Nutrition During Cancer Treatment: What Should You Eat?
- Megan Sandri
- Aug 28
- 8 min read
If you or someone you love is going through cancer treatment, one of the first questions you may have is:
"What should I be eating?"
It's an understandable question—and unfortunately, the answer can be difficult to find.
You may come across recommendations to eliminate sugar, follow a ketogenic diet, avoid certain foods, eat only organic foods, fast around chemotherapy, or take a long list of supplements. At the same time, your appetite may have changed, food may taste different, or eating may simply feel like another thing you have to manage during an already overwhelming time.
The good news is that nutrition during cancer treatment does not need to be complicated.
There is no single "cancer diet" that is right for everyone. Nutrition needs can change depending on your cancer type, treatment, symptoms, nutritional status, medications, and personal preferences.
Instead of focusing on finding the perfect diet, I generally encourage patients to focus on getting enough nutrition, maintaining strength and muscle, managing treatment-related symptoms, and choosing foods that are realistic for them.
Why does nutrition matter during cancer treatment?
Cancer and its treatment can affect nutrition in many different ways.
You may experience:
Reduced appetite
Nausea or vomiting
Changes in taste or smell
Mouth sores or difficulty swallowing
Diarrhea or constipation
Early fullness
Fatigue that makes shopping or cooking difficult
Changes in digestion
Unintentional weight loss
Changes in body composition
These challenges can make it difficult to eat enough food to meet your body's needs.
Inadequate nutritional intake and malnutrition are common concerns in people with cancer, which is why nutritional screening and appropriate nutrition support are important throughout the cancer journey.
Nutrition during cancer treatment isn't about achieving a perfect diet. Sometimes the priority is simply being able to eat enough to maintain your strength and nutritional status.
What should you eat during cancer treatment?
There isn't one eating pattern that is appropriate for everyone undergoing cancer treatment.
Your nutritional needs depend on factors including your cancer diagnosis, treatment, symptoms, current nutritional status, activity level, and goals.
However, there are several areas that are often worth paying attention to.
1. Prioritize adequate food intake
One of the most important nutrition goals during cancer treatment is making sure you're actually getting enough food.
This can sound obvious, but it can become surprisingly difficult when you're dealing with nausea, poor appetite, taste changes, fatigue, or digestive symptoms.
If you're struggling to eat, the "perfect" meal isn't necessarily the most important meal. The meal you can actually tolerate may be more useful.
This might mean:
Eating smaller meals more frequently
Keeping easy-to-eat foods available
Choosing higher-calorie foods when your appetite is low
Using smoothies or nutritional drinks when solid food is difficult
Eating at times of day when your appetite is best
Accepting help with grocery shopping and meal preparation
If you're experiencing significant or ongoing unintentional weight loss or difficulty eating, it's important to bring this up with your oncology team and consider referral to a registered dietitian or other qualified nutrition professional.
2. Pay attention to protein
Protein is important for maintaining muscle and supporting many functions in the body.
During cancer treatment, maintaining muscle mass and physical function can be particularly important. Cancer and its treatment can contribute to changes in body composition, and inadequate food intake can make it more difficult to meet protein needs.
Rather than worrying about getting the exact same amount of protein every day, consider including a source of protein at regular meals and snacks.
Examples include:
Tofu and tempeh
Soy milk
Beans and lentils
Eggs, if you eat them
Greek yogurt or other dairy products, if tolerated
Fish, poultry, or meat, if you eat animal products
Protein powders or nutritional supplements when appropriate
Your individual protein needs may be higher than those of a healthy adult, particularly if you're experiencing weight loss, malnutrition, or other factors affecting your nutritional status. Protein needs should therefore be individualized rather than based on a one-size-fits-all recommendation.
3. Don't forget carbohydrates and fats
There is a lot of fear surrounding carbohydrates in online cancer nutrition discussions.
Carbohydrates are not inherently "bad," and there is currently insufficient evidence to recommend a ketogenic or low-carbohydrate diet specifically to improve cancer treatment outcomes.
