Limiting ultra-processed foods may be key

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For people with type 2 diabetes, the negative effects of eating too many ultra-processed foods can negate 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 considered 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 foods that have been heavily processed and contain multiple food additives.

A new study suggests that people with type 2 diabetes should focus not only on the fiber, fat and sugar content of their food, but to 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 place a heavy emphasis on specific food groups such as whole grains, legumes (such as beans and lentils), nuts, fruits and vegetables.

ONE 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 people with type 2 diabetes.

The new study, published in American Journal of Clinical Nutritionfound 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 can cause premature death.

More studies have shown that diets rich in ultra-processed foods increase the risk of developing type 2 diabetes. However, no study has examined the link 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 Moli-sani studywho collected data from 24,325 people aged over 35 years 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 in relation to total food intake. They also assessed how healthy each person’s overall diet was 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 taken directly from nature
  • Group 2 contains “culinary ingredients”, such as salt, oil, sugar or starch, which are made from Group 1 foods
  • Group 3 contains “processed foods”, such as freshly baked bread, tinned 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 made with substances derived from Group 1 foods through heavy processing (e.g. hydrolysed proteins, maltodextrins, hydrogenated fats) and contain numerous food additives such as colourants, preservatives, antioxidants, flavor enhancers and sweeteners.

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

  • carbonated drinks, infant formulas and other highly processed drinks marketed as “milk” or “fruit” drinks
  • packaged snacks and mixes such as potato chips, sweets, cookies, cake mixes, breakfast cereals, 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 women and men, respectively) had a higher risk of death from all causes and from CVD compared with those who ate the least ultra-processed foods, and the risk increased with increasing ultra-processed food consumption.

The association 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, 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 solely related to the poor nutritional content of these foods, but are likely triggered by non-nutritional factors, such as food additives, pollutants from plastics, changing 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 treating 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 Leanprofessor of human nutrition at the University of Glasgow, who was not involved in the study, considers it a “well-conducted” study but is “not convinced that the treatment is dangerous” for a number of reasons.

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

“In studies of heart disease or mortality, smoking is the biggest causal factor. It is curious that this paper does not appear to have adjusted the data for smoking. The effect of medication is also important and seems neglected in this study.”

Another possible explanation for why people who ate more ultra-processed foods died faster, 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 whole study is actually missing the point that traditional foods are protective.”

Finally, he explained that there could be reverse causality. Professor Lean explained that people with diabetes may be “advised to eat portable ‘snacks’ between meals, which are often highly processed and packaged”. People whose diabetes is “more severe, less well controlled, or need more medication (…) are more likely to die and may well change their diets to get more of these foods.

Despite his reservations, Professor Lean said MNT that his personal preference is to “enjoy whole foods and traditional meals and rarely, if ever, buy processed foods.”

Some experts believe that the adoption of NOVA food labeling system informing 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 nutrition label on the front of the package, which indicates the nutritional value of a product on a scale from A to E.

When asked about the utility of such food labels, Dr. Bonaccio MNT: “At the moment, the nutrition declarations on the front are solely focused on the nutritional composition of the food (if you look at the content of fat, salt, sugar, fibre) without mentioning the degree of food processing. Our data also indicate that a truly effective nutrition labeling system should also warn the food processor.”

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