Staff Update

Spring 2006

What's in the News?

2005 Dietary Guidelines for Physical Activity

2005 Dietary Guidelines for Physical Activity:

Translating the Recommendations

By Glenn A. Gaesser, Ph.D.

            When the 2005 U.S. dietary guidelines were released on January 12, 2005, the new recommendations that received the most attention were the beefed-up guidelines for physical activity-up to 90 minutes per day of moderate-intensity activity.¹  In fact the 2005 guidelines provided three major recommendations regarding the amount of physical activity-for health, weight control, and maintenance of weight loss.  Specifically:

1.      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. For most people, greater health benefits can be obtained by engaging in physical activity of more vigorous intensity or longer duration.

2.      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.

3.      To sustain weight loss in adulthood: Participate in at least 60 to 90 minutes of daily moderate-intensity physical activity while not exceeding caloric intake requirements. Some people may need to consult with a healthcare provider before participating in this level of activity.

            The guidelines also suggested that physical fitness can be achieved by including cardiovascular conditioning, stretching exercises for flexibility, and resistance exercises or calisthenics for muscle strength and endurance.  But without question the most eye-opening of the new guidelines was the increased amount of physical activity recommended for weight control and maintenance of weight loss.  After all, the previous guidelines, released in 2000, merely recommended "be physically active each day."  The addition of physical activity guidelines that focused specifically on weight control undoubtedly reflected intensified efforts to address the obesity crisis in America.  The amount of physical activity necessary for weight control, however, may have been considerably overstated.

How the 2005 guidelines were created

            The version of the 2005 dietary guidelines released to the public is based on a report by the 13-member 2005 Dietary Guidelines Advisory Committee, appointed by the Departments of Health and Human Services and Agriculture.  Close inspection of the advisory committee's report reveals subtle differences in language between the final version of the 2005 guidelines released to the public, and the report prepared by the advisory committee.²

            For example, to manage weight and prevent weight gain, the guidelines state "engage in approximately 60 minutes of moderate-to-vigorous-intensity activity on most days of the week."  The actual advisory committee's report was more cautious in its recommendation for preventing weight gain.  In the overview of the report the committee stated that to prevent the gradual accumulation of excess weight in adulthood, "up to 30 minutes per day may be required over the 30 minutes for reduction of chronic disease risk and other health benefits," and in the conclusion stated that "many adults may need up to 60 minutes of moderate to vigorous physical activity on most days to prevent weight gain."  The difference between the advisory committee's language and that of the guidelines released to the public are the words "many adults" and "may need up to."  The advisory committee acknowledged that not all individuals need a full 60 minutes per day of physical activity.  By contrast, the version released to the public tends to imply that 60 minutes should be the goal for everyone.  [It must be noted that once the Advisory Committee submits its report to the Secretaries of Departments of Health and Human Services and Agriculture it is disbanded and no longer has any input with regard to the language of the final, official version released to the public.]

Recommendation #1: 30 minutes per day still a solid baseline for health benefits

The health-focused recommendation of at least 30 minutes of moderate-intensity physical activity on most days of the week is a well-documented.³  This recommendation is essentially the same as the Surgeon General's recommendation released in 1996, which has been the prevailing public health message for physical activity since that time.⁴  Such a level of activity is doable for the majority Americans, and the "on most days" qualifier allows for flexibility in individual's personal schedules.   The 2005 guidelines provide examples of moderate-intensity activity, which include such activities as hiking, light gardening, dancing, golf, walking (3.5 mph), weight lifting (light general workout), stretching, and bicycling (<10mph). 

Regular physical activity of a moderate-intensity has been shown to reduce the risk of certain chronic diseases, including high blood pressure, stroke, coronary artery disease, type 2 diabetes, colon cancer and osteoporosis.^1-4   Furthermore, the 30 minutes per day of moderate-intensity activity can be accumulated throughout the day, for example in 5- or 10-minute increments (e.g., several 5-to-10-minute brisk walks). 

