Over the last several decades, certain foods have been vilified as being potentially carcinogenic, or capable of causing cancer. So which ones are the biggest culprits? And how can you eat to prevent cancer or reduce the chances of a recurrence if you've been diagnosed?

The list of potentially cancer-causing foods includes:

• Red meat and processed meat.
• Sugar.
• Alcohol.
• Processed and packaged foods.

Red Meat and Processed Meat

For the carnivores among us, it’s probably tough to hear the news that red meat and processed meat are associated with a higher risk of certain types of cancer. “Red meat is defined as beef, veal, pork, lamb and goat,” says Cathy Leman, a registered dietitian nutritionist and founder of Dam. Mad. About Breast Cancer, a nutritional consulting firm aimed at helping breast cancer patients and survivors. “Processed meat refers to meat that has been salted, cured, fermented, smoked or other processes that enhance flavor or improve preservation.” Examples include hot dogs, luncheon meats, ham and bacon.

Jeannette Schenk, a public health researcher in the cancer prevention program at Fred Hutchinson Cancer Research Center in Seattle, says “there have been many epidemiological studies that have reported an association with high intakes of processed meat and red meat with an increase in cancer incidence and mortality.” According to the American Institute for Cancer Research a high intake of red meat is defined as more than three servings per week. A single serving of red meat is about 3 to 4 ounces – or one small hamburger, steak or a medium-sized pork chop. Your total weekly consumption, the AICR reports, should be under 350 to 500 grams (about 12 to 18 ounces cooked) each week.

The cancer risk associated with processed meat products is even higher. The International Agency for Research on Cancer, a branch of the World Health Organization, classifies processed meat as a Group 1 carcinogen, meaning that like other Group 1 carcinogens – tobacco, UV radiation and alcohol – research has proven that processed meat can cause cancer in humans. Eating just 50 grams of processed meat each day, the IARC reports, can elevate cancer risk by 18%. About four strips of bacon or one hot dog contains about 50 grams of processed meat.

Kailey Proctor, an oncology dietitian with The Center for Cancer Prevention and Treatment at St. Joseph Hospital in Orange, California, emphasizes, though, that the observed connection between meat and cancer “is an association, not a causation.” Nevertheless, she notes that processed meat products “are processed foods,” that should be consumed in moderation, aiming for one serving per week or less.

Why these meats appear to elevate cancer risk, particularly colorectal cancer, is believed to be because red meats and processed meats contain mutagens and carcinogens. Mutagens change genetic information by altering DNA, and carcinogens are cancer-causing agents. When meat is cooked at high temperatures or grilled, amino acids in the meat interact with the heat to form carcinogenic compounds called heterocyclic amines and polycyclic aromatic hydrocarbons. “Those have been linked with cancer risk,” Schenk says.

With processed meats, the cancer risk appears to be related to the way the meat is preserved and cooked. Specifically, the addition of preservatives called nitrates and nitrites may elevate cancer risk. Similarly, smoking meats can also create carcinogenic compounds, Schenk says.

Sugar

Sugar is also implicated in the development and progression of certain kinds of cancer. In the early 20th century, a German biochemist named Otto Warburg observed that cancer cells often rely on sugar to fuel their prolific growth. Called the Warburg effect, this process suggests that starving the body of sugar and carbohydrates that can be converted to sugar could theoretically starve cancer cells. As a result, the Ketogenic diet, which reduces carbohydrate intake to 10% or less of calories consumed and increases fat consumption to 70%, has been suggested as a way to slow the spread of cancer.

The effectiveness of the Keto diet to prevent or slow cancer haven’t been fully proven, but an association between sugar and cancer has been established. For this reason, “any food which has a very high glycemic index” can increase your risk of cancer and should be consumed in moderation, says Dr. Adil Akhtar, associate professor in the department of medical oncology and hematology at Oakland University-William Beaumont School of Medicine and director of Inpatient Clinical Operations at Karmanos-McLaren Oakland Cancer Center in Michigan. A food’s glycemic index is “defined by the rate at which a food when it’s digested will raise the level of sugar in the blood," explains Akhtar. Sugary foods, such as soda and candy, have a high glycemic index.

