Cancer and diet: Dispelling the myths

Many of the myths about cancer become obvious once one has a clear understanding of what this collection of diseases represents. Cancer is not a single disease. Cancer cells are ultimately normal cells in which mutations have caused dysregulation. Such dysregulation can lead to production of unusual substances but, more worryingly, can also cause cancerous cells to grow and spread uncontrollably to other tissues with fatal consequences.  Cancer cells are therefore almost identical to the normal cells from which they originate. This fact is the main reason that medicine has had such difficulty in identifying treatments which specifically target tumour cells without harming non-cancerous, normal tissues.

Adult cancers arise from multiple sets of multiple mutations, often nurtured by non-genetic environmental factors, and are almost always made up of heterogeneous collections of different cells which must adapt to the environment around them so that they can continue to grow and spread to threaten a person’s life.

We are all born with a basic risk of cancer. For those with inherited mutations, such as BRCA mutation, that risk is greater and cancer is more likely to occur at a younger age. The longer we live, the greater the chance that sufficient mutations may arise to generate cancerous cells, evading the multiple levels of anti-cancer defences that have evolved. 

A cancer does not simply form overnight. Rather it takes years to decades, time during which positive lifestyle behaviours, eg. exercise and screening/early detection, can greatly reduce the chances of the cancer ultimately proving fatal. 

Hence, cancer is much more common as we get older. Engaging in lifestyles or exposure to environments which increase the chances of mutations add to that .

Role of diet in cancer evolution

Our diet provides the basic chemical building blocks for all of the chemistry needed by our cells. The sum of this chemistry is incredibly complex. However, many of the broader principles of this dietary chemistry are now becoming evident as observational (epidemiological) and mechanistic (laboratory) research findings are merged.

The chemistry in our body is very tightly regulated to provide the optimal energy and biochemical environment needed to sustain life (the basic tenet of homeostasis). For example, our bodies need a blood concentration of glucose of approximately 4mmol/L to supply cellular energy demands and we have multiple layers of controlling systems to ensure that level varies very little, despite large loads from digestion or large demands from exercise.  

A basic mixed diet providing recommended levels of essential macro and micronutrients will therefore tend to balance out all of the chemical demands in our bodies and multiple levels of redundancy will overcome short-term changes and challenges. Supplementing this diet will have little, if any, benefit because of these powerful homeostatic mechanisms, most of which are saturable.

However, excess macro-nutrification, especially energy (high calorie nutrients), without compensatory demand (extra exercise) over time can lead to inappropriate energy storage in the body and ultimately obesity through disturbing storage and function in fat (adipocyte) and muscle (myocyte) cells. 

Research in recent decades has proven that these cells have very strong hormonal and regulatory functions, some of which can inhibit, alter or support growth of cancer cells while subtly altering important but hidden aspects of immune function. Taking in excess mutagens in that diet, again over long periods of time, for example, alcohol or meat preservatives which can be rendered mildly carcinogenic in the body, can increase the chances of a cancer occurring, especially in tissues in direct contact with these substances.  

In addition recently, strong associations between some cancers, such as bowel, and elements of the microbiome have also been described. Although this relationship is complex and not yet fully dissected, it is clear that diet plays a significant role in the breadth and constitution of that microbiome, providing for an additional level of dietary contribution to cancer risk, especially bowel cancer risk.

Taken together, these facts indicate that our diet can do relatively little to reduce a baseline risk of cancer, but a poor diet (excess calories, and/or rich in high concentrations of pro-mutagenic substances and poor in protective nutrients or giving insufficient variety to support a varied micrbiome) over a prolonged period of time can increase the risk of certain cancers, especially if not offset by the cancer-reducing benefits of exercise, which both utilises excess calorific nutrients and provides for cancer-reducing myokines from muscle.

Role of diet in cancer treatment

Diet can play a direct and pivotal role in the success of treatment. The complex energy and hormonal environment that a cancer can generate to support its growth can be hugely impactful on normal homeostasis. The majority of patients will, at diagnosis, display often subtle signs of this dysregulation, with sarcopaenia, often hidden by the generally larger body weights of modern humans and cachexia, which will already be more common with the advancing age of most cancer. Research, including that of Irish colleagues, clearly shows that weight loss is a significant and specific independent negative prognostic factor. 

