Dietary interventions for adult cancer survivors
International dietary recommendations include guidance on healthy eating and weight management for people who have survived cancer; however dietary interventions are not provided routinely for people living beyond cancer.
To assess the effects of dietary interventions for adult cancer survivors on morbidity and mortality, changes in dietary behaviour, body composition, health‐related quality of life, and clinical measurements.
We ran searches on 18 September 2019 and searched the Cochrane Central Register of Controlled trials (CENTRAL), in the Cochrane Library; MEDLINE via Ovid; Embase via Ovid; the Allied and Complementary Medicine Database (AMED); the Cumulative Index to Nursing and Allied Health Literature (CINAHL); and the Database of Abstracts of Reviews of Effects (DARE). We searched other resources including reference lists of retrieved articles, other reviews on the topic, the International Trials Registry for ongoing trials, metaRegister, Physicians Data Query, and appropriate websites for ongoing trials. We searched conference abstracts and WorldCat for dissertations.
We included randomised controlled trials (RCTs) that recruited people following a cancer diagnosis. The intervention was any dietary advice provided by any method including group sessions, telephone instruction, written materials, or a web‐based approach. We included comparisons that could be usual care or written information, and outcomes measured included overall survival, morbidities, secondary malignancies, dietary changes, anthropometry, quality of life (QoL), and biochemistry.
Data collection and analysis
We used standard Cochrane methodological procedures. Two people independently assessed titles and full‐text articles, extracted data, and assessed risk of bias. For analysis, we used a random‐effects statistical model for all meta‐analyses, and the GRADE approach to rate the certainty of evidence, considering limitations, indirectness, inconsistencies, imprecision, and bias.
We included 25 RCTs involving 7259 participants including 977 (13.5%) men and 6282 (86.5%) women. Mean age reported ranged from 52.6 to 71 years, and range of age of included participants was 23 to 85 years. The trials reported 27 comparisons and included participants who had survived breast cancer (17 trials), colorectal cancer (2 trials), gynaecological cancer (1 trial), and cancer at mixed sites (5 trials).
For overall survival, dietary intervention and control groups showed little or no difference in risk of mortality (hazard ratio (HR) 0.98, 95% confidence interval (CI) 0.77 to 1.23; 1 study; 3107 participants; low‐certainty evidence). For secondary malignancies, dietary interventions versus control trials reported little or no difference (risk ratio (RR) 0.99, 95% CI 0.84 to 1.15; 1 study; 3107 participants; low‐certainty evidence). Co‐morbidities were not measured in any included trials.
Subsequent outcomes reported after 12 months found that dietary interventions versus control probably make little or no difference in energy intake at 12 months (mean difference (MD) ‐59.13 kcal, 95% CI ‐159.05 to 37.79; 5 studies; 3283 participants; moderate‐certainty evidence). Dietary interventions versus control probably led to slight increases in fruit and vegetable servings (MD 0.41 servings, 95% CI 0.10 to 0.71; 5 studies; 834 participants; moderate‐certainty evidence); mixed results for fibre intake overall (MD 5.12 g, 95% CI 0.66 to 10.9; 2 studies; 3127 participants; very low‐certainty evidence); and likely improvement in Diet Quality Index (MD 3.46, 95% CI 1.54 to 5.38; 747 participants; moderate‐certainty evidence).
For anthropometry, dietary intervention versus control probably led to a slightly decreased body mass index (BMI) (MD ‐0.79 kg/m², 95% CI ‐1.50 to ‐0.07; 4 studies; 777 participants; moderate‐certainty evidence). Dietary interventions versus control probably had little or no effect on waist‐to‐hip ratio (MD ‐0.01, 95% CI ‐0.04 to 0.02; 2 studies; 106 participants; low‐certainty evidence).
For QoL, there were mixed results; several different quality assessment tools were used and evidence was of low to very low‐certainty. No adverse events were reported in any of the included studies.
Evidence demonstrated little effects of dietary interventions on overall mortality and secondary cancers. For comorbidities, no evidence was identified. For nutritional outcomes, there was probably little or no effect on energy intake, although probably a slight increase in fruit and vegetable intake and Diet Quality Index. Results were mixed for fibre. For anthropometry, there was probably a slight decrease in body mass index (BMI) but probably little or no effect on waist‐to‐hip ratio. For QoL, results were highly varied. Additional high‐quality research is needed to examine the effects of dietary interventions for different cancer sites, and to evaluate important outcomes including comorbidities and body composition. Evidence on new technologies used to deliver dietary interventions was limited.
Sorrel Burden, Debra J Jones, Jana Sremanakova, Anne Marie Sowerbutts, Simon Lal, Mark Pilling, Chris Todd
Plain language summary
Dietary intake in people living beyond cancer
Background- Diet has been linked to cancer, and dietary guidelines are available for cancer prevention. People after cancer have been found to have higher rates of other conditions including cardiovascular disease, diabetes, and other cancers. It is therefore sensible for people after cancer to look at changing their diet. It was important to undertake this review to assess the evidence on dietary advice for people who have survived cancer.
Aim of the review- This review evaluates evidence on dietary interventions for people after cancer.
