, for example. Body fatness is a ‘hot potato’ issue for many people; I like hot potatoes.

“Look, if it’s not my genes, it must be the environment?” I overheard someone say this in a pub. Well, yes and no. One of the visible aspects of urban environments – and let’s face it, most of us are urban now – is food. Ever-present junk food, aisles of frozen pizza and snack foods in the supermarkets. In the United Kingdom, which built much of its colonial power on the triangle of relationships among industrialization, slavery and plantation production, sugar is historically a huge industry, and you can see sugar-based products in stores everywhere. It hurts people’s lives through dental decay, obesity, and type 2 diabetes. In the United States, perfectly edible maize is systematically turned into high-fructose corn syrup, a substance that is even more damaging to health than sugar.

When I put on weight over Christmas, I tell myself I will burn it off in the summer, when I get out more. When summer comes around, I can’t resist a barbecue and a nice glass of red wine. When I put on weight across the summer, I tell myself I will take it off come September, when I get back to serious business again. The thing is, there is never a time in the future when I can take weight off by simply watching what I eat over a short period of time, so I just have to watch myself all the time. How can I not eat too much, when there is so much good and tasty food around, and when I love my food, as I always have? This chapter considers the misunderstanding that everyone can regulate their appetite and eat only what their share is, for a stable body weight and stable energy balance. It just doesn’t work like that. Some people can very easily overeat without noticeable effect, while many of us cannot and dare not, without putting on weight.

You know, you are not to blame if you put on excess body fatness, even if medical and political forces push it down on you. Generations of putting obesity onto individual responsibility reflects lazy politics and medical practice (or at least underestimating the complexity of the issue), not lazy people. Policy should help, not hinder, people’s desire to be healthy at whatever size they feel good at. The free market, however, sets the backdrop for the drama associated with weight gain, body fatness, and obesity.

In wealthy countries, the least well-off put on the most weight, as do people who are constantly under stress. Put them together, stress and under-privilege, and you have the makings of an imperfect storm, differently made in different contexts – just add ultra-processed food (UPF). Which is cheap, easily available in most places, and a significant contributor to obesity-causing food environments. Can’t you blame society, really? Before you can think about addressing this question, it is first important to have some idea of what society is. At base, a society is a group of people who are socially connected in some way, and/or occupy the same social or geographical space, usually bathing in the same political and cultural water. Social status matters, and this influences their behaviour, including in ways that can influence their body weight. If what I eat is shaped by what other people eat, because we regularly eat together (as with family) or because we as friends share common interests that extend to our eating patterns, then this aspect of society might influence the likelihood (or not) of me putting on excess weight.

People have asked me if their body fatness is genetic, to which I reply unhelpfully, yes and no. There is a very tiny proportion of any population that very easily puts on weight, where a small number of genes relate to, or are implicated in, excessive weight gain. There is a larger group of people with several genes that are triggered by one or several of a range of environmental factors to gain body fatness. And then there is almost everyone else, each person with thousands of genetic variants that have seemingly small individual effects in relation to obesity under circumstances that favour it. There are also those annoying people who can eat as much as they want, of anything they want, and not put on weight, seemingly with genes for thinness. The study of obesity genetics is steadily letting the genie out of the bottle – once you know something, you can’t unknow it, and we know enough about this area now to be able to reply with ‘It depends’, when someone says, ‘My body fatness is down to my genes.’

How much exercise does it take to walk off an average single-person-sized chocolate bar? More than you might want to acknowledge, even though you probably already know that. No chocolate bar is calorie-free, and if you are an average-sized woman in the UK, eating a 100-gram chocolate bar will take around two hours of walking to burn off. In this chapter, I examine the idea that people put on excess weight because they don’t get enough physical activity. Most people in Western societies don’t get out enough, so why stigmatize a person with obesity for not being physically active? Sure, physical activity is great, especially for reducing stress, staying happy, and lowering blood pressure and other risk markers of chronic disease, but not especially so for burning calories and keeping body weight down. The best thing about regular exercise is that it helps you burn off and keep off the wrong kind of fat, the kind that can make you long-term ill. It also helps you eat to your energy requirement more closely than if you don’t exercise.

I go to the swimming pool and everybody’s body is on show, including my own. I don’t have rippling pecs, and I am in my 60s, an age when you think I wouldn’t care about my body anymore, but I do. Another swimmer, in her 30s, is just getting out of the water. She is ‘a big girl’, and gets looks, of the wrong kind, even though I have watched her plough the lanes and work hard, keeping enough stamina back to sprint her final lap. If I am self-conscious of my body, how self-conscious is she? Every look is a dagger to her self-esteem. I try to put myself in her place, chanting to myself, ‘Don’t put me down, don’t put me down.’ People who say, ‘You’ve got yourself to blame’ have got it wrong. Even though the evidence is that body stigma only contributes to obesity, people stigmatize large body size – especially in the Global North among poorer people, females, and Black and Indigenous peoples. I discuss how obesity stigma comes from the type of moralizing thought that is embedded in present-day Western societies. I go on to consider how obesity stigma is used to develop and maintain social hierarchies in times of food-plenty.

The first time I went to Japan, nearly three decades ago now, I took a short walk from my hotel near the University of Tokyo into the foggy and still night without a map, without the World Wide Web, without any knowledge of the Japanese language. It was November, a thick white blanket of almost frozen vapour covering everything outside, including my visual and mental perception. As my spectacles fogged up, adding another layer to my perceptual fogginess, I walked a hundred paces one way down the street then back again. Then another hundred in the other direction. Turning a corner to the left, then back again. Then two hundred in the other direction. You get the picture; I was building an image, a mind-map, of an unusually silent foggy island within the usually hustle-bustling city of Tokyo. When I felt I had done enough mental mapping I went back to my hotel room and drew a physical map on a scrap of paper of my walk. I have it somewhere still.