Patients therefore need to maintain adequate nutrition to maximise their likelihood of a successful treatment outcome. Nutrition may be hampered by significant physiological and psychological aspects of the treatment, in combination with the typically older age of many cancer patients. They will often need specialist support as challenges such as taste, swallowing issues and energy balance will play a significant role in treatment toleration and side-effects. 

Elements of the diet, such as furanocoumarins from grapefruit, may also directly impact the pharmacokinetics of cancer drugs with negative consequences. With such multi-layered complexity, it is hardly surprising that the provision of expert dietetic support is increasingly recommended for all patients undergoing cancer treatment.

Role of diet post-treatment

While often effective, modern treatment regimens can take an enormous toll on the body and diet will play a significant physiological and psychological role in recovery. Many of the dietary guidelines already described for reduction of cancer risk will be as, if not more, important in the cancer recovery phase as the body seeks to heal treatment-associated damage and restore or provide additional components for nutrient homeostasis. 

Many patients will seek out advice and support during this time, often describing their recent cancer treatment as providing an impetus to change long-term dietary and lifestyle habits. Some aspects of treatment will tend to generate an increased risk of obesity or bone malabsorption, so support in managing weight and additional nutrient requirements may be relevant for recovery from some malignancies. 

Additionally, recovering cancer patients are at much higher risk of several other illnesses, such as circulatory and cardiovascular disease, so dietary modifications that reduce the likelihood of these conditions may be very important in reducing all-cause mortality, rather than just the risk of cancer recurrence.

Common myths

Superfoods can prevent or treat cancer

When it comes to cancer, there is no such thing as a ‘superfood’. Our dietary needs and cancer risks are best mitigated by an overall mixed, varied and balanced diet which is not unduly burdened by energy intake (so moderation of portion size can be important). 

With cancers taking years to decades to evolve, only overall dietary pattern has been shown to have significance and the dietary pattern recommendations encapsulated in the food pyramid have as much relevance to cancer as to many other illnesses. Related to this, there is also no evidence to support an organic food diet as having any anti-cancer benefits.

Indeed, there are suggestions that additional costs of organic produce may discourage disadvantaged people from accessing appropriate levels of vegetables and fruits. 

Cancer is an ‘acidic disease’ and switching to ‘alkaline’ foods will have an impact on it

The body works very hard to maintain a constant pH environment so only the most radical modifications (IV bicarbonate, for example) will change that pH in the wider body as a whole and such treatments will greatly compromise wider health long before they could possibly impact tumour growth. This is an ill-informed fad and indeed many of the foodstuffs proposed to modify pH are actually quite acidic in composition. 

Specialist diets such as Keto diets, Gerson diets and ‘clean’ eating, juicing etc. will overcome cancer

Several of these myths are particularly pervasive at the minute, particularly due to celebrity endorsements. While each of the claims pertaining to such diets can be comprehensively rebutted taking account of the previous discussion, it should also be pointed out that such diets may also be very harmful to overall health as they may significantly impact nutrient balance, which may impact cardiovascular risk and bone health too. 

Such diets can also be very damaging to those on treatment who may need specialist support in maintaining overall nutritional requirements while evidence-based treatments are allowed focus on the cancer cells.

Sugar feeds cancer

Often citing the concept of the ‘Warburg hypothesis’, proponents of this myth claim that cancers are fed by sugar and eliminating all sources of sugar (carbohydrate) will impact these conditions.

With sugar levels (glucose) being tightly regulated in the body as a vital element of normal cellular functioning, reducing carbohydrate intake will not impact cancer growth but can stimulate gluconeogenesis aggravating sarcopaenia. However, excess intake of sugar, or any energy dense nutrient, will tend to drive an obesogenic environment in the longer term, so reducing energy intake, for example through portion size reduction as part of an overall weight management strategy, is to be recommended.

Such is the prevalence of dietary cancer myths, those involved in treatment and care will typically encounter such myths impacting patients on a daily basis. 

Two case studies (see case studies table) illustrate the practical day-to-day impact of these myths for the patient and their caregivers.

Facts

Cancer is an all too common complex set of cellular disorders which can have devastating consequences. The modern preoccupation with lifestyle matters, fed by an unregulated and often exploitative media, has generated an enormous volume of misinformation and myths, some of which can negatively impact overall health and undermine the enormous strides that medicine has made in improving cancer outcome. 

Professionals must help ensure that the wider community is fully and thoroughly informed of the fact-based relevance of diet for their health.