Plant-based Diet and Cancer – where is the evidence?
by Maia Bedson
This is a question often posed, and used as a deterrent, by people with a bias against the prospect of cancer being more than just a chance occurrence, bad luck, a punishment or solely from genetic factors. A bias that repudiates the idea that it is our lifestyle that is more predictive of cancer and influences the outcome. The argument goes that, if there are no Random Controlled Trials (RCT’s) – considered to be the customary, and indisputable standard, then there is no scientific basis to prove that, by changing our diet, we can affect our health outcome, especially when it comes to cancer.
This is a curious concept as it is well established in cardiology that what a patient eats has a direct effect on the function of their heart. Why not in cancer medicine?
An interesting theory referred to as “The Tomato Effect”, appeared in the Journal of the American Medical Association (JAMA) in the 1980’s. This describes the rejection of beneficial therapies and practices by the medical establishment when they go against the orthodoxy of the day. By 1560, the tomato had become a staple of the diet in Europe whereas at that time, and for a couple of centuries later, it was considered poisonous and rejected in North America. It was not until the 1800’s when someone publicly demonstrated surviving the eating of a tomato, that this changed and tomatoes as a commercial crop in the US went on to become a billion-dollar industry.
Another example is scurvy, which caused the death of countless numbers of people, particularly those undertaking extensive sea voyages. It had been proven for over one hundred years that lemons and oranges cured scurvy (due to their vitamin C content) before it was accepted by the medical and scientific community who had rejected the signs as this went against their belief that a mere fruit could not be of benefit in the disease.
And in more recent times, there were over 7000 studies, none of them RCT’s, showing the link between smoking and lung cancer before this was finally accepted. Unfortunately, in the meantime, countless numbers of smokers had already died.
To date, the only RCT on diet and cancer is the Ornish Study which showed that a plant-diet and lifestyle program could reverse the progression of prostate cancer. i
RCT’s in the area of diet and lifestyle are complex and difficult – humans are not laboratory rats or mice that can be bred to be clones, confined and controlled. Nor is there a product to profit from. However, it seems as if the commonly held medical view is that if a study isn’t conducted this way, then it doesn’t count.
A humorous sendup of this view of RCT’s being the only valid data appeared in the British Medical Journal written as a legitimate research study.ii
The stated objectives were:
“To determine whether parachutes are effective in preventing major trauma related to gravitational challenge” via a systematic review of RCT’s.
The results were:
“We were unable to identify any randomised controlled trials of parachute intervention”.
“As with many interventions intended to prevent ill health, the effectiveness of parachutes has not been subjected to rigorous evaluation by using randomised controlled trials. Advocates of evidence-based medicine have criticised the adoption of interventions evaluated by using only observational data. We think that everyone might benefit if the most radical protagonists of evidence based medicine organised and participated in a double blind, randomised, placebo controlled, crossover trial of the parachute”.
This light-hearted parody is highlighting how epidemiological and observational data, and clinical experience have been downgraded to the point of being disregarded.
So, what is some of the good quality data that can be found to show the benefits of this lifestyle medicine approach to cancer?
The World Cancer Research Fund (WCRF) has published a systematic literature review on “The Association between Food, Nutrition and Physical Activity and the Risk of Breast Cancer” analysing the research on cancer prevention and survival (published May 2017) and comprising 2199 pages. It reviewed evidence from 119 studies covering 12 million women and concluded there was strong evidence that a high plant-food diet, regular exercise, low alcohol consumption and maintaining a healthy weight reduced the risk of breast cancer.iii
The World Health Organisation (WHO) stated goal is to build a healthier future for people all over the world and to combat diseases such as cancer.
They publish a fact sheet on a healthy diet that is research-based.iv
Their key facts include eating at least 5 portions of fruits and vegetables per day; reducing the total fat intake to less than 30%; and decreasing salt and sugar intake.
