Do Ultra Processed Foods Lead to Weight Gain?

A study published in Cell Metabolism investigated the relationship between consuming ultra processed foods, weight gain, and overeating.  The results may (or may not) surprise you.  Much has been written about ultra processed foods (UPF’s) and weight gain.  To date there have been no randomized controlled trials to show a causative relationship.  Until now.

What Are Ultra Processed Foods?

According to the NOVA classification of processed foods, UPF’s are defined as: “the ones that use many ingredients including food additives that improve palatability, processed raw materials (hydrogenated fats, modified starches, etc.) and ingredients that are rarely used in home cooking such as soy protein or mechanically separated meat. These foods are mainly of industrial origin and are characterized by a good pleasantness and the fact that they can be stored for a long time.”

In other words, 90% of what is for sale in grocery stores would be classified as “ultra processed.”

Avoiding and systematically eliminating ultra processed foods from your diet is a hallmark of the BWCLP.

About the Study

Lead author Kevin Hall is well known for his studies looking at long term outcomes for participants on the Biggest Loser.  This paper titled, “Ultra Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake,” looked at the difference between eating a diet of ultra processed foods, versus minimally processed foods.

20 People were randomly assigned into two different groups.  One group would consume a diet consisting of ultra processed foods, while the other group ate a diet made of prepared whole foods with minimal processing.  At the end of two weeks the two groups would switch over to the opposite group.  This is known as a “Crossover” because the two groups “crossed over” to the other group.  Basically, all participants ate both of the diets for 2 weeks to eliminate any sampling bias.

The diets were matched for carbohydrates, fats, proteins, and calories provided.  However, participants in both groups were allowed to eat ad libitum until satiation.  In other words, they were allowed to eat freely until they felt full.

What Did the Study Find?

Both groups ate an additional 500 calories when they were on the ultra processed diets.  The additional calories came in the form of additional carbohydrates and fat, but not protein.  In addition, both groups gained an average of .9 KGS during the two weeks on ultra processed foods, and lost .9 KGS (1.8 pounds) during the 2 weeks of minimally processed foods.  .4 KGS of the weight gain on average was increased fat mass.

What Does It Mean?

In short, both groups ate more and gained additional weight while consuming the UPF’s. Subjects tended to LOSE an equal amount of weight while eating whole foods.  Despite the fact that they were allowed to eat freely during the entire study, they consumed on average 500 less calories during the two weeks of eating unprocessed foods.

Why Is This Significant?

Online diet gurus and charlatans love to argue over which fad diet is the best.  This internet bravado has lead to increased skepticism about nutrition science and confusion around which “diet” is best.  We teach that the best starting point for any diet is to eliminate UPF’s first and foremost.  (Yes, even the “all natural and organic” ultra processed junk foods at Trader Joe’s and Whole Foods).

This study is the first to show a causative relationship between UPF’s and overeating.  Previous studies have shown correlations, but this is the first to show a degree of causation!

While UPF’s are inexpensive and have a long shelf life, the convenience may not be worth the health risks associated with them.

Long story short, eat real food.