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For people with type 2 diabetes, the negative effects of eating too much ultra-processed foods may cancel out the benefits of healthy eating, such as following a Mediterranean diet. zepp1969/Getty Images
  • The Mediterranean diet, which is rich in fiber and healthy fats and low in sugar, is currently viewed as one of the best diets for people with type 2 diabetes.
  • But a new study suggests that the negative effects of a diet rich in ultra-processed foods may outweigh the benefits of following a Mediterranean diet.
  • Ultra-processed foods refer to food items that have been heavily processed and contain several food additives.

A new study suggests that people with type 2 diabetes should not be focusing only on the fiber, fat, and sugar contents of their food but reduce or eliminate ultra-processed foods from their diet.

Current advice for managing type 2 diabetes mostly focuses on eating foods high in fiber, healthy fats, and low in sugar.

Two specific diets are often recommended: the Mediterranean Diet and the DASH Diet. These diets give a lot of importance to specific food groups like whole grains, legumes (like beans and lentils), nuts, fruits, and vegetables.

A 2023 review of 107 studies concluded that higher intakes of fish, whole grains, fiber, and n-3 polyunsaturated fatty acids were inversely associated with all-cause mortality in individuals with type 2 diabetes.

The new study, published in the American Journal of Clinical Nutrition, found that a diet rich in ultra-processed (highly processed) foods increases the risk of death for people with type 2 diabetes, regardless of adherence to the Mediterranean diet.

These findings add to the growing body of evidence that high consumption of ultra-processed foods may cause premature death.

Several studies have shown that diets rich in ultra-processed foods increase the risk of developing type 2 diabetes. However, no study has investigated the relationship between ultra-processed foods and mortality in people already diagnosed with type 2 diabetes.

This was the relationship that researchers at the Institute for Research, Hospitalization and Health Care (IRCCS) Neuromed in Pozzilli (Italy) set out to investigate.

The Neuromed study used data from the Moli-sani Study, which collected data from 24,325 people aged over 35 and living in the south-central Italian region of Molise between 2005 and 2010.

From the Moli-sani cohort, the Neuromed researchers identified 1,065 individuals who had type 2 diabetes at study entry. These individuals had been followed up for a median period of 11.6 years.

Using data from a comprehensive food intake questionnaire, the researchers calculated the percentage of ultra-processed foods to total food intake. They also assessed how healthy each person’s overall diet was by using the Mediterranean Diet Score.

The term ‘ultra-processed foods’ is based on a food classification method called NOVA.

The NOVA system divides foods into four groups according to the extent and purpose of food processing rather than in terms of nutrients:

  • Group 1 contains “unprocessed or minimally processed foods,” namely the edible parts of plants or animals that have been taken straight from nature
  • Group 2 contains “culinary ingredients,” such as salt, oil, sugar, or starch, which are produced from Group 1 foods
  • Group 3 contains “processed foods,” such as freshly baked bread, canned vegetables, or cured meats, which are obtained by combining Group 1 and Group 2 foods.
  • Group 4 contains “ultra-processed foods”. This refers to products that are made with substances derived from Group 1 foods through heavy processing (e.g., hydrolyzed proteins, maltodextrins, hydrogenated fats) and contain several food additives, such as colorings, preservatives, antioxidants, flavor enhancers and sweeteners.

According to the NOVA system, products considered to be ultra-processed include, but not limited to:

  • carbonated drinks, infant formulas, and other highly-processed beverages marketed as “milk” or “fruit” drinks
  • packaged snacks and mixes such as potato chips, candies, cookies, cake mixes, breakfast cereal, etc.
  • ready-to-heat or “instant” products, such as cup noodles, frozen pizza, hot dogs, and other reconstituted meat products

The researchers found that, on average, 7.4% of the participants’ total food intake consisted of ultra-processed foods.

Individuals who ate the most ultra-processed foods (≥10.5% and ≥9% of total food eaten by females and males, respectively) had a higher risk of death from any cause and from cardiovascular disease compared to those who ate the least ultra-processed foods, and the risk increased with increasing ultra-processed food consumption.

The link between higher ultra-processed food consumption and higher mortality risk remained even when comparing individuals whose diets had similar nutritional compositions, as reflected by their Mediterranean Diet Scores.

Marialaura Bonaccio, Ph.D., study first author and epidemiologist at IRCCS Neuromed, explained to Medical News Today that “there are several potential mechanisms that could explain the observed associations between UPF [ultra-processed foods] and poor health outcomes.”

“The well-documented adverse health effects of UPF are not exclusively related to the poor nutritional content of these foods, but are likely triggered by non-nutritional factors, such as food additives, contaminants from plastics, alteration to the food matrix, etc. This has been clearly supported by our study, showing that the mortality risk associated with high UPF intake remains even after accounting for adherence to the Mediterranean Diet.”

– Dr. Bonaccio

Dr. Bonaccio told MNT that while traditional advice on the management of type 2 diabetes focuses on the nutritional composition of foods, these findings suggest that people should also seek to limit their consumption of ultra-processed foods.

Dr. Michael Lean, Professor of Human Nutrition at the University of Glasgow, who was not involved in the study, considers it to be a “well conducted” study but is “not persuaded that the processing is hazardous” for a number of reasons.

Prof. Lean pointed out that “this is a study of associations, not causes,” and the role of other factors in causing mortality cannot be ruled out.

Another possible explanation for why people who ate more ultra-processed foods died sooner, according to Professor Lean, is that “people who eat more processed foods are the same people who eat less whole foods and traditional meals. So maybe the entire study is actually missing the point that traditional foods are protective.”

Finally, he explained that this could be a case of reverse causality. Professor Lean explained that people with diabetes might be “advised to eat transportable ‘snacks’ between meals which are often heavily processed and packaged”. People whose diabetes is “more severe, less well controlled, or needs more medication, […] are more likely to die and may well change their diets to have more of these foods.

Despite his reservations, Professor Lean told MNT that his personal preference is to “enjoy whole foods and traditional meals, and seldom, almost never, buy processed foods.”

Some experts believe that adopting the NOVA food labeling system to inform consumers about the level of food processing (on a scale of 1 to 4) would help to limit the consumption of ultra-processed foods. Currently, several countries use the Nutri-Score front-of-package nutrition label, which indicates the nutritional value of a product on a scale of A to E.

When asked about the usefulness of such food labels, Dr. Bonaccio told MNT: “Currently, the front-of-pack nutrition labels are exclusively focused on the nutritional composition of foods (looking at content of fat, salt, sugar, fiber) with no mention to the degree of food processing. Our data also indicate that a truly effective nutrition labeling system should also warn about the food processing.”