While a cancer diagnosis can be daunting, advancements in screening, early detection, vaccinations, and treatments have significantly improved survival rates. However, prevention remains the most effective strategy for reducing the overall impact of cancer. Lifestyle factors, including diet, play a crucial role in cancer prevention. According to the World Health Organization (WHO), 30-40% of the cancer burden can be attributed to modifiable lifestyle risks such as tobacco smoking, alcohol consumption, a diet low in fruit and vegetables, overweight and obesity, and physical inactivity.
Understanding Cancer Risk Factors
Each individual's cancer risk is influenced by a unique combination of environmental and lifestyle factors. While some risk factors, like genetics, are beyond our control, a significant portion of cancer risk is modifiable. Research suggests that approximately 70% of lifetime cancer risk can be influenced by lifestyle choices, including diet.
The Role of Diet and Nutrition
An overall healthy dietary pattern has the potential to lower cancer risk by 10-20%. The association between diet and cancer incidence varies by cancer sites and also by sex, but the recommended components of a healthy diet are often similar. In 2022, according to the American Cancer Society, research shows that nearly 25% of overall cancer cases could be prevented with diet and nutrition alone.
World Cancer Research Fund/American Institute for Cancer Research Recommendations
The World Cancer Research Fund (WCRF) and the American Institute for Cancer Research (AICR) have developed 10 cancer prevention recommendations on diet and nutrition based on the continuous update project of evidence in cancer research. These recommendations promote a lifestyle encompassing a healthy dietary pattern, regular physical activity, and effective weight management.
Maintaining a Healthy Weight
Maintaining a healthy weight is crucial for cancer prevention. Body Mass Index (BMI) and waist-to-hip ratio (WHR) are useful tools for assessing weight status and associated health risks.
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- BMI: BMI measures one’s weight in relation to height. A BMI between 18.5-25 is classified as normal, 25.1-29.9 overweight, and 30 or higher obese.
- WHR: A waist-to-hip ratio (WHR) measures one’s waist size divided by hip size. The WHO recommends a healthy WHR to be 0.9 or less in men and 0.85 or less in women. People who carry more weight in the belly (apple shape) are at higher risk for cancer and other chronic diseases than those who carry more weight in the hips (pear shape).
Incidence of obesity-related cancers is also rising in young adults.
The Importance of Physical Activity
Physical activity is defined as any movement that uses skeletal muscles and requires more energy than does resting. Regular physical activity is associated with a reduced risk of several cancers.
- A 2009 meta-analysis showed that the most physically active individuals had a 24% lower risk of colon cancer than those who were the least physically active.
- A 2013 meta-analysis showed that the average breast cancer risk reduction associated with physical activity was 12%, and the protective effect was stronger for postmenopausal women. After menopause, women who increase their physical activity may also have a lower risk of breast cancer than women who do not.
Sedentary behaviors, such as spending an extended amount of time sitting, reclining, or lying down, may also increase cancer risk.
Key Dietary Recommendations for Cancer Prevention
1. Embrace a Plant-Based Diet
Plant-based diets are full of fruits, vegetables and legumes, with little or no meat or other animal products. In research studies, vegans, people who don't eat any animal products, including fish, dairy or eggs, appeared to have the lowest rates of cancer of any diet.
Plant-based foods do more than taste delicious. They are full of chemicals compounds, called phytochemicals, that protect the body from damage. Phytochemicals also interrupt processes in the body that encourage cancer production. There are many delicious options in a plant-based diet. Cost can be a factor in selecting a plant-based diet menu, as fresh fruits and vegetables may be more expensive. Good alternatives are frozen fruits and vegetables. They are flash-frozen to preserve nutrients and are less expensive. Canned options are available, as well, for people with a stricter budget.
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Phytochemicals: Phytochemicals offer many benefits. This type of phytochemical protects the body from damage. Cancer develops when DNA in cells are damaged. This causes abnormal cells to divide uncontrollably, which can infiltrate and destroy normal body tissue. Cell damage also can be caused by radiation, viruses and exposure to other chemicals. The body's natural metabolism creates oxidants that can cause cell damage, as well. Antioxidants neutralize these damage processes while protecting and restoring cells.
