It has been widely proven that there is a correlation between weight and cancer. Being overweight increases the cancer risk 52-62% compared to people with a healthy weight because excess body fat causes an increase in hormones that promote tumor growth. This result begs the question- is there a link between diet and cancer?
Unfortunately, the search for an answer has led to an overabundance of pseudo-scientific claims that profess diet-based preventative measures for cancer. These range from fasting (the thought being that if you starve, the cancer cells starve) to living on a diet rich in flaxseed oil mixed with cottage cheese. However, the evidence to support these claims is dubious.
These erroneous studies arise due to the simple fact that cancer is a complicated disease. It has existed as long as humans have, the earliest documentation of it being around 3000 BC. Although a lot of progress has been made in understanding the causes of cancer, there are several aspects that remain elusive. For instance, the interplay between diet and cancer.
There is conclusive evidence that certain foods increase the incidence of cancer. For example, processed red meat contains both artificial and natural chemicals that have been linked with increased cancer risk. The natural chemicals include heme, a red pigment responsible for the color of blood. When heme is broken down in the digestive system, the chemicals released serve as irritants in the body. The most common artificial chemicals associated with cancer are preservatives. As with all food, the ingested amount matters. For every 100 g/day increase in processed red meat consumption, there is a 14% increase in the risk of developing colorectal cancer. Furthermore, cooking techniques such as grilling or barbecuing, which char meat, can also release cancer-causing chemicals or carcinogens, such as heterocyclic amines and polycyclic aromatic hydrocarbons.
Foods high in sugar can also be a threat. The magnitude of danger is based on the glycemic index, which measures how quickly foods release sugar into the blood. Foods with a high glycemic index, including sugar-sweetened soft drinks, fruit juices, and processed food, are associated with an increased risk. However, foods with a low glycemic index, such as beans, lentils, and peas, are associated with a lower risk of cancer.
Many foods are good for your overall health, but cannot conclusively be linked to a reduction in cancer risk. The list includes calcium and vitamin D-rich foods, which are good for the bones, garlic, tea, and whole grain cereals such as barley and oats. However, the evidence remains ambiguous either because of contradictory studies or because these foods show no discernible effect when a large population of people is monitored.
On the bright side, the old adage about eating your veggies seems to apply even to cancer prevention. Although the anti-cancer activity of carotenoids themselves is unclear, a study published in April 2018 showed that a diet with high-fruit and high-vegetable content nourishes the microbes in the gut, causing them to transport more nutrients, which may help fight cancer, to the human host. Cruciferous vegetables, including broccoli, brussels sprouts, cabbage, cauliflower, and turnips, also show anticancer effects to varying degrees. It has been hypothesized that glucosinolates, the compounds responsible for the bitter flavor of these vegetables, are broken down during digestion to form indoles and thiocyanates, both of which have been studied for their anticancer effects.
Dissecting the association between diet and cancer remains difficult for several reasons. Each class of cancer is unique. Consequently, studies usually focus on one type of cancer. This is a problem because there may be a small effect of a particular food on lung cancer, for example. However, a different study that looks at the same food group on rectal cancer may yield contradictory results. Thus the preventative effects of one cancer type are not necessarily the same for others.
Population studies have the benefit of reducing bias due to the sheer number of participants. However, the process of conducting studies on human subject is complicated. Usually, observational studies are carried out, where there is no attempt to change the diet in the population. Interpreting these studies can be difficult as most people cannot precisely recall what they have eaten, meaning self-reported data may not be completely accurate. Because of this, cancer studies favor using mouse models. Although these models can give us some insights, using mouse-based studies alone is not sufficient because their metabolic processes differ from humans. However, using a combination of mouse models and population studies might make it possible to better understand the correlation between diet and cancer. Additionally, using tightly controlled, randomized trials where one population is fed with one food group whereas that food group is excluded from the diet of the second population may give better insights.
Although there are several contradictory studies, there is one indisputable conclusion: Eating healthy matters. It is important to maintain a healthy lifestyle, reduce the intake of processed food, follow proper cooking times, and increase the intake of fresh fruits and vegetables.
Domingo, J. L., & Nadal, M. (2017). Carcinogenicity of consumption of red meat and processed meat: A review of scientific news since the IARC decision. Food Chem Toxicol, 105, 256-261. doi: 10.1016/j.fct.2017.04.028
Hajdu, S. I. (2011). A note from history: landmarks in history of cancer, part 1. Cancer, 117(5), 1097-1102. doi: 10.1002/cncr.25553
Cross, A. J., & Sinha, R. (2004). Meat-related mutagens/carcinogens in the etiology of colorectal cancer. Environ Mol Mutagen, 44(1), 44-55. doi: 10.1002/em.20030
Gallicchio, L., Boyd, K., Matanoski, G., Tao, X. G., Chen, L., Lam, T. K., . . . Alberg, A. J. (2008). Carotenoids and the risk of developing lung cancer: a systematic review. Am J Clin Nutr, 88(2), 372-383. doi: 10.1093/ajcn/88.2.372
Djuric Z., Bassis C.M., Plegue M.A., Ren J., Chan R., Sidahmed E., Turgeon D.K., Ruffin M. T., Kato I., Sen A. (2018) Colonic Mucosal Bacteria Are Associated with Inter-Individual Variability in Serum Carotenoid Concentrations. Journal of the Academy of Nutrition and Dietetics. Doi: https://doi.org/10.1016/j.jand.2017.09.013
Good Food Display – NCI Visuals Online