Tip: Ultra-Processed vs. Unprocessed Diets

Twenty weight-stable adults were assigned to one of two diet groups: either a diet containing ultra-processed foods or an unprocessed-food diet. Think: "dirty vs. clean."

The food was provided by the research group and meals were matched for presented calories, energy density, macronutrients, sugar, sodium, and fiber. (The meals were matched for those presented variables, although the participants had the choice to eat more or less of the different foods on their plates.)

The study was designed as two, 2-week diet periods in a randomized crossover intervention trial. That just means the groups switched diets after two weeks.

What exactly constitutes ultra-processed vs. unprocessed foods? Ultra-processed foods have been described as "formulations mostly of cheap industrial sources of dietary energy and nutrients plus additives, using a series of process and containing minimal whole foods."

Translation: Apple cinnamon crunch cereal vs. whole apples. Turkey sausage vs. turkey breast. French fries vs. potatoes. Corn chips vs. corn on the cob, etc.

Here are two sample meals actually used in the study:

At baseline, their diets were somewhere in between an ultra-processed food-rich diet and an unprocessed food-rich diet. Since this was a crossover study, each participant completed both diet groups which controls for baseline confounding variables.

When they began the study, those in the ultra-processed diet group started eating a little more while those in the unprocessed group started eating a little less. By the end of the study, this amounted to a 500 calorie per day difference.

Those extra 500 calories generally came from refined fats and carbs. Think about it: How easy is it to overeat french fries verses a baked potato? Also, "meal eating rate" was over two times faster in the ultra-processed food group. Mac 'n cheese goes down faster than steamed broccoli. In fact, most ultra-processed foods are engineered to be eaten with minimal chewing.

Participants in both groups reported similar levels of hunger, fullness, satisfaction, and eating capacity. They were similarly pleased and familiar with the foods and meals in both diets. In other words, those eating the unprocessed foods weren't hungrier or less satisfied than those eating frozen chicken tenders.

Not surprisingly, when the participants were in the unprocessed diet arm of the study they lost weight, whereas when they were in the ultra-processed diet arm they gained weight, primarily as body fat.

Somewhat surprisingly, despite these differences in body composition, metabolic parameters were largely unaffected. No change in fasting blood glucose or insulin levels, no change in blood glucose or insulin levels during an oral glucose tolerance test. Most likely, two weeks is too short to show significant alterations with changes of the magnitude in food intake / body composition seen in this study.

Look at your meals. There are simple ways to substitute unprocessed foods for ultra-processed ones without significantly influencing your satisfaction. Ultra-processed food leads to mindless overeating. Don't sabotage your goals!

1. Hall KD et al. Ultra-processed diets cause excess calorie intake and weight gain: A one-month inpatient randomized controlled trial of ad libitum food intake. Cell Metab. 2019 Jul 2;30(1):67-77.e3. PubMed.