Exercise is an important component of weight loss interventions 5, 14
. However, few studies examining the specific dose and intensity of exercise that may be required to enhance long-term weight loss have been conducted that exceed 6 to 12 months in duration. Previous results from this study reported that weight loss at 12 months was approximately 10% of initial body weight in response to energy restriction combined with prescription of a high dose of exercise (~2,000 kcal/wk), whereas approximately 8% weight loss was observed in response to energy restriction combined with prescription of a moderate dose of exercise (~1,000 kcal/wk); however, these differences were not statistically significant 6
. Prescribed intensity (moderate versus vigorous) did not influence weight loss outcomes, but this may have been a result of lack of adherence to the prescribed intensity over the duration of this study. Unfortunately, the results presented here show that this level of weight loss was not maintained, with a mean weight loss of 5% sustained at 24 months regardless of prescribed dose or intensity of exercise ().
Weight regain in this study was approximately 50% of the weight that was achieved following the initial 6 months of the intervention. This approximates the weight regain previously reported in the literature. Wing 4
concluded that weight regain was approximately 43% across a 40 month period following initial weight loss, and similar results have been reported by Perri and Corsica 3
Analysis based on randomized group assignment did not portray a favorable contribution of exercise on weight loss maintenance. LTPA increased by 1235 kcal/wk from baseline to 6 months; however, only a 720 kcal/wk increase above baseline was sustained at 24 months (). Moreover, the randomized groups did not sustain the prescribed differences in LTPA, which may have contributed to the non-significant differences in weight loss between these groups. Studies of a similar duration have shown comparable results, with physical activity initially increasing before gradually decreasing over time 7, 21
. Thus, the inability to sustain weight loss appears to mirror the inability to sustain physical activity.
When subjects were categorized based on the magnitude of weight loss achieved at 24 months, the importance of physical activity to sustain weight loss became more apparent. Individuals achieving and maintaining a weight loss ≥10% of their initial body weight reported participating in approximately 1800 kcal/wk of LTPA at both 6 and 24 months (Figures , , ). This is approximately 1500 kcal/wk, which corresponds to 275±254 min/wk (55 min/d on 5 d/wk), above the baseline level of LTPA. This level of physical activity is consistent with our previous findings 6, 7
, and supports the levels of physical activity that should be targeted for successful weight loss12,14,15,11
. The 338 min/wk reported at 24 months approximates 68 min/d on 5 days per week. This would suggest that the level of physical activity that may be necessary to sustain weight loss for as long as 24 months is approximately twice the minimum consensus public health recommendation for physical activity 10, 22
. This appears to be consistent with the amount of energy expenditure reported by Schoeller et al. 9
and recommended in the US Dietary Guidelines for prevention of weight regain 11
. However, it is important to highlight that this is approximately 1,500 kcal/wk, or 275 min/wk, above baseline activity levels for relatively sedentary overweight adults.
Forty-seven of the 191 subjects (25%) were able to sustain a weight loss of ≥10% at 24 months. In addition to sustaining relatively high levels of LTPA, individuals sustaining ≥10% weight loss at 24 months completing more telephone contacts with the intervention team during months 6-24 (81.5% of contacts completed) compared to individuals achieving <5% weight loss at 24 months (<69% of contacts completed). The ability to sustain a higher level of contact may have contributed to the higher level of LPTA and greater engagement in eating behaviors consistent with weight control reported by these participants (). Perri and Corsica 3
have recommended that weight loss interventions follow a chronic-care model that sustains contact between the interventionists and participants. The results from this study support this recommendation; however, this contact may not need to be in-person. Wing et al. 23
reported that delivering an 18-month weight loss maintenance intervention via in-person or internet contact significantly reduced the proportion of participants gaining ≥2.3 kg. Marcus et al. 24
reported that non-in-person contact (i.e., internet, print) can be effective at increasing physical activity in sedentary adults.
Compliance to dietary recommendations may also have contributed to improved weight loss at 24 months. Individuals sustaining ≥10% weight loss at 24 months reported engaging in more weight loss eating behaviors, as measured by the EBI, and lower intake of dietary fat compared to individuals sustaining lower levels of weight loss (see ). The failure to detect a difference in total energy intake between those individuals sustaining and not sustaining a 10% weight loss at 24 months may be a result of limitations when using a food frequency questionnaire. Howard et al. 25
reported that compliance to dietary guidelines facilitated the maintenance of a 2.2 kg weight loss over a period of 7.5 years, supporting the importance of also targeting this aspect of energy balance. However, the greater magnitude of weight loss achieved in this current study may be a result of a greater emphasis on reduction in energy intake along with the inclusion of physical activity, both of which were not included in the study conducted by Howard et al. 25
A potential limitation is that physical activity was based on self-report and not objective techniques to quantify physical activity, which may partially explain the high variability in physical activity reported in this study. Thus, objective assessment of physical activity should be included in future studies which examine this important research question. Moreover, this study did not include a diet only comparison, which prohibits the ability to examine the additive effect of different doses of physical activity above what can be achieved with diet alone. However, this study tested an intervention approach that is recommended by both the National Institutes of Health 5
and the 2005 US Dietary Guidelines 11
, which recommends the combination of changes in both eating and physical activity behaviors to reduce body weight. The results of this study are clinically relevant and provide guidance to health-care professionals regarding the magnitude of physical activity that needs to be included in behavioral interventions for weight loss and weight loss maintenance.
An intensive intervention was implemented that required regular contact via in-person or telephone over a period of 24 months. While higher amounts of contact were predictive of long-term weight loss, this amount of contact may not translate to what is permissible in clinical and community interventions. The optimal frequency of contact that can reasonably be provided in these settings to enhance weight loss outcomes needs to be addressed, and this may involve the integration of alternative modes of contact.
This study demonstrated the difficulty in sustaining weight loss of ≥ 10% of initial body weight, with approximately 30% of individuals in this study meeting this criterion at 24 months. However, relatively high levels of physical activity appear to contribute sustained weight loss. In excess of 1,800 kcal/wk of LTPA, which is 1,500 kcal/wk (275 min/wk) above the baseline level for sedentary individuals, appears to be important for sustaining ≥10% weight loss. This clarifies the dose of physical activity that should be targeted for achieving and sustaining this magnitude of weight loss, but also demonstrated the difficulty of sustaining this level of physical activity. Research is needed to improve long-term compliance to this targeted level of physical activity. Moreover, continued contact with the intervention staff and the ability to sustain recommended eating behaviors also may be important contributing factors to sustaining weight loss, suggesting that physical activity does not function independently of these other behaviors for enhancing maintenance of significant weight loss that exceeds 10% of initial body weight.