Carbohydrate-containing foods can provide an important source of energy and may be particularly useful when appetite or food intake is limited.
Depending on your individual needs and tolerance, these might include:
Oats
Rice
Potatoes or sweet potatoes
Whole-grain breads and cereals
Pasta
Fruit
Beans and lentils
Similarly, dietary fats can provide a concentrated source of energy and contribute important nutrients.
The right balance of carbohydrate, protein, and fat will depend on your individual circumstances.
4. Eat the foods you can tolerate
This may be one of the most important pieces of advice during treatment.
Cancer treatment can change the way food tastes and smells. Foods you once loved may suddenly be unappealing, while other foods may become easier to tolerate.
If nausea is making a large meal impossible, smaller meals may work better.
If vegetables are difficult to tolerate, you may need to temporarily rely on other foods while working toward a more varied diet when you're feeling better.
If cold foods are easier to tolerate than hot foods, use that to your advantage.
Nutrition during cancer treatment needs to be flexible.
The goal isn't to eat perfectly. The goal is to support your nutritional needs in a way that works for you right now.
5. What about fruits and vegetables?
For many people, fruits and vegetables are an important part of a balanced eating pattern and provide fibre, vitamins, minerals, and other beneficial compounds.
However, you may need to modify how you eat them depending on your symptoms and treatment.
For example, someone experiencing diarrhea may temporarily tolerate cooked or peeled vegetables better than large amounts of raw vegetables. Someone with constipation may benefit from gradually increasing fibre and fluids if appropriate.
It's also worth noting that the old idea of following a strict "neutropenic diet" that eliminates raw fruits and vegetables to prevent infection is not supported by current ASCO guidance.
Food safety, however, remains important. Your oncology team may have specific recommendations depending on your treatment and individual risk factors.
6. What about sugar and cancer?
This is one of the most common questions I hear.
"Does sugar feed cancer?"
The relationship between dietary sugar, overall diet, metabolism, and cancer is much more complicated than the statement "sugar feeds cancer" suggests.
Your body maintains blood glucose even when you don't eat sugar or carbohydrates, and cancer cells are not uniquely dependent on dietary sugar in a way that means eliminating sugar will starve a tumour.
At the same time, a diet that is very high in added sugars may displace more nutritious foods and contribute to other metabolic health concerns.
So rather than trying to eliminate every gram of sugar from your diet during treatment, it is generally more useful to consider your overall dietary pattern and nutritional needs.
And if you're struggling to eat enough, avoiding foods simply because they contain sugar may actually make it harder to meet your energy needs.
7. Do you need to fast around chemotherapy?
Fasting and time-restricted eating have attracted a lot of attention in cancer research.
There are interesting biological questions being studied, but that doesn't mean fasting is appropriate for everyone receiving cancer treatment.
Current ASCO guidance found insufficient evidence to recommend fasting or specific dietary patterns to improve quality of life, treatment toxicity, or cancer control during active treatment.
For someone who is already struggling with appetite, losing weight, or having difficulty meeting their nutritional needs, intentionally restricting food intake may be counterproductive.
If you're considering fasting during treatment, this is something to discuss with your oncology and nutrition care team rather than trying it on your own.
8. What about supplements?
Supplements are another area where I encourage caution.
Cancer treatment can involve multiple medications, and some supplements or concentrated natural products can interact with medications or affect how treatments are processed by the body.
That doesn't mean all supplements are harmful or that supplements can never have a role in cancer care.
It means that they should be considered individually.
Before starting a new supplement during cancer treatment, consider:
What is the evidence for using it?
What benefit are you hoping to achieve?
What dose is being used?
Could it interact with your cancer treatment or other medications?
Is there a reason to avoid it in your particular situation?
"Natural" is not synonymous with "safe," particularly when you're receiving cancer treatment.
Nutrition during chemotherapy: a practical approach
If you're currently receiving chemotherapy and don't know where to start, I would encourage you to keep things simple.
