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Richard N. Fogoros, M.D.

Do Women Really Need To Exercise An Hour A Day?

By March 24, 2010

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An article appearing this week in the Journal of the American Medical Association is creating quite a buzz, at least among women.

The study examined the exercise and weight histories of over 34,000 women who were enrolled in the Women's Health Study, and concluded that only women who exercised an hour a day (at an intensity equivalent to walking at about a 3 mph pace) maintained their weight. Any less than that, the study said, and the women gained weight.

Consequently, headlines across the land are blaring, "Women Need An Hour of Exercise a Day To Keep From Getting Fat!"

This conclusion is not quite accurate. Plus, in an era when obesity is already being demonized, and especially with new healthcare reforms now in place which (some maintain) will end up collectivizing healthcare resources (such that your obesity will impact my ability to get the healthcare I think I deserve), the notion that women who fail to exercise an hour a day are a menace to society might lead to all kinds of trouble. (One visualizes college-aged members of the proposed Civilian Security Corps showing up each day, and conducting ranks of neighborhood housewives in hour-long forced marches.)

So let's quickly examine the real meaning of this study before the headlines become irreversibly incorporated into the anti-obesity dogma.

1) The study really didn't evaluate the amount of time these women exercised each day. Rather, it evaluated the number of METS (metabolic equivalents) the women expended each week. Roughly speaking, one MET is equivalent to the amount of calories you burn while sitting quietly for 1 hour. So expending 3 METS means you are burning three times the calories you burn while sitting. The investigators found that women whose exercise burned 21 METS per week tended to maintain their weight, while women who burned less than 21 METS gained weight. So, if the exercise you are doing burns 3 METS per hour (such as walking 3 mph), then you would need to exercise 7 hours a week. But if you chose to engage in more vigorous exercise, such as running 12-minute miles (8 METS), then you would only need to exercise around 2 1/2 hours a week to maintain your weight.

2) The study was not a randomized, controlled trial, but was an observational study only, which, furthermore, was based on self-reported exercise levels, and self-reported weights, over a 13-year period. We simply cannot reach any definitive conclusions from this study.

3) It is fundamentally incorrect to equate weight gain (or loss) to exercise levels. One's weight is determined by at least two essential factors: the amount of calories you burn, and the amount of calories you eat. It is entirely possible to lose weight with less than an hour of exercise a day, or to gain weight with more than an hour of exercise a day, depending on how much you eat.

This study threatens to cause the same kind of frustration that was caused a few years ago by an Institute of Medicine report that also recommended that we should all exercise for at least an hour a day. Namely, it might cause those of us who work pretty hard to exercise, but who, at the same time, are mere humans, to throw up our hands in utter frustration, and reach for the Twinkies. The fact is, we can gain a lot of benefit by exercising substantially less than an hour a day.

Here is a discussion of how much exercise is really necessary.

Sources:

Lee IM, Djousse L, Sesso HD, et al. Physical Activity and Weight Gain Prevention. JAMA. 2010;303(12):1173-1179.

Comments
March 29, 2010 at 2:52 pm
(1) Dr.Grant Sayer says:

My first impression after reading your protest was to think that you yourself are overweight. However you make some good points, in that, it is extremely difficult for the average person to balance work, travelling times, the demands of modern children and household chores plus adequate sleep, into a 24 hr period.
There are common denominators amongst my overweight friends. They stay up late at night watching the “idiot box” and then do not have the energy to get up at 0500 to exercise; they walk like a snail instead of alternating walking 100m with running 100m (interval training); they avoid hills (great for raising your VO2 max); they fail to move outside their “comfort zone” when exercising, ( this is mandatory for improvement); they eat junk food; they drink “industrial rust converter” – Coke (phosphoric acid) and they regularly eat until absolutely full (Golden rule – “Never empty – Never full) Humans were meant to graze, not to have three large meals a day.
My exercise regime? Boot Camp sessions x 2 wk; trail running, cycling, weightlifting and indoor rowing, but I go to bed at 8pm and get up at around 0430 and the children have all left home.
Graham, medical scientist

March 31, 2010 at 1:00 am
(2) docli says:

@no1:Humans are not meant to graze-just have a look at the teeth and compare it with a grazing species (i.e. horse, rabbit). The closest species to humans would be pigs (bunodontes -omnivores) wich means we are meant to eat a whole range of different diets.
Vet

March 31, 2010 at 1:13 pm
(3) hotflash says:

Whatever veracity your comments might have got lost in your patronizing view of women as “neighborhood housewives”.

April 2, 2010 at 6:07 am
(4) Ciara says:

While the era of “neighbourhood housewives” diet out circa 1950 (at least in Europe at any rate) the Dr. may make some relevant points. However, consider this. I order to exercise 1 hour per day, still commutre an hour and start work at 8.30, I would need to get up at 5.45 which means to get the amount of sleep I need in order to have a quality of life, I would nee to go to sleep around 9.30. Now considerign I only reach home at 6.30 this leaves me 3 hours i totla in the evening to cook a meal, eat, wash, relax and actually have a meaningful relationship with my partner. Add children to the mix who also have to be gotten up, fed, prepared for schhol / childcare and dropped off at same + collected after work and homework attended to + play and there quire simply just is not time in the day. It is simply mathematics. If I cut back on sleep I get sick – medical fact in may case. If I could back on work my productivity and performance suffers wich is just not acceptable. If I cut back on time at hoime my relationship or children suffer.

April 2, 2010 at 8:41 am
(5) Donna says:

I agree with the supposition that by assuming that exercise is a pass/fail endeavor, over-worked, over-stressed, time-limited individuals may not attempt to engage in a battle lost before beginning. However, I was offended by the initial comments regarding the housewives and the minimization of the problem of obesity. It seems to assume that the target group for the exercise recommendation is those lazy homemakers who, ironically, might be one of the few groups who might actually squeeze in an hour of exercise. Is the general response to obesity an over-reaction? I don’t know, but having been a middle school principal, I have seen first-hand the increase in the number of obsese children and we should be concerned.

April 5, 2010 at 10:39 am
(6) dennis says:

Interesting and valuable comments.As a primary care physician with some experience among athletes-the point is movements that are meant to improve health are beneficial. So the house wife can think of her chores along an exercise lne of thought thus converting her activity at home into exercises.As an example hanging out clothes or moving chairs as if to exercise and neat the house will do much more benefit to the cardio-vas system.
Never look at the chore as a hard and boring job. Mentally the brain recognises these and converts your intentons and you will benefit.
Thanks

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