Daryl Gioffre, a chiropractor, celebrity nutritionist and author of “Get Off Your Acid: 7 Steps in 7 Days to Lose Weight, Fight Inflammation and Reclaim Your Health and Energy,” says that if you’re concerned about cancer, you should eliminate all refined sugar from your diet. “Common sense-wise, this is a bad food because sugar literally feeds cancer cells.” He points out that some diagnostic tests for cancer use radioactive glucose to pinpoint tumors on PET scans because most cancer cells have such an affinity for sugar that they suck up glucose molecules faster than noncancerous cells, thus showing themselves on the scan. By the same token, he says “cancer hates fats, so metabolically, the goal is to move the body away from burning sugar as its primary fuel to using fat,” with the emphasis on using healthy fats, such as those found in avocados and olive oil.

Alcohol

Alcohol is actually a type of sugar, so it’s also on the list of foods that can increase your risk of cancer. “Alcohol is an established risk factor for mouth, pharynx, esophageal, liver, colorectal, breast and pancreatic cancer,” Schenk says.

Exactly how alcohol increases risk is not clearly understood, but “it’s possibly related to DNA damage” incurred by the cells after exposure to alcohol, Schenk says. “In addition, it could be an indirect contributor because calories from alcohol contribute to weight gain. Alcoholic beverages are the fifth largest contributor of caloric intake in the U.S. adult population, and it has low nutrient value, so it’s one of those added foods that we need to be limiting,” she says.

The federal government’s Dietary Guidelines for Americans 2015-2020 states that if you don’t drink, don’t start. It also recommends that moderating intake is an important way to curb cancer risk in people who do choose to consume alcoholic beverages. Moderate alcoholic drinking is defined as one drink per day for women and up to two drinks per day for mean. A drink is defined as 12 ounces of beer, 8 to 9 ounces of malt liquor, 5 ounces of wine and 1.5 ounces of 80-proof distilled spirits. In her opinion, Leman says that "for prevention, it’s best not to drink alcohol."

Processed and Packaged Foods

Akhtar says certain processed foods can also raise your risk of developing cancer. “Things like microwaved popcorn have compounds that are linked with cancer,” and even seemingly healthy foods, such as farmed salmon, may contain “a chemical compound we call PCP, which is also associated with cancer.” The Environmental Working Group raised the alarm about a chemical called PFOA that was used to coat the inside of popcorn bags as a likely carcinogen, prompting the FDA to ban its use in food packaging in 2006. However, a subsequent EWG investigation suggested that the replacement chemicals (needed to prevent oils in the bag from soaking through the paper) are also potentially carcinogenic and likely contain perfluorinated chemicals. The Agency for Toxic Substances and Disease Registry, a division of the Centers for Disease Control and Prevention, reports that these chemicals, known as PFCs, may increase the risk of cancer.

Other ultra-processed foods, such as packaged baked goods and snacks, fizzy drinks, sugary cereals, ready meals and reconstituted meat products, have also been linked with an increase risk of certain types of cancer, according to a 2018 study in the British Medical Journal. The study, which included 104,980 healthy French adults, found that a 10% increase in the proportion of ultra-processed foods in the diet was associated with increases of 12% in the risk of overall cancer and 11% in the risk of breast cancer. No significant association was found for prostate and colorectal cancers. Ultra-processed food products also tend to be higher in calories, salt, sugar and saturated fats, all of which may contribute to obesity, which is a known risk factor for cancer.

How Should I Eat to Avoid Cancer?

While some foods have been associated with an increased risk of certain kinds of cancer, other foods are believed to help reduce your risk. Most notably, bight leafy green vegetables and colorful fruits contain antioxidants and a host of other helpful nutrients that keep the body working the way it’s supposed to. In addition to the vitamins, minerals, fiber and “other bioactive components that may directly impact cancer risk,” vegetables and fruits may also “potentially have an indirect impact” on cancer risk, Schenk says. “Individuals who eat more fruits and vegetables tend to have less weight gain and a lower risk of developing obesity and there’s a strong link between obesity and cancer risk.”

