How Your Metabolism Changes In Your 20s, 30s And 40s

Remember those days when you were little and you could eat whatever you wanted? Candy, fast food, pizza. You could shove it all down your throat and it didn’t impact your weight at all! Now, you eat all the vegetables you can manage and struggle to lose a few pounds. What gives?

As you’ve probably guessed, your metabolism changes as you get older. It begins to slow and this impacts your waistline. Here are the ways your calorie-burning ability changes as you age and all the things you can do to keep it humming.

In Your Twenties…

You Hit Your Peak

The majority of women reach their highest basal metabolic rate (the number of calories you burn just by being alive) in their twenties. Some will hit it a little earlier, some a little later. Genetics can play a role in this but so can your activity level. The more you walk around campus, play intramural sports, or work the weight room at the gym, the more muscle you will build and the higher your metabolism will be. Your body continues to build bone until you are about 25, a process which also burns calories.

But It Doesn’t Last Long

The American Council on Exercise says that your basal metabolic rate drops 1 to 2 percent per decade! “By the late twenties, many women notice that they can’t eat the same things they used to without gaining weight and that the weight doesn’t fall off as easily as it once did,” says  Christopher Ochner, Ph.D., weight-loss expert at Mount Sinai Hospital in New York. And since this drop happens around the same time that people start to begin their sedentary careers, your new, cushy office job might be to blame.

In Your 30s…

​The Fattening Cycle Continues

As you lose muscle, your metabolism drops even more. And as you lose muscle and gain fat, fat can develop into the muscle and cause weight gain and metabolic dysfunction, says Caroline Cederquist, M.D., creator of bistroMD and author of The MD Factor. To make matters worse, in your thirties you aren’t producing as much human growth hormone as before. Which means no more growth spurts but also a drop in your metabolic rate. But all is not lost! Strength training can help you rebuild muscle and produce human growth hormone which will keep your metabolism going like it was in your twenties.

Pregnancy Can Go Either Way

If you decide to have a baby, pregnancy can give your metabolism a little bump but not enough of a bump that you need to start eating for two.  “Yes, you need to eat for yourself and the baby, but that baby might only be a couple millimeters large, so you don’t need that many extra calories,” says Wesley Delbridge, R.D., a spokesperson for the Academy of Nutrition and Dietetics. During pregnancy you can burn up to 200 extra calories a day. If women are at a healthy weight before they get pregnant, they should only gain about 25-35 pounds over the course of the pregnancy. Unfortunately, a 2015 study found that more than half of women gain too much weight which can lead to metabolism destroying insulin resistance.

Breastfeeding to the Rescue

Breastfeeding can provide a huge calorie burn. An average woman, breastfeeding full time can expect to burn 500 to 1,000 extra calories per day, says Delbridge. When you stop breastfeeding, your metabolism returns to where it was pre-pregnancy.

In Your Forties…

Your Hormones Tank

In your early forties, your levels of estrogen, progesterone, and (again) human growth hormone decrease, says Cederquist, and your metabolism goes right along with them. That means you’ll have to focus on reducing your caloric intake during your forties in order to maintain your weight, says Delbridge. If you work out, this may mean eating 150 fewer calories a day. If you don’t exercise, you’ll probably have to cut more calories to stay looking trim.

Building Muscle Becomes a Non-Negotiable

Strength training is important at any age but around age 40, your body’s natural decline in muscle mass, called sarcopenia, sets in. To fight this loss of lean mass and keep your metabolism going, you will NEED to strength train. Although any activity you do at the gym will burn you some calories, strength training provides your body with the biggest boost after the workout is complete. On top of lifting, eating 100 to 120 grams of protein a day will help your efforts to get stronger. “A woman who was sedentary in her twenties and thirties can actually have a higher metabolic rate in her forties if she exercises and changes her diet,” says Cederquist.

If that isn’t a good enough reason to start strength training today, I don’t know what is!


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