There are many reasons why exercise should be a part of a healthy routine. It builds strength, aids muscle health, improves mood and can even aid mental health. But it’s not very effective at burning calories. New analysis of existing research on how exercise impacts calorie burn found the results aren’t impressive.
“We’re an evolved species. Our bodies are built to be clever and adaptable to try to keep the energy we burn every day within a narrow range,” said lead author Dr. Herman Pontzer of the Duke Global Health Institute.
When you first start a workout routine, your body may burn a lot of calories because it is unused to the situation. However, your body adjusts to the change and conserves energy as the exercise becomes a part of your normal routine. We are “wired to conserve energy.” It is a survival trait that is biologically designed to keep us alive in times of scarcity. Your body doesn’t use more fuel than it has. It has a “built-in energy cap,” so if you use calories exercising, it uses fewer for other processes. But times have changed, we’re no longer hunter-gatherers. We all have fridges with food in them, and it’s no longer a useful trait.
“If you only have exercise by itself — no change in diet — then you cancel out about 50 percent of the exercise calories that you burn,” said Dr. Pontzer. “Unfortunately for weight loss, if you don't control your diet, you will eat the other 50 percent, so there will be no imbalance between calories eaten and calories burned, resulting in little or no weight loss.” Dr. Pontzer said it’s the diet changes, not the exercise, that guide your weight loss.
The researchers found that, for calorie burning, strength and resistance training burned more calories than the body could compensate for. Those exercises build muscle, and muscle burns more calories at rest than fat. You are rebuilding your body to burn more calories.
The researchers stressed that their findings do not suggest that exercise isn’t helpful. “From a health standpoint, exercise is one of the most valuable tools we have,” said Dr. Kristen Howard of Virginia Tech. “It improves focus and attention, sleep, body composition, cardio/cerebrovascular risk, dementia risk, depression, frailty in aging, disability, joint pain, bone loss… the list goes on.”
“You have to think about diet and exercise as two different tools for two different jobs,” said Dr. Pontzer. “Diet is the tool for managing your weight. Exercise is the tool for everything else related to health — from mental health to cardiometabolic disease.”
