By Sandra Dunham

Is there a topic more discussed than diet? Do you ever wonder what is true and what is not true?

A recent study by the National Institutes of Health, published in the July issue of Cell Metabolism , examined the effects of highly processed foods on weight. The study randomly divided subjects into two groups. One would spend two weeks eating ultra-processed foods followed immediately by two weeks eating unprocessed foods. The other group had the order of food groups flipped, eating unprocessed foods for two weeks before ultra-processed foods for two weeks.

Quick facts about the study:

  • Processed and non-processed diets were matched for calories, sugar, fat, fiber, sodium, and macronutrients;
  • Meals were substantially different, however, in the ratios of added to total sugar; insoluble to total fiber; saturated to total fat, and omega-6 to omega-3 fatty acids;
  • Subjects were presented with three meals per day and invited to eat as much as they wanted in the 60-minute meal period;
  • Subjects were asked to rate the diets on pleasantness, familiarity, hunger, fullness, and satisfaction.

The results? The authors concluded that “eliminating ultra-processed foods from the diet decreases energy intake and results in weight loss, whereas a diet with a large proportion of ultra-processed food increases energy intake and leads to weight gain.” Further, while this study does not fully understand the relationship between processed food and weight, it did uncover some interesting findings, including an association between a) eating unprocessed foods and b) both an increase in the appetite-suppressing hormone PYY as well as a decrease in the hunger-creating hormone ghrelin.

Like any good research, this paper outlines the limitations of its study. For instance, the authors point out that consumer choice plays a large factor in selecting processed and unprocessed food, including the increase in cost and time associated with unprocessed foods. Indeed, the study points out that at the large local supermarket where they purchased their food, the processed food cost $106 per week compared with $151 for the unprocessed food.

The study did not investigate the cause of the differences, and therefore can only be seen as illustrating correlation rather than causation. The researchers admit they still have much to learn about the relationship between processed foods and weight, including the burning question: Why do people eat more when the food is processed?

This article appears in the October 2019 version of Critical Links.