Junkfood Science: Reading comprehension — Or, why we shouldn’t believe in sloths

September 19, 2007

Reading comprehension — Or, why we shouldn’t believe in sloths

You’ve no doubt read the one about how about two-thirds of us are sedentary and don’t get the recommended amounts of physical activity. The data sounds impressive and dutifully ominous, so it’s easy to believe it’s true. Trouble is, it’s a creation of careful wordsmiths, not facts.

The government’s recommendations for physical activity — issued by an expert panel of the Centers for Disease Control and Prevention and the AmericanCollege of Sports Medicine (ACSM) — were published in a 1995 issue of the Journal of the American Medical Association. It said that to enjoy health benefits:

Every U.S. adult should accumulate 30 minutes or more of moderate (in intensity) physical activity on most, preferably all, days of the week.

Pressures have been mounting for years to create a crisis of inactivity, as well as bad diets, to support the growing budgets of government anti-obesity programs. Not coincidentally, the CDC’s Division of Nutrition and Physical Activity budget has increased 2,000 percent since 1999, and the National Alliance for Nutrition and Activity (NANA) has grown to more than 300 state and national organizations, agencies and nonprofit groups — all making their bread and butter promoting activity and eating “right” as part of the war on obesity and “inactivity-related diseases.”

As we’ve talked about, it is extremely easy to create a poll or survey to arrive at whatever conclusions researchers wants to “find.” If they want to show how inactive people are, they can simply frame the questions they ask in order to give results that can mislead us. Similarly, if they want to show the health benefits of physical activity, they will ask other carefully derived questions. You’ll quickly see how they’ve managed to create a false crisis of sloth....

The CDC, along with the President’s Council on Physical Fitness and Sports, ACSM, and NANA have for years, and with growing exigency, been saying that most all of us are sedentary. The March 2002 issue of the President’s Council on Physical Fitness and Sports’ Research Digest reported that 42% of U.S. adults did less than 30 minutes of physical activity each day. Their definition of sedentary living, they said, was based on the CDC/ACSM recommendations:

Our definition of sedentary therefore includes those who undertake no leisure-time physical activity (28% of US adults) and those who undertake less 30 minutes of physical activity each day. Thus, by our health threshold definition, about 70% of US adults are sedentary.

The government’s Healthy People 2010 program says “few individuals engage in regular physical activity” and that “40 percent do not participate in any regular physical activity [and] only 15% of adults report physical activity for 4 or more days per week for 30 minutes or longer.” A close look at the source of their data, and that of the President’s Council, however, gives a different perspective.

The source of their data is the National Health Interview Surveys, conducted by the CDC’s National Center for Health Statistics. It reports “leisure-time physical activity” and “vigorous physical activity.” Its figures actually say that 40% of adults don’t engage in leisure-time activity and two-thirds of all adults don’t engage in vigorous activity three or more times a week.

The just-released report of the National Health Interview Survey from the CDC’s National Center for Health Statistics, also seemed to provide evidence of our supposed inactivity, saying:

Overall, 62% of adults never engaged in any periods of vigorous leisure-time physical activity lasting 10 minutes or more per week, and 24% engaged in such activity three or more times per week.

That doesn’t mean people aren’t active.

Even common sense tells us how ridiculous the notion is that two-thirds of us are sedentary. As anyone knows, it’s uncomfortable to be stationary for prolonged periods of times. The squirming starts and you just have to move to feel better. Our bodies, all bodies, naturally want to move around. And not many of us have servants waiting on us hand and foot to even be able to enjoy a life of complete leisure.

With any claims about exercise, look closely at the fine print for these two tactics:

First trick: Leisure time activity is not the same as no physical activity. But by asking about leisure time activity, a researcher (and the government) is more likely to find evidence of an association with better health and to find fewer people “physically active.” Why? Those with the most leisure time, and the time and energy to exercise outside work, also tend to be wealthier, with fewer socioeconomic stresses and better access to healthcare. Leisure activity is mostly a marker for wealth, rather than a measure of the true total physical activity that people accumulate in a day. If they’d asked how much physical activity a person did in the course of their work, they’d likely find greater physical activity among the poor, who do more manual work. But that wouldn’t support their claim that most of us are inactive.

