The mechanics of Metabolism

Stop blaming it for those pesky extra pounds --------------------------------------------------------------------------------
By Linda Stahl

Poor metabolism.

How often is it blamed for a weight problem?

Too often, according to Dr. Kara Gallagher of the University of Louisville’s Department of Health and Sport Sciences.

One of the biggest misconceptions people have about their metabolism — the way their bodies create and use energy — is the assumption that it is slow.

“They say, ‘It’s just my metabolism,’” said Gallagher, who recently joined the UofL faculty after leaving the University of Pittsburgh, where she was assistant director of a physical-activity and weight-management research center.

“But slow metabolism is very rare,” she said. “And the heavier you are — the more you weigh — the higher (faster) your metabolism, because your body needs additional calories to maintain that weight and carry it around.”

In working with overweight individuals in Pittsburgh, Gallagher sometimes tested their metabolism when they went for weeks without losing weight — even though they said they were sticking to a calorie-restricted diet and getting more exercise than before they entered the program.

Question: Was it their metabolism keeping them from losing or were they not being honest about their behaviors — misjudging portion sizes or not paying close attention to how food is prepared, for example?

“It was never their metabolism,” said Gallagher. “Not one had slow metabolism.”

So rather than calling their metabolism bad names, people might stop and do an honest assessment of their lifestyle, Gallagher suggests.

It’s not unusual to overestimate how much exercise you are getting and underestimate how many calories you are consuming.

Being on your feet all day in your job isn’t the same as taking what Gallagher called a purposeful walk or engaging in some other exercise activity.

If after doing an honest assessment you feel you don’t overeat or under exercise, then maybe you should have your metabolism checked.

Metabolism is the physical and chemical processes within the body that create and use energy — such as breathing, digesting your food, circulating your blood, regulating your body temperature and eliminating your body wastes.

Metabolism is typically measured in calories. The resting metabolic rate (RMR) is the number of calories a person needs each day just to maintain their bodily functions. Sometimes it is called basal metabolic rate.

Numerous things influence your RMR, including your age, gender, hormones, size and body composition — how much of you is bone, muscle and fat, Gallagher said.

Lean muscle burns more calories than fat.

Does metabolism slow with age? Yes, studies show it does. One recent calculation says that the average sedentary person starts to lose a quarter of a pound of muscle per year starting in their late 30s or early 40s so that by age 80 they have lost about a third of their muscle mass and have lowered their metabolism.

Less muscle means slower metabolism. “So that’s just from being inactive, from letting life take control of the reins and not participating in activity on a regular basis,” Gallagher explained.

While studies show the “average Joe Schmo” experiences a decline in metabolism rate as he ages, that doesn’t mean it is caused by aging, said Dr. Ann Yelmokas McDermott of the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston.

“The body meets our demands. The decline in lean muscle mass is because we don’t make demands” on our bodies, she said.

“The muscle of a 100-year-old person will respond to exercise the same way the muscle of an 18-year-old person does,” she said.

“For me to increase someone’s metabolic rate, my goal is to increase the size of their muscles. I want to demand that each muscle fiber become bigger. I want to encourage new blood vessels to grow and to deliver nutrients to these muscles. I want to encourage new nerve endings to grow. This is regardless of age,” she said.

You should work toward total body fitness and exercise all the large muscle groups, McDermott said. She is a big proponent of resistance training, which is also called strength training or isometric or anaerobic exercise.

Typically it is done by using free weights, weight machines, rubber bands, tubing or the weight of your own body (as in doing pull-ups or push-ups) to build muscle strength.

McDermott said some changes in metabolism can be gained with weight training. In addition, people with stronger muscles often feel more fit and so move more briskly and seek out more physical activity.

People also must change their exercise programs, especially weight lifting, about every three months to vary how much weight they lift and at what speeds. Otherwise they won’t see results, because the muscles get efficient as they get used to routines.

McDermott, who is a swimmer, mixes up speed work with slower swimming. If you walk or run, you should do likewise. You have to crank up the speed for portions of a workout to make different demands on muscles, she said.

So how much of our metabolism can we attribute to genetics and how much to lifestyle?

More than 50 percent of our weight status — fatness — has something to do with genetics, said McDermott, whether it is a positive or negative influence.

“But we can control more than half” through diet and exercise, she said.

Gallagher said it a little differently:

“I’d say that over 50 percent of pure metabolism is genetically determined, but that’s only one piece of the equation. Even if metabolism was 100 percent related to genetics and there was nothing we could do about it, metabolism in terms of body weight regulation is only one factor. You can control how much energy you go out and expend on any given day. Also, you control what you eat.”