Why am I not losing weight even though I work out?

Because a workout burns less than it feels like, and your body makes up part of it. In a 10-month trial, people who burned 400 or 600 calories a session, five days a week, lost 4 to 6% of their weight without dieting. That’s real, and it’s slower than most people hope. What you eat sets the pace.

Where the calories go

• The body adjusts. In a 2016 study of 332 adults in five countries, the calories people burned in a day rose with activity at low levels, then leveled off at higher levels. The body seems to spend less elsewhere when you move a lot.
• Very active people don’t burn much more. The Hadza of Tanzania walk miles a day to hunt and forage. In a 2012 study of 30 Hadza adults, their daily energy use was about the same as Westerners’ once body size was counted.
• You may be gaining muscle. In an 8-month trial of sedentary adults, the people who lifted gained about 2.4 pounds of lean mass, which hides fat loss on the scale.

The body works like a household budget on a fixed income. Spend more on one thing, and it quietly spends less on others.

Keep training anyway

Exercise still matters. It keeps muscle while you lose fat, and it’s one of the habits of people who keep weight off. In a registry of people who lost at least 30 pounds and kept it off, the members averaged about an hour of activity a day.

What to do

• Set your calories first, with the calorie calculator, and don’t eat back the calories a watch says you burned.
• Measure your waist once a month. If it’s shrinking and your weight isn’t, you’re likely trading fat for muscle.
• Give it four weeks before you judge any change. A week of scale data is mostly water.