Healthy diet following cancer treatment

I am very grateful for the opportunity to write an article on a subject that is extremely close to my heart. I hope I will be able to convince you that a healthful life is a choice open to all of us if only we allow ourselves the opportunity to understand the fundamentals of nutrition. In many aspects of our lives we often feel a lack of control. As a patient, you have had to relinquish control over treatment choices to health professionals. However, in one aspect of our lives, in my opinion the most important, we have ultimate control; that is what we put into our body. What we eat and drink is directly related to our health and sense of wellbeing.

I am a Consultant Haematologist at King’s College Hospital, London. I specialise in looking after patients with lymphoma, a cancer of the lymphatic system. Over the last 4 years I have educated myself in the field of nutrition. This has been a personal journey for me, mainly arising from an ethical choice to live a vegan lifestyle, that is, to eliminate the unnecessary use of animals for food, clothing or any other purpose as far as possible and practicable. Veganism is an ethical position, rather than a diet per se. You can be a very unhealthy vegan by living off chips and crisps. However, what I have learnt is that the most healthful diet is a vegan one; that is a whole-food plant-based (WFPB) diet. Is being vegan a conflict of interest or does it make me biased? I don’t believe so. The weight of current scientific evidence supports a predominantly plant-based diet for optimal health.

This article is mainly aimed at those of you who have completed cancer treatment and looking to optimise your physical and mental health. What many patients find surprising and difficult to accept is that once treatment is completed or at least the most intensive part, haematologists give very little advice on how to maintain good health. In certain academic institutions around the world, patients with cancer are provided with information on how to maintain a healthy lifestyle; that is an ‘after cancer care’ programme. These programmes focus on maintaining physical health through diet and exercise and mental wellbeing through focus on techniques such as mindfulness, yoga and meditation.

What is a healthful diet?
One of the most common questions I get asked by patients diagnosed with cancer is ‘what should I eat? I truly believe I know the answer to this question, having made it a focus of research for my own benefit. However, it will perhaps surprise you to know that most doctors have very little knowledge of nutrition. Most medical schools provide minimal if any education in nutrition science. The focus of undergraduate and postgraduate medical education is the treatment of disease, not the maintenance of good health. For most of us, what we consider a healthful diet is influenced by our cultural background, our upbringing and our exposure to mainstream media. When it comes to nutrition in the media, my opinion is that the aim is to keep the public in a permanent state of confusion so that we can be sucked into the hype over the latest ‘fad’ diet. In addition, the meat and dairy industry spend millions of pounds a year on advertising aimed at persuading us to eat animal products. However, there is no such corporate budget assigned to promoting fruit and vegetables. So, depending which doctor or haematologist you ask, you will likely get a different answer. If a patient asks me, I tell them that a WFPB diet is the most healthful and this statement is backed up by numerous scientific studies.

Lifestyle-related diseases
For those of you that have completed treatment with chemotherapy and/or radiotherapy, we know that medium to long term side effects of these treatments are heart disease and second cancers. These diseases are also of concern to our family and friends as they are amongst some of the biggest killers in high-income countries and in part related to lifestyle choices. In fact around the world, lifestyle-related diseases account for more than 50% of all causes of death, with diet-related diseases forming a large part.

A major manifestation of lifestyle-related disease is obesity and we are in the midst of a worldwide epidemic. Obesity is a direct consequence of poor nutrition and leads to an increased incidence of other lifestyle-related diseases such as diabetes, heart disease and cancer. However, you don’t have to be obese to be at risk of these lifestyle-related diseases because it is not the subcutaneous (under the skin) fat that is directly related to disease, but the visceral (organ) fat in places such as the liver and heart, that increase our risk. I am sure we can all think of people we know that are of normal weight but have diabetes or heart disease. Such individuals are sometimes called TOFI; thin on the outside, fat on the inside. This abnormal deposition of fat in the organs is directly related to our diet. Studies that have followed large populations over time have shown that those eating a predominately plant-based the diet are more likely to be a healthful weight than those following a meat-based, omnivorous diet. In addition, plant-based diets are the most effective for sustained weight loss.

What do we know about the impact of nutrition on health?
I accept that the scientific literature can at times be confusing, partly because many nutrition studies have been conducted by those that have a vested interest in the results; the dairy, meat and egg industry. When interpreting scientific data in the field of nutrition you need to make note of who is funding/sponsoring the study before interpreting the findings. There are now irrefutable scientific data supporting the role of a WFPB diet in the prevention and reversal of lifestyle-related diseases, including but not exclusively heart disease, diabetes and cancer.

There have been several, large epidemiological studies (study of causes and effects of disease in populations) involving hundreds and thousands of people that have studied the impact of diet on health and disease. They have all shown the same results. A diet high in animal foods (meat, dairy and eggs) is associated with a higher incidence and risk of death from diseases such as heart disease, diabetes and certain cancers. In contrast, a diet high in whole plant foods is associated with a reduced incidence and risk of death from the same diseases. When you combine the results of all these studies, a plant-based diet reduces the risk of heart disease by 30% and cancer by 19%.

A well-studied group of people are the Seventh Day Adventists. By virtue of their religious beliefs they are vegetarian or vegan, they don’t smoke tobacco and mostly abstain from drinking alcohol. When compared to groups of individuals eating a standard Western diet high in animal foods, they have a significantly lower incidence of heart disease, diabetes and cancer and live longer.

