© Steve Silver\age fotostock(© Steve Silver\age fotostock )

If you think you’ve put on a few extra pounds because your metabolism has slowed down, you may be only half right. It could be you who’s slowed down. Does metabolism really slow with age? Can things like green tea or diet aids speed it up? What works? Here’s a refresher on how your body burns energy and what you need to do to take those pounds off.

What is metabolism, anyway?

Most of us think of metabolism as the rate at which we burn calories. That’s only part of the story. “Metabolism is the breakdown of metabolic fuels we have in the diet,” explains Christopher Newgard, director of the Sarah W. Stedman Nutrition and Metabolism Center at Duke University Medical School. “The primary nutrients in foodstuff can be classified as fats, proteins or carbohydrates. I think of metabolism as the way the cells, organs and tissues in our bodies handle those kinds of fuels.” In other words, it's not just about burning up the food we eat, but about how the various nutrients from that food help us maintain a healthy body.

Ever feel like you’re fighting a losing battle to shed pounds? At some level, you are. Basically, our bodies are built to store fat. It’s not just about energy in versus energy out. Newgard gives the example of primitive man who manages to kill a woolly mammoth. “There’s a feast, but then the food source becomes nonexistent or scarce. So we have pathways that allow us to store in times of plenty to be ready for times of deprivation. Unfortunately, today we have ‘feast and feast some more and then feast again.’ That creates problems because our bodies are designed to store fat efficiently.”

Does metabolism slow or do we?
Both. But the slowing of metabolism is a real thing. “The primary thing that seems to occur is that mitochondria in the cells slow down with age,” says Newgard. (Think of mitochondria as little energy factories in cells that convert nutrients to power.)

And that’s not all. Barry Stein of Wake Forest University School of Medicine is writing a book about staying fit after 50. As he explains, “As we age, we are subject to sarcopenia—muscle wasting. Since muscle burns more energy than fat, this means the metabolic load goes down and metabolism reflects that.” That is, if you do nothing about your loss of muscle with age, it will take you longer to burn off a candy bar at age 60 than at 20.

Being overweight due to what Newgard calls the “feast and feast economy” seems to slow metabolism as well. An overweight person burns fat even less efficiently. Moreover, all the calories that aren’t used get converted to fat for storage—all in preparation for the famine that never comes. It’s a vicious cycle.

Add to this the fact that we tend to become less active as the years go by, and you can see why the inches start to gather around your waist.

How to slow the slowing
If you’re tempted to throw up your arms and give in to the extra inches (who can argue with mitochondria?), think twice. There are things you can do to keep your metabolism efficient. Exercise is No. 1. “Exercise actually increases the number of mitochondria. And also increases their metabolic activity,” explains Newgard.

Exercise also simply burns calories. Twins Tammy and Lyssie Lakotos, authors of Fire Up Your Metabolism, recommend both cardiovascular activity and weight training. “Cardiovascular activity burns calories while you do it. Additionally, you could burn about 20-30 additional calories afterwards, which may not seem like a big amount daily, but adds up over a lifetime,” says Tammy Lakotos. Strength training is effective long after you’ve put down the barbells because muscle burns more calories than fat while you’re at rest.

Eat balanced meals
It may sound simple and boring, but there’s good reason that balanced diets are what the nutrition experts always recommend. “Each of the primary food fuels has important individual contributions to make to the whole metabolic scheme,” Newgard says. Fatty acids are important in the synthesis of cell membranes. Carbs are a quick energy source and used for a whole plethora of biochemical reactions, including building DNA. Amino acids build protein—the structural basis of our cells. Again, all of this is part of metabolism—converting and using nutrients to maintain healthy cells, organs and tissues. Diets that eliminate an entire food group will take a toll on the body in the long run.

The twins recommend having whole-grain carbs with each meal (for brain and muscle fuel), but also including protein, which takes longer to digest and will keep you going longer. This means a turkey sandwich on whole wheat with mustard or whole-wheat pasta with chicken and veggies.

Eat often

Don’t skip meals, say the twins. “You can get away with it in your 20s but eventually your body gets smart and starts to conserve when you go for awhile without eating. Skipping meals can lead to overeating because you’re hungry and then you are taking in extra calories when your body is starting to conserve,” adds Tammy.

“I describe it as the fed and fast states,” says Newgard. “ ‘Fed’ is when you’ve eaten a meal and there is energy coming into your system, whereas ‘fast’ is Saturday morning at 10 after eating at 7 the night before, so you’ve had no nutrients for 12 to 15 hours.” Your biochemistry is different in these two states and that directly affects when you feel hungry and full. “You may think that your cravings are controlled by you and your willpower. But in fact there’s a whole hormonal circuitry that controls these feelings.” So give your willpower a boost by eating a healthy breakfast.

Drink water
“Every process in the body takes place in water,” says Lyssie Lakotos. “Drinking water helps with digestion and metabolism efficiency.” Plus, when you are dehydrated, you feel lethargic, you move less. “You don’t get up out of your office chair, and burn less energy that way too,” she adds.

What about green tea or diet aids? Do they speed metabolism?

You have to be careful with supplements that have caffeine and other herbs, as they are not necessarily safe. The twins steer people away from bitter orange (also known as citrus aurantium), which is especially popular now that ephedra is banned. “[Bitter orange] may increase risk of heart irregularities, increase blood pressure and interfere with some medications,” Tammy warns. When it comes to green tea, on the other hand, drink up. Studies have indicated that drinking about five cups of green tea a day may increase metabolism slightly. Plus it’s a great source of antioxidants.

In the end, age will slow us down. But by staying active and eating well, the experts agree: You can slow the effects of a slowing metabolism.