Food decisions are usually everyday choices. After a cancer diagnosis, everyday meals often become one of the few areas people feel they can still influence. Cancer treatment is usually discussed in detail, while nutrition receives less sustained attention in day-to-day care.
What should I eat, what should I avoid, and am I doing this right?
Nutrition advice during cancer treatment is abundant but often contradictory. Online guidance, well-meaning family members, and headlines about “anti-cancer diets” can make it difficult to know what information is relevant or reliable.
What nutrition supports during cancer treatment
During cancer treatment, nutrition serves practical functions that affect how the body copes with therapy. Rather than acting as a treatment itself, nutrition supports the body’s capacity to withstand the physical demands of chemotherapy, radiotherapy, surgery, or targeted therapies.
In practical terms, nutrition helps to:
maintain body weight and muscle mass
support recovery between treatment cycles
reduce fatigue and functional decline
manage side effects that interfere with eating
For this reason, there’s no fixed “best” diet during cancer. Nutritional needs shift with treatment type, side effects, age, cultural habits, and existing health conditions. What works at one stage may no longer be suitable a few weeks later.
There’s no single cancer diet. Nutritional support needs to fit the individual and the phase of treatment they’re in.
Lynn, a dietitian, explains that nutritional needs change across the cancer journey and vary depending on the phase of treatment.
At the point of diagnosis, when a doctor proposes a treatment plan, it’s important to maintain a well-balanced diet and avoid being overly restrictive or eating “too clean,” as this may lead to weight loss and potentially affect the body’s ability to tolerate treatment.
During treatment, particularly chemotherapy and immunotherapy, these same principles remain important, with greater emphasis on adequate carbohydrate intake to provide consistent energy throughout the day, as treatment drugs often cause fatigue. Sufficient protein intake is also important to help reduce muscle wasting, which can affect physical function.
She advises requesting a dietitian consultation early if weight loss occurs or if eating well becomes difficult due to symptoms such as poor appetite, nausea, oral ulcers, swallowing difficulties, or diarrhoea. Poor nutritional intake during treatment can reduce treatment tolerance and may lead to delays or even termination of treatment. At Singapore Cancer Society (SCS), early referral to a dietitian is often emphasised, as timely and personalised nutritional support can make a significant difference to treatment tolerance and recovery.
During the recovery phase, healthy eating remains important. This includes consuming a wide variety of fruits and vegetables, whole grains, and adequate protein to support regular exercise, while avoiding processed meats and alcohol whenever possible. This approach aligns with the World Cancer Research Fund’s cancer prevention guidelines and is commonly discussed in the context of reducing the risk of cancer recurrence.
Why eating becomes difficult during treatment
Many people are unprepared for how quickly eating changes once treatment begins.
Common experiences include:
- food tasting metallic, bitter, or unusually bland
- feeling full after only a few bites
- nausea triggered by smells or textures
- mouth pain, ulcers, or swallowing discomfort
- fatigue that makes cooking or eating feel overwhelming
These changes are commonly linked to treatment effects rather than individual behaviour.
Cancer and its treatment can significantly affect appetite and taste, making it difficult for some patients to eat enough or enjoy foods.
In these situations, small, frequent meals are often more manageable than three large ones. Drinking nourishing fluids such as soy milk, fresh milk, barley water, or coconut water can also help support intake, rather than relying on plain water alone.
Adding extra calories to familiar foods can be another practical strategy. This may include spreading thicker peanut butter, jam, soft margarine, or cheese on bread or crackers, or drizzling sesame oil into porridge and olive oil into soups. This approach, known as fortification, allows energy intake to be increased without needing to eat larger portions.
If eating remains challenging despite these adjustments, supplementing the diet with a nutritionally complete formula, such as Ensure, Isocal, or Fortisip, may be helpful.
In SCS’s nutrition counselling sessions, the focus is often placed on small, achievable steps that prioritise nourishment and enjoyment rather than strict dietary rules. Seeking a dietitian referral can provide more personalised advice and help determine which supplement is best suited to individual needs.
When “eating right” adds pressure
Well-meaning advice often arrives quickly:
During active treatment, dietary restriction can increase the risk of weight loss, muscle depletion, and reduced tolerance to therapy. For people already dealing with nausea, taste changes, or early fullness, rigid food rules often make eating harder than healthier.
As treatment progresses, nutritional priorities shift toward adequacy. Meeting energy, protein, and fluid needs often matters more than dietary ideals, particularly when appetite or tolerance is limited.
Incorporating a patient’s cultural food preferences and traditions is an important part of cancer nutrition planning, particularly when certain staple foods may not easily align with treatment-related dietary needs. Lynn notes that this becomes especially relevant when dietary practices are closely tied to religious or cultural beliefs.
A common example involves patients who follow a vegetarian diet for religious reasons. These practices should be respected, yet many patients who are vegetarian may struggle to meet their increased protein requirements during cancer treatment.
To address this, patients are educated on vegetarian-friendly protein sources such as tofu, beancurd skin, nuts and seeds, edamame, tempeh, and beverages like milk and soy milk. Individual protein requirements are discussed, along with practical strategies to help patients meet their needs within their usual eating patterns.
For those who continue to find it difficult to achieve adequate protein intake through diet alone, suitable protein supplements may also be suggested to support their nutritional requirements.
What balanced looks like during treatment
During cancer treatment, balance tends to shift rather than follow fixed rules.
For many patients, priorities often include:
| Nutrient type | Function |
|---|---|
| Protein | Supports muscle maintenance and healing |
| Carbohydrates | Maintains energy, particularly when fatigue is prominent |
| Fats | Increases calorie intake when appetite is low |
| Fluids | Reduce the risk of dehydration |
Fruits and vegetables remain important, but they don’t need to be raw, green, or trendy. Cooked vegetables, blended soups, and familiar cultural foods all play a role in meeting nutritional needs. Nutrition that fits daily routine and preference is more sustainable than externally imposed dietary standards.
