How Your Metabolism Changes With Age: BMR by Decade and What You Can Do

Estimated BMR by Age

Using the Mifflin-St Jeor equation for a man at 75 kg and 175 cm, and a woman at 62 kg and 165 cm, with weight and height held constant, the estimated BMR falls by 50 calories per decade. Remember that the equation is a population average and not a measurement for any individual.

The practical effect is small year to year: about 5 calories per day per year of age. Over 40 years it adds up to 200 calories a day, roughly a snack, which is enough to produce gradual weight gain over time if nothing else changes.

What the Research Shows

A 2021 analysis of thousands of people across the lifespan found that metabolism, adjusted for body size and composition, was stable in adulthood between about 20 and 60, then declined about 0.7% a year after 60. In infancy and childhood the rate was higher, peaking at around age 1. These findings challenge the idea of a midlife crash in metabolism.

That said, total daily energy expenditure also depends on physical activity, which tends to fall with age. A person who sits more, walks less, and loses muscle will burn fewer calories without any change in their metabolic rate per kilogram of tissue.

Muscle Mass Is the Biggest Lever

Muscle tissue burns about 13 calories per kilogram per day at rest, while fat tissue burns about 4.5. Losing 4 kg of muscle and gaining 4 kg of fat therefore reduces resting expenditure by roughly 34 calories a day. That is modest in itself, but muscle also determines how much you move and how intensely you can train. Resistance training twice or three times a week maintains and builds muscle at any age, protecting strength, independence, and metabolic health.

Adequate protein, especially after age 50, supports this effort.

Adjusting Intake as You Age

If your weight is stable, your intake already matches your needs. If you notice a creeping gain, reducing portions by 5% to 10%, increasing daily steps, and prioritizing protein and vegetables can offset the difference. Track weight and waist measurements regularly. Remember that women may experience changes in body fat distribution after menopause that are driven by hormones rather than calories alone.

Do not drop calories too low in later life. Older adults risk undernutrition, and unintended weight loss is a clinical warning sign.

Practical Habits

Stay active in many ways: walk daily, climb stairs, garden. Lift weights or use resistance bands. Sleep adequately, manage stress, and limit alcohol. Recalculate your energy needs every few years, and use your actual weight trend as the final authority.