Diet to Prevent Cancer

There are an estimated 13 million new cases of cancer annually and 8 million deaths worldwide. Many of these cases, unfortunately, are due to currently preventable tumors.

Prevention of cancer deaths can be done either by diagnosing the tumor in very early stages, allowing intervention before the cancer develops, or by modifying environmental factors or living habits that increase the risk of cancer, such as smoking, poor nutrition and excessive sun exposure.

Cancer risk factors
Cancer risk factors

Cancer prevention

Much of our current knowledge about cancer prevention comes from observational epidemiological studies, which are those that after years of observation try to find relationships between different lifestyle habits and different types of environmental exposures with the onset of specific cancers.

We know today that about 50% of cancers can be prevented. Through studies, we have identified some modifiable risk factors, which account for up to 1/3 of all cancer deaths worldwide. Are they:
  • Smoking
  • Excessive consumption of alcohol
  • Diet rich in red meats and fats
  • Overweight
  • Sedentary lifestyle
  • Unprotected sex
  • Urban air pollution
  • Exposure to combustion of solid fuels, mainly wood and coal
  • Excessive solar exposure

In this first part of the article we will specifically talk about the main risk factors of cancer related to food, explaining what types of measures are scientifically proven to reduce the chance of having a malignant tumor.

Relationship between diet and cancer

The relationship between diet and cancer has been extensively studied over the last few years. Unfortunately, the results have not been conclusive, with much disagreement between the different studies. It is currently agreed that a balanced, low-fat, high-fiber, fruit and vegetable diet lowers the risk of various types of cancer, but the actual effect seems to be less relevant than previously thought. In addition, it was not possible to individualize any food of the so-called healthy diet that is responsible for this protective effect. When thinking about cancer prevention, it seems to be more important to have a healthy diet that allows the individual to maintain an ideal weight, than to look for individual foods that may have some protective effect.

This text aims to inform what is currently a consensus in the scientific environment. There is a lot of distorted information about the actions of certain foods in relation to the incidence of cancer. This is mainly because of the difficulty some people have in interpreting scientific studies. Often, studies with flaws in their design are treated as fully valid, providing wrong results that can never be duplicated by other works. There is also an industry of food supplements that benefits from false advertising over vitamins and other nutrients supposedly protective against cancer.

This first part of the text can be a little frustrating if you are looking for special food tips that might lower your risk of getting cancer. Contrary to all the propaganda that appears in the media, it does not seem that this is how things work.

1. Fats

Fat-rich diets are a proven risk factor for cardiovascular disease, obesity, diabetes, and hypertension. However, its direct relationship with cancer has not yet been fully elucidated. We know that obesity raises the risk of several cancers (I'll explain in the second part of the text), so indirectly, a high-fat diet can be considered a risk factor. However, when you eliminate the obesity factor, studies can not prove the direct relationship of a high-fat diet with cancer, including colon cancer or breast cancer. The only tumor that showed a positive and direct relationship with fat intake was prostate cancer.

While total fat intake directly does not appear to significantly affect cancer risk, we are still uncertain whether certain types of fat (saturated, unsaturated, or trans fats) affect risk differently, and whether fat intake in childhood or adolescence carries a greater risk than intake during adult life. These are questions still under study.

In recent years, consumption of omega-3, a type of healthy fat found in cold-water fish and vegetable oils, has been fashionable, mainly because of its protective effect on cardiovascular disease. However, recent studies have concluded that omega-3 consumption does not provide protection against at least 11 different cancers studied.

In summary, the current consensus for cancer prevention indicates that avoiding an overfat diet, especially to avoid gaining weight beyond desirable.

2. Red meat

Red meat is one of the few proven villains of the diet in relation to cancer. The frequent ingestion of red meat, including beef, pork, veal and lamb, has been shown to be associated with a higher risk of colon and rectum cancer in men and women. Processed meats such as sausages, sausages, bacon, etc. also increase the risk of cancer.

People with high consumption of red meat and low consumption of white meat, have up to 50% more chance of developing cancer. For people who eat red meat or processed meat every day (or most days of the week), every 50 grams of processed red meat or every 100 grams of unprocessed red meat in the diet, there is an increase of 18 % in the risk of developing colon cancer.

It is estimated that annually 50,000 people die worldwide from cancers derived from the consumption of red meat, processed or not. Just as a comparison, cigarette smoking is responsible for 1 million deaths every year, and alcohol consumption per 600,000 deaths.

The current consensus for cancer prevention is that the diet should have more white meat (fish and poultry) than red meat.

