How Diet and Physical Activity Impact Cancer Risk

Acrylamide is a chemical used in some industrial processes. It’s also found in tobacco smoke and certain foods. In food, acrylamide forms when the amino acid asparagine reacts with sugars at high cooking temperatures, such as frying, baking, or roasting. Common food sources include french fries, potato chips, crackers, bread, cookies, breakfast cereals, canned black olives, prune juice, and coffee.

The International Agency for Research on Cancer (IARC) classifies acrylamide as a “probable carcinogen,” based mostly on animal studies. But research in people has not found clear evidence that eating foods with acrylamide increases the risk of cancer.

Antioxidants are compounds that may help protect against damage to body tissues that constantly occurs as part of normal metabolism. This type of damage has been linked with increased cancer risk.

Antioxidants in the diet include vitamin C, vitamin E, carotenoids (related to vitamin A), and many other food components. Eating lots of fruits and vegetables, which are rich in antioxidants, has been linked to a lower risk for some cancers. But it’s not clear if this benefit comes from their antioxidant content or from other healthy parts of these foods.

Studies of antioxidant supplements have mostly shown little to no benefit in lowering cancer risk. Some studies have found a higher risk of cancer in people taking supplements. The best way to get antioxidants is through eating whole food sources rather than supplements.

Arsenic is a natural element found in rocks, soil, water, air, plants, and animals. It’s also used in some industrial and farming products. The US National Toxicology Program (NTP), IARC, and others classify arsenic as a human carcinogen.

Arsenic is found in two main compounds: 

• Inorganic compounds: Found in contaminated water and some industrial or building products (like “pressure-treated” wood). This form is more toxic and linked to cancer.

• Organic compounds: Found mostly in some foods, such as fish and shellfish. This form is much less toxic and is not thought to be linked to cancer. 

People are exposed to arsenic in many ways. Two of the more common ways related to diet are through: 

• Water: In some areas of the US (Southwest, New England, and Upper Midwest), drinking water may have higher levels of arsenic. Levels also tend to be higher in drinking water that comes from ground sources, such as wells.

• Food: For most people, food is their largest source of arsenic exposure, although much of this is in the less harmful organic form. Seafood, rice, rice products, mushrooms, poultry, and some fruit juices can contain arsenic.

Studies have found that exposure to arsenic in drinking water may cause lung, bladder, and skin cancers. Because arsenic has been linked to cancer and other unwanted health effects, several US government agencies regulate arsenic levels and exposures.

There are several ways you can reduce your potential exposure to arsenic. Be sure to:

• Check your local water quality report if you use public water.
• If you use a private water source, such as a well, have your water tested by a certified lab.
• Consider using bottled water or other safe sources if you live in an area with high arsenic levels. Common household water filters do not effectively remove arsenic.
• Limit foods with higher arsenic levels like seafood, rice and rice products, and fruit juice. When preparing rice, research has shown that you can reduce arsenic levels by washing it and cooking it in lots of water (like you would pasta).
• Getting enough folate (a B vitamin) may also help your body eliminate arsenic.

Researchers have long studied whether coffee affects cancer risk. Overall, evidence suggests that drinking coffee may help lower the risk of several cancers.

Cancers with lower risk: Drinking coffee is linked with a reduced risk of liver and possibly endometrial cancer. It may also lower the risk of cancers of the mouth, throat, voice box, and basal cell skin cancer in both men and women, and possibly melanoma in women, although the evidence is not as strong. 

Hot beverages and cancer: Some studies have shown that drinking very hot beverages (coffee and/or tea) may increase the risk of esophageal cancer. To be safe, it’s best to avoid drinking beverages when they are extremely hot.

Roasted coffee contains hundreds of biologically active compounds, including caffeine, flavonoids, lignans, and other polyphenols. These substances may:

• Protect cells from damage
• Help repair DNA
• Reduce inflammation
• Slow or prevent cancer spread (metastasis)
• Affect digestion and how the liver processes cancer-causing substances

These effects may explain why coffee appears to lower the risk of some digestive cancers.

Genetically modified (GM), or bioengineered, foods are made by adding genes from other plants or organisms. This can make the plant more resistant to insects, spoil more slowly, be easier to transport, or have better flavor or nutrition.

Foods made with GM crops have been sold in the US since the mid-1990s. Today, more than 70% of ultra processed foods (also known as UPFs) in US supermarkets, such as pizza, chips, cookies, ice cream, salad dressing, corn syrup, and baking powder, contain ingredients from bioengineered soy, corn, or canola. Public concerns about GM foods, in part, led to a 2016 federal law requiring clear labeling of foods with GM ingredients.

