We know that a healthy diet and good nutrition might contribute in reduction of risk of certain cancers. Diets that are high in plant foods – such as fruit, vegetables, wholegrains and beans – may protect against certain cancers. For example, diets with a high proportion of these fibre-rich foods can protect against bowel cancer. This may be because fibre helps to move food more quickly through the bowel.
While the link between diet, cancer risk and prevention is well-established in some cancers, the impact of a person with cancer’s diet on their outcomes is much less well understood.
To find out more, researchers at the University of Texas MD Anderson Cancer Center in Houston and King’s College London looked at studies that investigated the impact of nutrition on some of the molecular targets that cancer researchers think may play a role in how tumours develop. Their review looked at three aspects of nutrition: the link between fibre intake and the genes in the bacteria in our gut; a type of diet called the ketogenic diet; and fasting and a restricted calorie diet.
Fibre and the gut microbiome
The gut microbiome refers to the genetic makeup of all species contained within the gut. There’s growing interest in whether what we eat or certain dietary supplements can alter the gut microbiome in a way that might have an effect on cancer biomarkers – substances that indicate the presence of cancer in the body. For example, one study suggested a diet predominated by fibre-rich plant-based foods can shift the microbiome to beneficially increase the production of short-chain fatty acids (SCFA), compounds that have been linked to a protective role in colon cancer. Similarly, a diet largely composed of animal foods, including red and processed meats, affects the production of potentially harmful compounds and stomach acids. The researchers say these studies are “exciting” , but call for more studies to address the many unanswered questions about the relationship between fibre, the gut microbiome and cancer.
The ketogenic diet
Most of the cells in our body prefer to use blood sugar, which comes from carbohydrates, as the body’s main source of energy. In the absence of circulating blood sugar from food, we start breaking down stored fat into molecules called ketone bodies. A ketogenic diet causes the body to release ketones into the bloodstream.
We have solid evidence that a ketogenic diet reduces seizures in children, sometimes as effectively as medication. Because of these effects on the brain, questions have been raised about the possible benefits of a ketogenic diet for brain cancers. However, there are no human studies to support recommending a ketogenic to treat these diseases.
There are hypotheses under investigation looking at the ketogenic diet in a brain cancer called glioblastoma multiforme. But the researchers are very cautious about the role of the ketogenic diet in tumour development and emphasise that research is at a very early stage. “It remains unclear whether therapies through diet and/or drugs are sufficiently specific and potent for targeting tumours and what unintended effects there may be on immune function or normal cells,” they write.
Fasting and nutrient restriction
In addition to specific diets, there is now emerging evidence suggesting that nutrient timing and quantity are important in cancer. Studies in animals have shown that fasting – going without nutrition for a period of time – or mimicking the effects of fasting can limit the toxicity of chemotherapy treatment, as well as enhance the anti-cancer effects of white blood cells called T cells, and affect our metabolism in ways that may play a role in cancer development.
Again, scientists stress that more research is needed. “Further exploration of the application of [fasting] in cancer may pave the way for patients to have several dietary intervention options, thus promoting… favorable clinical outcomes,” they write.
The authors conclude that there is scope to learn more about the role of nutrition in cancer and tumour development, because “despite [the] long-appreciated contributions of diet and nutrition to cancer risk, nutrition has historically been neglected” when considering how to manage people with cancer. They call for “targeted research” to find out if these kinds of nutritional changes could fit into precision cancer treatment.
Journal reference: Holly AE, et al. Patient Nutrition: An Overlooked Yet Emerging Variable in the Precision Oncology Equation. Journal of Immunotherapy and Precision Oncology (2020) 3 (3): 108–112. https://doi.org/10.36401/JIPO-20-7
 World Cancer Research Fund https://www.wcrf-uk.org/uk/preventing-cancer/what-can-increase-your-risk-cancer/poor-diet-and-cancer-risk (accessed 31/08/20)