What is a healthy weight?
Body mass index (BMI) assesses whether people are a healthy weight for their height. A BMI of 18 to 25 shows a healthy weight, a BMI over 25 indicates being overweight, and a BMI over 30 indicates obesity.
Breast cancer and weight
People with a BMI over 25 are more likely to develop a recurrence of their breast cancer. Obesity can also affect people's quality of life (well-being) and can lead to serious and life-threatening conditions, including type 2 diabetes, coronary heart disease and stroke. After successful treatment for breast cancer, people with a BMI over 25 are advised to lose weight.
The most common method for losing weight is to reduce the number of calories eaten and to increase physical activity. A healthy, reduced-calorie diet and regular exercise may be combined with psychosocial support. Some weight loss programmes include all three elements.
Why we did this Cochrane Review
We wanted to identify which weight-loss programmes work best to help overweight and obese breast cancer survivors to lose weight; and whether the programmes had advantages or unwanted effects.
What did we do?
We searched for studies that assessed weight loss programmes in survivors of early-stage breast cancer who had a BMI over 25 and no evidence that their cancer had returned. We looked for randomised controlled studies, in which the programmes people received were decided at random. This type of study usually gives the most reliable evidence about the effects of a programme.
We wanted to know how weight loss programmes affected:
-how long people lived;
-whether their breast cancer returned;
-the length of time before the cancer returned;
-how many people died;
-measurements of waist size;
-people's quality of life (well-being); or
-had any unwanted effects.
Search date: we included evidence published up to June 2019.
What we found
We found 20 relevant studies in 2028 women. The studies compared participation in a weight-loss programme to not participating in one but receiving usual care, a placebo (dummy) treatment, a different type of weight-loss programme, written information, or being on a waiting list instead. All the programmes included dietary changes; some combined these with exercise or psychosocial support, or both.
Most studies were conducted in the USA. The weight loss programmes lasted from two weeks to two years; the people participating were followed for three months to 36 months after starting their programme.
None of the studies reported results for: how long people lived; or the length of time before their cancer returned, or how many people died. Few studies reported about the effect of weight loss programmes on the return of breast cancer.
What are the results of our review?
Compared with those not participating in a weight loss programme, breast cancer survivors with a BMI over 25 who take part in one may:
-lose more body weight;
-have greater reductions in their waist size and BMI; and
-improve their well-being.
Taking part in a weight loss programme did not cause more unwanted effects.
Programmes combining diet with exercise or psychosocial support, or both, seemed to reduce body weight and waist size more than programmes based on dietary changes alone.
Our confidence in these results
Our confidence in these results is generally low. We identified limitations in the ways that some of the studies were designed and conducted, and the people taking part and those assessing them knew who received which treatments, which could have affected the study results.
Weight loss programmes may help overweight and obese breast cancer survivors to lose weight, reduce their BMI and waist size, and may improve their quality of life, without increasing unwanted effects. We did not find evidence about whether they could help people live longer, or delay the return of breast cancer.
We need more studies to find out which weight loss programmes work best to help breast cancer survivors lose weight, and whether this helps them to live longer.
Weight loss interventions, particularly multimodal interventions (incorporating diet, exercise and psychosocial support), in overweight or obese breast cancer survivors appear to result in decreases in body weight, BMI and waist circumference and improvement in overall quality of life. There was no increase in adverse events. There is a lack of data to determine the impact of weight loss interventions on survival or breast cancer recurrence. This review is based on studies with marked heterogeneity regarding weight loss interventions. Due to the methods used in included studies, there was a high risk of bias regarding blinding of participants and assessors.
Further research is required to determine the optimal weight loss intervention and assess the impact of weight loss on survival outcomes. Long-term follow-up in weight loss intervention studies is required to determine if weight changes are sustained beyond the intervention periods.
Studies suggest that overweight and obese breast cancer survivors are at increased risk of cancer recurrence and have higher all-cause mortality. Obesity has an impact on breast cancer survivor's quality of life (QOL) and increases the risk of longer-term morbidities such as type 2 diabetes mellitus and cardiovascular disease. Many cancer guidelines recommend survivors maintain a healthy weight but there is a lack of evidence regarding which weight loss method to recommend.