Not only do we know that the chances of getting various diseases can be reduced by your diet choice, we also know that diseases can be reversed through changes in diet. Therefore it is never too late to have a positive impact on your health. As long ago as 1995, Dean Ornish, an American physician, and founder of the Preventive Medicine Research Institute in California, USA, showed that when individuals with coronary artery disease were placed on a WFPB diet, he was able to reverse the disease. There was literally regression of the atherosclerotic plaques seen in the coronary arteries. No pharmaceutical medication has ever shown such results, yet the benefits of a WFPB diet are seldom shared with patients. Dr Ornish did a similar study in patients with early stage prostate cancer. Patients were divided into two groups. Those that adopted a plant-based diet (meals delivered to their doors daily!) showed regression of prostate cancer after 1 and 2 years, whereas the group that did not make the diet changes showed progression of prostate cancer over the same time period. Another disease that can be reversed in most people is type II diabetes. Several studies have now shown that if you adopt a WFPB you can reverse diabetes.

Aren’t some diseases genetic?
Of course there is some influence of your genes in determining what diseases you get. However, the impact of your genes on disease is at most around 10% and you can still influence your chances of getting a disease, despite have a ‘bad’ gene, through lifestyle choices. Take breast cancer as an example, we know that there is a genetic component to this disease, but at most the breast cancer genes are responsible for less than 5% of these cancers. We know that the chance of developing breast cancer is higher in obese individuals and those that eat a diet high in animal foods. We also know that a healthful diet consisting mainly of plants can positively impact the risk of breast cancer progression. With regards to heart disease, a recent study has shown that even if you have ‘bad’ genes, you can reduce your risk of heart disease by 50% by adopting a healthy lifestyle, specifically being a healthy weight, not smoking, eating a healthy diet and doing some physical activity. More evidence that lifestyle choices trump genetics.

What about haematological cancers?
Although blood cancers are not specifically related to lifestyle, studies have shown that there is a higher incidence of blood cancers in obese individuals and those that consume the most animal products, particularly chicken and eggs. The reverse is also true, that is, the incidence of blood cancers is lower in populations that consume a predominantly plant-based diet. This fact should make us curious about the potential positive impact of a healthful diet on blood cancers.

Why are animal foods so bad for our health?
There are a multitude of reasons, too many to cover in a short article. Take dairy products made from cow’s milk as an example. In nature, cow’s milk is a growth fluid for baby cows allowing them to grow from a 65Ib calf to a 700lb cow as fast as possible. Therefore, this growth fluid contains growth hormones including bovine growth hormone and insulin-like growth factor. In addition, the dairy industry keeps cows pregnant at the same time as milking them and so cow’s milk will also be high in female hormones such as oestrogen. In humans, exposure to these bovine hormones can result in abnormal growth of cells and increase the risk of cancer, especially those cancers that are hormone driven like prostate and breast cancer. These cancers have the highest incidence in populations that consume the most dairy. Alarmingly, bovine leukaemia virus, a cancer-causing virus in cattle, has been found in a large proportion of human breast cancers. You have to ask why no other species on this plant drinks milk after weaning, certainly not the milk of another species.

With regards to meat, one reason for its adverse effect on health is that when animal muscle is heated to high temperatures it forms carcinogens (cancer causing substances), including heterocyclic amines, that have been implicated in cancer development. The iron found in animal foods is also toxic to cells and generates cancer forming substances. In addition, meat is devoid of dietary fibre and has little in the way of vitamins or minerals. You should know that the World Health Organisation has classified processed meat as a class 1 (definite) carcinogen and red meat as a possible carcinogen. Why these foods don’t come with a health warning is surprising. All animal foods are high in saturated fat and cholesterol, with animal foods being the only source of dietary cholesterol. Plant foods do not contain cholesterol. Saturated fats and cholesterol have a negative impact on heart health and increase the risk of certain cancers.

What is a whole-food plant-based?
This is a diet that is made up of vegetables, fruits, whole grains, nuts, seeds, and legumes (beans and lentils). It should also be low in fat (added oil) and salt. Such a diet will be made up of around 80% carbohydrates, 10% fat and 10% protein, a combination that is perfect for optimal health. It is a diet that is naturally high in dietary fibre and micronutrients, including vitamins and minerals. By definition it is a diet that excludes animal foods, and avoids processed foods so will be low in processed/added sugars and saturated fat. On a WFPB you will be able to maintain a healthy body weight without counting calories. Spices and herbs should be liberally included in cooking as they have natural healthful properties including anticancer, anti-inflammatory and antibacterial. The picture below illustrates what I mean by a WFPB diet (with permission from I assure you that this diet will improve both your physical and mental health.

I hope this article has stimulated your interest in finding out what a healthful diet is and how your diet can impact positively on your health. If this is the first time you are reading about a WFPB diet then you will have many questions. I refer you to some excellent sources of information. These sources act as references for all the statements I have made in this article. Happy eating!

Documentary; Forks over Knives, available on Netflix

Books; The China Study, by T. Colin Campbell and Thomas M. Campbell. The latest edition has just been released but an older version is available free on line

How not to die, by Michael Greger

Proteinaholic by Garth Davis

Healthy eating for life, by Neal Barnard

The Complete Idiot’s Guide to Plant-Based Nutrition, by Julieanna Hever


Dr Shireen Kassam