Many studies have looked at the role of dietary factors in increasing or reducing the risk of cancer. Most studies have shown that dietary factors are only associated with a change in cancer risk, but not completely responsible for it. To prove association of a dietary factor and cancer is challenging as there are numerous dietary constituents and numerous cancers. Many dietary factors may not act in isolation and it may be their interaction with other dietary, lifestyle and/or genetic factors.

Dietary factors have been thought to contribute to about 30% of cancers in Western countries, making diet second only to tobacco as a preventable cause of cancer. The contribution of diet to cancer risk in developing countries has been considered to be lower, perhaps around 20%.

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What is the role of calories in causing cancer?

The most important impact of diet on the risk of cancer is mediated through body weight. Overweight, obesity, and inactivity are major contributors to cancer risk (visceral obesity). Obesity causes increased estrogen synthesis, insulin resistance. And altered adipokine and cytokine production. These factors cause increased angiogenesis, cell proliferation and survival, predisposing to various types of cancer.

Cancers most commonly caused are colorectal cancer, postmenopausal breast cancer, uterine cancer, pancreatic cancer, and gallbladder cancer.

How does alcohol increase the risk of cancer?

Besides body weight, alcohol consumption is the best-established dietary risk factor for cancer. If alcohol is consumed, it should be done in moderation. Moderate alcohol consumption refers to 2 drinks per day in men and 1 drink per day in women. Heavy alcohol consumption is 5 or more drinks any day or 15 or more drinks in a week for men, and 4 or more drinks any day or 8 or more drinks in a week for women. The risk of alcohol associated cancers increase with the duration and amount of alcohol intake.

Cancers predisposed with alcohol intake are breast, liver, esophagus, pharynx, oral cavity, larynx, and rectum.

Watch this video to understand harmful affects of alcohol.

What is the role of dietary fat in causing cancer?

  • Dietary fat and breast cancer – High dietary fat gets converted to heterocyclic aromatic hydrocarbons that can cause breast cancer. Also, increased obesity may lead to excessive production of estrogen that is carcinogenic for breast tissue. On the other hand, there is an inverse association between monounsaturated fat (eg. Olive oil) and breast cancer.
  • Dietary fat and colon cancer – High dietary fat causes increased excretion of bile acids which causes ROS mediated DNA damage. Also, heterocyclic aromatic hydrocarbons produced from fat, heme iron in meat and anabolic hormones used for meat production may promote carcinogenesis.
  • Dietary fat and prostate cancer – Animal fat strongly associated with the incidence of aggressive prostate cancer, and may cause the transition from indolent form to the more lethal form of this malignancy.

To summarize, High intake of animal fat early in adult life may increase the risk of premenopausal breast cancer, increased risk of colorectal cancer. And prostate cancer, particularly the aggressive forms.

Is a diet deficient in fruits and vegetables risk factor for cancer?

Although fruits and vegetables supply less than 5% of total energy intake, the concentration of micronutrients in these foods is greater than in most others. They are rich in Antioxidants, Minerals, Fiber, Potassium, Carotenoids, Vitamin C, Folate and other vitamins.

Consumption of fruits and vegetables appears to be less important in cancer prevention than previously assumed. With fortification of breakfast cereal, flour, and other staple foods, the frequent consumption of fruits and vegetables has become less essential for cancer prevention. Though, a high consumption of fruits and vegetables during childhood and adolescence could be more effective in reducing cancer risk than consumption in adult life due to the long latency of cancer manifestation.

Related video: Top 10 healthiest vegetarian food

What is the protective role of carotenoids and lycopene?

Carotenoids are antioxidants prevalent in fruits and vegetables. They enhance cell-to-cell communication, promote cell differentiation, and modulate immune response. But studies have not revealed evidence of a protective effect of beta-carotene.

Lycopene is a carotenoid mainly found in tomatoes and has antioxidant properties. Frequent consumption of tomato-based products may be associated with a decreased risk of prostate, lung, and stomach cancers.

How effective are soy products and nuts in cancer prevention?

Soybeans contain isoflavones, phyto¬estrogens that compete with estrogen for the estrogen receptor. In Asian countries, which have a high consumption of soy foods, breast cancer rates have been low. Soy consumption may affect estrogen concentrations differently depending on the endogenous baseline level.

Studies have shown that there is a modest decrease in the risk of breast cancer with soy consumption, with childhood consumption being more effective. In a recent meta-analysis of 18 epidemiologic studies, including over 9,000 breast cancer cases, frequent soy intake was associated with a modest decrease in risk (odds ratio = 0.86; 95% CI, 0.75 to 0.99). Wu et al. observed that childhood intake of soy was more relevant to breast cancer prevention than adult consumption.

Nuts are rich in unsaturated fatty acids, high-quality protein, Fiber, vitamins (e.g., folate, niacin, and vitamin E), minerals (e.g., potassium, calcium, and magnesium), and phytochemicals (e.g., carotenoids, flavonoids, and phytosterols). They have anticarcinogenic, antiinflammatory, and antioxidant properties.

Studies have shown their consumption to reduce the mortality with breast and pancreatic cancer. In two large, independent cohorts of nurses and other health professionals, the frequency of nut consumption was inversely associated with total and cause-specific mortality, independently of other predictors of death for breast cancer and pancreatic cancer.

What is the role of dietary fibre?

Dietary fiber contains plant polysaccharides and lignin which are resistant to hydrolysis by the digestive enzymes. They have the following effects-

  • “Bulking” effect, which reduces colonic transit time
  • Binding of potentially carcinogenic luminal chemicals.
  • Fiber may also aid in producing short-chain fatty acids that may be directly anticarcinogenic
  • Fiber may induce apoptosis.

But studies till date do not indicate an important role for dietary fiber in the prevention of cancer.

Role of Vitamin D

Other Factors

In cancers of the oral cavity, pharynx and esophagus, dietary factors that may be protective are fruits and vegetables, micronutrients like riboflavin, folate, vitamin C and zinc. Consuming drinks and beverages at high temperature may be causative.

Nasopharyngeal cancer particularly common in Southeast Asia is associated with a high intake of Chinese style salted fish, especially during early childhood. Chinese-style salted fish is a special product which is usually softened by partial decomposition before or during salting.

Ingestion of foods contaminated with the mycotoxin aflatoxin is an important risk factor for Hepatocellular carcinoma.

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