In theory, added genes could create substances that trigger allergies or raise certain compounds to harmful levels. But so far, there is no evidence that GM foods now on the market are harmful to people, or that they affect cancer risk.

Major health and science organizations – including the World Health Organization (WHO), the American Medical Association, the National Academy of Sciences, Engineering, and Medicine (NASEM), and the American Association for the Advancement of Science – agree that GM foods approved for sale are safe to eat.  

Gluten is a protein found in wheat, rye, and barley. For most people, it causes no problems.

In people with celiac disease, gluten triggers an immune reaction that damages the lining of the small intestine and may increase cancer risk.

Some people without celiac disease report experiencing gluten sensitivity, which may cause intestinal inflammation. This could possibly raise the risk of gastrointestinal cancers, but the evidence is weak.

For the general population, there is little to no evidence that eating gluten increases cancer risk. In fact, research shows that eating whole grains, including those with gluten, likely lowers the risk of colon cancer. Unless you have celiac disease, there’s no evidence that a gluten-free diet lowers cancer risk.

The glycemic index (GI) measures how much a carbohydrate-rich food raises blood sugar compared with pure glucose.

• High-GI foods (like refined grains, sugary foods, and some starchy vegetables) cause blood sugar to rise quickly.
• Low-GI foods release sugar more slowly, leading to a smaller rise in blood sugar.

The glycemic load (GL) takes this a step further by considering both the type of carbohydrate (quality) and the amount eaten (quantity). GL provides a better picture of how much a food actually raises blood sugar.

Research suggests that diets high in GL may increase the risk of endometrial cancer. More studies are needed to understand how the GI and GL affect the risk of other types of cancer.

Food irradiation is a process that uses ionizing radiation to kill germs and insects, helping food stay safe and last longer. It works in a similar way to pasteurizing milk or canning fruits and vegetables.

Irradiation doesn’t make food radioactive, reduce its nutrition, or noticeably change its taste, texture, or appearance. In fact, the changes are so small that most people wouldn’t know if a food has been irradiated.

The US Food and Drug Administration (FDA) has studied irradiated food for more than 30 years and found it to be safe. Other organizations – including the WHO, the US Centers for Disease Control and Prevention (CDC), and the US Department of Agriculture (USDA) – also support its safety. There is currently no evidence that food irradiation causes cancer or harms human health.

Juices can be a convenient way to get some nutrients from vegetables and fruits. In moderation, they can be part of a healthy diet. But juices have less fiber, fewer nutrients, and more natural sugar than whole fruits and vegetables, so they are not the best source of plant-based nutrition.

Some people try juice cleanses or juice detoxification (detox), where they drink only juice for one or more days. These diets are promoted as a way to remove “toxins,” but there is no scientific evidence that they reduce cancer risk or improve health. Your kidneys and liver already remove toxins from the body, whether you eat solid food or drink juice.

While vegetable juices can add nutrients, relying only on juice can leave out important nutrients. In some cases, large amounts of juice can even be harmful, such as raising the risk of kidney problems.

The methods we use to cook, store, and preserve our foods may add or produce chemicals that impact cancer risk.

Ideally, how we cook and store food should:

• Remove or inactivate harmful bacteria or chemicals
• Avoid creating or adding harmful substances
• Keep nutrients intact and available

But research shows that how foods are cooked may impact cancer risk. Cooking meats like red meat, poultry, or fish at very high temperatures by grilling, smoking, or pan-frying can create heterocyclic amines, chemicals that may increase cancer risk. However, microwaves use non-ionizing radiation to cook foods, which does not increase cancer risk.

How foods are preserved may also impact cancer risk. Some ways of preserving red meats add nitrates, which can form cancer-causing N-nitroso compounds in the stomach. However, proper canning or freezing of fruits and vegetables preserves nutrients and expands access to these foods.

Concerns about containers or cookware

Some plastics can release substances such as phthalates (some of which are classified as possible carcinogens) or bisphenol A (BPA, a probable carcinogen) during storage or microwave heating. Teflon-coated pans may release perfluorooctanoic acid (PFOA, a known group 1 carcinogen) when heated. These chemicals can affect biological processes, such as puberty timing, which may influence long-term cancer risk.

For those who want to minimize exposure, using glass or metal storage containers and cookware is a safe alternative.  

Non-nutritive sweeteners (also called sugar substitutes), like sucrose, corn syrup, honey, or agave nectar, are used instead of regular sugars to sweeten foods and drinks. Common FDA-approved sweeteners include aspartame, acesulfame potassium, saccharin, sucralose, and stevia. These sweeteners have few or no calories and are often much sweeter than sugar, so only small amounts are needed.

