Diets high in minimally processed foods do not necessarily provide greater nutritional benefits than those containing more ultra-processed foods. A study comparing two Western diets found similar nutritional results, but noted that minimally processed foods were more expensive and had a shorter shelf life.
A new study questions the level of processing as an indicator of food quality.
Recent research challenges the idea that minimally processed foods automatically lead to healthier diets, revealing that minimally or ultra-processed diets can be equally nutritious or lacking in nutritional value. The study highlighted that minimally processed diets may be more expensive and have a shorter shelf life without additional nutritional benefits, highlighting the complexity of defining diet quality by processing levels alone.
Food choices and processing levels
New research shows that eating mostly minimally processed foods, as defined by the NOVA classification system, does not automatically constitute a healthy diet. It suggests that the types of foods we eat may matter more than the level of processing used to prepare them.
Comparing two menus that reflected a typical Western diet — one emphasizing minimally processed foods and the other emphasizing ultra-processed foods, as categorized by the NOVA classification system — the researchers found that the less processed menu was more than twice as expensive and reached its expiration date three times faster without providing any additional nutritional value.
Examples of a more processed (left) and less processed (right) breakfast. None of the ingredients used to prepare the less processed meal are considered ultra-processed (the bread and jam are homemade), while almost all of the components of the more processed meal are considered ultra-processed. Credit: Courtesy of USDA-ARS
Research findings on processed and minimally processed diets
“This study shows that it’s possible to eat a poor-quality diet even if you choose mostly minimally processed foods,” said Julie Hess, Ph.D., a nutrition researcher at the USDA-ARS Human Nutrition Research Center in Grand Forks, who led the study. “It also shows that more or less processed diets can be equally nutritious (or not nutritious), but that the more processed diet may have a longer shelf life and be less expensive.”
Mark Messina, PhD, director of nutritional sciences and research at the Soy Nutrition Institute Global, recently presented the findings at NUTRITION 2024, the flagship annual meeting of the American Society for Nutrition.
Assessment of the nutritional quality of different diets
The new study builds on a study the team published last year that showed it was possible to create a high-quality menu that met dietary guidelines while getting most of its calories from foods classified as ultra-processed. For the new study, the researchers asked the opposite question: Is it possible to create a low-quality menu that gets most of its calories from “simple” foods?
To find out, they created a less processed menu, with 20% of calories coming from ultra-processed foods, and a more processed menu, with 67% of calories coming from ultra-processed foods. The level of processing involved in each menu was determined using the NOVA classification system.
Both menus were calculated to have a healthy eating index of about 43-44 out of 100, a relatively low score that reflects low adherence to dietary guidelines for Americans. The researchers estimated that the less processed menu would cost $34.87 per day per person, compared to $13.53 per day for the more processed menu. They also calculated that the median expiration time for the less processed menu items was 35 days, compared to 120 days for the more processed menu items.
The study draws attention to the disconnect between food processing and its nutritional value. Hess noted that some nutrient-dense packaged foods can be classified as ultra-processed, such as unsweetened applesauce, ultrafiltered milk, liquid egg whites and some brands of raisins and canned tomatoes.
“The results of this study indicate that developing a nutritious diet is not limited to considering food processing as defined by NOVA,” Hess said. “The concepts of ‘ultra-processed’ and ‘less processed’ foods need to be better characterized by the nutrition research community.”
Unprocessed, but sad: A standard American diet of less processed foods is still a standard American diet
Presenting authors:
Julie M. Hess, Ph.D., Grand Forks Human Nutrition Research Center, USDA-ARS
Mark Messina, PhD, MS, Director of Nutrition Science and Research, Soy Nutrition Institute Global
Co-authors:
Madeline E. Comeau, MS, Grand Forks Human Nutrition Research Center, USDA-ARS
Angela J. Scheett, Grand Forks Human Nutrition Research Center, USDA-ARS; University of North Dakota
Anne Bodensteiner, Ph.D., RDN, LRD, University of North Dakota
Allen S. Levine, University of Minnesota, USA
Daniel Palmer, USDA-ARS Human Nutrition Research Center in Grand Forks
The trend toward healthy eating, which involves eating primarily foods with simple ingredients, suggests that eating fewer processed foods is a necessary aspect of a healthy diet. However, research indicates that a menu containing primarily ultra-processed foods (UPFs) can meet the nutritional quality and dietary recommendations of the Dietary Guidelines for Americans. Whether a diet consisting primarily of foods with simple ingredients can provide a poor-quality diet remains to be determined. The objective of this study was to compare the dietary quality, shelf stability, and cost of two similar Western-style menus, one containing energy primarily from UPFs and the other containing energy primarily from less processed foods, as defined by the Nova Food Classification System.
First, a less processed version of a Western menu (least processed Western, LPW; most processed Western MPW) with a Healthy Eating Index (HEI) score of approximately 43 was developed to align with the previously developed MPW HEI score. The level of processing was determined by Nova categorizations assigned by external raters. The final menu was assessed for nutrient content and HEI score. Shelf stability of foods was determined using information from food storage guidance manuals. The condition of each food at the time of purchase (shelf stable, frozen, refrigerated) was used to estimate days to expiration. Food and menu costs were determined using retail prices from a Midwestern grocery chain in the fall of 2023.
LPW and MPW had similar nutrient densities and HEI scores (44 and 43, respectively). LPW included 20% of energy (kcal) from UPF, while MPW included 67% of energy from UPF. The relative percentages of shelf-stable, frozen, and refrigerated foods were similar between the two. Using the Kaplan-Meier survival analysis method, the median time to expiration for LPW menu items was 35 days versus 120 days for MPW menu items. The “per person” cost was $34.87/day for LPW and $13.53/day for MPW.
Both the less-processed and more-processed menus provided poor-quality diets. However, LPW was more than twice as expensive as MPW and had a shorter overall shelf life. The level of processing is not a proxy for diet quality, and less-processed foods may be more expensive and have a shorter shelf life.
Funding: USDA Agricultural Research Service Project Grant No. 3062-51000-057-00D