This study investigated the associations of diet quality with overweight and treatment-related side effects among breast cancer patients undergoing treatment, with most of them underwent chemotherapy alone with a mean duration of therapy was less than 9 months. In this study, the consumption of whole grains, dairy, fatty acids and refined grains were low. This finding was consistent with earlier studies23,24. Avoidance and abstinence of certain foods are common among cancer patients, owing to belief that animal products is the cause of cancer development19,20 or treatment-related side effects that alter the taste perception25. On the other hand, dairy products are not habitual intakes of Malaysian 33, which may further attribute to the low consumption pattern of dairy products among the patients.
Despite dairy products are good sources for protein, multivitamins and minerals which are essential for bodily function, breast cancer patients may limit their dairy intake attributed to the concern about the safety of growth hormone usage in animal products20. World Cancer Research Fund (WCRF) reviewed that the strength and direction of the effect of dairy products on cancer risk is varied across the cancer sites, including of prostate, breast and colorectal cancers34,35. More studies are needed to confirm the impact of dairy products especially on breast cancer. Contrary to popular belief, the intake of whole grain products that commonly known as healthy food was reduced in breast cancer patients. During treatment, cancer patients experience various side effects which could interfere with the ability of consuming a balanced diet25,36,37, in spite of the high awareness of practising healthy eating. The compliance towards refined grain guideline could be deduced from the assessment of whole grains, where both of these components yield identical interpretation. As compared to whole grains, breast cancer patients prefer refined grains products with softer texture such as white rice, white bread or any food made with white flour. With regards to fatty acid component, the low score is originated from inadequate consumption of mono- and poly-unsaturated fatty acids. The individual component of saturated fat reflected that patients limited the food that are high in saturated fat, however, they did not adhere to the guidelines for unsaturated fatty acids. Although there is limited information regarding the fatty acid ratio, a consistent finding of the good compliance with saturated fatty acids intake was documented23,24. Polyunsaturated fatty acids from marine sources are suggested to ameliorate treatment-related side effects and improve treatment efficacy via antineoplastic effect38. In addition to saturated fatty acid, it is essential to assess the patients’ intake of unsaturated fatty acids particularly during treatment. The biggest barrier to adherence to healthy fats recommendation could be high food prices39, for instance, margarines with low saturated fat are more expensive than butter that high in saturated fat. This finding may suggest an enhanced accessibility to healthy food by offering affordable price or lower rate than less healthier options. Furthermore, Malaysians hardly consume raw vegetables or fruits accompanied with oil-based dressings, which is not their ordinary food habit. This elucidates that an unhealthy eating habit in general could persist over cancer diagnosis, which may influence patients’ prognosis especially during the critical treatment period.
Current finding demonstrated that a better diet quality has protective effect against overweight among breast cancer patients, as supported by Custódio et al. (2016)24. Similar relationship between diet quality and obesity has been widely reported by public health studies40–42. On the other hand, the finding of the relationship between diet quality and cancer risk or mortality was not consistent13,43. As cancer is a multi-site disease with different treatment, the relationship of diet with cancer prognosis should be studied according to various cancer types, whereby the development of cancer site-specific diet quality tools is deemed necessary. As previous studies indicated the negative impact of obesity on quality of life44 and survival4,5 of cancer patients, being overweight is not a desirable outcome for cancer patients who are usually considered to be malnourished. Adopting a healthy eating habit should be a bedrock of lifestyle strategy to achieve a normal weight range as well as to maintain an overall good health. Drenowatz et al. (2014) highlighted that high consumption of protein, sodium and empty calories were the contributors of overweight or obesity among healthy adults41, indicating the necessity of achieving an adequate, balanced, moderate and varied diet. In view of the significant role of healthy eating in disease prognosis, the utilization of diet quality indices is relatively pragmatic for breast cancer patients. Despite the unhealthy dietary behaviour is strongly attributed to poor education in public health area10, current finding failed to show the significant relationship between education and diet quality. This could be because that the distribution of studied population according to education level was not widely covered, which may reduce the ability to determine the significant result.
