Common Questions About Diet, Activity, and Cancer Risk

These questions and answers are part of the American Cancer Society (ACS) Guideline for Diet and Physical Activity for Cancer Prevention. The full guideline article (including references), which is written for health care professionals, is available online in CA: A Cancer Journal for Clinicians at: https://acsjournals.onlinelibrary.wiley.com/doi/full/10.3322/caac.21591

Acrylamide

What is acrylamide, and is it linked with an increased risk of cancer?

Acrylamide is a chemical used in industrial processing. It is also found in some foods and in tobacco smoke. Acrylamide in food is formed as a by-product when the amino acid asparagine reacts with certain sugars when they are heated to high temperatures. The major sources of acrylamide in our diets are French fries, potato chips, crackers, bread, cookies, breakfast cereals, canned black olives, prune juice, and coffee.

Acrylamide is classified by the International Agency for Research on Cancer (IARC) as a “probable carcinogen,” based mainly on experiments in animals. However, a large number of studies in humans have found no strong evidence that dietary acrylamide is linked with an increased risk of any type of cancer.

Antioxidants

What are antioxidants, and what do they have to do with cancer?  

The body uses certain nutrients and other compounds to help protect against damage to tissues that is constantly occurring as a result of normal metabolism. Because this type of damage is linked with increased cancer risk, some antioxidants are thought to protect against cancer. Antioxidants in the diet include vitamin C, vitamin E, carotenoids (compounds related to vitamin A), and many other food components. Studies suggest that people who eat more vegetables and fruits, which are rich sources of antioxidants, may have a lower risk for some types of cancer. But this does not mean that the benefits of vegetables and fruits are from their antioxidant content, rather than from other food components. 

Most clinical trials of antioxidant supplements have not found they reduce cancer risk. In fact, some studies have found an increased risk of cancer among those taking supplements. 

When it comes to reducing cancer risk, the best advice is to get your antioxidants through whole food sources rather than supplements.

Arsenic

What is arsenic? Does it cause cancer?

The International Agency for Research on Cancer (IARC), the US National Toxicology Program (NTP), and others have classified arsenic as carcinogenic to humans. Arsenic is a naturally occurring element that can be found in rocks and soil, water, air, plants, and animals, as well as in industrial and agricultural compounds.

Arsenic is found in two forms: 

• Inorganic arsenic compounds are used in industry and in building products (such as some “pressure-treated” woods) and are found in arsenic-contaminated water. This tends to be the more toxic form of arsenic and has been linked to cancer.
• Organic arsenic compounds are thought to be much less toxic than the inorganic arsenic compounds and are not thought to be linked to cancer. 

The main sources of human exposure to arsenic are water and food. 

• Water in some areas of the United States, especially in the Southwest, New England, and the Upper Midwest, may be higher in arsenic. Natural arsenic levels tend to be higher in drinking water that comes from ground sources, such as wells. 
• For most people, food is the largest source of arsenic, although much of this is likely to be in the less dangerous, organic form. The highest levels of arsenic in foods are found in seafood, rice and other rice products, mushrooms, and poultry, although many other foods, including 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. 

While arsenic is a naturally occurring element and can’t be avoided completely, there are things people can do that may lower their exposure. Those whose drinking water comes from a public source can obtain publicly-available information about the levels of certain substances in drinking water, including arsenic. People who get their water from a private source such as a well can have arsenic levels tested by a reputable laboratory. Those who live in areas with high levels of arsenic in the water may consider using alternate sources of drinking water, such as bottled water. Common household water filters do not effectively remove arsenic. Avoiding excess consumption of foods known to contain high levels of arsenic, including seafood, rice and rice products, and fruit juice can also help lower exposure, and maintaining adequate folate levels is important for the elimination of arsenic in the body.

Coffee

Does drinking coffee affect cancer risk?  

Whether coffee lowers or raises the risk of different types of cancer has been an active area of research. Studies have suggested that drinking coffee likely lowers the risk of liver and endometrial cancers, although the link to endometrial cancer may be confounded by smoking. There is some evidence that coffee lowers the risk of cancers of the mouth, throat, and voice box, as well as basal cell skin cancer in both men and women, and possibly melanoma in women. 

