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food for thought

Plenty of large studies conducted over long periods of time have shown that consuming a diet with lots of ultraprocessed foods increases the risk of obesity, Type 2 diabetes, hypertension, cardiovascular disease, depression and early death.

Most of these highly processed foods – e.g., soft drinks, sweet and salty packaged snacks, margarine, mass-produced breads, instant noodles, sausages, hot dogs, precooked/ready-to-heat meals, ice cream, cookies, pastries, cake mixes, sweetened yogurt – are high in calories, unhealthy fats, added sugars and sodium, while being low in fibre, vitamins and minerals.

Now, a study published Aug. 31 in The BMJ, has linked a high intake of ultraprocessed foods to a greater risk of colorectal cancer in men. The findings also suggest that attributes of these foods – beyond poor nutrient quality – are responsible for their harmful effects.

Minimally processed, processed and ultraprocessed foods

The NOVA food classification system classifies all foods into four groups based on the extent of their processing. Group 1 includes “unprocessed [natural] and minimally processed foods,” which are natural foods altered by processes such as drying, crushing, filtering, roasting, fermenting, pasteurizing and freezing.

Group 2 foods are “processed culinary ingredients” including oils, lard, sugar and salt.

Group 3 are “processed foods” such as canned vegetables, canned fruit in syrup, tinned fish in oil, some processed animal foods (ham, bacon, pastrami, smoked fish) and natural cheese with added salt. These foods are made by adding processed culinary ingredients to unprocessed and minimally processed foods.

Group 4, “ultra-processed foods,” are formulations of ingredients, typically created by a series of industrial techniques. They’re made by deconstructing whole foods, altering them and then recombining them with additives to make them convenient, attractive and hyperpalatable.

The latest findings

For the study, researchers from Harvard University and Tufts University examined the association between ultra-processed foods and colorectal cancer risk among 206,248 men and women who were followed for up to 28 years.

Participants completed diet questionnaires every four years and gave information on medical and lifestyle factors every two years. The researchers assigned the foods that participants consumed to a NOVA food group.

During the study 3,216 cases of colorectal cancer occurred.

Overall, men whose diets contained the most ultraprocessed foods had a 29 per cent greater risk of developing colorectal cancer than did those whose diets had the smallest amount. There was no link between ultraprocessed foods and cancer risk in women.

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The researchers looked at subgroups of ultraprocessed foods and found that ready-to-eat food products made with meat, poultry and seafood, as well as sugar-sweetened drinks, were tied to a higher risk of colorectal cancer in men.

It’s unclear why an association between ultraprocessed foods and colon cancer risk was not observed in women. It’s possible that women make different ultraprocessed food choices than men do. Sex hormones may also be involved.

Colorectal cancer risk attributed to ultraprocessed foods was largely independent of risk factors such as body mass index and poor diet quality, suggesting that other aspects of ultraprocessed foods are to blame in colon cancer development.

Beyond poor diet quality

Ultraprocessed foods contain additives, such as emulsifiers and artificial sweeteners, some of which may alter the composition of the gut microbiome in a direction that promotes inflammation.

Potential carcinogens can also be formed during food processing. Acrylamide, for example, produced when foods are heated to high temperatures (e.g., French fries, potato chips, cereal products), has been linked to increased oxidative stress and inflammation.

Ultraprocessed foods may also contain contaminants that are transferred from their plastic packaging, such as bisphenol A. As well, during processing these foods are stripped of protective phytochemicals and nutrients found in whole foods.

What to do?

The latest findings add to mounting evidence that both nutritional quality and degree of food processing need to be considered when evaluating the relationship between diet and health and when revising dietary guidelines.

Some progress is being made. Canada’s food guide, for example, updated in 2019, advises limiting intake of highly processed foods.

Make a list of the ultraprocessed foods you and your family eat on a regular basis. Put strategies in place to buy them less often.

Make homemade versions of commercially prepared granola bars, baked goods, pasta sauce, soups and salad dressings. Roast a turkey breast or grill chicken for sandwiches and salads.

Choose whole and minimally processed snacks such as popcorn, whole and unsweetened dried fruit, nuts and plain yogurt. As often as possible, choose foods with ingredients you’d find in your own pantry.

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

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