Gioffre says adding turmeric – a bright orange spice found in many Indian dishes – to your diet may help reduce inflammation in the body. Inflammation is a hallmark feature of cancer and other chronic diseases such as diabetes and Alzheimer’s disease, and many doctors and researchers believe that decreasing inflammation can reduce the risk of cancer. Increasing your intake of fiber might also help reduce your risk of cancer, specifically colorectal and gastric cancers, Proctor says. “Fiber also gives us a sense of fullness so we are less likely to snack between meals, which helps maintain a healthy body weight.”

Maintaining a healthy body weight is an important part of controlling cancer risk. “We do know maintaining a healthy body weight is one of the best ways to reduce your risk for cancer. A healthy body weight is considered to be a BMI between 18.5 and 24.9 kg/m2.” BMI is a metabolic assessment based on height and weight. You can calculate your own BMI using the National Heart, Lung and Blood Institute's online BMI calculator. Aim to stay in the healthy BMI range between 18.5 and 24.9 – being underweight can pose health risks, Proctor says.

While there foods to avoid and include to help fight cancer, Akhtar notes there’s not one specific diet that will solve the cancer question. He likes the Mediterranean diet for its balance of nutrients, low levels of sugar and focus on whole foods: “Eat a balanced diet that is rich in fruits and vegetables” and limits carbohydrates and sugars. Eat smaller portions of lean meat and healthy fats included in fish, nuts and olives. If you look at the list of different diets, all the healthy diets will have these basic components with a little bit of modifications.” He also recommends avoiding processed meats and “not drinking or limiting alcohol.” He also tells patients to review the American Cancer Society’s nutritional guidelines.

The American Institute for Cancer Research recommends a mostly plant-based diet for cancer prevention, Proctor says. “Their ‘New American Plate’ model suggests having two-thirds of your plate plant-based foods, such as fruits, vegetables, whole grains, beans and legumes. The remaining one-third of the plate should be a lean source of protein, such as chicken, turkey and seafood.”

Adding more plants to the diet is believed to confer some protective benefits against cancer, but “it’s important to stress that we don’t yet have 100% cancer prevention through diet,” Leman says. “But we do have strong evidence to use in developing dietary guidelines for reducing risk.”

She recommends the following guidelines to reduce cancer risk:

• Eating a diet rich in whole grains, vegetables, fruit and beans (legumes, lentils).
• Eating a diet that provides at least 30 grams of fiber per day.
• Eating a diet high in all types of plant foods.
• Eating at least five servings (2.5 to 3 cups total) of non-starchy vegetables and fruit daily

For people who’ve been recently diagnosed with cancer or who are in survivorship, the above guidelines may also help, Leman says. “That said, people who are newly diagnosed, post-treatment, or living with metastatic cancer can benefit from individualized nutritional guidance to support treatment outcomes, strong survivorship and to manage side-effects of chronic cancer treatments. While undergoing active treatment, people often have special nutritional requirements. Working with an oncology dietitian for individualized nutritional care and guidance can help patients manage side-effects like nausea, loss of appetite, fatigue, changes in bowel habits, etc.”

“While it’s not necessary to eat a vegetarian or vegan diet, it’s wise to limit intake of red meat to 18 ounces per week, and enjoy processed meats like ham, bacon and sausage on occasion,” Leman says.

Schenk hesitates to name a specific diet when talking about how to eat to reduce your risk of cancer and recommends taking a more holistic approach. Focus on eating more whole foods – vegetables, fruits and whole grains – that are nutrient-dense, while limiting added sugars and alcohol. “We have to consider the diet as a whole. We’re shifting at looking more at dietary patterns versus individual foods with respect to impact on cancer risk and cancer prevention.”

Akhtar agrees that looking at food in context and “eating a balanced diet” are the best ways to approach using your diet to help combat cancer. And your mom was right – eat your vegetables.