Frequently used weight-loss method is light on evidence
Although the transtheoretical model stages of change (TTM SOC) method is frequently used to help obese and overweight people lose weight, a newly published Cochrane systematic review indicates there is little evidence that it is effective. "The use of TTM SOC only resulted in 2kg or less weight loss, and there was no conclusive evidence that this loss was sustained," says study leader Nik Tuah, who works at Imperial College London.
The transtheoretical model describes a step-by-step way in which individuals move from unhealthy behaviours to healthy ones. The model helps clinicians and patients by showing the sorts of benefits that can be expected for each step in the sequence. The five stages of change that the model anticipates are pre-contemplation, contemplation, preparation, action and maintenance.
"A key assumption underlying this model is that people do not start off by being ready to change their behaviours, so any intervention that starts by asking for change is unlikely to be taken up," says Tuah. TTM SOC tries to overcome this by introducing stages that lead people to the place where they can see the need to change their behaviour and are willing to give it a go. Only then do you introduce the active interventions.
Leading a team of researchers, Tuah looked for studies that had investigated the effectiveness of TTM SOC. They identified five appropriate studies involving 1834 people who received an intervention and 2076 people who were placed in control groups. The trials varied in length from six weeks to 2 years. Drawing all the findings together showed that there was no convincing evidence that the intervention produced any significant sustainable weight loss. There was, however, some indication that when TTM SOC was combined with exercise and dieting, people's physical activity or eating habits did change a little.
One of the adverse outcomes noted by a single trial was that some people gained weight while using TTM SOC. None of the trials asked whether TTM SOC improved a person's health-related quality of life, or whether it reduced the risk of them getting ill. Also, none looked at the cost of taking patients through TTM SOC.
"Given that obesity and overweight are such important issues, and that TTM SOC is so widely used, it is really important that we do more high quality randomised control trials, preferably with large numbers of people, and follow them for many years. Then we may get a better indication of how well it really works," says Tuah. "This review does not necessarily challenge the notion that diet and exercise are effective weight loss strategies, but instead raises questions about how to approach lifestyle changes for individuals who want to adopt them."