Slowing metabolism when I hit 30?

Hi Alice,

I'm a 22-year-old woman. Many of my friends in their late 20s and early 30s (and older) have been warning me about an inevitable metabolism slow-down and subsequent weight gain around my 30th birthday. They say, "You just wait. When I was your age, I sat around all day eating pizza and I never gained a pound. Now I can't lose weight no matter what I do."

I am sure there's some truth to this, but I DON'T sit around eating pizza all day. I run three to four times a week and eat very healthfully. Will these habits ease the slowing down of my metabolism? Or should I expect some weight gain no matter what I do (as they say will happen)?


— Slim 'n healthy, and wants to stay that way

Dear Slim 'n healthy, and wants to stay that way,

Like a vintage wine, people gain a variety of finer qualities with age, but physical signs of aging such as wrinkles, aches, or pains may be less welcome for some. It's understandable that you're thinking about your health habits for the long term. A variety of factors may contribute to age-related weight gain, including changes in body composition, hormonal fluctuations, genetics, and physical activity and nutrition habits. While you can't stop the aging process altogether, maintaining your balanced diet and physical activity habits can help you preserve muscle mass, which tends to decrease as people get older. This, in turn, may affect how much weight people may or may not gain.

Gaining weight after your twenties isn’t inevitable, but many people do notice some weight gain as they transition into later adulthood. As your friends shared, it's true that metabolism slows as people get older. This is because the aging process depletes muscle while increasing fat deposits. Fat burns fewer calories than muscle, so as the body's proportion of muscle shrinks, metabolism slows down as well. In addition, the mitochondria (which provide energy in the body's cells) both decrease in number and change in composition, contributing to this decrease in skeletal muscle mass.

As noted, hormones change as people age. Some researchers posit that the hormonal shifts that accompany this change of life affect the way the body breaks down and stores fat, leading to weight gain. Although most people more or less experience a decrease in hormone levels, studies have found that women are more likely to feel the effects of this transition in relation to weight gain when compared to men. To begin with, women tend to have less muscle mass than men, and age-related weight gain may also be linked to menopause. These pounds may also gather in a different place in the body, as weight gain shifts from common patterns of gathering around the hips to around the middle. Weight gain triggered by menopause usually appears after age 40, so these changes occur a bit later than the ones to which your friends are likely referencing.

Another explanation for weight gain as you age is genetics. Due to genes, people are simply pre-disposed to different body types. Observing the general body type of your family may offer some clues as to what's in store for you. That being said, bodies are unique, and it may be helpful to examine your relationship with your body. What are your expectations for how your body looks? Are your expectations realistic? How much of this is influenced by an “ideal” promoted by outside influences? What factors may support or hinder your body’s functioning, regardless of size, throughout your life? In what ways may that change over time? Thinking about this may help you frame your mindset as you look to the future.

Although many factors related to weight gain are out of your control, two of them — diet and physical activity — may be more within your influence. Eating a diet full of produce, whole grains, and lean proteins can help to ensure that your body gets the nutrients that it needs. Being physically active can encourage the body to burn fat for fuel. It seems as though you’re satisfied with your current diet and regular activity habits. If this is the case, then maintaining them may aid you in reducing age-related weight gain. It’s also good to know that you may need to adjust these habits as you age. Older folks generally need fewer calories due to their decreased muscle mass and lower activity levels. Additionally, a diet richer in protein sources can help offset the expected loss of muscles mass.

Continuing to be physically active and eating well is a great way to keep the body going overall. Because you can't stop the clock, it's also helpful to have reasonable expectations about growing older. Here's to building healthy habits for life!

Last updated Nov 27, 2020
Originally published Sep 11, 2009

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