On a related topic, some studies have suggested that consuming very hot beverages, such as coffee and/or tea, may increase the risk of esophageal cancer. Therefore, it may make sense to avoid drinking coffee and other beverages at very high temperatures.

The potential ways in which coffee may lower the risk of cancer are not completely understood. Roasted coffee contains hundreds of biologically active compounds, including caffeine, flavonoids, lignans, and other polyphenols. These and other compounds have been shown to increase energy expenditure, protect against cellular damage, regulate genes involved in DNA repair, have anti-inflammatory properties and/or inhibit cancer spread (metastasis). Coffee also influences the amount of time food is in the intestines, as well as liver metabolism of carcinogens, which may also contribute to a lower risk for some digestive cancers.

Genetically modified crops

What are genetically modified crops, and are they safe?  

Genetically modified (also known as bio-engineered) crops are made by adding genes from other plants or organisms to increase a plant’s resistance to insect pests, slow spoilage, or improve transportability, flavor, nutrient composition, or other desired qualities. 

Certain foods made from genetically modified crops have been approved for sale in the US since the mid-1990s, and more than 70% of all highly processed foods in US supermarkets—including pizza, potato chips, cookies, ice cream, salad dressing, corn syrup, and baking powder—contain ingredients from bio-engineered soybeans, corn, or canola plants. Growing public concern about the potential harmful effects of genetically modified foods, in part, led to federal legislation in 2016 requiring uniform labeling of foods containing genetically engineered ingredients.

In theory, these added genes might create substances that could cause reactions in sensitized or allergic people, or result in high levels of compounds that could cause other health effects. However, at this time there is no evidence that foods now on the market that contain genetically engineered ingredients or the substances found in them are harmful to human health, or that they would either increase or decrease cancer risk. The World Health Organization, the American Medical Association, the National Academy of Sciences, and the American Association for the Advancement of Science have all taken the stance that current evidence suggests that foods containing genetically engineered ingredients are safe.  

Gluten-free diet

Does eating a gluten-free diet help reduce cancer risk? 

Gluten is a protein in wheat, rye, and barley. In most people, it causes no ill effects.

For people with celiac disease, gluten triggers an immune response that damages the lining of the small intestine and could increase the risk of cancer. 

Some people experience gluten sensitivity without overt celiac disease. In these people, gluten may contribute to inflammation in the intestines, which might in turn increase the risk of gastrointestinal cancers. However, this possible link is not well-proven.

There is very little evidence linking gluten intake to risk of gastrointestinal cancers in the general population.

The bottom line: For people without celiac disease, there is no evidence that consuming a gluten-free diet is linked with a lower cancer risk, and many studies suggest that consuming whole grains, including those containing gluten, probably reduces the risk of colon cancer. 

Glycemic index and glycemic load 

What are these, and do they impact cancer risk?  

Glycemic index is a measure of the increase in the blood level of glucose (a type of sugar) after eating a specific carbohydrate-rich food, compared with eating a standard amount of glucose. Foods with a high glycemic index release glucose quickly and lead to a rapid rise in blood glucose. Foods with a low glycemic index release glucose into the blood more slowly, with a lower overall peak in blood glucose over time. In general, high glycemic index foods are highly refined, processed grain products with added sugars and low fiber content, as well as some starchy vegetables. The glycemic index can be considered a measure of carbohydrate-rich food quality.

Beyond glycemic index, glycemic load captures both the quality and quantity of carbohydrates consumed. The glycemic load gives a truer picture of how blood glucose is elevated in relation to intake of a specific food item. 

A lot of research has looked at the potential impact of the glycemic load of a diet and cancer risk. Most recent reports have found that eating a dietary pattern high in glycemic load is linked with a higher risk of endometrial cancer. More research is needed to determine the impact on other types of cancer.

Inflammation and anti-inflammatory strategies

Do anti-inflammatory diets reduce cancer risk?

