Battle of the middle-years bulge

August 28, 2006 7:55 AM

"When you hit your 30s and 40s, your metabolism slows, resulting in weight gain." What does this mean, in raw biological terms? Is it rational to aim for a sub 10% bodyfat level after 40, assuming we're not marathon runners?

Yep, everybody's told me that a slower metabolism after 30 (or 40, or 50) is the primary reason for the middle age bulge. But this sounds way counter-intuitive: If the body's digestive and energy-producing systems are less efficient, shouldn't it require *more* calories to produce the same activity and energy level for us? What's involved in the "slower metabolism," in biological terms, and has it been substatiated?

If we're all destined to slower metabolisms, is there any point in dieting beyond a certain amount? Should we blithely accept moderate padding, or is a 10% or less bodyfat (slightly more for women) achievable through diet and moderate exercise?

Personal anecdotes welcome!

posted by Gordion Knott to health & fitness (12 comments total)

Just some stats to guide your thinking

"Dr. C. Everett Koop's site, ShapeUp.com, breaks down healthy body fat ranges by both gender and age. Men under 39 years of age should have 8-19% body fat, and women under 39 years of age should have 21-32%. Older men may range from 11% to 24%, and older women may range from 23% to 35%. "

10% is doable of course, but I would say it would take a whole hellava lot of training, I mean to the point of this being the center of your life. I have heard that after 27 your metabolisms starts slowing 3% a year, but I don't really know. I would think this means cutting a little out of your diet or adding a little more exercise, its not like we are destined to get fat, we are just destined to need to pay a little more attention.
posted by stormygrey at 8:11 AM on August 28, 2006

Using your body as an engine and calories as fuel is a bad metaphor when trying to explain more complex biological processes. Changes in hormonal levels (more predominatly associated with women) are the primary reason for non-activity based weight gain. Your body isn't inefficiently processing food per se, but due to hormonal changes it begins to move away from focusing on building muscles and maintaining organs (and everything else) and storing it away in fat cells. Muscles and everything else require more calories per pound than fat does, so really your body is needing less input. I can't remember the specific article I read this in, but it was in PubMed somewhere. I would venture to say that most older adults, given an ideal active lifestyle and proper eating habits would still retain what would be considered a bulge.
posted by geoff. at 8:27 AM on August 28, 2006

The other thing that happens, which is very much apropos when thinking about bodyfat percentages, is that people who are less active begin to lose muscle and gain fat as they get older. This can result in constant weights with increasing bodyfat percentages.

Sub 10% is, of course, possible without being a super athlete, but an awful lot depends on where you're starting off. If you've got 15% now and you want to lower it to 10%, you're going to have to work a lot harder as a 42 year old than you would have had to as a 22 year old.
posted by OmieWise at 8:59 AM on August 28, 2006

Yep, everybody's told me that a slower metabolism after 30 (or 40, or 50) is the primary reason for the middle age bulge. But this sounds way counter-intuitive: If the body's digestive and energy-producing systems are less efficient, shouldn't it require *more* calories to produce the same activity and energy level for us? What's involved in the "slower metabolism," in biological terms, and has it been substatiated?

Your slowing metabolism is due to loss of muscle mass. If you were to maintain the same amount of muscle and daily activity levels as you aged, your metabolism would stay the same. But as you grow older it takes more effort to maintain the same level of muscle, so for most people this equates to a "slowing" metabolism.
posted by justkevin at 9:25 AM on August 28, 2006

Below 10% is very low... just to add that fat, in women, helps with estrogen production, which compensates a little for the overall loss of estrogen during menopause, and might be partially why there is a tendency towards weight gain in the forties.
posted by jokeefe at 10:57 AM on August 28, 2006

justkevin writes "Your slowing metabolism is due to loss of muscle mass."

I'm pretty sure that this is just plain wrong. Googling "age-related metabolism decline" shows several studies that 1) demonstrate changes in metabolisms all across the body as we age; 2) explain the mechanisms of those declines with scientific data other than higher fat/lower muscle body compositions; 3) measure differences in metabolism even when the studies control for the differences in body fat compostion among participants.

This survey of studies seems good and indicates that mitochondrial dysfunction plays a role. The really good news is in this study which does confirm that regardless of bodyfat comp resting metabolic rate slows by about 10% as people age, but demonstrates that aerobic exercise reverses the declines or prevents them. This, by the way, contradicts the notion that muscle building alone is going to see you through the slowing. There may be studies which demonstrate that, but I didn't find them (I also didn't look for them specifically).
posted by OmieWise at 12:54 PM on August 28, 2006

Here's the conclusion from another study which looks at men's rates in relation to exercise and food intake. The conclusion is that one's RMR need not decline, but the decline is correlated with overall exercise volume (hours per week regardless of volume):(FFM is fat-free mass)

These results indicate that 1) RMR, per unit FFM, declines with age in highly physically active men; and 2) this decline is related to age-associated reductions in exercise volume and energy intake and does not occur in men who maintain exercise volume and/or energy intake at a level similar to that of young physically active men.

