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Forum: Toward Evidence-free Exercise
February 8, 2008
January is a month of rebirth. It’s an opportunity to kick old habits, pick up new ones, and clean out the closet—metaphorical or otherwise. I’ve always wanted to make a New Year’s resolution with major, life-altering consequences, then amaze everyone—myself included—by sticking to it. Previous ideas have included training for a marathon (which would be akin to climbing Mount Everest for me) and learning a new language (a bit difficult when I don’t have time to take courses or even listen to the CDs). But since I’m usually a little overextended, and maybe a little lazy, I tend to fall back on the familiar: diet and exercise. I’m already a StairMaster devotee, but I know I could crank up the intensity level. I’d be better off if I reduced my intake of processed carbs, and I should definitely consume less NutraSweet.
Feeling motivated in early January, I started going to the gym five times per week instead of three to four. I also increased the duration of my aerobic workouts from 30 to 40 minutes. My fiancé, who’s also a physician, decided to step up his fitness program as well (without so much as a suggestion from me, I might add).
He started doing more cardiovascular work and attended several personal training sessions focusing on weightlifting and conditioning. After his first training session, he jabbered as excitedly as a kindergartener after the first day of school. “My trainer says I need to eat 140 to 160 grams of protein per day. Within 30 minutes of a workout, I should have a protein bar. Milk products are good for you because they contain casein … and it’s good to drink chocolate milk after a workout because it has carbs, too. Apparently, people who mix conditioning with cardio burn more calories than people who do cardio alone…” and so forth.
“Wait, wait, wait,” I said. “Where’s the data? What do you mean when you say that you burn more calories when you lift weights? Does that mean that it’s better to run for 40 minutes and lift weights for 20 than to run for 60? Where’d your trainer get all that from?”
He paused. “Mmmm, I don’t know. He just said it’s better to mix cardio and strength training.”
“Well, I’m sure if you’re a guy with 100 pounds of muscle and you increase it to 150, you’ll burn more calories,” I countered.
“No, he said it’s true for women, too.”
“Really? I better start lifting weights, then!” And I jumped on the strength-building, protein-packing bandwagon.
After about a month, I’ve lost a couple of pounds, and I do enjoy exercising more, if only because my workouts are more varied. But I’m uncomfortable that my new regimen is not based on hard science. I recently admitted to myself that few of my beliefs on diet and exercise—the same beliefs that I proffer to patients—are supported by data from well-designed clinical trials. Sure, I took a nutrition course in medical school, and since then, I’ve skimmed a few papers comparing various diets. I can summarize the extent of my knowledge from these efforts: Weight Watchers good; Atkins bad; everything else somewhere in between. Even if I can’t remember all the details of the large trials on commercial diets, at least the data are out there.
Wondering if research on exercise was as robust, I did a quick PubMed search for controlled trials on “weight loss” and “exercise.” With the exception of two articles that compared various types and intensities of exercise, most of the studies had little to do with exercise or only looked at exercise as a binary variable, superimposed on a background of dietary change.
Why the dearth of good science where exercise is concerned? There are several forces at play. First, these kinds of studies are logistically difficult to do. Even if researchers can come up with a group of patients who are willing to participate, the patients might not stick to their assigned exercise plans. Poor adherence and dropouts reduce a study’s power to show a clinically meaningful outcome. Second, weight-loss studies don’t generally provide services that aren’t available elsewhere. Sure, it’s nice to receive counseling on diet and exercise without paying, but you might have to submit to a battery of tests first—and on the basis of those tests, you could be excluded from the trial.
But I can’t put all the blame on the patients. We clinicians don’t scrutinize lifestyle interventions as critically as medications and procedures. Patients can make a lot of diet and exercise changes without our help, so there’s often a certain sense of detachment on our part. Conversely, when we do invest time and effort in these issues, patients rarely follow our advice to the letter, if at all. We become frustrated, and we’re less likely to address these issues at subsequent visits. And if we don’t even bring up diet and exercise with our patients, all the data in the world can’t help them lose weight.
I’ve resigned myself to the likelihood that we will never know the optimal combination of diet and exercise for maintaining a healthy weight. Like most things in medicine, I’m sure it varies somewhat from patient to patient. Conventional wisdom—eat less, move more—is probably more valuable than my statistics-oriented mind is willing to admit. I’ll keep lifting weights because I like having better muscle tone, but I’ll never drop the cardio. And if I hadn’t spent so much time anxiously analyzing these issues, I might have spared myself a few hundred calories in snack food.
Nicole Martin, HMS ’06, is a resident in internal medicine at Massachusetts General Hospital.
The opinions expressed in this column are not necessarily those of Harvard Medical School, its affiliated institutions, or Harvard University.