Quality of evidence- The quality of evidence is generally low to very low. Most studies did not evaluate dietary interventions for key review outcomes, particularly mortality and morbidity. However, a few study outcomes with moderate‐certainty evidence focused on dietary intake and physical measurements. Included studies compared dietary interventions versus control or usual care. We pooled data from similar randomised controlled trials (RCTs) to provide a summary estimate of the effects of an intervention, and we judged how confident (certain) we were of these findings by using an established method (GRADE).
Main findings- We identified 25 RCTs involving 27 different comparisons. For some outcomes, we found absence of evidence for dietary interventions. We found some evidence showing that dietary interventions probably did not modify energy intake; however, some evidence shows what is probably a slight increase in fruit and vegetable intake (moderate‐certainty evidence). Evidence on dietary fibre was mixed for different advice on weight reducing or healthy eating. Dietary interventions compared to control probably improved the Diet Quality Index (moderate‐certainty evidence). For physical measurements, we found a probable reduction in body mass index (BMI) with dietary interventions compared to controls (moderate‐certainty evidence) but little evidence showing any change in waist‐to‐hip ratio (low‐certainty evidence). For quality of life (QoL), results were mixed due to the wide variety of tools used. No adverse events were reported.
Conclusion- Available evidence shows that dietary interventions can be helpful in modifying fruit and vegetable servings and diet quality; modification of fibre intake was variable, and some benefits were seen for anthropometric measurements, including BMI. Most of the evidence is based on women with breast cancer, so more research is needed for patients with other cancers. Gaps identified in the evidence involved the use of new technologies, comorbidities, and body composition data.
Sorrel Burden, Debra J Jones, Jana Sremanakova, Anne Marie Sowerbutts, Simon Lal, Mark Pilling, Chris Todd
Implications for practice
Moderate‐certainty evidence shows that dietary interventions can modify food and nutrient intakes and can positively affect some anthropometric measurements, particularly for women after breast cancer. Outcomes that showed evidence of some probable improvement were intake of fruits and vegetables and diet quality. Energy intake was not shown to be affected by dietary interventions. Body mass index was probably slightly reduced with dietary interventions. Lack of evidence from one included study suggests that dietary interventions improve overall mortality, and we found no evidence on the effects of dietary interventions on morbidities. Short‐term changes in dietary intake and in anthropometric measurements were not always shown to be sustained over a longer period.
In relation to quality of life (QoL), we are uncertain about study results.
Included studies described some positive benefits of dietary intervention for cancer survivors, although inconsistencies between included studies suggest that people may benefit differently from dietary interventions in terms of alterations in dietary intake and anthropometry, depending on type of cancer, nutritional status, and regular eating habits.
Different personnel administered the dietary interventions, but dietitians did so in most studies. It is important to note that training and appropriate understanding are required when dietary interventions are provided to people who have survived cancer. Some studies described in detail the behaviour change strategies used, and it is important to note that as modifications to dietary intake represent a behaviour change, it is essential to incorporate these behaviours into dietary interventions used in practice.
Implications for research
Implications for future research include the following.
We identified 26 ongoing studies that are relevant to this review, including 11 studies on breast cancer, three on colorectal cancer, three on gynaecological cancer, and nine on mixed cancer types, indicating that this area is developing rapidly. Studies are now being undertaken to examine previously neglected cancer sites. In addition, long‐term follow‐up data on participants already randomised into cohorts are being reported, adding to the evidence base as studies mature.
Evidence in some areas is incomplete or lacking, and further research is required, including evaluation of dietary interventions for participants with cancer at sites other than the breast. These tumour sites could include colorectal or endometrial cancer, where a link has been established between occurrences and either dietary intake or obesity, making these important areas for future research. Moreover, a number of large ongoing studies recruiting participants with colorectal cancer will add substantially to the evidence.
In relation to measurement of outcomes, we found a lack of data on body composition when routinely available imaging was used to evaluate changes in body composition. Use of mobile or digital applications to deliver interventions was limited, and this may well be an approach that will facilitate delivery of dietary interventions in the future. Developing outcomes that make use of digital technologies and routine imaging in assessment of dietary interventions would add to future research. No studies in this review included comorbidities as an outcome measure, and this is a huge reason why modifying dietary intake studies that include comorbidities as an outcome would enhance findings in future research.
We identified some high‐quality studies, although not all trials followed CONSORT guidelines and could be improved in relation to quality and standards of reporting. There were only a few studies that attempted to blind assessors; this would be a feasible way to decrease risk of bias in future research.
This review is focused on survivors who were enrolled into studies after all treatments were completed, so it would be interesting to undertake further review of dietary interventions in patients who are living with cancer, particularly in light of the advancement of biological agents and hormone therapies used in prostate, breast, and gynaecological cancers. The optimal time to administer dietary interventions for healthy eating within cancer pathways for all cancer sites is a topic that remains controversial, as different studies included participants at different time points after their cancer treatment. Determining the optimal time to deliver dietary interventions is therefore worthy of further research.
Studies investigating dietary interventions and changes in anthropometrics need long‐term follow‐up to identify differences in clinical outcomes including mortality and morbidity. This is often difficult due to the resource implications of conducting studies with long‐term follow‐up. The use of surrogate markers as early indicators for tumour recurrence may offer an advantage in studies where cancer recurrence is an important outcome in the evaluation of dietary interventions.