Misconceptions about so-called “anti-cancer diets” are common, and many patients encounter conflicting advice that can be confusing or unnecessarily restrictive. Lynn observes that questions about sugar, soy, and red meat are among the most frequent concerns raised during consultations.
One common belief is that “sugar feeds cancer cells.” While glucose may be a primary fuel source for cancer cells, it’s also the main source of energy for all healthy cells in the body. Avoiding sugar or significantly restricting carbohydrates doesn’t selectively starve cancer cells, as the body will instead draw on stored protein and fat for fuel. Over time, this can contribute to unintended weight loss and malnutrition. For most people, including complex carbohydrates as part of regular meals is appropriate. Limiting refined sugars is generally advised only for individuals with diabetes or specific metabolic concerns.
Concerns around soy intake are also frequently raised, particularly among people with breast cancer. Although soy contains isoflavones that are structurally similar to oestrogen, these compounds interact differently with the body’s oestrogen receptors. Lynn adds that current evidence suggests consuming soy in amounts typically found in Asian diets is safe and may even be beneficial for those at risk of, or living with, breast cancer. These potential benefits are thought to come from the dietary fibre, phytochemicals, and other nutrients present in whole soy foods. A practical guideline is one to two servings of whole soy foods per day, providing about 10-40 mg of soy isoflavones daily, for example 1 cup (250ml) of soy milk and half a block of silken tofu in a day.
Red meat is another area of confusion. Beef, pork, and lamb are classified as Group 2A carcinogens, meaning they are probably carcinogenic to humans if taken in excess. Haem iron in red meat can be broken down during digestion to form N-nitroso compounds, which may increase the risk of bowel cancer. At the same time, red meat is a source of protein, iron, vitamin B12, and zinc. Lynn emphasises that moderation, rather than complete avoidance, is recommended, with the World Cancer Research Fund advising a limit of 350 to 500 g of cooked red meat per week (about 3 palm-sized portions), or up to 750 g raw weight per week.
To avoid being misled by unproven or restrictive advice, patients are encouraged to be cautious about information from online or social media sources, particularly when claims sound absolute or fear-driven. Seeking guidance from healthcare professionals allows dietary decisions to be grounded in evidence and tailored to individual needs, treatment plans, and cultural contexts.
Supplements and the need for caution
Many people assume supplements are harmless because they are widely available. During cancer treatment, that doesn’t always hold.
Some supplements may:
- interact with chemotherapy or radiotherapy
- affect how drugs are absorbed or metabolised
- increase side effects rather than reduce them
This doesn’t mean supplements are universally inappropriate, but they require careful consideration. Decisions around their use are best made with professional input rather than online recommendations or anecdotal advice.
Many patients consider supplements or herbal products during cancer treatment, but these should always be discussed with the oncologist or healthcare professionals involved in their treatment before use.
There’s evidence suggesting that taking antioxidant-rich supplements during cancer treatment may be associated with a higher risk of cancer recurrence and mortality. This is thought to occur because antioxidants can interfere with the effectiveness of certain cancer treatment drugs, particularly those that rely on oxidative mechanisms to damage cancer cells.
Herbal products can also pose risks. Supplements containing pomegranate extract, for example, may reduce the breakdown of some cancer medications and potentially lead to higher drug levels and toxicity. For this reason, patients are encouraged to inform their oncologist before starting any supplements or herbal products.
If a patient is interested in traditional or herbal remedies, this should be discussed openly with the oncology team. In some cases, referral to a TCM practitioner experienced in managing patients undergoing cancer treatment may be appropriate, allowing herbal use to be reviewed alongside medical care rather than taken independently.
From a clinical nutrition perspective, open communication is essential. SCS’s dietitians often work closely with oncology teams to ensure that nutrition support and supplement use are safely integrated into each patient’s care plan.
The Singapore Cancer Society also provides free or subsidised nutrition counselling and other supportive care services for individuals affected by cancer. For more information or to access these programmes, please visit our website listed below.
When a nutrition consultation becomes relevant
Nutrition support is often introduced later in treatment, despite being useful well before severe weight loss or advanced stages.
A consultation may be helpful if:
Early guidance can help limit nutritional decline and reduce uncertainty for both patients and caregivers.
For caregivers: Adjusting expectations around food
Many caregivers describe increasing frustration around meals. Encouragement can gradually turn into pressure, and food may signal progress or decline.
Support often improves when:
- choices are offered rather than enforced
- comfort is prioritised over portion size
- intake is considered across days rather than individual meals
Caregiving around food often involves adjusting expectations as needs change, rather than relying on fixed rules.
How nutrition fits into cancer care
Cancer treatment is medically complex, yet eating difficulties are often treated as secondary. In practice, nutrition shapes how people cope with therapy, manage side effects, and maintain functional capacity throughout treatment.
When food becomes confusing or stressful, it often reflects a shift in clinical needs rather than a personal shortcoming. Earlier attention to nutrition can reduce avoidable strain for both patients and caregivers, even though it doesn’t alter the underlying disease.
In cancer care, that distinction remains important.
This article was produced by Healthful For You. The views and opinions expressed throughout are those of the authors and do not necessarily reflect those of the Expert Contributor. The Expert Contributor has provided input solely for the EXPERT INSIGHT and TIP segments, based on their professional expertise. These comments are intended to offer general guidance and may not apply to all individuals. Any interpretations or conclusions beyond that section are those of Healthful For You. This article is not a substitute for personalised medical advice, diagnosis, or treatment. Please consult your doctor or a healthcare professional regarding your specific health needs.
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