A study published in the Cancer Journal for Clinicians found that “Most cancer incidents and deaths are a result of modifiable lifestyle choices, including diet” and attributed risk factors to include red and processed meat intake and low intake of fruits, vegetables and dietary fibre.”v
In the European Journal of Cancer, researchers reviewed meat consumption and cancer incidence rates for over 262,000 women over a 7-year period. Those who consumed the most processed meats per day (only around 20 grams/day which is less than half the size of a hot dog) increased their risk for breast cancer by 21%. The processed meat in this study was defined as bacon, ham, sausages, meat pies and burgers and chicken nuggets.vi
Another study which analysed the diet and lifestyles of almost a thousand people diagnosed with stage III colon cancer over a period of seven years found that those who followed a diet high in fruits, vegetables and whole grains, and low in red and processed meats had longer overall survival and disease-free survival rates compared with patients who did not meet these parameters.vii
In Spain, researchers have followed more than 4000 people looking at the risk for colorectal cancer in relation to both lifestyle and genetic factors. They found that changes in lifestyle, such as consuming less meat and more vegetables as well as maintaining a healthy weight, influenced cancer risk more than genetics.viii
In the prestigious Journal of the National Cancer Institute, researchers tracked cancer rates for almost 500,000 participants which found that, compared to people born in the 1950s, those born in the 1990s have double and quadruple the risks of colon and rectal cancers, respectively, due to low plant food consumption, high consumption of processed meats and low physical activity. ix
Several studies show that the higher the intake of fruits and vegetables and the lower the intake of meats, the more protected from cancer a person is. An example reported in the International Journal of Epidemiology reviewed 95 studies and concluded that eating just 2.5 serves of fruits and vegetables per day could reduce the risk for not only cancer, heart disease, and stroke but also all-cause mortality by up to 10 percent. However, increasing the consumption of fruits and vegetables to 7.5 serves per day, gave the greatest protection against cancer. This is above the common recommendation of 5 servings per day. x
There have been numerous studies investigating the link between dairy products and prostate and breast cancer. A meta-analysis published in 2016 concluded that: “Dairy products increase the risk of dying from prostate cancer”. Researchers reviewed 11 studies with more than 700,000 participants and found that “Male participants who consumed the most whole milk increased their risk of death from prostate cancer by 50 percent compared with those who consumed the least amount’.xi
An on-going study reported in the Journal of the American Medical Association Internal Medicine found that saturated and trans fats increase the risk of death from cancer. This study monitored the dietary fat intake and mortality for more than 83,000 women and almost 43,000 men and reported that “these findings support recommendations to limit foods high in saturated fat, including animal products in favour of low-fat, plant-based foods.”xii
There are many more studies I could quote linking lifestyle factors, especially diet, to cancer mortality and other diseases which point to the impact that factors such as inflammation, free radical DNA damage, oxidative stress, fibre, saturated fat, gut bacteria, impaired insulin resistance, IGF-1 growth hormone and antioxidant blood levels have on our health but the intelligent question to ask ourselves is – do we wait until more RCTs are published before making lifestyle changes, or do we individualise medicine and conduct a personal research study with the n:1?
Experimenting with a wholefoods, plant diet, in our clinical experience of over 30 years, has only beneficial side effects and may just heal your body.
Let’s open the parachute.
i Ornish D, Weidner G, Fair WR, Marlin R, Pettengill EB, Raisin CJ, Dunn-Emke S, Crutchfield L, Jacobs FN, Barnard RJ, Aronson WJ, McCormac P, McKnight DJ, Fein JD, Dnistrian AM, Weinstein J, Ngo TH, Mendell NR, Carroll PR. Intensive lifestyle changes may affect the progression of prostate cancer. J Urol. 2005 Sep;174(3):1065-9; discussion 1069-70.
ii BMJ 2003; 327 doi: https://doi.org/10.1136/bmj.327.7429.1459 (Published 18 December 2003)Cite this as: BMJ 2003;327:1459
iii, iv, v Islami F, Goding Sauer A, Miller KD, et al. Proportion and number of cancer cases and deaths attributable to potentially modifiable risk factors in the United States. CA Cancer J Clin. November 21, 2017
vi Anderson JJ, Darwis NDM, Mackay DF, et al. Red and processed meat consumption and breast cancer: UK Biobank cohort study and meta-analysis. Eur J Cancer. 2017;90:73-82
vii Van Blarigan E, Fuchs CS, Niedzwiecki D. (2017) American Cancer Society
viii Ibanez-Sanz G, Diez-Villanueva A, Alonso MH, et al. Risk model for colorectal cancer in Spanish population using environmental and genetic factors: results from the MCC-Spain study. Sci Rep 2017
ix Siege lRL, Fedewa SA, Anderson WF, et al. Colorectal cancer incidence patterns in the United States, 1974-2013 J Natl Cancer Inst. Published 2017
x Aune D, Giovannucci E, Boffetta P, et al. Fruit and vegetable intake and the risk of cardiovascular disease, total cancer and all-cause mortality – a systematic review and doseresponse meta-analysis of prospective studies. Int J Epidemiol. 2017
xi Lu W, Chen H, Niu Y, Wu H, Xia D, Wu Y. Dairy products intake and cancer mortality risk: a meta-analysis of 11 population-based cohort studies. Nutr J. 2016;15:91
xii Wang DD, Li Y, Chiuve SE, et al. Association of specific dietary fats with total and cause-specific mortality. JAMA Intern Med. July 2016
Therapist, Facilitator, The Gawler Cancer Foundation & Yarra Valley Living Centre
DipHol Couns, Grad DipCounsHS, Grad DipClinNut
Maia is a counsellor, meditation instructor, a practitioner of various forms of natural therapies who has worked in the area of energetic healing for over 25 years, and has worked at The Gawler Cancer Foundation since 2000. She has a Graduate Diploma in Clinical Nutrition as well as formal qualifications in plant-based nutrition, counselling and psychotherapy. Maia uses her various skills and the experience gained from her own healing to inspire and support others on their path to wholeness and has a particular interest in helping people to access their own inner wisdom.