3. Vegetables

Although there is a long-standing consensus that high intakes of fruits and vegetables are associated with a significant reduction in cancer incidence, more recent studies have yielded less consistent results. Most studies have found evidence that protection is very weak, only occurring when comparing people with large fruit or vegetable intake with people with no, or almost no, intake of these foods.

The evidence is slightly stronger when one studies the link between prostate cancer and tomato consumption. Several studies have shown a small but statistically significant reduction in the risk of prostate cancer in men with higher intakes of tomatoes and tomato products.

A large study concluded that ingestion of high amounts of soy (20 mg per day of isoflavones) in Asian women is associated with a decreased risk of breast cancer. However, this consumption of soybeans researched is very high, well above what the average Western populations usually consume, which is less than 0.5 mg per day. Probably because of this, studies in Western women have not been conclusive, since even those that consume much soy to the western standard, still fall far short of the Asian diet. The flavonoids found in tomatoes, green peppers, red fruits and citrus fruits have also been associated with a modest decrease in the risk of breast cancer.

The current consensus for cancer prevention indicates regular consumption of large amounts of fruits and vegetables, including soy-based foods.

4. Dairy products

Several studies suggest that the intake of low-fat milk and dairy products may protect against breast cancer, especially in women of childbearing age. In contrast, a large co-analysis of the eight prospective studies comprising mainly postmenopausal women did not find the same result, suggesting that this protective effect may be restricted only to women of childbearing age.

5. Fibers

Regular fiber intake is associated with reduced risk of cardiovascular disease and diabetes, but its effect on reducing the risk of cancer is still uncertain. The results have been discordant among the large epidemiological studies. In recent years, a supposed preventive relationship between fiber consumption and colon and rectum cancer has been widely disseminated, however, studies to date are inconclusive. The most correct is to say that it is possible that fiber consumption has a protective effect against colon cancer, but this theory has not yet been proven.

Vitamins and minerals

In general, the use of vitamin and mineral supplements for cancer prevention has been disappointing. Contrary to what happens in different types of diet, where the studies often present discordant and inconclusive results, in the cases of vitamins and minerals, the results are more uniform, almost always showing no protective effect. For example, two large long-term observational studies, one including more than 160,000 women, with follow-up of about eight years, and the other comprising more than 180,000 participants of various ethnicities with 11 years of follow-up found no evidence of preventive effect with the regular use of multivitamins.

Among the exceptions, we can mention the consumption of calcium. Interestingly, studies have pointed to both a protective effect and a deleterious effect of calcium, depending on the amounts consumed. Currently it is accepted that a consumption of more than 700 mg/day of calcium has a preventive effect on colon and rectum cancer, however, an intake above 2000 mg/day may increase the risk of prostate cancer in men.

Among the vitamins and minerals that do not have scientific evidence to prevent cancer are:
  • Vitamin A
  • Vitamin B
  • Vitamin C
  • Vitamin E
  • Folic acid (except in people with high alcohol consumption where folate appears to have a protective effect)
  • Selenium
  • Iron
  • Betacarotene
  • Zinc

Specific foods

There are thousands of studies on thousands of foods and their effects on cancer prevention. It is impossible to speak of everyone in this text, so I selected some to make brief comments:
  • Coffee: There is no evidence that coffee or caffeine has anything to do with the onset of cancers.
  • Garlic: it is very fashionable today, especially in relation to colon cancer, however, there are no conclusive studies on its protective effect.
  • Onion: same situation of garlic.
  • Sweeteners: There is no evidence that sweeteners, including aspartame, saccharin and sucralose, have any effect on the risk of cancer.
  • Organic foods: it is now widely accepted in the scientific community that organic foods are healthier because they are bred without the addition of pesticides, hormones, antibiotics, or any other unnatural substance. However, for all theoretical reasons, organic food has not yet been shown to decrease the incidence of cancer.
  • Sugar: There is no direct relationship between sugar and cancer risk, but excess carbohydrates can lead to obesity, which is known to be a risk factor for various types of cancer.
  • Green tea and black tea: in animal studies green tea and black tea showed evidence of cancer prevention, but in human studies the results were not similar, and there is no scientific evidence to date that teas play any role in cancer prevention.
  • Pepper: There is no evidence that the consumption of pepper interferes with the risk of cancer.


Regular alcohol consumption is associated with an increased risk of various types of cancer.

A prospective study with more than one million women (mean age 56 years) found that 10 g of alcohol (one drink) per day increases the risk for cancers of the oropharynx, esophagus, larynx, rectum, liver and breast. Alcohol also appears to potentiate the risk of cancer of the respiratory tract of smokers.

It is also worth noting that alcoholic cirrhosis is a major risk factor for the development of liver cancer.

For reasons still unclear, moderate alcohol consumption has been associated with a decreased risk of kidney cancer.

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