To evaluate the therapeutic effectiveness of diet, exercise, and diet plus exercise, for weight loss in obesity.

MEDLINE was searched from 1969 to 1994 for studies published in the English language in peer-reviewed journals. Extensive cross-referencing and manual searches were also performed.

Study designs of evaluations included in the review

The authors do not state that any specific study designs were included or excluded. It seems that the included studies were retrospective or prospective studies that compared the participants' weight before and after the intervention.

Specific interventions included in the review

Diet (e.g. calorie restriction or reduced energy intake), aerobic exercise, or diet plus aerobic exercise, for weight loss in obesity.

Participants included in the review

Participants aged 18 to 68 years who were overweight. Overweight was defined as in the primary studies, or as being either greater than 120% ideal body weight, a body mass index of more than 27, or greater than 30% body fat.

Outcomes assessed in the review

The weight change during the intervention was assessed.

How were decisions on the relevance of primary studies made?

The authors do not state how the papers were selected for the review, or how many of the authors performed the selection.

The authors do not state that they assessed validity.

The same investigator extracted data from the original research report. With the exception of gender and programme type, all the extracted data were numerical.

How were the studies combined?

The effect size was calculated by dividing the mean change in a variable measured for a group, by the standard deviation for that group. Since standard deviations were not available in many studies, the actual group mean reported in the primary studies was also used.

How were differences between studies investigated?

An analysis of variance was used to evaluate the association between the effect size and other covariates, including initial body weight, initial percentage body fat, and length of programme intervention.

Four hundred and ninety-three study groups with more than 16,000 patients were included.

Exercise programmes were the least effective in producing body compositional changes. The effect sizes for weight loss in obese adults following diet, exercise, or diet plus exercise were 5.1 kg (standard error, se=0.5), 2.1 kg (se=0.5) and 5.5 kg (se=0.7), respectively. The actual weight loss through diet, exercise, and diet plus exercise was 10.7 kg (se=0.5), 2.9 kg (se=0.4) and 11.0 kg (se=0.6), respectively. At the one-year follow-up, diet plus exercise tended to be the superior programme.

The finding that exercise programmes did not produce as great a change in body composition as the diet and diet plus exercise programmes was fairly consistent, whether the analyses were performed with or without covariates.

Weight-loss research has focused on a middle-aged population that is only moderately obese, while the interventions have lasted for only short periods of time. The data showed, however, that a 15-week diet or diet plus exercise programme produce a weight loss of about 11 kg, with a maintained weight-loss of 6.6 kg (se=0.5) and 8.6 kg (se=0.8), respectively, after one year.

The inclusion criteria were described. The study characteristics were summarised and discussed in the review, although the study details were not presented. The literature search was limited to only one database, and more relevant studies may have been identified if other databases had also been searched. The validity and design of the included studies were not assessed. The authors discussed several limitations about the evidence reviewed, such as the small sample size, the use of short-term interventions, the problem of generalisability, and the problem in defining overweight. The potential of publication bias was also mentioned. The evidence presented in the review was basically observational, thus the review's conclusions need to be interpreted with great caution.

Eleanor Naylor Dana Charitable Trust.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.