How Has Your Metabolism Changed with Age?

Credit: Johanna Parkin / Getty Images

One of the most obvious measures of how well one ages is the eyeball test: If your waist has pushed out inches and your face has lost its angles, you fail. There are a lot of failures. Between the ages of 30 and 70, sedentary American males lose half their muscle mass and double their pounds of fat.

But what few realize is the fat accumulating on the outside is driving a host of age-accelerating metabolic changes on the inside. A gut conspires against us in a slew of grotesque ways.

The problem begins when you eat (and drink) more than you can burn off. Over time, your blood sugar level rises, which can lead to clogged arteries and blocked blood flow. The higher blood sugar level inhibits muscle growth and boosts belly fat no matter what you're doing in the gym. The visceral fat that begins to collect around your internal organs doesn't just sit inert, either. It acts like a giant gland, producing chemicals that push you in an ever rounder, softer, and more feminized direction. One of those chemicals, the enzyme aromatase, converts some of your testosterone to estrogen. (Man boobs, anyone?) Meanwhile, hormones called adipokines promote insulin resistance, which causes you to gain even more weight.

With that added fat comes more inflammation. As fat cells age, they, like your immune cells, turn old and cranky — senescent in scientific lingo — and spit out inflammatory biomolecules into the bloodstream. "These cells are some of the worst aging culprits," says Christiaan Leeuwenburgh, head of the Division of Biology of Aging at the University of Florida. "When researchers take them out in animals, the animals live longer." The human health toll came into clear focus with a 2013 study that tracked 3,000 middle-aged workers for 10 years and found that those with high levels of inflammation had double the odds of developing heart disease, type 2 diabetes, and Alzheimer's.

Because your metabolic health is so closely tied to your weight and lifestyle, as opposed to "pure" aging, Raffaele assigns it a letter grade instead of a Physio Age. In this case, a gentleman's C should be avoided.

How to Better Your Metabolism

Know Your Numbers

Ask your doctor for tests for blood sugar and hs-CRP inflammation. (Insurance usually covers both; otherwise CRP runs about $55.) To gauge fat distribution, look at waist-to-hip ratio. "If your waist is wider than your hips, you're in trouble," says Raffaele. Low testosterone could also contribute to a metabolic slowdown. By their sixties, a third of men are clinically deficient in T. If a test reveals your number is low, and you've also noticed fatigue, inability to lose weight, and low libido, then ask your doctor if lifestyle fixes are enough to move the needle, or whether supplementation is an option worth considering.

Try Fasting

"You lose weight, you lose inflammation," says Dr. Tim Church, chief medical officer at ACAP Health. Intermittent fasting is one way to do it, and it's shown to stress the metabolism in a helpful way. Experiment: Eat an early dinner at 6 or 7 pm, and a late breakfast at 10 am. This puts you in fasting mode for a few hours daily. Raffaele has had success guiding patients on a tougher approach, the "5-2 program": Most of the week you eat normally, but for two days you eat only 600 calories.

Hit the Weights

Cardio is important, but "nothing eats up sugar like muscle," says Church. In his recent JAMA study, diabetics saw the most improvement in blood sugar when they combined strength training with cardio.

Here is your guide to assessing — and slowing — everything from your cognitive age to your metabolic decline. 

What Is Your Cognitive Age?

How Old Are Your Lungs?

What Is the Real Age of Your Heart?

How Old Is Your Immune System?