At my local networking group, someone brings in breakfast every week. It’s usually chicken biscuits or donuts. And without fail, the moment people start eating, someone says some version of: “I’m going to have to work this off later.”
I hear this a lot, often with a tone of apology in their voice as though they are somehow letting me down personally by eating something so calorie-dense, even when I’m standing right next to them, eating the same thing.
The idea that we need to “earn” the caloric value of food we enjoy has a couple of problems. From a mental perspective, it puts us at odds with our own bodies and is the seed of a lot of frustrating cycles of self-criticism (a topic for another post). But there’s also a physiological reason why this way of thinking doesn’t hold up.
It goes by a few names depending on context: energy compensation, metabolic adaptation, or constrained energy expenditure. These terms have distinct meanings, but they share a common foundation: your body may not burn as many calories as you are estimating. The constrained energy model states that our bodies can compensate for the energy we use during physical activity by using less energy at rest. If you go for a run and burn 500 calories, your body may quietly conserve 200 of those calories throughout the rest of the day for a net burn of 300 calories. This effect varies by person, and even varies within the same person depending on circumstances. The latest research suggests it is more pronounced when someone is in a calorie deficit and when the activity is aerobic, compared to resistance training.
This makes actually tracking your daily calorie burn nearly impossible without laboratory-grade equipment. It is also one of many reasons I put no faith in the calorie estimates wearable fitness trackes provide.
A quick clarification: it is still quite possible to track the calories you eat or drink in a day. Pairing that with consistent weight tracking can give you a reasonable picture of your actual daily expenditure, and there are well-made apps that do this reliably. That said, I wouldn’t recommend going down that road unless you are a competitive bodybuilder or competing in a weight-regulated sport. The logistics are manageable, but the mental overhead usually isn’t worth it.
So what do you do with all of this?
Academically, the constrained energy model represents a fascinating potential evolutionary adaptation, one that could have helped many animal species survive lean times. A more practical takeaway is that this phenomenon is one of many reasons why I advocate against thinking of exercise as a “ledger balancing” method for your daily energy expenditure. It’s much more constructive to think of the other meaningful benefits exercise provides, which can include:
- Enjoyment of the activity itself
- Getting stronger, faster, or moving better
- Significant long-term health benefits: lower disease risk, better balance and resilience as you age, and possible reduction in cancer risk
- Potential for social connection
- Regulating your mental state
And if weight loss is a goal exercise still matters, just not in the way most people frame it. It helps regulate blood sugar, stabilize appetite, and improve sleep. And yes, for most people, regular exercise does increase total daily calorie burn, so it is likely supporting your weight loss directly.
It just stops being useful when you try to make it a transaction. Your body is made up of remarkable biological machinery, but it is much more than a calorie-burning machine.