Second trick: Vigorous activity is not the same as no physical activity. By asking about vigorous activity, a researcher (and the government) may be more likely to find evidence of an association with better health and to find fewer people “physically active.” But it’s typically simply a marker for important confounding factors. Vigorous, extreme exercisers (pursuing such activities in their leisure time, to boot) are mostly younger, natural athletes and again, of higher socioeconomic status. Even the CDC’s report states: “Educational attainment, family income, and non-poverty status were inversely associated with engaging in periods of vigorous leisure-time physical activity... 74% of adults in poor families never engaged in periods of vigorous leisure time physical activity compared with 55% of adults in families that were not poor.”

But framing the question in terms of vigorous activity — or “exercise” as some surveys do — is disingenuous because those aren’t even the recommendations from the government. And there is no evidence in decades of research, as even the government’s own guidelines note, to support public recommendations for vigorous activity. Moderate activity during the course of our day is all that is recommended to see benefits.

And those benefits come with a lot less activity than most people think. Renowned aerobics researchers Dr. Timothy S. Church, M.D., M.P.H., Ph.D., now at Pennington Biomedical Research Center, and Steven Blair, PED, currently a professor in the Arnold School of Public Health at the University of South Carolina, conducted the longest, largest studies of exercise and health in the world while at the Cooper Institute. To enjoy health benefits, formal exercise isn’t required, they said, and it takes surprisingly little activity, while simultaneously eliminating the risks associated with “exercise.” Moderate (intensity) activity can be little things like walking, gardening, housework, bicycling, swimming, dancing, golfing, woodworking, painting, hobbies and other activities enjoyed in the course of our days, or in the course of our work, all count.

There is no credible support for the idea that more is better. As Dr. Dean Edell, M.D., author of Eat, Drink & Be Merry, wrote:

You need less exercise than you think to accrue most of the health benefits...exercise is not a magic cure for all that ails you and it can even have some very negative consequences...I place almost the highest premium on having fun...Over the years I’ve noted a growing belief that all mega-exercise is good for everyone.

People who are living their lives to the fullest are doing things, but it's a very rare centarian who spent their lives “exercising.” Dr. Edell added:

The real good news is that if you decide to get in shape, you don’t have to go for a 5-mile run every morning. Listen to this, from the Institute: “The greatest reduction in relative risk occurs between the lowest level of fitness and the next-lowest level of fitness.”

The already abundant body of evidence for this grows steadily. The results of the DREW trial, the largest, single-center, controlled trial of exercise amounts in women, were also recently published in the Journal of the American Medical Association. This 6 month study, led by Dr. Church, studied women commonly believed to be most at risk for developing heart disease and who might most benefit from adhering to an exercise program: nonexercising, postmenopausal fat women. The women underwent tightly controlled amounts of exercise, with all exercise completed in the laboratory and extensive monitoring of exercise energy expenditure, heart rate, and steps taken outside of the structured exercise prescription. Their aerobic fitness was assessed on a cycle ergometer and quantified as peak absolute oxygen consumption.

“Despite the changes in fitness that we observed, there were no substantial changes in many of the cardiovascular risk factors or weight...or body fat percentage” they reported. There was also no changes in systolic blood pressure related to the amount of exercise, which was “consistent with the findings of other large exercise and blood pressure studies that have reported exercise training to have minimal benefit to systolic blood pressure.” [Remember, those health indices are not measures of good behavior.]

While they noted a dose relationship with fitness, it was also unrelated to the women’s weight, but: “Perhaps the most striking finding of our study is that even activity at the [lowest] 4-kcal/kg per week level (a mere 72 minutes a week, about 10 minutes a day) was associated with a significant [and largest] improvement in fitness compared with women in the nonexercise control group....This information can be used to support future recommendations and should be encouraging to sedentary adults who find it difficult to find the time for 150 minutes of activity per week, let alone 60 minutes per day.”

As growing numbers of researchers are also recognizing, exercise as such, is not always good for everyone. For example, Dr. Matthew Lancaster, of Biological Sciences at the University of Leeds, recently reported that exercise does not reverse the normal effects of aging on the heart, as is popularly believed, but can actually increase the risk of heart arrhythmias and lead to sudden death or the need to have a pacemaker. The older heart is significantly different in its response to exercise when compared with responses seen in the young. Not to deter people from exercising, but as a note of caution, he said: “ Exercise does not make an old heart young again.” Older people not engaging in vigorous activity could be said to be older and wiser.

The next time you hear another report claiming that two-thirds of us are sedentary, you’ll know what’s really going on.

© 2007 Sandy Szwarc

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