Recommendation #2: 60 minutes per day for weight control may not be necessary

            The Dietary Guidelines Advisory Committee acknowledged the difficulty in making this recommendation, and thus emphasized that many adults "may need up to" 60 minutes per day of moderate-to-vigorous activity.  Strictly speaking this could mean anywhere from 31 minutes to 60 minutes of additional activity (i.e., above the 30 minute-per-day baseline), which sounds much less imposing than the way this recommendation was actually worded in the official version released to the public (e.g., "approximately 60 minutes" could be interpreted as 50 or 55 minutes, but just as easily as 65 or 70 minutes-but definitely not 35 or 40 minutes).

            As a rationale for this recommendation, the Dietary Guidelines Advisory Committee mentioned that 30 of 36 longitudinal studies that the committee examined revealed an inverse relationship between physical activity and overweight status, and also cited a consensus statement of the International Association for the Study of Obesity, entitled, "How much physical activity is enough to prevent unhealthy weight gain?"⁵  This consensus statement concluded that roughly 45 to 60 minutes per day of moderate-intensity daily physical activity is needed to prevent the transition from what it defined as a healthy weight [Body Mass Index (BMI) <25] to an unhealthy weight (i.e., BMI>25).  In view of this 2003 report it is understandable how the Dietary Guidelines Advisory Committee could arrive at its "up to 60 minutes per day" recommendation for prevention of weight gain.

However, the wording of the 2005 guidelines includes "vigorous" activity in this recommendation (i.e., approximately 60 minutes of moderate-to-vigorous-intensity activity on most days of the week).  Because vigorous activity elicits a greater calorie expenditure than moderate-intensity activity, the 45 to 60 minutes per day recommendation could be shortened considerably if someone chose to exercise at a more-than-moderate intensity.  And it must be noted that "vigorous" is not all that intense, certainly not exhaustive.  The 2005 guidelines provides these examples of vigorous activity:  running/jogging (5 mph), bicycling (>10mph), swimming (slow freestyle laps), aerobics, walking (4.5 mph), heavy yard work, weight lifting (vigorous effort), and basketball.

Another important point to make is that "healthy weight" and "unhealthy weight" cannot be defined without also considering lifestyle, in this case physical activity.  Many of the health benefits of physical activity are achieved independently of weight loss.^6-10   This is one very important reason for maintaining regular physical activity (even if it's the minimum, as recommended in Guideline #1)-you get benefits regardless of what the scale indicates.

Nonetheless, many individuals in America are concerned with body weight and would like to avoid gaining an unnatural amount of weight as they age.  On an individual level it should be obvious that physical activity may need to be modified accordingly.  With this in mind it is worth noting that the Dietary Guidelines Advisory Committee also cited the 2002 Institute of Medicine report that concluded from its analysis of the literature that two-thirds of adults who maintain their energy balance (i.e., low-risk for adult weight gain) had a daily energy expenditure consistent with engaging in approximately 60 minutes per day of moderate-intensity activity.

Therefore, in looking at this solely from the perspective of energy balance, without regard to health outcomes, the Dietary Guidelines Advisory Committee's recommendation that many Americans may need up to 60 minutes per day of at least moderate-intensity activity in order to minimize risk of weight gain during adulthood, has a good deal of scientific support.  The additional physical activity is likely to confer increased health benefits as well-but these benefits are more likely to occur from the additional activity itself rather than the weight "not gained."

Recommendation #3:  60-90 minutes per day to sustain weight loss is overstated

In developing this recommendation the Dietary Guidelines Advisory Committee addressed this question: How much physical activity is needed to avoid weight regain in weight-reduced persons?  Because so many people attempt weight loss, this is an important question.  Physical activity is perhaps the best predictor of weight maintenance following weight loss.¹¹  However, the amount of physical activity necessary to prevent weight regain is dependent on how much weight is lost initially.  Maintaining a weight loss of 5 to 10 pounds, for example, could logically be expected to require less physical activity than maintaining a weight loss of 50 or 60 pounds.  Yet the current 60-to-90 minute per day guideline comes largely from data on people who have lost 50 or more pounds!