Carotenoids: These are fat-soluble compounds, which means they need to be accompanied by a fat source to be absorbed. Carotenoids are naturally present in many fruits, grains, oils and vegetables such as carrots, sweet potatoes, squash, spinach, apricots, green peppers and leafy greens. They are highly pigmented, so look for natural foods that are red, orange, yellow and green. Examples of carotenoids include beta carotene, lycopene, and lutein. Many plant-based foods are also high in provitamins called alpha and gamma carotene. When consumed, these vitamins can be converted to vitamin A. This nutrient is important to vision, growth, cell division, reproduction and immunity.
2. Prioritize Whole Grains, Vegetables, Fruit, and Beans
Make whole grains, vegetables, fruit, and pulses (legumes) such as beans and lentils a major part of your daily diet. Vegetables (including beans) and fruits are full of vitamins, minerals, fiber, and other substances that may help prevent cancer. Eating vegetables and fruits may also control weight, since they are low in calories, high in fiber, and have lots of water. Whole grains keep all parts of the original grain, so they have more fiber and nutrients than refined (or processed) grains. These include things such as whole wheat, brown or wild rice, oats, and corn. Studies show that eating whole grains might lower the risk of colorectal cancer.
Consumption of whole grains can reduce the risk of cancer at various anatomic sites. According to the 1997 report produced by the American Institute for Cancer Research and the World Cancer Research Fund, increasing daily consumption of vegetables and fruit from 250g to 400g may lead to 20% fewer cases of cancer worldwide.
3. Limit Alcohol Consumption
There is strong evidence that consumption of alcoholic drinks is a cause of cancers of the mouth, pharynx and larynx, esophagus (squamous cell carcinoma), liver, colorectum, and breast (particularly postmenopause). Every 10 grams of alcohol (as ethanol) consumed per day elevated the risks of these cancers by 4-25%. The evidence shows that alcoholic drinks of all types have a similar impact on cancer risk. Alcohol use is linked to an increased risk of cancer as the third most modifiable lifestyle factor.
Read also: Managing Pancreatic Cancer with Diet
4. Limit "Fast" Foods
Fast foods are readily available convenience foods that tend to be energy-dense and are often consumed in large portions. Most of the evidence on fast foods is from studies looking at burgers, fried chicken, French fries, and high-calorie drinks (containing sugar, such as soda; or unhealthy fats, such as shakes).
5. Limit Red and Processed Meat
Red meat includes all types of muscle meat from a mammal, including beef, veal, pork, lamb, mutton, horse, and goat. Processed meat has been transformed through salting, curing, fermentation, smoking, or other processes to enhance flavor or improve preservation. Although these products are often made from red meat (i.e., ham, salami, bacon, and some sausages such as frankfurters and chorizo), other meats can also be processed (i.e., turkey bacon, chicken sausage, and deli-sliced chicken). Processed meat has been cured, smoked, salted, or fermented to improve or preserve flavor. Examples include bacon, sausage, hot dogs, and deli meats.
Evidence that red and processed meats increase cancer risk has existed for decades, and many health organizations recommend limiting or avoiding these foods. In 2015, the International Agency for Research on Cancer (IARC) classified processed meat as “carcinogenic [cancer-causing] to humans” (Group 1) and red meat as “probably carcinogenic to humans” (Group 2A), based on evidence that they increase the risk for colorectal cancer. It isn’t known if there is a safe level of red or processed meat to eat.
While both red and processed meat were suggested to increase the risk of a number of other cancers, the evidence was most convincing for colorectal cancer. The risk of colorectal cancer increased by 16% with every 50g/day of processed meat intake, and by 12% with every 100g/day of red meat intake. Because meat can be a valuable source of nutrients, in particular protein, iron, zinc, and vitamin B12, the recommendation is to limit rather than completely avoid minimally processed red meat. However, poultry and seafood are generally healthier sources of protein as well as many of these other nutrients.
Consuming moderate amounts of red meat provides a good protein, iron, zinc and vitamin B12 source.
6. Limit Sugar-Sweetened Drinks
There is convincing evidence that sugar-sweetened drinks is a cause of weight gain, overweight, and obesity in both children and adults, especially when consumed frequently or in large portions. Added sugars and other high-calorie sweeteners (such as high-fructose corn syrup) are often used in sugar-sweetened beverages and energy-dense foods (for example, traditional “fast food” or ultra-processed foods (or UPFs). Although research hasn't shown a direct link between eating sugar and cancer risk, eating too much sugar over time can lead to obesity, which is a known risk factor for cancer. Also, research suggests that higher amounts of added sugars can lead to insulin resistance, as well as elevated insulin levels and insulin-like growth factor-I (IGF-I).