Inflammation has long been recognized as the body’s response to tissue injury, and its link to infections was recognized hundreds of years ago. However, the role of inflammation in causing cancer has been recognized more recently, and the relationships between diet, inflammation, and the risk of cancer (as well as heart disease and dying at an earlier age) are still an evolving area of research. 

A combination of lab and human studies has identified certain foods and chemicals in them that promote inflammation in certain body tissues. This is the basis of anti-inflammatory dietary patterns, which share some traits with the recommendations in this guideline, such as being high in vegetables and fruits and low in red and processed meats.

Irradiated foods

Why are foods irradiated, and can these foods increase cancer risk? 

Food irradiation (applying ionizing radiation to food) is a technology that improves the safety and extends the shelf life of foods by reducing or eliminating germs and insects. Like pasteurizing milk and canning fruits and vegetables, irradiation can make food safer. Irradiation does not make foods radioactive, affect nutritional quality, or noticeably change the taste, texture, or appearance of food. In fact, changes made by irradiation are so minimal that it is not easy to tell if a food has been irradiated.

The US Food and Drug Administration (FDA) has evaluated the safety of irradiated food for more than 30 years and has found the process to be safe. The World Health Organization (WHO), the US Centers for Disease Control and Prevention (CDC), and the US Department of Agriculture (USDA) have also endorsed the safety of irradiated food. There is currently no evidence that irradiation of foods causes cancer or has harmful human health effects.

Juicing/cleanses/detox

Can periods of limiting food intake to juices remove toxins and help protect against cancer?

Fruit and vegetable juices can be a convenient way to get some healthy food components from vegetables and fruits. In moderation, they can be a worthwhile part of healthful dietary patterns. However, juices contain less fiber, lower levels of some other healthy nutrients, and more naturally occurring sugar than the whole fruits and vegetables they are made from, so they are not the best way to get nutrients from plant-based foods.

There is no scientific evidence to support claims that consuming only juices for one or more days, known as juice cleansing or juice detoxification, reduces cancer risk or provides other health benefits. This kind of diet is promoted as a way to remove “toxins” from the body, but this claim is not supported by scientific evidence. Toxins that enter our body through foods and beverages are constantly removed by the kidneys and liver, regardless of whether a person is consuming liquid or solid foods. Although vegetable juicing may be one way to increase nutrient intake, a diet limited to juice may also be lacking in some important nutrients, and in select cases it may contain dangerous levels of some substances that can cause kidney damage and other health problems.

Microwaving food and general food preservation, preparation, and storage

Can using microwave ovens or other cooking methods increase cancer risk?

Microwaves are a form of non-ionizing electromagnetic radiation, and their use in cooking does not increase cancer risk.  On the other hand, grilling, smoking, or pan-frying meats (including red meats as well as poultry and fish) at high temperatures can cause chemical reactions that form cancer-causing heterocyclic amines. 

Goals of food preservation, processing, and preparation that are relevant to individual and public health include: 

• Removing or inactivating any harmful chemical or microbiological contaminants
• Avoiding addition or production of harmful substances
• Maintaining the amount and availability of nutrients

For example, proper canning or freezing methods can help maintain the nutrient content of vegetables and fruits, which can expand consumers’ access to these products. On the other hand, certain methods of preserving red meats introduce nitrates into them, which can be converted in the stomach into cancer-causing N-nitroso compounds. 

Contamination of foods by substances from storage containers or cookware is another concern of some consumers. Plastic containers can release substances such as phthalates (some of which are classified as possible carcinogens) or phenolic compounds such as bisphenol A (a probable carcinogen) during storage of food or during cooking in a microwave oven. Use of Teflon-coated cookware may release perfluorooctanoic acid (PFOA, a possible carcinogen) into foods. These substances have been found to have negative biological effects in some lab studies, and they may influence onset of puberty, a possible factor in the long-term risk of some cancers such as breast cancer. However, evidence of the impact of long-term exposure to these chemicals on cancer risk in human studies is lacking. Nonetheless, people who are concerned about possible harm from these exposures can choose glass or metal storage containers and cookware. 

Non-nutritive sweeteners/sugar substitutes

Do non-nutritive sweeteners/sugar substitutes cause cancer? 

