Avoid Weight Gain by Avoiding Ultra-Processed Foods

By Emma Ryan and Annie Chen

A study finds that packaged snacks, pre-prepared meals, and other “ultra-processed” foods lead to weight gain; unprocessed foods lead to weight loss

There remains debate over which diet is “best” for weight loss and maintenance, but one thing nearly everyone agrees on is to decrease intake of “ultra-processed” foods. Ultra-processed foods typically include at least five ingredients, concentrated doses of sugar and refined carbohydrates, and long shelf lives (i.e., they don’t spoil quickly). Processed foods often include substances not found in home-cooked meals like dyes, artificial flavors, non-sugar sweeteners, and preservatives. See examples of processed and unprocessed foods at the end of the article!

A recent study showed that people who ate ultra-processed foods consumed approximately 500 more calories per day than those who ate unprocessed, whole foods. Those eating ultra-processed foods gained an average of two pounds in weight in over two weeks. Conversely, consuming an unprocessed diet over two weeks caused an average of two pounds of weight loss.

The study examined 20 adults who alternately ate an ultra-processed diet and an unprocessed diet for two weeks at a time. The two diets included meals that presented the same number of calories, energy density (number of calories per gram of food), macronutrients (e.g. fat, protein, carbohydrate), and total sugar, sodium, and fiber. However, due to the nature of ultra-processed foods, this diet had substantially more added sugar (i.e., extra sugar put in by the manufacturer) and saturated fat. Participants could eat as much or as little as they wanted.

The researchers found that the increase in calorie intake from the ultra-processed diet was driven by fats and carbohydrates – participants did not increase their protein intake. Participants did not report significant differences in the pleasantness or familiarity of the two diets, suggesting that the increased calorie intake due to the ultra-processed diet was not a result of better-tasting or more appealing food. However, subjects on the ultra-processed diet did eat more quickly. One hypothesis is that these foods disrupt signaling between the digestive system and the brain that helps us determine how much food to eat.

This carefully designed study suggests that limiting – and ideally avoiding – processed foods may be an effective strategy for weight loss and maintenance. In fact, the American Diabetes Association’s (ADA) recent Nutrition Guidelines emphasized that limiting processed foods is a key recommendation among all effective nutrition choices.

See examples of processed and unprocessed foods below and several photos of the meals in the study in this article. Michael Pollan’s fantastic, short book, Food Rules, has a number of memorable quotes about processed foods:

• “The whiter the bread, the sooner you'll be dead.”

• “It's not food if it arrived through the window of your car.”

• “If it’s a plant, eat it. If it was made in a plant, don’t.”

• “Don’t eat breakfast cereals that change the color of your milk.”