7. Increase Fiber Intake
Many plant-based foods are also high in natural fiber. This has been shown to reduce cancer risk and moderate insulin levels. Young women who ate the most fiber-rich diets were 25% less likely to get breast cancer later in life, a study found. Healthy bacteria in the digestive track can ferment fiber and other starches to produce compounds known to help promote normal colon development and reduce inflammation.
Dietary fiber is found in plant foods such as beans, whole grains, fruits, vegetables, nuts, and seeds. Eating these foods may help prevent excess body weight, which can lower the risk of cancer.
8. Choose Whole Grains Over Refined Grains
Instead of sugary soft drinks, sweetened cereals, white bread, pasta and processed foods like pizza, opt for unrefined whole grains like whole wheat or multigrain bread, brown rice, barley, quinoa, bran cereal, oatmeal, and non-starchy vegetables.
All carbohydrates you eat are turned to sugar - it’s the main energy source for your body. But for some carbs, this process takes longer, which gives your body more time to deal with the sugar. This is why brown rice, whole wheat pasta and whole wheat bread are healthier for you. The extra fiber slows down digestion, helps you avoid a sugar spike and makes you feel full for longer.
9. Focus on Food, Not Supplements
Dietary supplements include vitamins, minerals, amino acids, herbs/botanicals, and other ingredients. While dietary supplements can provide some benefit, they also have risks. Dietary supplements are not regulated the same way as medicines are. Eating a diet rich in vegetables, fruits, and other plant foods may lower cancer risk, but there’s little consistent evidence that dietary supplements do the same. Some high-dose supplements containing nutrients such as beta-carotene and vitamins A and E may actually increase the risk of some cancers. Vegetables and fruits contain many different compounds that probably work together to have healthful effects. Some supplements claim to provide the same nutrition as vegetables and fruits, but they usually contain only a small fraction of what whole foods provide. Food is the best source of vitamins, minerals, and other important food components.
10. Be Mindful of Cooking Methods
Cooking meats at very high temperatures can produce cancer-causing compounds called heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs). Additionally, frying foods in oil and butter adds extra unhealthy fats that can raise your risk of obesity and certain cancers.
When cooking vegetables, steam only until tender. This preserves more of the vitamins and minerals. Overcooking vegetables removes many of the vitamins and minerals. Use slow, low temperature cooking methods like baking or roasting.
Additional Tips for Cancer Prevention Through Diet
- Eat the Rainbow: Consume a variety of colorful fruits and vegetables to ensure a wide range of nutrients and phytochemicals.
- Snack Smart: Choose healthy snacks like fruits, vegetables, nuts, and seeds.
- Read Labels: Be mindful of added sugars and processed ingredients in packaged foods.
- Flavor with Herbs and Spices: Use immune-boosting herbs and spices like garlic, ginger, turmeric, basil, and rosemary.
- Wash Produce Thoroughly: Wash all fruits and vegetables before consuming.
- Limit Carcinogen Exposure: Avoid charred or burned foods, and be cautious with microwaving in plastic containers.
- Consider Organic Foods: If concerned about GMOs and pesticides, buy organic or local foods.
Diet and Cancer Survivorship
With improved early detection and availability of more advanced treatment options, people diagnosed with cancer are living much longer. Research on the effects of diet, nutrition, and physical activity on the risk of cancer in cancer survivors is growing, but much more limited than that on risk. Although evidence is not strong enough to reach firm conclusions, there are indications of links between lifestyle factors and cancer survivorship with improved quality of life and longer survival, especially for more common cancers. These recommendations are also helpful for managing or preventing other chronic diseases after a cancer diagnosis.
After treatment, cancer survivors should follow the recommendations for cancer prevention.
The Macrobiotic Diet: An Alternative Approach
The macrobiotic diet is a dietary regimen used to prevent and treat many diseases. In addition to the dietary provisions of macrobiotics, however, other applications of macrobiotic principles-eg, increased emphasis on physical activity; minimized exposure to pesticides, other chemicals, and electromagnetic radiation; and stress reduction- may also be beneficial for cancer prevention. The standard macrobiotic diet avoids foods that include meat and poultry, animal fats (eg, lard and butter), eggs, dairy products, refined sugar, and foods containing artificial sweeteners or other chemical additives. All recommended foods are preferably organically grown and minimally processed.
Given that macrobiotics endorses a diet high in consumption of vegetables and whole grains, a logical assumption is that the practice of macrobiotics should also reduce the risk for cancer. However, few studies specifically suggest macrobiotics as an effective cancer prevention method.
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