success rate of diets on their own. Most studies look at diet-only or an exercise-with- diet combination (for a review, see Avenell, Brown, McGee, Campbell, Broom, Jung, & Smith, 2004). Miller, Koceja, and Hamilton (1997) did a meta-analysis of 25 years (1969-1994) of the research on weight loss interventions focusing on diets and exercise programmes. Their review included studies that had investigated either a diet-only intervention (D), an exercise-only intervention (E), or a diet-plus-exercise intervention (DE).
Exercise programmes in the studies they included were limited to aerobic exercise only, while the diet interventions required a reduced energy intake. This limited the studies they included to those that did not take into account the effect of possible extraneous variables on weight loss (variables other than reduced energy
consumption or energy expenditure) (Miller et al., 1997).
The meta-analysis performed by Miller et al. (1997) showed that results for the participant group in the exercise-only (E) programme were fundamentally different to those for participant groups in the diet (D) and the diet-and-exercise (DE)
programmes. The D and DE programmes tended to be more successful with regard to body changes. Results showed greater weight loss and reduction in fat
percentage, and lowered BMI, when compared with participants in the E programme. The E programme achieved 20-60% of the success of D and DE programmes.
A one-year follow-up of all of the programmes showed no significant difference in terms of weight loss maintenance. The one-year follow-up showed that the E group had maintained 70% of their weight loss, while the D and DE groups had maintained 73%. The meta-analysis states that there is little significant difference between the E, D, and DE programmes with regard to weight loss maintenance. However, Miller et al. (1997) state that the E programme was the least effective in terms of body compositional change.
Miller et al. (1997) criticise the narrow focus of the research. There is little variance in the studies for each of the programme types for variables of age, initial body weight, BMI, and body fat percentage. This suggests that most of the research focuses on the same subset of people – those who are morbidly obese, and around 40 years old. Another critique of the research was that the E programme was conducted on a completely different subset of people than the D and DE programmes. It is thus important to remain cognisant of the potential dangers of interpreting comparative differences between programme types.
Their analysis showed that the D and DE programmes were the most effective short- term weight loss management strategies. Participants in the D programme lost an average of between 10 and 12 kg, while those in the DE programme lost an average of 9 kg. However, at the stage of their meta-analysis, there was little information on the maintenance of the weight loss in diet, exercise, and exercise-and-diet
intervention programmes. The 16 studies of D and DE programmes with a three to four-year follow-up showed a 6-7 kg reduction in weight.
Skender, Goodrick, Del Junco, Reeves, Darnell, Gotto and Foreyt (1996) performed a study similar to those included in the review by Miller et al. (1997). They found that a year after intervention (diet, exercise, and a combination of diet and exercise) no significant differences were noted among the participant groups. The diet-only group lost 6.8 kg, the exercise-only group lost 2.9 kg, and the combination group lost 8.9 kg. In the second year, the diet-only group regained weight, reaching 0.9 kg above baseline; the combination group regained to 2.2 kg below baseline; and the exercise- only group regained to 2.7 kg below baseline (Skender et al., 1996). The results of Skender et al. (1996) demonstrate that dieting alone is associated with weight loss, followed by regain after treatment ends, whereas exercise alone produced smaller weight losses but better maintenance.
More recently, Curioni and Lourenc (2005) conducted a meta-analysis of randomised control trials, examining the efficacy of obesity treatments that utilised both diet and exercise, with a specific focus on long-term weight loss maintenance. They found that programmes using both exercise and diet as an intervention to overweight and obesity produced better results than treatments using diets alone. The results applied both directly after the intervention and after a one-year follow-up. The combined programme also resulted in positive health outcomes, such as reduced risk of cardiovascular disease, improvement of glycaemic control and
hyperglycaemia in people with diabetes, and improvements in total cholesterol (decreases in LDL cholesterol and triglyceride levels and increase of HDL-
cholesterol concentrations). However, following the one-year maintenance period, 50% the participants experienced weight regain. This demonstrated that adding exercise to diets does not necessarily improve long-term weight maintenance (Curioni & Lourenc, 2005). Greater initial weight loss was demonstrated to be the most difficult to maintain.
The meta-analysis concluded that a combination of diet and exercise leads to very successful short-term weight loss, and improved health outcomes for participants. Additionally, they cautioned that this weight loss is not sustainable, and attribute this to participants returning to their former behavioural patterns.
These studies demonstrate somewhat inconsistent results. However, they suggest that diets, and diet-and-exercise combination interventions, are more successful for short-term weight loss than exercise-only interventions. Furthermore, they reveal that all three interventions result in similar weight loss maintenance, but that exercise only produces slightly better weight maintenance outcomes.
2.6.4 Surgical interventions. Some researchers argue that surgical interventions