As described in the Dietary Guidelines Advisory Committee's report, the 60-to-90 minute per day physical activity recommendation is based on cross-sectional data from the National Weight Control Registry (NWCR),¹² two metabolic studies that assessed energy balance over a period of weeks,^{13, 14} and one published review of observational studies and randomized control trials.¹⁵  As described below, each of these studies has limitations with regard to generalizability.

Even if the self-report data from the NWCR can be accepted as valid, the minimum requirement for enrollment in the NWCR is a 30-pound weight loss maintained for at least 1 year (it could be argued that the 1-year criterion does not represent "long-term" maintenance).  However, in the publication cited by the Dietary Guidelines Advisory Committee, men and women in the NWCR reported a weight loss of approximately 30 kg (~66 pounds) maintained for about 6 years.¹²  This is extraordinary, and certainly not representative of most studies.¹¹  Women in this study reported expending an average of 2,545 kcal per week in physical activity; men reported expending an average of 3,293 kcal per week.  This corresponds to approximately 60 to 90 minutes per day of moderate-intensity activity, which is ~30 miles per week of brisk walking, or about 4-5 miles per day!

In one of the metabolic studies, participants consisted of 32 women who had recently lost an average of more than 50 pounds during the preceding year.¹³  During a one-year "free-living" follow-up period, the physical activity threshold level for weight maintenance was demonstrated to be the energy equivalent of approximately 80 minutes per day of moderate-intensity activity. 

The second metabolic study, on premenopausal women with BMIs <25, was a bit more complicated.¹⁴  A total of 61 women were studied before and after a ~1-year period of non-intervention (i.e., free living).  Thirty-three of the women had initially lost >22 pounds in order to reduce BMI to <25, before entering the study.  The other 28 women had not lost weight prior to the initiation of the study.  After the ~1-year follow-up, researchers divided the women into three groups: 27 "maintainers" (i.e., no weight change during the follow-up period); 20 "gainers" (average weight gain = 21 pounds during the year); and 14 women gained weight at an intermediate rate (i.e., something less than 21 pounds).   Analysis of metabolic data collected indicated that the "weight gain difference" (which was mostly body fat) between the "gainers" and "maintainers" corresponded to a daily energy expenditure equivalent to approximately 77 minutes per day of moderate-intensity physical activity.  In other words, if the women who had gained the 21+ pounds during the year had engaged in an additional 77 minutes per day of at least moderate-intensity activity throughout the year, they presumably would not have gained that weight. 

As might be expected, almost all--19 of 20-of the "gainers" had previously lost weight, suggesting that weight loss of this magnitude (i.e., 22 pounds or more) is difficult to maintain.  Only 6 of the initial 33 women who had previously lost weight (18%) were classified as "maintainers" after just one year.

Therefore, two of the studies that the Dietary Guidelines Advisory Committee relied on used participants who had reported losing an average of ~50 to 66 pounds.  The third study compared a small group of reasonably weight stable women with an even smaller group of women who had regained (after dieting) an average of 21 pounds in one year.  The review article cited by the Dietary Guidelines Advisory Committee generally supported the findings of these three studies, but there were some noted inconsistencies.¹⁵

These studies may provide insight into physical activity requirements necessary to maintain rather extreme weight loss, but probably are not entirely applicable to the millions of individuals who would like to maintain lesser amounts of weight loss.  For persons who lose a more modest amount of weight (e.g., ~10 to 20 pounds), the amount of physical activity necessary to maintain weight loss is probably a lot less.  Unfortunately, little, if any, published information is available to address the question minimum physical activity levels necessary to prevent weight regain after a relatively small weight loss.^16, 17

