Vickery tells mindbodygreen that while it was originally believed that a person’s metabolism would begin slowing down at the age of 30 (in increments of 2% to 5% per decade), “recent studies have shown this may not be the case.”
According to a 2021 Science review, metabolism stays pretty consistent1 throughout your life: The findings suggest that, initially, the metabolism of a newborn is akin to that of an adult, but increases in the first year of life. From there, metabolism is thought to “gradually decline” until age 20 and maintain its speed through age 60.
But again, your metabolism doesn’t plummet when the clock strikes midnight on your 60th birthday. After 60, the total energy expenditure and BMR of the study’s participants only declined by 0.7% per year, which suggests that metabolism doesn't drastically slow down with age.
Generally speaking, there’s no definitive age at which every human body’s metabolism will start to slow down, nor does it happen dramatically. That said, a person’s metabolism can significantly slow down as a result of hormonal or energetic fluctuations, nutrient deficiency, loss of muscle mass, or a higher burden of toxin exposure.
According to Kyrin Dunston, M.D., FACOG, a board-certified OB/GYN with fellowship training in anti-aging, metabolic, and functional medicine, you should seek an assessment from a professional health care provider if you notice a drastic shift in your metabolism in your 20s or 30s “to prevent further complications down the line” and improve your metabolic health. This should also be a person’s first course of action should they notice their metabolism has significantly sped up. Vickery warns metabolic health changes can be caused by an underlying culprit (e.g., thyroid issues) and can have “unwanted consequences on the body if left unaddressed.”