An Unexpected Reason Why Moving Is Good for You

What Herman Pontzer’s “Constrained Energy Model” teaches us about the smart way our bodies allocate energy.

On the vast savannas of northern Tanzania, near Lake Eyasi, live the Hadza — one of the last remaining hunter-gatherer communities in the world. Every day, they cover many kilometers across the dry grasslands to find food. Their days are filled with physical activity — up to 14 times more than the average Westerner. This lifestyle fascinates anthropologists: the gap between the Hadza way of life and our modern Western routines may help explain many of today’s health issues.

music for today: D’Angelo – Africa (demo)

When the American anthropologist and physiologist Herman Pontzer began measuring their energy expenditure, he expected their daily calorie burn to be sky-high. It seemed logical: people who are constantly on the move must burn far more energy than those who sit behind a screen all day, right? But Pontzer’s measurements revealed a surprising discovery.

Despite their intense activity, the Hadza burned no more energy per day than the average Westerner. And it wasn’t due to a measurement error — Pontzer used the so-called doubly labeled water method, the gold standard in energy research.

Soon, some people concluded: “See? Even traditional cultures don’t move that much, we Westerners don’t need to exercise so much to stay healthy.”However, extensive studies using GPS trackers and accelerometers show that the Hadza and other hunter-gatherer groups do, in fact, move far more than we do.

The Hadza’s bodies turned out to save energy in ingenious ways, as if there were an internal ceiling for how much energy we can spend in a day. This led to the Constrained Total Energy Expenditure (CTEE) model: the idea that our total energy use doesn’t increase indefinitely with more activity but instead stabilizes within narrow limits.

A Smart Energy System, Not a Lazy Engine

The classic view of energy expenditure is linear: the more you move, the more calories you burn. We already spend a lot of energy at rest (breathing, circulation, temperature regulation, growth, cellular processes, digestion). And it seems logical that as we move more, our total energy use simply rises (see Figure 1).

Figure 1. The additive total energy expenditure model: the more you move, the more energy you use. (PA: physical activity)

But Pontzer’s research shows our bodies work differently. They behave more like budget managers, carefully deciding where energy goes. When we move more, the body compensates by reducing energy spent on other biological processes. That may sound counterintuitive, but evolutionarily, it makes perfect sense: energy is costly, and managing it wisely improves survival. More movement does require more energy — but that energy is reallocated from other systems (see Figure 2).

Figure 2. The Constrained Total Energy Expenditure model: more movement doesn’t raise total energy use — it diverts energy from other processes. (PA: physical activity)

This “energy stealing” might sound harmful, but it’s actually beneficial for health. Some processes that receive less energy are ones we’d rather keep under control:

1. Less Energy Toward Inflammation

Chronic, low-grade inflammation lies at the root of many modern diseases: heart disease, diabetes, dementia, depression, and musculoskeletal problems. Exercise “redistributes” energy: since the total energy budget remains fixed, the immune system receives less energy when it’s overactive. The result: fewer inflammatory processes and a calmer immune response. This explains why regular physical activity powerfully protects against inflammation-related diseases.

2. Less Energy Toward Stress Responses

The stress system also consumes large amounts of energy. With regular movement, the stress response becomes more efficient, shorter, and less harmful. Pontzer’s model helps explain why physical activity keeps the stress system under control.

3. Less Energy Toward Reproductive Processes

Regular exercise lowers circulating reproductive hormones (estrogen, progesterone, testosterone). In physically active traditional societies, these hormone levels are significantly lower than in the average Westerner. Suppressing the reproductive system may sound negative, but generally, it’s quite the opposite: exercise is one of the most effective ways to reduce the risk of reproductive cancers (like breast and prostate cancer), partly by moderating hormone levels.

Can You Move Too Much?

You’ve probably guessed there’s a flip side: it’s possible to demand too much energy through physical activity, leaving too little for vital processes. The best-known example is overtraining syndrome. Some athletes train so intensely that there’s not enough energy left for essential systems: female athletes may (temporarily) lose fertility (menstrual cycle stops); overtrained athletes fall ill easily because their immune system is underpowered. Even basic cellular processes may falter, leading to poor recovery, fatigue, and mental burnout.

The CTEE model teaches us that simply eating more calories doesn’t fix this — only a significant reduction in training load helps.

The Sweet Spot

As so often, there’s a “sweet spot” — a zone of energy expenditure that turns out to be optimal: more than the typical sedentary Westerner does, but far less than an overtrained athlete. We’ve known this intuitively, but where exactly does that sweet spot lie?

First, it’s more likely a zone than a precise point: you don’t need to measure your activity levels daily. Second, that zone lies further to the right — the “more movement” side — than most people think.

Hunter-gatherers move a lot, every day at moderate intensity, with regular bursts of high intensity. They do so from childhood to old age. Trying to offset a sedentary lifestyle with three half-hour jogs per week just isn’t enough.

The WHO guidelines (150 minutes of moderate aerobic activity, 75 minutes of vigorous activity, and two strength sessions per week) are likely still conservative, especially for moderate-intensity activity. It’s probably closer to 150 minutes per day.

Figure 3. The optimal zone or “sweet spot.”

Weight Loss

The CTEE model also explains another familiar phenomenon: exercise often doesn’t work well for weight loss. More precisely, the calories you burn through movement don’t necessarily translate into more fat burned. It sounds counterintuitive, though anyone who’s tried to lose weight through exercise alone may have noticed this. Still, exercise can support weight loss indirectly, and it certainly remains one of the most powerful tools for improving health overall.

Adaptive Systems

The Constrained Energy Model teaches us that our bodies aren’t simple machines that endlessly burn more as we work harder. They’re adaptive systems, shaped by millions of years of evolution — designed for survival, not for fat loss.That insight doesn’t make movement less important, but it helps us appreciate why it matters.

This blog is largely based on the work of Herman Pontzer. If you’re interested in his research, check out his scientific publications or his book Burn: The Misunderstood Science of Metabolism.

Cheers,

Pieter