Non-nutritive sweeteners are substances used instead of sugars like sucrose, corn syrup, honey, agave nectar to sweeten foods, beverages and other products. Several non-nutritive sweeteners are now approved by the FDA, including aspartame, acesulfame potassium, saccharin, sucralose, and stevia. These sweeteners contain few or no calories, or nutrients. They may be derived from herbs and other plants, or sugar itself, and typically are many times sweeter than sugar, allowing smaller amounts to be used. Other sugar substitutes include sugar alcohols such as sorbitol, xylitol and mannitol.

There is no clear evidence that these sweeteners, at the levels typically consumed in human diets, cause cancer. Questions about artificial sweeteners and cancer risk arose when early studies showed that saccharin caused bladder cancer in lab animals, but studies in humans have shown no increased cancer risk. 

People with a rare genetic disorder called phenylketonuria (PKU) aren’t able to metabolize aspartame normally, which can result in nervous system toxicity, so they should avoid aspartame in their diets. With this exception, all these sweeteners appear to be safe when used in moderation, although larger amounts of sugar alcohols may cause bloating and abdominal discomfort in some people.

Organic foods

Are foods labeled “organic” more effective in lowering cancer risk? 

The term “organic” is used to designate foods grown without the addition of artificial chemicals. Under USDA regulations, animal-derived foods that are labeled as organic come from animals raised without the addition of hormones or antibiotics to the feed they eat. Plant foods that are organic come from agricultural methods that do not use most conventional pesticides or herbicides, chemical fertilizers, or sewage sludge as fertilizer. Organic foods also exclude the use of industrial solvents or food irradiation in processing, and genetically modified foods are also excluded.

A main benefit of consuming organic foods is to support environmentally sustainable agricultural practices. Many consumers also believe that organic foods may provide health benefits, but there is little evidence that organic produce has higher nutrient levels than conventionally grown produce.

Little research has been done on the link between organic food consumption and cancer risk, although a recent study found eating more organic produce was linked with a lower risk of non-Hodgkin lymphoma. While this finding needs to be confirmed by other studies, it is in line with the strong and consistent link between workplace pesticide exposure and this type of cancer.

Washing conventionally grown produce can remove some of the pesticide residue. It’s also important to wash all produce to limit the risk of health effects from microbial contamination.

Because organic produce is often more expensive than similar conventionally produced items, it’s important that people with limited resources recognize that meeting the recommendation for vegetable and fruit intake is a higher priority for cancer prevention and overall health than choosing organic produce.

Pesticides and herbicides

Do pesticides in foods cause cancer? 

Insecticides and herbicides can be toxic when used improperly in industrial, agricultural, or other workplace settings. The International Agency for Research on Cancer (IARC) classifies 3 common agricultural herbicides (glyphosate, malathion, and diazinon) as ‘probable human carcinogens.’ All 3 are linked with a higher risk of non-Hodgkin lymphoma. In addition, malathion is linked with a higher risk of prostate cancer, and diazinon is linked with a higher risk of lung cancer.

Currently, scientific evidence supports the overall health benefits and cancer‐protective effects of eating vegetables and fruits, regardless of whether they are grown using organic or conventional practices. Washing conventionally grown produce can remove some of the pesticide residues, and is also important to minimize the risk of microbial contamination.

Sleep

How does sleep affect diet, physical activity, and cancer risk?

Increasing evidence suggests important interactions among sleep, diet, physical inactivity, and cancer risk:

• Disordered sleep has been linked with higher cancer risk, and sleep deprivation (usually defined as less than 7 hours a night) has been linked with a higher risk for obesity and overeating, as well as metabolic syndrome, which is a known risk factor for several types of cancer.
• Alternately, a healthy sleep pattern has been linked with better weight maintenance after weight loss.
• Studies have found high levels of sedentary time (time spent sitting or lying down) are linked with poor sleep quality and shorter sleep duration.
• Inadequate sleep has been linked with higher levels of stress hormones and inflammation, which are known mechanisms affecting cancer risk.

Soy and soy products

Can soy‐based foods reduce cancer risk?

