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Evidence from many studies has suggested that lifestyle factors – including diet – play an important role in preventing colorectal cancer.

Now, an updated analysis of existing research has concluded that a number of dietary factors are clearly linked to colorectal cancer risk.

In addition to certain diet factors being strongly tied to a lower occurrence of the cancer, dietary patterns such as the Mediterranean diet and vegetarian diets were also found to offer protection.

The latest findings

For the analysis, published last week in the journal JAMA Network Open, researchers examined 45 meta-analyses of observational studies that investigated the association between diet and colorectal cancer risk. (A meta-analysis is a merging of data from many studies; it’s used to summarize the results of multiple studies.)

The researchers ranked the strength of the evidence according to five classifications: convincing, highly suggestive, suggestive, weak and nonsignificant.

The evidence was “convincing” for the link between red meat (high versus low intake) and alcohol (more than four drinks per day versus little or none) and an increased colorectal cancer risk. In contrast, convincing evidence was found for a lower risk and higher (versus lower) intakes of fibre, dietary calcium and yogurt.

The evidence was graded “highly suggestive” for protection against colorectal cancer from a higher intake of total dairy products (milk, yogurt, cheese).

It was also highly suggestive that a moderate alcohol intake (more than one and up to three drinks per day) was associated with a greater risk of the cancer.

“Suggestive” evidence was found for protection from a higher intake of whole grains and adherence to a Mediterranean diet, pesco-vegetarian diet and semi-vegetarian diet. A Western diet, characterized by higher intakes of red and processed meat, refined grains and highly processed foods, was tied to a higher risk.

A pesco-vegetarian follows a mostly vegetarian diet but also eats fish and seafood. A semi-vegetarian, or flexitarian, eats a plant-based diet that occasionally includes meat.

Diet and lifestyle recommendations

According to the Canadian Cancer Society, colorectal cancer was expected to be the third most commonly diagnosed cancer in 2020. Findings from this latest research, as well as other studies, suggest the following lifestyle modifications may help guard against the cancer.

Eat less red and processed meat

Choose fish, chicken, turkey and beans and lentils (pulses) more often than red meat (e.g., beef, lamb, pork, goat). Eat processed red meats (e.g., ham, salami, sausage, bacon) sparingly, if at all.

Cooking red meat at high temperatures forms compounds (heterocyclic amines, polycyclic aromatic hydrocarbons) linked to precancerous colon polyps. Certain additives in processed meats may also play a role in its cancer link.

Limit alcohol

Keep alcohol intake to no more than one daily drink for women and two for men. One drink is 5 ounces of wine, 12 ounces of 5 per cent beer or 1.5 ounces of 80-proof distilled spirits.

The 2020 cancer prevention guideline from the American Cancer Society states that is best not to drink any alcohol.

Increase fibre

Include whole grains in your daily diet such as oats, brown rice, farro, freekeh, whole wheat pasta and 100 per cent whole grain breads. Add 100 per cent bran cereal to yogurt and smoothies.

Include fruit and/or vegetables at every meal and snacks. Nuts, pulses and bean pastas are also excellent fibre sources.

Meet daily calcium requirements

Adults, ages 19 to 50, need 1,000 mg of calcium each day. After 50, women require 1,200 mg; daily requirements for men to increase calcium to 1,200 mg after age 70.

One cup of milk, three-quarters of a cup of yogurt and 1.5 ounces of cheese each supply roughly 300 mg of calcium. Other good sources include calcium-fortified plant “milks”, canned salmon with the bones, tofu made with calcium, cooked greens, pulses, almonds, almond butter and tahini.

Calcium is thought to bind to toxic compounds in the intestinal tract, preventing harm to colon cells. Other components in dairy may also play a protective role.

Weight control, exercise

Staying at a healthy weight throughout adulthood is associated with a lower risk of colorectal cancer. So is getting at least 150 minutes of moderate-intensity exercise each week.

Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD