It helps to understand what people mean when they talk about “metabolism”, says James Betts, professor of metabolic physiology at the University of Bath. Usually, they’re referring to metabolic rate; the amount of energy your body burns in a given time. This is largely determined by factors such as your size, age, sex and body composition.
Your daily energy expenditure comes from three main sources: your resting metabolism (the energy needed to keep your organs and tissues functioning), the calories burned processing food, and physical activity. Of those, exercise and movement are by far the most variable.
“When people say they want to boost their metabolism, what they really mean is they want to burn more energy,” says Betts. “But resting metabolism is actually very predictable. For most people, we can estimate it fairly accurately from things like body weight, age and sex.”
So does eating every few hours help? Only in a very limited sense.
Digesting food requires energy – a process known as the thermic effect of food. Roughly 10% of the calories you eat are used for chewing, digesting and absorbing nutrients. But that does not mean frequent snacking gives your metabolism a meaningful boost.
“I tend to compare it to a tax,” says Betts. “Just as your net take‑home pay is less than your gross salary due to tax, if you eat the 100 calories on your plate you may only have a net gain of 90 calories since you must invest around 10 to access what is in your food.”
This means eating can expend a little energy, but not enough to offset the fact that you have eaten. If your goal is to increase energy expenditure, there’s a much more effective strategy, says Betts: “Move more.”
