Hidden Truths about Cancer Nutrition

Cancer is, no doubt, a frightening condition to think about; “anti-cancer” has become a byword in marketing, and cancer sufferers will often try anything in the hope of improving their chances at recovery. Unfortunately, all this has led to many false and exaggerated claims in the health industry, from companies trying to profit off people’s fear of the disease. 


In the search for a silver bullet or that single magical nutrient, few are given a full understanding of their nutrition priorities. As a result, many proceed to over-restrict their diet, leading to an estimated 20% of cancer deaths from malnutrition instead of the disease itself. Read on to find out more about cancer nutrition from Lead Clinical Dietitian Anna Lim and avoid falling prey to such health companies.

Important Note:

There is one thing to get clear before any discussion on this topic, which is that Nutrition for Cancer Prevention and Nutrition for Cancer Treatment are very different things. One common mistake is assuming that the body needs the same things when it is healthy versus when it is ill. The “pre-cancer (or healthy)” stage has significantly different goals and requirements from the “disease stage”, when the body’s overall condition has changed drastically. Some main differences:

The differences are like night and day; it would not be fair to read anything on “cancer-busting/ fighting” or “anti-cancer” and assume that this will treat/ cure cancer once it has appeared. Most of the common advice seen online is in fact usually more useful in the “prevention” stage, but with the onset of disease and treatment, a battle has begun and the “war strategy” should change accordingly. 

1. Fruit and Vegetables will not “fight” cancer

This makes up the bulk of “anti-cancer” articles, advice and supplements. The most popular logic is that antioxidants, found in fruit and vegetables, will fight tumour formation, support the immune system and a myriad of other benefits. Besides antioxidants, almost any component can also be touted for its “cancer-fighting” properties – often to convince sufferers to buy a product. 


Having said this, there is definitely a benefit to including more fruit and vegetables in the diet; it has been proven to reduce cancer risk, especially for certain types like colorectal cancer. Note that this refers to cancer prevention, and not curing cancer. For cancer patients, the focus should be on macronutrients like protein, and ensuring overall adequate calories (Refer to Point 3), instead of getting caught up in the hundreds of other nutrients which have less impact.

2. Supplements and Health Foods are Likely to be a Waste of Money

Note: “Supplements” as mentioned in this point refers to complementary/ alternative products such as vitamin/ mineral/ herbal supplements. There is another category of medical nutrition products called Oral Nutrition Supplements, which are designed as complete nutrition and may have a place in a patient’s diet. One should still consult a Dietitian, however, to use these correctly.


The market for oncology (the medical term for the study of cancer) nutrition is estimated to reach 2.2 billion USD in 2023, but the overall market for supplements is estimated at 27 million USD every year in the USA alone. Why are these figures relevant? Simply because people often turn to supplements as the first port of call; knowing how much money the industry is worth may encourage them to think critically about whether the health claims are truly accurate, or just exaggerated. 


The range of supplements is vast, and so is the variety of benefits these supplements claim to have. While there may be some truth to these claims, the reality is that the effect is never as dramatic as advertised, for the following reasons: 

  • Products may not be absorbed the way we assume, or may actually be broken down during digestion, rendering them useless
    • Example: Enzyme supplements are a popular cancer supplement, however all enzymes are protein, which are broken up into pieces during digestion
  • By zeroing in on one nutrient or category of nutrients, the patient neglects other nutrients which are equally or more important 
    • Example: Religiously taking antioxidants daily, while neglecting protein and calories, which are in fact the most well-researched and proven nutritional factors in improving outcomes
  • The effects may be “proven” in the lab, but with the human body’s countless other metabolic processes, products may not reach the concentration required for the intended purpose
  • The dosage required is too much for an average person to consume – and even if possible (from concentrated supplements), this often affects other metabolic functions


Supplements may, of course, be the icing on the cake if overall nutrition is otherwise adequate, however this is rarely the case. Coping with cancer is an overwhelming time, so if patients were to focus on any nutrient at all, it should be the most impactful one(s). 

3. The Most Impactful Nutrition: Adequate Calories and Protein

The above points may seem distressing to some, as they are basically saying the popular dietary routes are ineffective. However, patients can take heart in the knowledge that the most important nutrition already exists in their daily diet, and does not require the purchase of special products. 


All body tissues contain protein and require protein for maintenance. Already a crucial nutrient in healthy individuals, this becomes doubly important for cancer patients. Adequate protein helps to: 

  • Maintain the immune system, thus reducing other infections 

  • Improve outcomes such as reducing recovery time and length of stay (in hospital)

  • Maintain physical functionality and mobility (like walking, dressing and eating independently) by preserving muscle 


It is one of the most researched and proven nutrition recommendations for cancer patients, yet most people are not aware of how much protein they require, and it is often overlooked in cancer nutrition. Requirements differ from person to person, but below is an example of how requirements increase significantly once disease sets in.

A prime example of why most people should be eating more instead of less when they are ill. No evidence exists to support any form of restriction during cancer, especially not so for high-protein foods. 


Calories come from carbohydrate, protein and fat – these are known as macronutrients. Adequate calories are also required for maintenance of muscle, tissue and overall strength. 

Carbohydrates tend to be demonised as “feeding cancer” and “causing weight gain”, among other claims. Patients can be reassured, however, that there is no benefit to restricting carbohydrates, and that they should in fact continue with standard portions of carbohydrate foods.

While true that cancer cells feed on sugar (which comes from digested carbohydrate foods), one should remember that all cells, including the good cells, feed on sugar. Restricting carbohydrates does more harm than good as the body is deprived of up to 50% of its required energy. 

Fat (the solid form) and oil (liquid form) is the last macronutrient, and a golden opportunity for cancer patients to boost their calorie intake. As it is high in calories and can be added to almost any dish, it can truly be a valuable tool in food preparation.

Unfortunately, most are under the impression that the diet should be as fat-free as possible, unwittingly depriving themselves or their loved ones of crucial energy. All types of fat and oil are equal in calories, but those who need to watch their cholesterol can choose unsaturated sources such as canola, peanut, olive or sunflower oil.

Top Tips

Dealing with nutrition for cancer is unique to each individual; different cancers may take different pathways and each person has a different background, food preferences and requirements. In addition, potential interactions with other medications and medical conditions have to be considered instead of following generic advice. 

The most common nutrition efforts are often to the detriment of the patient. To effectively optimise nutrition, the best course of action is to see a dietitian experienced in cancer management.