As with other beans or legumes, soy and foods derived from soy are excellent sources of protein, so they provide a healthier alternative to meat. Soy contains several bioactive food components, including isoflavones, which have a similar structure to estrogens and can bind to estrogen receptors on cells. The effects of this binding can vary, depending on conditions, the specific body tissue, and the amount consumed.

There is some evidence from human and lab studies that consuming traditional soy foods such as tofu may lower the risk of breast and prostate cancer, but overall the evidence is too limited to draw firm conclusions. Many of the studies that have found such links looked at Asian populations with high lifelong consumption of soy foods, and their relevance to soy consumption at lower levels and for shorter durations in Western populations remains uncertain. 

There are no data to support the use of supplements containing soy phytochemicals or soy protein powders used in some food products for reducing cancer risk. In fact, a recent study found increased risk for estrogen receptor (ER)-negative breast cancer (an aggressive type) among users of soy supplements. Therefore, while soy from food sources appears to be safe and may even have beneficial health effects, soy supplements should be used with caution, if at all.

Sugar

Does sugar increase cancer risk? 

Several types of sugars are found in foods and beverages. These sugars vary in their chemical structures, but once they are consumed, they all have similar metabolic effects in the body. All sugars in foods and beverages add to calorie intake, which can lead to obesity, so eating a lot of sugar can indirectly increase cancer risk. There is also evidence that a dietary pattern high in added sugars affects levels of insulin and related hormones in ways that may increase the risk of certain cancers.

Brown (unrefined) sugar contains the same chemical form of sugar (sucrose) as white (refined) sugar. It also contains extremely small amounts of other substances that affect its color and flavor, but they don’t influence the unfavorable effects of sucrose on body weight or insulin levels.

Fructose, the natural sugar in fruit and in many sugar-sweetened beverages in the form of high-fructose corn syrup, is similar to sucrose in its effects on weight and insulin levels, as is honey, which contains a mixture of fructose and glucose (another form of sugar).

Lab studies have shown that metabolism of glucose (the main sugar used as an energy source in the body) is faster in cancer cells than in normal cells. This fact is often misinterpreted by people, who assume (incorrectly) that sugars in foods and beverages directly “feed” cancer cells.

Nonetheless, limiting highly processed foods that contain high levels of added sugars, such as cakes, candy, cookies, and sweetened cereals, as well as sugar‐sweetened beverages such as soda, sports drinks, and energy drinks, can help reduce calorie intake, limit weight gain, and promote a healthier body weight. It can also lower insulin secretion in people with metabolic conditions such as pre-diabetes or type 2 diabetes.

Vegetarian/vegan diets

Do vegetarian diets reduce cancer risk? 

Vegetarian diets can include many healthy features: 

• They tend to be low in saturated fat
• They tend to be high in fiber, vitamins, and other bioactive food components
• They do not include red and processed meats

Thus, vegetarian diets may be helpful for cancer risk reduction. Many studies of vegetarians indicate a lower risk of cancer overall, compared to people who also eat meat. But whether vegetarian diets confer any special health benefits over diets that include smaller amounts of animal products than are typically consumed in Western diets is less clear. Indeed, in a large British study, people who ate fish but not other meats appeared to have the same overall cancer risk as vegetarians.

The available evidence supports the recommendation of a dietary pattern that is mainly foods from plant sources, with limited if any intake of red and processed meats.

In addition to a modest level of risk reduction for some forms of cancer, vegetarian dietary patterns are linked with lower risks of heart disease and type 2 diabetes and are generally more affordable. 

People on strict vegetarian diets that omit all animal products (including milk and eggs), referred to as vegan diets, often need supplementation with vitamin B12, zinc, and iron (or foods fortified with these nutrients), especially for children and premenopausal women. They should also aim to get enough calcium, as people consuming vegan diets with relatively low calcium content have been shown to have a higher risk of bone fractures compared with people consuming vegetarian or meat‐containing diets.

It's important that people on strict vegetarian diets, referred to as vegan diets that do not include animal products (including milk and eggs), talk with their doctor or a dietitian or nutritionist about supplements they may need.