Iron status of cancer patients should be closely monitored as the incidence of anemia could compromise greatly their quality of life45. Current finding showed that higher quality diet was associated with reduced risk of low serum hemoglobin only after adjusting for physical activity and BMI (Model 2), suggests that diet quality might indirectly improve anemia by reducing excess body weight. It is noteworthy that the low serum hemoglobin could be owing to multiple nutrient deficiencies46,47 rather than a single nutrient. Vegetables and soy food that rich in iron or components enhancing iron absorption were found to associate positively with serum hemoglobin among middle-aged adults and elderly population47,48. Vitamin C, in addition to iron, was found to be essential to prevent iron deficiency for obese patients who undergone bariatric surgery49. Vegetables and soy groups are mainly included in Healthy Eating Index assessment, elucidating the necessity of consuming these components in line with the dietary guidelines. Likewise, Mardas et al. (2017) showed that a whole food rather than a single nutrient was related with chemotherapy-induced gastrointestinal symptoms50. Iron rich food or dietary enhancers of iron absorption could be somehow beneficial to anemic cancer patients, despite the low hemoglobin level is generally attributable to cancer or treatment-related factors. With regards to the incidence of anemia, Thomson et al. (2011) recommended to keep body weight within a healthy range46. Inadequate diet intake could predispose patients to iron deficiency while obese women are likely to experience interrupted iron absorption46,48. In view of the potential inter-relationship between health indicators, investigation on the mediating effect of body mass index in respect to the association between diet quality and low serum hemoglobin are warranted. Despite the potential linkage of diet quality with serum hemoglobin, this marker should be interpreted carefully as it may be affected by cancer prognosis related inflammation51.
Breast cancer patients were shown to be more likely to adhere to dietary guidelines within the shorter duration of diagnosis. Despite earlier studies demonstrated non-significant relationship of diagnosis time with diet quality in mixed cancer population or survivors15,52, such relationship was implicitly supported by the study of Custódio et al. (2016)24. Over the cancer treatment, a decline in diet quality was evident at the intermediate cycle of chemotherapy24. In general, poor diet quality is attributed to lack of food varieties or an imbalanced diet. As a result of cancer treatment, nutrition impact symptoms, for instance, taste changes and nausea25 could act as barriers to consuming a good quality diet. In making a decision for treatment plan, comorbidity is always a major issue for cancer patients in light of its potential dual burden on quality of life and survival53. In the present study, patients with comorbidities were shown to have poorer diet quality. Noting of the non-prospective study design, this finding does not preclude the notion of substantial impact of poor diet quality on the burden of multiple health outcomes. Despite demographic factors are considered as the risk factors of unhealthy diet in the causation pathway for non-communicable diseases10, none of the variables was shown to associate with diet quality in current study. This could be explained by the varying extent of demographic influences on diet behaviour across the population groups.
Present study yields new insights into how a quality diet was linked to the clinical outcomes of patients with breast cancer, with the evaluation of the degree of conformance in consumption of various food groups with dietary guidelines. Achieving a healthy weight range has been set as a primary goal to prevent nutrient deficiencies and to ensure an optimal health for cancer population54. The assessment of diet quality in breast cancer patients, particularly those receiving treatment, therefore, provides valuable information for the identification of patients’ nutritional status during this critical phase. Moreover, the association between diet quality and treatment-related side effects was performed using multivariate analysis, together with the adjustment of multiple confounders. This minimizes the bias that resulted from the factors that are out of study interest.
The limitations of this study included cross sectional design which determined both exposure and outcome simultaneously, whereby, the causal effect of poor diet towards treatment-related side effects could not be assured. The limited sample size of this study may result in the issue of data sparsity, which may not be representative of the overall findings. In light of the need for increased power of study and strength of evidence, a larger sample size should be considered in the future studies. The significant associations between diet quality and overweight or low haemoglobin should be interpreted with cautious as the confidence interval for odds ratio were closed to null value of 1 indicates weak implication of results. As the patient-reported outcomes rely on cancer types and treatment factors, these findings may not be generalized to other cancer groups or trajectory phases. For instance, the study population were mainly characterized by non-terminal stage, in which the study finding could not be extrapolated to breast cancer patients under hospice care with poor prognosis. The measurement periods of blood serum or body weight were inconsistent across phases of cancer treatment, which does not allow parallel comparison with 1 month of diet history. This implies that the dietary assessment over the past one month is insufficient to reflect the overall dietary pattern during treatment and the assessment period should be extended considering the data reliability without compensating patients’ burden. Besides, short assessment period of laboratory measures and body weight may also be insufficient to reflect the nutritional status of patients throughout the treatment, which may undermine the study findings.
Despite Healthy Eating Index was found to be a well-established tool to predict obesity55, it does not consider the key principle of balance, as referring that each food groups should be taken in right amount or proportion. In regard to this limitation, an underestimation of over-eating might be existed. For instance, though protein is important for muscle building, over-consumption of proteins can contribute significant calorie which could lead to overweight. Lack of nutrition information, particularly for saturated, mono- and polyunsaturated fatty acids, may underscore the component of fatty acid in overall diet quality evaluation. However, additional food databases with higher availability of food items or nutrients were utilized in order to minimize such bias.