The trouble with Calories

Western society is, we're told, an increasingly overweight one. Depending on how we define 'overweight', it seems that between 30% and 50% of American adults are overweight. The situation isn't much better in most of the industrialized world.

For years we were taught, and then went on to teach, that this problem is simple to fix, at least conceptually: it's just a matter of Calories in and Calories out. So long as these two figures match, you'll neither gain nor lose weight. If more of us are overweight, it's because increasingly we either eat too much, or exercise too little. Simple.

The problem with this view is that, while the biochemistry is correct in a notional, abstract sense, in real life it's bollocks.

The reason the "Calories in, Calories out" mantra is nonsense is because it neglects a fundamental aspect of human physiology: our bodies adjust to our environment. An excellent example of this can be seen in the Hadza people of Tanzania, one of the few remaining hunter-gather communities. Oh, boy, do those guys exercise! Men typically walk or run more than twenty miles every day to track game, while women dig for roots in the hard, dry ground most of the day. They do this every day, for most of their lives. They are, as you might expect, all supremely fit. Diabetes and coronary artery disease are almost unknown.

We used to imagine that people like the Hadza would have to eat a colossal amount, to sustain their relentless workload. But no: Hadza men typically consume about 2,500 Calories per day: more-or-less the same as most western men.

If you're running or walking for, perhaps, ten hours every day, what's your Calorie expenditure likely to be? We typically assume that brisk walking requires about 400 Cal/hour, so that's 4,000 Calories each day. That's not including a person's basal metabolic needs -- that's the energy we all need just to keep our hearts beating and our brains cogitating.

So why don't the Hadza people all starve? Where does all the extra energy come from?

The only plausible explanation for this phenomenon is that the Hadza people don't need 400 Cal/hour to walk, as we assume westerners do. Perhaps they only need 50 Cal/hour. Moreover, if you watch them on videos, you'll see that, when they're not active, they're completely still. Statue still, in a way that western people probably can't imitate. They scarcely even move their eyes. Moving needs energy, and they don't have any Calories to spare on extraneous activity. The Hadza demonstrate how we humans can adapt our biochemical processes to cope even with harsh lives.

Over my lifetime I've seen many people try to control their weight with diet and exercise -- including me. My observation is that this works well -- once. Then it works less well and, eventually, it doesn't work at all. The Hadza show us why it stops working: our bodies are adaptive. Reducing from, say, 2500 Cal/day to 1200 Cal/day is initially a shock to the system but, in time, we adapt to the new intake. So when this regime stops working, we have to reduce to 800 Cal/day, or whatever. And then we adapt to that. And so it goes on.

Similarly, if you've done little exercise in your life, the first time you go jogging, or play tenis, or whatever, one hour is exhausting. A few weeks later, you're exercising harder, for longer, and it's less exhausting. But you're no longer losing any weight by doing it: you've adapted. By the time you're my age, you're following my regime: 600 Cal/day, and two hours of brutal exercise every single day, and it's less and less effective.

The modern "solution" to this problem is GLP-1 agonists like tirzepatide and semaglutide. All these drugs really do is to make you better able to tolerate a miniscule food intake. As such, in the long term they add to the problem, rather than solving it. The elephant in the sitting room -- the thing that nobody in healthcare wants to talk about -- is that once you start on these meds, you're going to be on them for life, with an escalating dose. Your body adjusts to the reduced food intake caused by the meds exactly as it does with dieting.

What all this means is that if you ever have to diet, at any time in your life, you've started on a path that leads to a bad place. Once you even start thinking about Calories, when you even know what a Calorie is, you're screwed.

I believe there actually is a solution to this problem, but it's an uncomfortable one, and one that few people would relish: we all have to learn to be hungry, all the time, from birth. That's not dieting -- it's a way of life, and it's life-long. It's how life would have been for our hunter-gather ancestors, after all. We must wake up hungry, spend the day hungry, and go to bed hungry. We must ensure that nobody ever becomes even an ounce overweight. Sadly, most of us will only be able to tolerate this with pharmaceutical support, and who relishes injecting infants with Ozempic and the like?

In practice, I doubt my plan can be implemented. This means that, so long as we live in a time of plenty, we're going to have a large proportion of the population overweight. That's going to be a burden on our medical services, but probably no more than the burden already created by people living longer. We're going to need to make more plus-sized clothes, and sturdier furniture. Seats on public transport will need to be bigger.

Most importantly, we need to stop telling people to count Calories because, in the long run, it makes things worse for most people who do it.

Published 2026-03-02, updated 2026-03-02

The trouble with Calories

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