A common-sense explanation of recommendations and ramifications
by Steven N. Blair and James R. Morrow, Jr.
The U.S. Department of Health and Human Services (HHS) and the Department of Agriculture released Dietary Guidelines for Americans 2005 in January. These reports are developed every five years and, typically, have a major influence on government policy.
Of special interest to club operators and fitness professionals is the fact that the new edition of Guidelines includes a more extensive set of recommendations on physical activity than any of the previous versions did.
Three physical-activity recommendations are now provided: one for health benefits (30 minutes per day); a second for the prevention of weight gain (60 minutes/day); and a third (90 minutes/day) for the maintenance of weight loss in formerly obese people who have lost a substantial amount of weight and kept it off for several years.
It's easy to become confused about these recommendations, as was apparent in many of the press accounts that appeared following the release of the Guidelines. The following represents our attempt to clarify the recommendations and the issues they raise.
Physical activity for health benefits
Recommendation: "To reduce the risk of chronic disease in adulthood: Engage in at least 30 minutes of moderate-intensity physical activity, above usual activity, at work or home on most days of the week."
It's clear that this dose of physical activity provides substantial health benefits, and we believe that weight control is among them. This recommendation has emerged from a critical evidence-base of findings produced by multiple lines of scientific inquiry, including epidemiology, small laboratory-based experimental studies, and large-scale, randomized, controlled clinical trials. It was first described in a 1995 joint report from the American College of Sports Medicine (ACSM) and the Centers for Disease Control and Prevention (CDC), and has since been endorsed by a number of leading health organizations.
Some news reports about the Guidelines stressed that the 30 minutes of moderate-intensity physical activity at least five days per week should be considered a "minimum" recommendation. The tone of these articles tended to minimize the importance and health value of this amount of regular activity. We disagree with this interpretation.
There is an enormous amount of data, both from observational studies on morbidity and morality, and controlled clinical trials on physiological and psychological outcomes, that support the 30-minute recommendation as providing substantial health benefits.
Prevention of weight gain
Recommendation: "To help manage body weight and prevent gradual, unhealthy body-weight gain in adulthood: Engage in approximately 60 minutes of moderate-to-vigorous-intensity activity on most days of the week, while not exceeding caloric intake requirements."
This is the recommendation for which the empirical evidence is most sparse, and, also, one that incorporates a logical fallacy: e.g., any amount of physical activity is adequate to prevent weight gain if the subject is "not exceeding caloric intake requirements." As long as energy intake doesn't exceed energy expenditure, a person could, conceivably, avoid gaining weight without exercising at all. The key question, however, is how much activity is required to prevent weight gain for a typical person.
Several investigators report studies in which less than 60 minutes a day was enough to achieve that end. Among them is a 2004 paper that reported on the weight, over a five-year period, of 2,501 men who were examined four times at the Cooper Clinic in Dallas. Men with an initial, low-activity level who increased to a moderate activity level (about 30 minutes of moderate-intensity activity per day) lost 0.4 pounds per year, as compared with those who remained in the low-activity category; those who moved from low to high activity lost even more (0.68 pounds per year). This is consistent with other observational studies of large populations. The value of 30 minutes of activity per day in preventing weight gain has also been demonstrated by randomized clinical trials, including Project Active and the Midwest Exercise Trial.
Thus, it seems that this dose is enough to prevent weight gain for some, probably many, individuals, while some others may require 31 minutes, or 32, or as much as 60 minutes or more. In fact, even 60 minutes isn't enough to prevent weight gain in everyone. The amount of activity required is highly individualized, and may be largely genetically determined. Thus, while 60 minutes per day is right for some people, it's incorrect to imply it's a "magic" number that will prevent weight gain for all.
It might be better to word this recommendation in the following way: "30 minutes of moderate-intensity physical activity per day, for at least five days each week, provides important health benefits and is sufficient to prevent weight gain for some individuals. Others may require more activity to allow them to regulate their energy intake to match energy expenditure." If a person is meeting the primary recommendation of 30 minutes/day of activity, but is gaining weight, they should increase their activity and/or reduce caloric intake until they're in energy balance and at a stable weight.
Prevention of weight regain in formerly obese individuals
Recommendation: "To sustain weight loss in adulthood: Participate in at least 60-90 minutes of daily, moderate-intensity physical activity, while not exceeding caloric intake requirements."
This recommendation has been misinterpreted by some, who think that this dose is a prescription for weight loss. In fact, the Guidelines don't include any activity recommendation for losing weight. There is solid data to support the 90-minute proposal for maintaining weight loss, both from observational studies such as the National Weight Loss Registry (NWLR) and other investigations. This recommendation has to do with formerly obese individuals who have lost a large amount of weight, e.g., 30-50 pounds, and have kept it off for several years. In all probability, they owe their ongoing success to careful monitoring of their dietary intake and a lot of physical activity (80-90 minutes a day). This recommendation may be discouraging to obese individuals, who face the daunting, twin challenges of losing and keeping off pounds, but it's based on solid evidence.
Summary: One of our primary concerns about the Guidelines is that they may be viewed as a major change from earlier physical-activity recommendations. If the public and health professionals mistakenly think, "Now the government has doubled, or tripled, the physical-activity recommendation-can't it ever make up its mind?", promoting healthy levels of activity will become more difficult. It's important to communicate to everyone that the Guidelines don't represent a major departure from previous recommendations. In fact, the new ones are essentially identical to those published earlier by a consensus conference organized by the International Association for the Study of Obesity (IASO).
We recommend that all of the interested parties concentrate on the major public-health problem posed by physical inactivity, focusing on the fundamental recommendation of 30 minutes of moderate-intensity physical activity per day on most (five or more) days of the week, stressing that this will provide substantial health benefits and prevent weight gain for some. The additional two recommendations are important for subgroups of the population, but we definitely shouldn't leave the public with the impression that the recommendation for physical activity has been increased to 60-90 minutes per day.
(To view the complete Dietary Guidelines for Americans 2005 and related documents, log on to http://www.healthierus.gov/dietaryguidelines.)
