# Nutrition in metastatic breast cancer
Nutrition and disease progression
In metastatic breast cancer, nutrition plays a role at multiple levels. On one hand, a healthy eating pattern can help maintain overall health and energy levels during treatment. On the other hand, certain nutritional components can influence biological processes in the body that are related to cancer growth and immune function.
Research on nutrition in metastatic breast cancer is less extensive than in early-stage cancer. What is known comes partly from studies in breast cancer patients in general and from research on nutrition and immune function.
ResearchediPositive results in clinical studies, not yet standard treatment
Long-term changes in eating patterns are linked to survival outcomes, but the relationship is complex and individually diverse.
Plant-based dietary pattern
A dietary pattern with many plant-based products (vegetables, fruit, whole grains, legumes, nuts) is associated in research with better immune function and lower inflammation markers.
ResearchediPositive results in clinical studies, not yet standard treatment
Patients who follow a plant-based dietary pattern sometimes report improved energy levels and fewer side effects, but strong scientific evidence is still limited in metastatic disease.
This type of diet provides many vitamins, minerals and plant compounds (flavonoids, polyphenols) that have antioxidant and anti-inflammatory properties. For patients in active treatment, a predominantly plant-based pattern can be beneficial as long as it supports nutritional values and calorie intake well.
Fat and nutritional intake status
ProveniIncluded in official guidelines, or approved by EMA or FDA
Adequate calorie and protein intake is essential to maintain muscle mass and immune function, especially during chemotherapy or immunotherapy. Malnutrition actually weakens the immune system.
The type of fat that receives attention concerns the ratio between saturated and unsaturated fats.
ResearchediPositive results in clinical studies, not yet standard treatment
A pattern with relatively more unsaturated fats (from oils, fish, nuts) and less heavily processed food is seen as supportive, among other things because of effects on inflammation markers.
Very low-fat diets are not recommended because fat is needed for absorption of fat-soluble vitamins (A, D, E, K) and for hormonal balance. Balanced intake is the goal.
Nutritional interactions with treatment
Some nutritional components can interact with cancer treatments. This is essential to know because it can affect medication efficacy or side effects.
ProveniIncluded in official guidelines, or approved by EMA or FDA
Certain herbs and supplements (for example St. John's wort, certain types of herbal tea in large quantities) can interact with hormone therapies or targeted medicines through effects on liver metabolism of medications. This should always be discussed with your healthcare provider before using new products.
Grapefruit and grapefruit juice can inhibit or enhance certain medications. Consistency in daily diet helps keep medication administration more stable.
Weight and physical activity
ResearchediPositive results in clinical studies, not yet standard treatment
Weight stability and moderate regular exercise (combined with nutrition) are associated with better treatment tolerance and less fatigue. Environmental factors, such as food availability and safe places to exercise, also play a role.
Weight gain or loss can both cause problems. Weight gain can increase inflammation markers; extreme weight loss weakens muscle tissue and immune function. The goal is usually stability.
Symptom management through nutrition
Certain food choices can help with treatment side effects, although this is highly dependent on individual circumstances.
- **For nausea and altered taste**: Small, frequent meals; preference for food at room temperature; mild spices.
ResearchediPositive results in clinical studies, not yet standard treatment
Ginger (fresh or in tea) can help relieve nausea for some people.
- **For fatigue**: Regular meals with a balance of proteins, carbohydrates and healthy fats helps keep energy levels more stable.
ProveniIncluded in official guidelines, or approved by EMA or FDA
Malnutrition worsens fatigue.
- **For digestive complaints**: Diet adapted to tolerance; adequate fluid intake. Some patients tolerate specific food groups better than others, which varies individually.
Supplements and herbs
The landscape of supplements in cancer is complex. Much is claimed, but only a few claims have strong supporting evidence.
ExperimentaliOngoing in study setting, outcome still unknown
Certain plant compounds (curcumins from turmeric, polyphenols from green tea) show properties of interest to cancer biology in laboratory studies, but their efficacy and safety in human cancer treatment have not yet been established.
UnproveniNo scientific evidence that it works
Many given supplements such as certain vitamins in megadoses, special extracts or commercial "anti-cancer" products lack sound scientific evidence in metastatic disease.
Advised againstiProven ineffective or harmful, or dangerous in combination with your treatment
Very high doses of certain antioxidants can theoretically undermine certain chemotherapies, and some supplements can interact with medications. This must always be coordinated with doctor and dietitian.
Self-supplementation without consultation with the treating physician is unwise because interactions can be serious.
Fluid balance and kidney function
ProveniIncluded in official guidelines, or approved by EMA or FDA
Adequate fluid intake helps keep kidneys and urinary tract healthy, especially important because certain cancer treatments stress the kidneys. Water is usually best; some patients tolerate warm drinks better with nausea.
Too much concentrated juice or sugar can be problematic for some, especially for patients with altered glucose tolerance.
Nutrition and immune function
ResearchediPositive results in clinical studies, not yet standard treatment
Certain dietary patterns (plant-based, with many different colored vegetables, whole grains, healthy fats) support the gut microbiota and immune function better than highly processed foods. This may be relevant in immunotherapy, where immune function is crucial.
Extreme diets or radical dietary changes shortly before or during intensive treatment can, however, also be stressful. Gradual adjustments are usually better.
Psychosocial aspects of eating
Eating is not only nutrition, but also comfort, habit and social connection. With serious illness, eating can become complex: taste changes, loss of interest, or even strong attachments to certain foods can occur.
ResearchediPositive results in clinical studies, not yet standard treatment
Patients who receive support with food choices (from dietitians, family, integrative care teams) report better food and medication tolerance and less psychological distress around eating.
Practical approach
The best dietary choice is one that:
- Provides sufficient energy, protein and nutrients
- Aligns with personal tolerance and preference
- Causes no interactions with medications
- Is supported by the treating physician and preferably a dietitian
For personal nutrition planning and adjustments during treatment, collaboration with a dietitian or nutrition specialist familiar with cancer treatment is strongly recommended. They can check for interactions, address symptoms, and help optimize nutritional intake per phase of disease.
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_This information never replaces a doctor's judgment. Always discuss your situation with your own healthcare provider._