To assess the effects of different body weight loss approaches in breast cancer survivors who are overweight or obese (body mass index (BMI) ≥ 25 kg/m2).
We carried out a search in the Cochrane Breast Cancer Group's (CBCG's) Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL, Issue 6), MEDLINE (2012 to June 2019), Embase (2015 to June 2019), the World Health Organisation International Clinical Trials Registry Platform (WHO ICTRP) and Clinicaltrials.gov on 17 June 2019. We also searched Mainland Chinese academic literature databases (CNKI), VIP, Wan Fang Data and SinoMed on 25 June 2019. We screened references in relevant manuscripts.
We included randomised controlled trials (RCTs), quasi-RCTs and randomised cross-over trials evaluating body weight management for overweight and obese breast cancer survivors (BMI ≥ 25 kg/m2). The aim of the intervention had to be weight loss.
Two review authors independently performed data extraction and assessed risk of bias for the included studies, and applied the quality of the evidence using the GRADE approach. Dichotomous outcomes were analysed as proportions using the risk ratio (RR) as the measure of effect. Continuous data were analysed as means with the measure of effect being expressed as the mean differences (MDs) between treatment groups in change from baseline values with 95% confidence intervals (CIs), when all studies reported exactly the same outcomes on the same scale. If similar outcomes were reported on different scales the standardised mean difference (SMD) was used as the measure of effect. Quality of life data and relevant biomarkers were extracted where available.
We included a total of 20 studies (containing 23 intervention-comparisons) and analysed 2028 randomised women. Participants in the experimental groups received weight loss interventions using the core element of dietary changes, either in isolation or in combination with other core elements such as 'diet and exercise', 'diet and psychosocial support' or 'diet, exercise and psychosocial support'. Participants in the controls groups either received usual care, written materials or placebo, or wait-list controls. The duration of interventions ranged from 0.5 months to 24 months. The duration of follow-up ranged from three months to 36 months.
There were no time-to-event data available for overall survival, breast cancer recurrence and disease-free survival. There was a relatively small amount of data available for breast cancer recurrence (281 participants from 4 intervention-comparisons with 14 recurrence events; RR 1.95, 95% CI 0.68 to 5.60; low-quality evidence) and the analysis was likely underpowered.
Overall, we found low-quality evidence that weight loss interventions for overweight and obese breast cancer survivors resulted in a reduction in body weight (MD: -2.25 kg, 95% CI: -3.19 to -1.3 kg; 21 intervention-comparisons; 1751 women), body mass index (BMI) (MD: -1.08 kg/m2, 95% CI: -1.61 to -0.56 kg/m2; 17 intervention-comparisons; 1353 women), and waist circumference (MD:-1.73 cm, 95% CI: -3.17 to -0.29 cm; 13 intervention-comparisons; 1193 women), and improved overall quality of life (SMD: 0.74; 95% CI: 0.20 to 1.29; 10 intervention-comparisons; 867 women). No increase was seen in adverse events for women in the intervention groups compared to controls (RR 0.94, 95% CI: 0.76 to 1.17; 4 intervention-comparisons; 394 women; high-quality evidence). Subgroup analyses revealed that decreases in body weight, BMI and waist circumference were present in women regardless of their ethnicity and menopausal status.
Multimodal weight loss interventions (which referred to 'diet, exercise and psychosocial support') appeared to result in greater reductions in body weight (MD: -2.88 kg, 95% CI: -3.98 to -1.77 kg; 13 intervention-comparisons; 1526 participants), BMI (MD: -1.44 kg/m2, 95% CI: -2.16 to -0.72 kg/m2; 11 studies; 1187 participants) and waist circumference (MD:-1.66 cm, 95% CI: -3.49 to -0.16 cm; 8 intervention-comparisons; 1021 participants) compared to dietary change alone, however the evidence was low quality.