It ranks right up there with "the check is in the mail," "the dog ate my homework," and "I will never lie to the American people." Of course, we're talking about "It isn't me, it's my metabolism."
Well, if you're over age 40, the oldest cop-out in the book may have some truth to it after all. Yes Virginia, you really can blame it on your metabolism.
But only a little.
Even if you're sitting or lying down while reading this article, your body is still burning calories; the rate at which it does so is called your resting metabolic rate. As you age, your metabolism tends to decelerate by about 5% for every decade of life past age 40, so that if your resting metabolic rate is, say, 1,200 calories per day at age 40, it will be around 1,140 at age 50.
"At age 40 to maintain your weight, that is to not gain weight, you're going to have to eat 100 calories less a day, and that has nothing to do with anything other than the natural course of aging. That means your resting metabolic rate," Madelyn Fernstrom, PhD, director of the University of Pittsburgh Medical Center Weight Management Center and associate director of the UPMC Nutrition Center in Pittsburgh.
But metabolism is really only a small part of the story. Age and life tend to conspire against us in the battle to lose weight over 40, Fernstrom says.
"As we age, our lives become more complicated, whether it's with children, with work, with aging parents, and so we have less time really to be more physically active and pay attention to what we're eating. Food is available 24 hours a day, seven days a week, in large portions that are relatively economical and so food is always around, and we tend to have more mindless eating and cut down on activities," she says.
When it comes to pinning blame on changes in metabolism there are handful of prime suspects, says Pamela Peeke, MD, assistant clinical professor of medicine at the University of Maryland School of Medicine in Baltimore, who specializes in nutrition and stress, particularly among adults on the far side of 40.
"Metabolism is based upon three different factors," Peeke tells WebMD. "The first factor is genetics. We're good, but we can't fudge with that yet -- give us time, however.
"Number two is thyroid function, and interestingly enough, here's where we get gender specificity. Women have much greater thyroid issues than men, by at least 10 to 1, and it's quite gradual, so women may find that they're losing some of that metabolic edge during their 40s also because thyroid issues begin to spring up."
The third factor affecting metabolism, Peeke says, is muscle mass. In the 40s and beyond, "lifestyle changes rather dramatically and it's sort of a keen grasp of the obvious that everyone's sitting on their ass. So what's happening is if you don't use it, you lose it, and in your 40s you don't just lose it, it melts."
Recent research suggests that women on average will lose muscle mass twice as fast as men the same age, and that can make a huge difference in their ability to lose or at least maintain weight, Peeke says. Muscle is far more "metabolically active" than fat, meaning that lean, more muscular people have an easier time burning calories at rest than to people with higher proportions of body fat.
"Let's say I've worked out at the gym and I have a new pound on board, or, for that matter, I take an old muscle mass on me that's untrained and now I train it and preserve that pound. That muscle mass may now burn between 35 to 50 calories extra a day, versus the same pound of fat, which would burn anywhere from 5-10 calories a day.
"So it's extremely important to know that muscle is very metabolically active and that you don't want to lose it. That being said, a typical can man can lose over the course of the age of 30 through the age of 50 anywhere between 5 and 10 pounds of muscle mass. A woman could definitely lose that -- that's a given because she, through repeated dieting and decreased physical activity, will lose that," Peeke says.
Old Wives' Tales?
Of course, if you wait long enough, say about 25 years, the weight gains that started to accelerate may begin to reverse themselves, says a researcher who studies metabolism in people in their 70s, 80s, and beyond.
"People tend to gain weight steadily, on average -- not everybody -- and get more fat and tend to lose lean mass up to about age 65, and then what happens is that there's a downward trend: Now people start to kind of slowly lose weight -- again, not everybody, but the trend is that as you get older -- the general population I see is in the 70s and 80s -- they tend to lose weight," says Michi Yukawa, MD, MPH, acting instructor in the department of medicine and the division of gerontology and geriatric medicine at the University of Washington in Seattle.
"Why they lose that is the topic of my research. It may be various hormonal changes, metabolic changes, and the fact that they just don't eat as much as they used to. They lose their appetite, which can be due to a variety of factors, such as stress, loss of spouses and friends, money issues, or many other things."
But you don't have to wait for age to take its course, Fernstrom says.
"Even if we do have a small, let's say, biological sabotage built in, it does not mean everyone is destined to gain weight as they grow older. It's sort of an old wives' tale that you'll gain 30 or 40 pounds as you continue through middle age -- it can easily happen, but it's very easy to offset the change in metabolic rate," she tells WebMD.
"For most people that's going to be 100 calories a day approximately, and, you know, you look at 100 calories, if you are over consuming just that 100 calories, you can gain 10 pounds in a year if you are out of sync 100 calories a day. So you don't have to have a lot of extra calories to have what I call weight creep."
Regular exercise is also key to getting metabolism back on your side, Peeke adds.
"The kind of physical activity that people are choosing to do in their 40’s is nowhere near as intense as it's supposed to be. So to get over that metabolic speed bump we ask for an increase in intensity on the part of these happy campers. What does that mean? Instead of walking on the flat, throw in some hills. Ramp up the resistance on your resistance training, or for that matter the resistance on a cross-trainer. It's all the same.