Tuesday, December 14, 2010

A Lifetime of Exercise Won't Prevent Weight Gain

Does sticking to a regular exercise program year after year, decade after decade, keep you from gaining weight? According to a study just published in JAMA, the bad news answer is no. The only good news is that regular exercise is associated with less weight gain.

Sound disappointing? To millions of Americans that think they can regularly make up for yesterday's second donut with today's treadmill session, it should be. And to the processed food industry, it's an inconvenient truth.

The Coronary Artery Risk Development in Young Adults (CARDIA) multi-center study started in 1985. It enrolled 5115 young adult volunteers ranging in age from 18 to 30. Participants returned at 2, 5, 7, 10, 15 and 20 years. At each review, subjects were asked about their overall activity and exercise levels (for example, jogging, cycling, swimming, dancing or home maintenance). Those data were plugged into a simple scoring table and points were awarded that, depending on the individual activity, ranged from 108 to 288. They were then added up to yield a total score. To put things into perspective, the DMCB took the time to access the JAMA web site to find out more about the scoring. Doing home maintenance plus regularly playing golf led to 254 points. If jogging was included, the score jumped to 532 points. The authors estimated that meeting the U.S. government's activity guidelines would result in about 300 points.

To correlate the CARDIA score with body mass index, the authors grouped the study population by gender into "high," "medium" and "less" tertiles. To be assigned a tertile, participants had to score into one of the three tertiles for 2/3 of their visits over the 20 years of the study.

Men at the higher levels of exercise consistently scored greater than 608, moderate was 340 to 607 and less was below 340. Higher exercising women were greater than 398, moderate was 192-397 and less was below 192. Persons who failed to keep the "two thirds rule" were lumped into an "inconsistent" category.

At the 20 year mark, there were 3554 individuals with usable data. After controlling for age, race, educational level, tobacco use, alcohol use, food intake and starting BMI, increasing exercise levels were associated with the a lower rate of weight gain. For men, higher or moderate exercise was associated with a per year BMI increase of .14 to .15, while lesser exercise led to annual BMI increases of .20. For women, the BMI at higher tertile levels of exercise increased at a rate of .17 per year versus .25 for moderate and .30 for lesser. Everyone started out at a BMI of about 24 and over the years it increased to the 28-30 range. You can get an idea of what different BMIs look like here.

What can the DMCB conclude?

While it's a bummer, the study only confirms what has been known for years: exercise by itself does not prevent weight gain and cannot be used to decrease weight. All things being equal however, (and this study controlled for dietary intake) exercise by itself can blunt weight gain. Over twenty years, that can make the difference between being "overweight" (BMI less than 30) and being "obese" (BMI equal to or greater than 30). That's good from a public health perspective, but for us individuals, it's not going help us look good at the beach.

While it would appear that men seemed to need to exercise at a higher level compared to women to gain the benefit, the small print in the study showed no difference in the degree of weight gain between higher and moderate lifetime exercise levels. The authors noted that persons meeting the government's activity guidelines also gained less weight compared to the lowest group but the DMCB wonders if being in the 340-400 range (supplementing, say golf and housework with something else, like jogging, swimming or cycling) for both genders is where most of the benefit lies. For men, exceeding that level didn't confer any additional protection.

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