Exercise, weight loss, and keeping you alive – yet another tale of maps
For most of us, fear of flab is the reason we exercise, the motivation that drives us to the gym. It’s also why public-health authorities have taken to encouraging ever more exercise as part of a healthy lifestyle. If we’re fat or fatter than ideal, we work out. Burn calories. Expend energy. Still fat? Burn more. The dietary guidelines of the U.S. Department of Agriculture, for instance, now recommend that we engage in up to 60 minutes daily of “moderate to vigorous intensity” physical activity just to maintain weight—that is, keep us from fattening further. Considering the ubiquity of the message, the hold it has on our lives, and the elegant simplicity of the notion—burn calories, lose weight—wouldn’t it be nice to believe it were true? The catch is that science suggests it’s not, and so the answer to all of the above quiz questions is “no.”
Just last month, the American Heart Association and the American College of Sports Medicine published joint guidelines for physical activity and health. They suggested that 30 minutes of moderate physical activity five days a week is necessary to “promote and maintain health.” What they didn’t say, though, was that more physical activity will lead us to lose weight. Indeed, the best they could say about the relationship between fat and exercise was this: “It is reasonable to assume that persons with relatively high daily energy expenditures would be less likely to gain weight over time, compared with those who have low energy expenditures. So far, data to support this hypothesis are not particularly compelling.” In other words, despite half a century of efforts to prove otherwise, scientists still can’t say that exercise will help keep off the pounds.
The 30 minutes recommended by the AHA-ACSM report is a departure from the recent guidelines of other authoritative organizations—the Institute of Medicine of the National Academies and the International Association for the Study of Obesity—both of which, like the USDA, have recommended that we exercise for up to 60 minutes a day to avoid what the USDA calls “unhealthy weight gain.” But the reason for this 60-minute recommendation is precisely that so little evidence exists to support the notion that exercising less has any effect.
The report that these experts cite most often as grounds for their assessments was published in 2000 by two Finnish researchers who surveyed all the relevant research on exercise and weight of the previous twenty years. Yet the Finnish report, the most scientifically rigorous review of the evidence to date, can hardly be said to have cleared up the matter. When the Finnish investigators looked at the results of the dozen best-constructed experimental trials that addressed weight maintenance—that is, successful dieters who were trying to keep off the pounds they had shed—they found that everyone regains weight. And depending on the type of trial, exercise would either decrease the rate of that gain (by 3.2 ounces per month) or increase its rate (by 1.8 ounces). As the Finns themselves concluded, with characteristic understatement, the relationship between exercise and weight is “more complex” than they might otherwise have imagined.
As we saw with my previous post on heart health wisdom, the connection between commonly used markers of health and actual risk of death is weak, at least when various ethnic groups are examined. (Of course, these markers, such as amount of visceral fat, sedentary lifestyle, cholesterol levels, etc, may still hold within ethnic groups. But even then, that wouldn’t mean that those factors play a causal role in “early” death.) This suggests that genetic differences between groups may be involved in each group’s cardiovascular mortality rate. But, the New Yorker article made another point which I found interesting:
This is not to say that there aren’t excellent reasons to be physically active, as these reports invariably point out. We might just enjoy exercise. We may increase our overall fitness; we may live longer, perhaps by reducing our risk of heart disease or diabetes; we’ll probably feel better about ourselves.
That’s another big claim. If exercise is (by itself) largely useless for weight loss, could it at least reduce our chances of developing cardiovascular disease (and more importantly, dying from such diseases)? I wanted to subject this to a simple, albeit highly preliminary test.
I found data on the self-reported rates of physical activity in the European Union. Without having looked at anything else, I wanted to see if there was a relationship between a nation’s overall level of physical activity and rates of cardiovascular death.
This is a map of the percentage of people who report never engaging in regular exercise or playing sports (for a more detailed breakdown, please see the source paper), from data collected in 2009:
And, for completeness, this is a map of the percentage of people who say that they never engage in any physical activity outside of sport. We can take this to be a fairly decent gauge of sedentariness in these various countries:
Overall, the pattern appears to be that the least physically active people are those Southern and Eastern Europe. Now, let’s compare this with this previously featured map of the cardiovascular mortality rate across Europe:
This is an interesting contrast, to be sure. One could attempt to connect inactivity with cardiovascular mortality in Eastern Europe, but it seems the least active people are actually in Italy and the Iberian peninsula, regions with some of the lowest cardiovascular mortality rates! Spanish Paradox indeed.
At least for different peoples, the connection between cardiovascular health and diet is pretty shaky. Now, it is possible that within some or all of these groups, exercise is related to cardiovascular health (since “different peoples is different“, after all). But even then, it wouldn’t automatically be clear that exercise plays a causal role in such health. Perhaps people who are healthier to begin with are prone to (and more able to) exercise more. Stay tuned!