Scientists have not found a common link between ultra-processed foods and bowel cancer

Whole—grain bread, dairy products, and processed meats may end up in the same category - ultraprocessed food. But their association with bowel cancer, as shown by a study of almost half a million Americans, varies markedly. Participants who generally ate more of these foods did not get sick more often than others. At the same time, certain food groups were associated with both increased and decreased risk. Why a common label can hide important differences and what conclusions the new data allow us to draw can be found in the Izvestia article.

What did the study of almost half a million people show?

Scientists led by Erica Loftfield from the US National Cancer Institute studied data from 461,682 participants in the NIH-AARP Diet and Health Study project. At the time of inclusion in the study, in 1995-1996, the participants were between 50 and 71 years old. They filled out questionnaires in which they indicated how often they consume different foods. Based on these responses, the researchers assessed the composition of the diet and the amount of ultraprocessed food.

The researchers then tracked new cancer cases until 2018. The median follow—up was 18.8 years: half of the participants were followed for longer than this period, and half for less. During the study, 10,075 cases of colorectal adenocarcinoma, a malignant tumor of the colon or rectum, were registered.

When comparing participants with the highest and lowest intake of ultra-processed foods, no statistically significant difference in morbidity was found. The analysis took into account age, smoking, physical activity and other factors that could influence the result.

Why did products with the same name produce different results?

The ultra-processed food category combines products with very different compositions. It can include both meat products and some whole grains and dairy products. Therefore, the same characteristic of the production method does not mean the same nutritional value.

It is these differences that the researchers have tried to consider separately. They were interested not only in the total amount of ultraprocessed food, but also in what foods and nutrients the participants received from it.

Higher intake of whole grains, fiber, dairy products, and calcium from such sources was associated with a lower incidence of colorectal cancer. An inverse relationship was observed for meat from ultra-processed sources: with higher consumption, the incidence was higher.

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Thus, the overall indicator combined products for which opposite risk associations were found. The authors consider this as one of the possible explanations for why the study did not reveal an increase in morbidity for the entire category.

However, the data do not allow us to assert that industrial processing alone makes whole-grain or dairy foods healthier. The researchers observed a link between diet and subsequent diagnoses, rather than testing the effects of individual manufacturing technologies.

Which means a 2% reduction in risk%

Additionally, the scientists built a statistical model for replacing ultra-processed foods with minimally processed foods. In it, the share of the first category in the total weight of the diet was reduced by 10 percentage points, and the share of the second was increased by the same amount. This calculated substitution was associated with a decrease in the relative risk of colorectal cancer by about 2%.

Here we are talking about the mass of products, not their caloric content. A 2% reduction in risk also does not mean that the likelihood of getting sick has decreased by two percentage points: this is a relative difference between the compared diet options.

The participants were not given a specific set of products and were not offered to switch to a new menu. The researchers calculated a possible connection based on the data already collected. Therefore, the result cannot be taken as a promise that a specific replacement in the diet will necessarily give a person such an effect.

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This finding is consistent with the lack of a common link for all ultra-processed foods. Comparing the number of products in one category and calculating its replacement by another category answer different questions. In the second case, it also matters what kind of food appears in the diet instead.

What conclusions can be drawn about the diet

The authors believe that the results are consistent with existing recommendations for the prevention of colorectal cancer: consume whole grains and dietary fiber, consider sources of dairy products and calcium, and limit processed meat.

The study also shows why the designation "ultraprocessed" alone may not be enough to evaluate a diet. This category describes one side of a product, but does not replace information about its composition. To interpret the risk, it is important to understand how much whole grains, fiber, dairy and meat products are in the diet.

The work is specifically devoted to colorectal cancer. It does not establish how all ultraprocessed foods affect other tumors, cardiovascular diseases, or overall health. Therefore, the main practical meaning of the results is to take a closer look at what exactly a person eats. Foods combined by the same name can occupy different places in the diet and show different connections with the disease.