Ask yourself:
Am I eating enough?
If you're losing weight unintentionally or struggling to eat, addressing adequate energy intake may be the priority.
Am I getting enough protein?
Try incorporating a protein source regularly throughout the day.
What foods can I tolerate right now?
Work with your current symptoms rather than forcing yourself to eat foods that make you feel worse.
Am I drinking enough?
Hydration needs vary, but maintaining adequate fluid intake is important, particularly if you're experiencing vomiting, diarrhea, fever, or other causes of fluid loss.
What symptoms are making eating difficult?
Sometimes improving nutrition isn't about finding a better diet—it's about addressing the problem that is preventing you from eating.
Nausea, constipation, diarrhea, mouth sores, taste changes, pain, fatigue, and other treatment-related symptoms may all require their own strategies.
What if I've gained weight during cancer treatment?
Nutrition concerns during cancer treatment aren't limited to weight loss.
Some people gain weight during treatment because of changes in activity, appetite, medications, hormonal changes, or body composition.
That can be frustrating, particularly when you're being told to "eat healthy" while simultaneously trying to navigate treatment.
However, intentional weight loss during active cancer treatment isn't automatically the right goal. Current ASCO guidance found insufficient evidence to recommend intentional weight loss or prevention of weight gain during active treatment specifically to improve quality of life, treatment toxicity, or cancer control.
The appropriate approach depends on your individual circumstances.
In some cases, the focus during treatment may be maintaining adequate nutrition and physical function. In others, there may be opportunities to gradually address metabolic health and body composition.
The timing and context matter.
There is no single "cancer diet"
Perhaps the most important thing I want patients to know is that you don't need to find the perfect diet to support yourself through cancer treatment.
You don't need to eliminate sugar.
You don't necessarily need to go keto.
You don't need to fast around chemotherapy.
You don't need to buy every supplement marketed for cancer.
And you don't need to feel guilty when your diet doesn't look "perfect."
Nutrition during cancer treatment is about supporting your nutritional status, maintaining strength and function, managing symptoms, and finding an approach that is realistic for you.
The best nutrition plan is one that takes into account your cancer, your treatment, your symptoms, your nutritional needs, and your life.
When should you seek nutrition support?
Consider asking your oncology team about a nutrition referral if you are experiencing:
Unintentional weight loss
Persistent loss of appetite
Difficulty eating enough
Significant changes in your diet because of treatment
Difficulty swallowing
Persistent nausea or vomiting
Ongoing diarrhea or constipation
Significant taste or smell changes
Concerns about maintaining muscle or strength
Confusion about supplements or nutrition recommendations you've encountered online
Early nutrition support can be valuable, particularly when you're struggling to meet your nutritional needs.
A registered dietitian with oncology experience can provide specialized medical nutrition therapy, while other members of an integrative oncology team may provide additional support depending on your individual needs.
The bottom line
Nutrition during cancer treatment isn't about finding a miracle food or following the perfect cancer diet.
It's about making sure your body has the energy and nutrients it needs, supporting muscle and physical function, managing symptoms that interfere with eating, and adapting your approach as your needs change.
There is still a great deal we don't know about how specific dietary interventions affect cancer outcomes during active treatment. Good nutrition care therefore requires both an understanding of the evidence and an appreciation for the individual person sitting in front of you.
If you're navigating cancer treatment and feeling overwhelmed by nutrition advice, you don't have to figure it all out on your own.
Start with what your body needs, what you can tolerate, and what matters most to you.
Interested in individualized cancer nutrition support?
I provide evidence-informed integrative oncology care that can include individualized nutrition and lifestyle support alongside conventional cancer treatment.
A note on medical care
This article is intended for general educational purposes and is not a substitute for individualized medical or nutritional advice. Nutrition recommendations during cancer treatment should be tailored to your diagnosis, treatment plan, nutritional status, medications, symptoms, and individual needs. Always discuss significant dietary changes or supplements with your oncology team and qualified healthcare professionals.
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