What is the relationship between cancer and what we eat?

Poor eating habits are one of the main risk factors that contribute to the loss of healthy life years in the Portuguese population. Cancer is one of the leading causes of death and morbidity worldwide. But how do they both relate? 

In addition to therapies such as surgery, chemotherapy, radiotherapy, immunotherapy, there is a growing recognition that nutrition plays a central role not only in prevention, but also in supporting the patient during and after treatment. Diet influences factors such as inflammation, oxidative stress, immune function, body composition and metabolism, all of which have a direct impact on the risk, evolution and quality of life of the cancer patient. (1,2) 

In Portugal, clinical guides and associations highlight the importance of a healthy diet, inspired by standards such as the Mediterranean Diet, in supporting cancer patients. (3,4) 

Prevention 

About a third of cancers can be prevented by changing eating habits and adapting behaviours to a healthier lifestyle, such as not smoking, not drinking alcohol, exercising and having healthy sleep habits.  (1) 

Several epidemiological studies associate adherence to a Mediterranean diet with a decreased risk of various types of cancer. A systematic review showed that this dietary pattern, rich in fruits, vegetables, whole grains, fish, unsaturated fats (such as olive oil), is correlated with a lower incidence of colorectal, breast and digestive system cancer. (5,6) 

In Portugal, the Mediterranean Diet Food Guide includes vegetable products (legumes, vegetables, fruits), whole grain products, fish, olive oil as the main fat, and reduced consumption of red and processed meats, characteristics associated with lower cancer risk. (7) 

During treatment 

After the diagnosis of cancer, one of the main concerns is malnutrition, involuntary weight loss and sarcopenia (significant loss of muscle mass), which worsen the prognosis, increase complications and reduce quality of life. (8) 

The report "Nutritional Factors During and After Cancer: Impacts on Recovery, Survival, and Quality of Life" shows that nutritional factors such as weight loss, malnutrition, or excessive weight gain (depending on the type of cancer) are determinants of mortality, recurrence, or second primary cancer. (9) 

In addition, nutritional interventions during treatment can improve tolerance to therapy, reduce toxicity, decrease hospitalizations, and improve recovery. International guidelines, such as those from European Society for Clinical Nutrition and Metabolism (ESPEN), recommend regular screening of nutritional status, personalized assessment, dietary support and, if necessary, supplementation or parenteral nutrition as support. (10) 

During cancer treatment, patients may face nutritional challenges due to side effects such as nausea, loss of appetite, and changes in taste. An adequate nutritional intervention is essential to maintain nutritional status, improve response to treatment, and reduce complications. Regular monitoring of nutritional status and the implementation of personalized dietary strategies can benefit cancer patients. (1) 

During treatments, intestinal dysregulation may occur, resulting in diarrhea or constipation. Diarrhoea can be caused by infections and disease, compromising the digestion and absorption of nutrients, which can lead to dehydration and malnutrition. Constipation can be caused or aggravated by some medications, dietary changes, inadequate water intake, and inactivity. It may be accompanied by abdominal pain, a feeling of abdominal distension, flatulence and nausea. Constipation must be prevented or addressed early, otherwise its complications and discomfort become more difficult to resolve. (9)