Diet and Cancer

Reading time: 5 minutes

Emily Bonacquisti

With celebrity endorsements, social media, and your local personal trainers promoting the latest fad-diet, you’re probably hesitant to believe that any diet can do little more than shed the winter weight. However, behind the social media posts, there does exist significant amounts of science behind studying all types of diets and their role in disease prevention. This article will present the current science behind cancer prevention and occurrence of individuals following the Mediterranean, ketogenic, and vegetarian/vegan diet.

Current views on diet changes for cancer prevention

The World Cancer Research Fund has come to a consensus that 3-4 million cancer cases could be avoided or at least postponed by changing lifestyle habits. While 5-10% of cancers result from a genetic predisposition, the remaining 90-95% of cases are thought to be caused by an unfavorable environment. 35% of cancers of all cancers have been linked to dietary intake. While this might be a strong enough indication that changing what environment you put yourself in externally and internally (a change in diet), the types of food you should gravitate towards or avoid are not clear cut. The standard American diet, otherwise known as the Western dietary pattern, is known to contain high amounts of sugar and processed red meats, and this diet has been extensively linked to increase cancer risk. Because information about diet tends to be overblown or sometimes completely fabricated, we’re going to give you an unbiased summary of some of the most recent research done by top professionals studying different types of diet and their correlation to cancer.

Mediterranean Diet

The mediterranean diet places a strong emphasis on a relatively high consumption of olive oil, legumes, fruits, vegetables, and fish. This diet also places an emphasis on consuming low levels of non-fish meat products, and moderate dairy and wine consumption. The mediterranean diet is recommended in the US dietary guidelines as of 2015. 

A large-scale analysis of 83 studies, encompassing over 2.3 million patients worldwide across 14 different cancer types, was conducted by the Department of Epidemiology at the German Institute of Human Nutrition. Cancer risk and overall survival after diagnosis was analyzed against whether or not the patients followed a Mediterranean diet. This meta-analysis concluded that for cancers of tissues where food typically interacts, mainly gastrointestinal cancers, were less prevalent in individuals who maintained a Mediterranean diet. Risk of contracting breast, prostate, colorectal, and head and neck cancers also decreased with adherence to a Mediterranean diet, which was a new finding by these authors. However, they also concluded that if someone already has been diagnosed with cancer, the Mediterranean diet doesn’t significantly impact survival.

Ketogenic Diet

The ketogenic diet (KD) emphasizes a low intake of carbohydrates, a moderate intake of protein, and a high intake of fat. This diet has a 4:1 ratio of fat to proteins and carbohydrates, which effectively eliminates high-carbohydrate foods such as starchy fruits and vegetables, as well as pasta, bread, sugar, and grains. The KD was designed initially to treat pediatric epilepsy before effective anticonvulsant agents were readily available. 

The KD has also been adapted for cancer patients, as cancer cells rely on high levels of glucose (sugar) to keep up with their rapid division. The KD is thought to be beneficial as it mimics sugar starvation and produces ketone bodies, which cannot be processed by cancer cells. Clinical trials as of 2017 studying whether the KD can prevent cancer have not been successful, providing no information for agencies like the Food and Drug Administration (FDA) to give to the public. Medical professionals have advised against KD in the cases of patients with cachexia, or wasting syndrome, as they often cannot afford to lose any more weight. Cachexia occurs between 30-80% of cancer patients, so the KD will never be universally beneficial and should be thoroughly discussed with a doctor. 72% of pre-clinical data from studies conducted on mice and rats have shown some indication that the KD can prevent the growth of many different types of cancers.

As far as whether or not the KD prevents cancer overall, no long term studies have been conducted.

Vegan and Vegetarian Diet

The vegan diet abstains from all animal products, where vegetarians come in many different forms. The most common types of vegetarian diets are ovo-lacto and lacto-vegetarians, where the former eats eggs and dairy products, and the latter eats dairy but not eggs. These diets are centered around fruits, vegetables, legumes, and grains, and ideally avoiding processed foods.

Of the three diets mentioned in this article, vegan and vegetarian diets have arguably the most convincing evidence for cancer prevention. The World Cancer Research Foundation has curated substantial evidence that eating processed and red meat is associated with an increased risk of esophageal, lung, pancreatic, endometrial, prostate, breast, bladder, and oral cancer. Clinical studies across 38 countries have concluded that plant-based diets show no correlation to cancer mortality, in particular with breast cancer. Meat-free diets have been found to reduce overall cancer risk between 10-12%, but evidence for protection from specific cancers have not yet been studied. A 15-year study from Oxford studied meat eaters, pescatarians, and vegetarians, and vegans, all of whom regularly exercised, and found that the pescatarians and vegetarians were diagnosed with cancer 12-18% less frequently than the meat-eating group, and too few cancers were detected in vegans to be informative. In a separate meta-analysis, 18 human studies of vegetarian and veganism saw an 8% and 15% reduced risk of cancer, respectively.

While the benefits of this diet seems moderate, the risk of other chronic disease, heart disease, and obesity-related conditions also decreases dramatically. It was only recently when scientists began to link vegetarian and vegan diets with a decreased incidence of cancer, due to the rising popularity of this lifestyle choice.

Overall conclusions:

It’s very easy to get swept away reading headlines proclaiming “X diet prevents cancer”, but one of the most prevalent indicators of “bad science” are nonsensical headlines writing checks their data can’t catch. This article was designed as a quick reference to some dietary changes you might be considering for a healthier, happier life. The main conclusion: eat your fruits and vegetables, people!

Edited by Sara Musetti

Works Discussed

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https://en.wikipedia.org/wiki/Mediterranean_diet

https://en.wikipedia.org/wiki/Ketogenic_diet

https://en.wikipedia.org/wiki/Vegetarianism

Header Image: https://commons.wikimedia.org/wiki/File:Diet_(16866248345).jpg