Physical activity, eating behaviours and weight loss
We are well aware of the importance of exercise as an essential component of a successful weight management strategy. Exercise combined with dietary energy restriction has been shown in several studies to result in improved weight loss when compared with either diet or exercise interventions alone.1,2,3
Authors Jakicic, Wing and Winters-Hart attempted in their paper to investigate further the dietary and eating behaviours associated with changes in physical activity (Relationship of physical activity to eating behaviours and weight loss in women,
Med Sci Sports Exerc, Vol 34, No 10, pp1653-1659, 2002).
Jackicic et al believe that it is important to understand the mechanisms and pathways through which exercise affects long-term weight management, since there are undoubtedly sound physiological reasons for recommending physical activity in the overall management strategy. “Exercise has been shown to affect weight-related factors such as total daily energy expenditure, fat oxidation, insulin sensitivity and others,” they say. There is also a growing body of evidence to support the view that “for individuals participating in a weight loss programme, exercise participation may serve as a marker for compliance to other behaviours that can affect weight loss”. In this study, Jackicic et al attempt to answer two questions. Firstly, is physical activity behaviour associated with changes in dietary intake and eating behaviours? Secondly, what is the contribution of exercise to weight loss when these other behaviours are also considered?
Subjects and methods
The authors studied 104 overweight women participating in an 18-month behavioural weight loss programme. These women were 25-45 years of age and were 25-75% over their recommended body weight. Subjects were randomly assigned to groups so that the effects of long or short bout of exercise, plus short bouts of exercise combined with home exercise, could be examined. All subjects attended group meetings focusing on strategies for modifying both eating and exercise behaviours. These group meetings occurred weekly for the first six months, bi-monthly for the next six months and monthly for the last six months.
All subjects were instructed to reduce fat intake to 20-30% of total calorie intake (1200-1500 kcal per day) and structured meal plans were provided. In addition, all participants were asked to gradually increase their exercise time to 200 minutes per week (by week nine) and then maintain this level of physical activity throughout the programme. Exercise and physical activity was recorded in a diary reviewed by the intervention team.
A number of assessments were made before and after the 18-month intervention. These included body weight and height, an assessment of leisure time physical activity (Paffenbarger questionnaire), an assessment of dietary intake (Block Food Frequency Questionnaire) and an assessment of adherence to eating behaviours that are associated with improved dietary habits and weight loss (Eating Behaviour Inventory).
At the end of the study, the data were analysed to assess changes in physical activity, body weight, eating behaviours and energy intake throughout the 18-month programme. Besides reviewing the data changes from baseline, the authors also performed analyses to assess the relation between weight loss and other weight loss behaviours. Significant weight loss of 7.8kg (mean) was reported, and weight loss from baseline to 18 months was associated with a reduction in total energy intake and an increase in EBI score. Regression analyses were performed to investigate whether various eating behaviour parameters were predictive of weight loss. Subjects who had the greatest changes in physical activity and EBI lost significantly more weight than those who had the lowest changes in physical activity combined with low changes in EBI. “When grouped based on changes in physical activity and energy intake, subjects with the smallest changes in both behaviours lost significantly less weight than subjects with the greatest change in both behaviours,” say the authors.
“This study confirms prior findings in showing that physical activity is related to long-term weight loss,” say Jakicic et al. “However, it extends the findings of these previous studies and shows that physical activity is part of a constellation of behaviours that influence body weight.” And, while accepting that the correlations and regression indices are modest, the authors state that: “These results suggest that individuals who increase physical activity during a behavioural weight loss programme also appear to make meaningful changes in eating behaviours that may affect weight loss.” Jakicic et al hypothesise that shifts in mood states may in part at least offer an explanation for this observation.
In summarising the work of other researchers in this field, the authors stress that: “Treatment programmes should focus on modifying eating behaviours of overweight adults in addition to increasing physical activity participation.” In support of this comment, they also report that in their own study, eating behaviours accounted for 18-28% of the variance in long-term weight loss, whereas physical activity contributed to approximately 3-5%.
Yet a criticism of this study, raised by the authors themselves, is that physical activity, eating behaviours and energy intake were all assessed using self-reporting methods. When researchers have previously studied self-reporting techniques, it has not been unusual for energy intake to be under-reported (by 19-47%), while energy expenditure is over-reported (by 30-51%).
- Gordon NF et al, Comparison of single versus multiple lifestyle interventions, Am J Cardiol, 79:763-767, 1997.
- Hellenius ML et al, Diet and exercise are equally effective in reducing risk for cardiovascular disease, Atherosclerosis, 103:81-91, 1993.
- Stephanick ML et al, Effects of the NCEP Step 2 diet and exercise on lipoprotein in postmenopausal women and men with low HDL-cholesterol and high LDL-cholesterol, N Engl J Med, 392:12-20, 1998.
Energy intake and energy expenditure
As if to reinforce the point made by Jakicic et al regarding self-reporting of energy intake, authors Hill and Davies have investigated the energy intake and energy expenditure in elite lightweight female rowers (Med Sci Sports Exerc, Vol 34, No 11, pp1823-1829, 2002). Hill and Davies comment that the energy cost of a 2000m race may well only be 200-250 kcal, but that the energy required for the one to two hours of daily training is 1000-2000 kcal. Previous attempts to determine energy intake in heavyweight oarswomen (using a five-day, self-reporting food record) have reported a mean intake of 2633 kcal/day. “Given the energy cost of competition and daily training, these intakes appear to be too low,” say Hill and Davies.
Using seven elite oarswomen as their subject group, Hill and Davies assessed energy expenditure using a doubly labelled water (DLW) technique over the study period of 14 days. Body weight was also measured on each visit to the laboratory. Energy intake was measured using a four-day weighed dietary record carried out over two consecutive weekdays and two weekend days. Subjects were provided with scales and asked to record the quantity of all food and beverages consumed by weight or in household measures and to record brand names, methods of food preparation and ingredients of recipes. All food records were reviewed with each subject and analysed using nutritional software and databases.
“We found that the mean self-reported energy intake was substantially lower than energy expenditure as determined by the DLW technique,” say Hill and Davies. “These findings are consistent with investigations of other athletic populations. Comparison of the subjects’ adjusted energy intake to that reported suggest a bias to underreporting of 1133kcal or 34% of adjusted energy intake.” Commenting further on a brief review of other studies they also argue that: “There is a vast amount of literature that illustrates that underreporting of energy consumed occurs in many population groups including adults, children and adolescents, the obese and athletes.”
Courtesy of Fitness Professionals UK
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