Of course this would be exacerbated with a general loss of muscle mass and any gains in fat, since FFM would decrease and the metabolism of what's there also decreases.

I looked around some more, and the idea that the decreases in metabolism are primarily due to the loss of muscle are pretty prevalent but I've yet to find a cite that backs it up. In other words, it seems to be either a common misunderstanding or a simplification of what's actually going on. I'm interested in this myself for reasons of fitness, hence my googling around.
posted by OmieWise at 1:37 PM on August 28, 2006

Just another study which indicates that the decline is indeed real and related to normal aging:

We examined the hypothesis that a decline in Na-K pump activity contributes to the lower resting metabolic rate (RMR) in older males, independent of the loss of fat-free mass... Our results support the conclusions that: 1) the in vivo activity of the Na-K pump is related to RMR, and 2) the age-related reduction in Na-K pump activity is a partial contributor to the decline in RMR in older men.
posted by OmieWise at 1:40 PM on August 28, 2006

This is a really good question for me; I have wondered the same thing.

I am 51, and my hobbies are weightlifting and running (with a dog of course). Despite my improved workout regimen, I am still struggling with the body fat thing. I still have this little "paunch" that persists, even though I am in better shape than I was even in my 30's. (which says just how poorly conditioned I was in my 30's). Interestingly though, I can do more strength exercises than I could in my 30's, but I can't run near as fast or long.

Nevertheless, I suspect that justkevin has it correct; that you don't actually have a slowing metabolism, your body is not turning every calorie into muscle due to the declining muscle mass. Muscle I am told, is more effective at using or burning excess calories than is bodyfat.

I think that to reduce body fat levels even more (say to that 10%) is dependant upon your diet and heredity. That is to say, less bad fat, more fibre and cardio exercise, and even then, if you tend to the large and huggable, then you may still not be able get your fat levels to the 8-10% that you might be seeking.

As a scholarly question, I find it interesting. Hopefully, it is not because you are dissatisfied with your present appearance, cause its just, well, you know, your appearence.
posted by fox_terrier_guy at 2:02 PM on August 28, 2006

"Nevertheless, I suspect that justkevin has it correct; that you don't actually have a slowing metabolism, your body is not turning every calorie into muscle due to the declining muscle mass."

Do you have a citation for that, or is it just your gut instinct? I ask because I'd be really interested to read a "substantiated" explanation of metabolic slowing (you know, what the Gordian Knott asked for) that addressed this. Regardless, the papers I cited indicate that there is, in fact, slowing of the metabolism as people age.
posted by OmieWise at 4:19 PM on August 28, 2006

Yes, your metabolism slows down as you age. Its related to a whole bunch of factors and is complicated, as most systems with the body are.

Yes, you still can get ripped when you are older. Just take a look at some of the seniors bodybuilding competitions, or older triathletes. It just gets harder as you get older.

10% body fat is very lean. Just realize that male fitness models maintain between 6 and 10%, and that 10% is right around the threshhold of having clearly defined abs. Pro bodybuilders compete at around 5 or 6%, but they are also on a ton of drugs. For females add at least 6 points to these numbers. If you were overweight while growing up and while an adolescent, expect it to be harder.

So 10% or sub 10% is not impossible, but you would need to make serious lifestyle changes to reach it and maintain it. We are talking measuring all your food intake, tracking all your calories, and exercising strenuously at least 3-4x a week. Eating ceasar salads w/ chicken when everyone else you are out with is having pasta and bread sticks and dessert. Drinking one glass of red wine while your friends/family get tispy.

Some people can stay lean with poor habits while young, but that luck is very rare as you get older.
posted by rsanheim at 6:32 PM on August 28, 2006

As with any statistic, it is a generality, and there are exceptions to the rule. If you are working out and staying active throughout the day (nervous twitching burns lots of calories!), you can stay lean as you want. Eat your biggest meals early in the day: Big breakfast, big lunch. Eat very lightly, if at all, after 3PM. An old chinese proverb: "Walk 100 steps after dinner, live 99 years". And drink lots of water.

You can try going Atkins style and increase your protein and decrease your carbs, but I think it makes a bigger difference to simply cut out anything that has either corn syrup/sweetener, partially hydrogenated fats, or processed flour.
posted by Araucaria at 7:45 PM on August 28, 2006