What are the effects of dietary interventions or physical activity interventions, or both, based on the transtheoretical model (TTM) stages of change (SOC) to produce sustainable (one year and longer) weight loss in overweight and obese adults?
Generally, weight loss programmes tend to involve diet and physical activity interventions. The TTM describes a series of five SOC an individual goes through when changing from an unhealthy behaviour to a healthy one. In this review, we assessed the use of the TTM SOC in weight management programmes for overweight and obese adults especially in terms of the effects on weight loss, dietary habits, physical activity and behaviour changes.
Obesity (body mass index of at least 30 kg/m²) and overweight (body mass index of 25 to less than 30 kg/m²) are increasingly being recognised as important public health issues. Together, they contribute to serious health problems and extensive economic costs worldwide. Body mass index (BMI) is a measure of body fat and is defined as the individual's weight in kilograms divided by the square of the height in metres (kg/m²). The BMI should be considered as a rough guide only because it is mainly used for whole populations and may not correspond to the same degree of fatness in different individuals (like for athletes and physically non-active individuals).
We included three studies in our systematic review. Altogether the studies evaluated 2971 participants, with 1467 participants allocated to the intervention groups and 1504 to the control groups. The studies had a length of intervention of 9, 12 and 24 months.
This plain language summary was current as of December 2013.
The use of the TTM SOC in combination with diet or physical activity, or both, and other interventions in the included studies provided inconclusive evidence about the impact of such interventions on sustainable weight loss (mean difference in favour of the TTM SOC was between 2.1 kg and 0.2 kg at 24 months). However, other positive effects were noted, such as changes in physical activity and dietary habits that included increased exercise duration and frequency, reduced fat intake and increased fruit and vegetable consumption. The studies did not report other important outcomes such as health-related quality of life, illness (morbidity) and economic costs.
Quality of the evidence
Overall, the quality of the evidence was low or very low. The main limitations included incomplete reporting of outcomes, methodological shortcomings, extensive use of self-reported measures and insufficient assessment of sustainability due to the lack of long-term assessments.