Conclusion

            The 2005 Dietary Guidelines should be commended for emphasizing the important role of physical activity in health.  The health-oriented recommendation for accumulating at least 30 minutes per day of at least moderate-intensity physical activity is consistent with previous public health messages and has solid scientific support.  The two physical activity recommendations focused on weight control are a bit overstated.  Good health and weight control can most likely be achieved by many individuals with less than the ~60 minutes per day recommendation, although, as the Dietary Guidelines Advisory Committee cautioned, to prevent significant weight gain during adulthood many individuals may need up to 60 minutes per day of moderate-to-vigorous activity.              Unfortunately, the physical activity guideline that received the most attention was the 60-to-90 minute per day recommendation for maintaining weight loss.  As discussed above, this amount of activity is far more than necessary to maintain good health and reduce risk of many degenerative diseases, and pertains primarily to individuals who have lost a significant amount of weight (~20-66 pounds)^12-14  Physical activity requirements necessary to maintain more modest weight losses (i.e., <~20 pounds) are not clear, but at least one study suggests that ~150-200 minutes per week (i.e., ~20-30 minutes per day) of moderate-intensity exercise, such as walking, is sufficient.

References

1. Nutrition and Your Health: Dietary Guidelines for Americans. 2005; www.healthierus.gov/dietaryguidelines/
2. 2005 Dietary Guidelines Advisory Committee Report.  http://www.health.gov/dietaryguidelines/dga2005/report/
3. Pate RR, Pratt M, Blair SN, et al. A recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. JAMA 273:402-407, 1995.
4. U.S. Department of Health and Human Services (HHS). Physical Activity and Health: A Report of the Surgeon General. Atlanta, GA: HHS, Centers for Disease Control and Prevention. National Center for Disease Prevention and Health Promotion, 1996.
5. Saris WH, Blair SN, van Baak MA, et al. How much physical activity is enough to prevent unhealthy weight gain? Outcome of the IASO 1st Stock Conference and consensus statement. Obesity Reviews 2003; 4:101-114.
6. Fagard RH. Physical activity in the prevention and treatment of hypertension in the obese. Med Sci Sports Exerc 1999; 31 (Suppl), S624-S630.
7. Kraus WE, Houmard JA, Duscha BD, et al.  Effects of the amount and intensity of exercise on plasma lipoproteins. New Engl J Med 2002; 347: 1483-1492.
8. Lamarche B, Despres J-P, Pouliot M-C, et al.  Is body fat loss a determinant factor in the improvement of carbohydrate and lipid metabolism following aerobic exercise training in obese women? Metabolism  1992; 41, 1249-1256.
9. Cononie CC, Goldberg AP, Rogus E,  Hagberg JM.   Seven consecutive days of exercise lowers plasma insulin responses to an oral glucose challenge in sedentary elderly.  J Am Geriatr Soc  1994; 42, 394-398.
10. Hickey MS, Gavigan KE, McCammon MR, et al.  Effects of 7 days of exercise training on insulin action in morbidly obese men.  Clin Exer Physiol  1999; 1, 24-28.
11. Anderson JW, Konz EC, Frederich RC, Wood CL.  Long-term weight-loss maintenance: a meta-analysis of US studies.  Am J Clin Nutr 2001; 74, 579-584.
12. McGuire MT, Wing RR, Klem ML, Hill JO. Behavioral strategies of individuals who have maintained long-term weight losses. Obes Res 1999; 7(4):334-341.
13. Schoeller DA, Shay K, Kushner RF. How much physical activity is needed to minimize weight gain in previously obese women? Am J Clin Nutr 1997; 66:551-556.
14. Weinsier RL, Hunter GR, Desmond RA, Byrne NM, Zuckerman PA, Darnell BE. Free-living activity energy expenditure in women successful and unsuccessful at maintaining a normal body weight. Am J Clin Nutr 2002; 75(3):499-504.
15. Fogelholm M, Kukkonen-Harjula K. Does physical activity prevent weight gain - a systematic review. Obes Rev 2000; 1:95-111.
16. Votruba SB, Horvitz MA, Schoeller DA.  The role of exercise in the treatment of obesity.  Nutrtion 2000; 16: 179-188.
17. Schoeller DA.  But how much physical activity?  Am J Clin Nutr 2003: 78: 669-670.
18. Jakicic JM, Winters C, Lang W, Wing RR.  Effects of intermittent exercise and use of home exercise equipment on adherence, weight loss, and fitness in overweight women.  JAMA 282: 1554-1560, 1999.

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