Other sugar substitutes include sugar alcohols such as sorbitol, xylitol, and mannitol. These pose no health risk to humans but may cause bloating or stomach discomfort if eaten in large amounts.

There has been concern regarding the use of sugar substitutes and a potential link to cancer throughout the years. These first began in the 1980s when early animal studies linked saccharin to bladder cancer. But studies in humans later showed it not to have an increased cancer risk.

In 2023, the IARC classified aspartame as a possible carcinogen, based on limited evidence from studies using higher amounts than people usually eat. More studies are needed to find out how normal amounts of aspartame in the everyday diet affect cancer risk in people. For those who want to avoid or minimize exposure to aspartame, check ingredient labels before buying or eating foods or drinks. If aspartame is found in the product, it will be listed. Also, people with a rare genetic disorder called phenylketonuria (PKU) can’t process aspartame normally and should avoid it to prevent nervous system problems.

The term “organic” is used to refer to foods grown or produced without most artificial chemicals. These include:

• Animal products: Organic meat, milk, and eggs come from animals raised without added hormones or antibiotics.
• Plant foods: Organic fruits and vegetables are grown without most pesticides, herbicides, chemical fertilizers, or sewage sludge.

Organic processing also avoids industrial solvents, irradiation, and GM foods. A main benefit of organic foods is supporting environmentally sustainable farming. While some people think organic foods may be healthier, there is little evidence that they have more nutrients than conventionally grown foods.

Research on organic foods is limited. One study found that eating more organic produce was linked to a lower risk of non-Hodgkin lymphoma, but this needs confirmation. This aligns with evidence that pesticide exposure at work increases risk for this type of cancer.

Tips for all produce: Washing conventionally grown fruits and vegetables can reduce pesticide residue and limit the risk of ingesting harmful microbes.

Because organic produce is often more expensive, it’s important to focus on eating enough vegetables and fruits, organic or not, for cancer prevention and overall health.

Some insecticides and herbicides can be harmful if used improperly in workplaces or on farms. The IARC classifies 3 common agricultural herbicides, glyphosate, malathion, and diazinon, as “probable human carcinogens.” All are linked to a higher risk of non-Hodgkin lymphoma. Malathion is also linked to a higher risk of prostate cancer, and diazinon to lung cancer.

However, eating vegetables and fruits, whether organic or conventionally grown, has clear health benefits and may help protect against cancer. Washing conventionally grown produce can remove some pesticide residues and reduce the risk of harmful microbes.

Soy foods, such as tofu, edamame, and soy milk, can be healthy choices because they provide protein, fiber, healthy fats, and important nutrients like potassium and magnesium. Studies in people show that eating soy either lowers the risk of some cancers or has no effect on cancer risk. Research also shows that soy does not increase breast cancer risk, even for women at higher risk.  

In the past, there was some confusion based on animal studies that suggested soy compounds called isoflavones might promote breast cancer, but humans process these compounds differently, and they do not have the same effect. In fact, isoflavones may help protect against cancer by acting as antioxidants, reducing inflammation, and interacting with estrogen in ways that may prevent breast cancer cell growth. 

Eating soy foods as part of a normal diet is safe and may be beneficial, but taking soy isoflavone supplements is not recommended for cancer prevention. Studies show that soy from food either reduces cancer risk or has no effect, while results from supplements are less clear. More research is needed to understand how soy supplements might affect cancer risk, including for breast cancer. 

Vegetarian diets can have many healthy features:  

• They are usually low in saturated fat.
• They tend to be high in fiber, vitamins, and other beneficial plant compounds.
• They do not include red and processed meats.

Because of these features, vegetarian diets may help reduce cancer risk. Many studies show that vegetarians have a lower overall risk of cancer compared to people who eat meat. But it’s less clear whether vegetarian diets provide extra benefits over diets that include small amounts of animal products, such as fish. For example, a large British study found that people who ate fish but not other meats had a similar cancer risk as vegetarians.

Overall, evidence supports a diet that is mainly plant-based, with limited red and processed meats. Vegetarian diets also help lower the risk of heart disease and type 2 diabetes, and are generally more affordable.

Vegan diets (no animal products, including milk or eggs) require extra attention:

• People may need vitamin B12, zinc, and iron supplements or fortified foods, especially children and premenopausal women.

Adequate calcium is important since low calcium intake can increase the risk of bone fractures. Anyone following a strict vegetarian or vegan diet should talk with their doctor or dietitian about supplements and nutrient needs.