This undated photo provided by the National Institutes of Health in June 2019 shows an "ultra-processed" lunch including brand name macaroni and cheese, chicken tenders, canned green beans and diet lemonade. Credit: Paule Joseph Shavonne Pocock | AP

America has an obesity epidemic that is increasing our medical costs and decreasing the quality of life for many people. Evidence is accumulating that the increased amount of processed food in our diet is a major cause of this epidemic.

This evidence includes experiments with mice showing that when they are fed processed human foods, they become extremely obese — even when compared to their weight gain on a diet rich in fat and sugar.

There are many reports of overweight individuals returning to normal weights by eliminating processed foods from their diets. Moreover, several published diet trials show substantial weight loss when processed foods are eliminated from the diet, without any calorie counting by the subjects. These studies with people are highly suggestive but were not tightly controlled, leaving room for doubt.

For the first time, we now have a fully controlled study by researchers at the National Institute of Health that shows that highly processed foods can cause people to overeat. Half of the subjects were given a diet of highly processed foods for two weeks, followed by a diet of relatively unprocessed foods for two weeks. The order of the two trials was reversed for the other half of the subjects.

The highly processed diet was high in processed meat and white flour products with various amounts of added sugar and fat. In the less-processed diet, the protein came from lean meat and low-fat dairy; the carbohydrates were from whole grains, intact fruits and vegetables; the sugar was from intact fruit; and much of the fat was from olive oil and nuts. Subjects could eat as much as they wanted and were equally satisfied with both diets. The remarkable result was that they ate about 500 calories per day more on the diet of highly processed foods. This occurred even though the diets were matched for sugars, carbohydrates, fats and proteins.

From these results, it is clear that highly processed foods can overcome our weight regulation systems. This strongly suggests that if people want to lose weight, they will probably need to permanently decrease their consumption of many types of processed foods. Simply counting calories and using willpower to eat less will not be sustainable for most people.

Foods act on the brain via the same pathways involved in drug, alcohol and gambling addictions. Processed foods tend to overstimulate our brain reward pathways and cause us to overeat. This overeating often occurs without our being aware of it. To lose weight, people need to recognize the foods that they overeat and eliminate or limit them in their diets. As examples, snacks for the processed food diet in the above study were chips, crackers, salted peanuts and applesauce, while for the minimally processed diet the snacks were apples, oranges, raisins, walnuts and raw almonds.

Health professionals who advise their patients on weight loss, and especially those running weight loss programs, should incorporate these new results into their advice and programs. People do not become overweight because of their lack of discipline when they are eating. The important factor is the kind of foods that they are eating. Where discipline is needed is during food purchases — whether at the grocery store, restaurant, vending machine or at cash register displays. The foods readily available because of family members or coworkers are also important.

John Tjepkema is Professor Emeritus at the University of Maine School of Biology and Ecology. This column reflects his views and expertise and does not speak on behalf of the university.