Processed Foods Trigger Weight Gain: NIH study

We have published reports on numerous scientific studies over the past decade that have linked highly processed foods (and their additives) to weight gain and obesity.  The reason for so much interest and scientific inquiry is obvious:  With Big Food’s advent of new chemical concoctions and widespread marketing making their way into mainstream grocery stores, workplaces, hotels, airlines, schools, hospitals and more over the past several decades, U.S. consumers have become inundated with highly processed foods (comprised largely of industrialized and synthetic ingredients)* nearly every place they go and at the same time, weight gain and obesity rates–and the accompanying health-related problems–have spiked significantly in this country.  Numerous research studies have sought to uncover whether there is a genuine link between the two.

Now a new National Institute of Health (NIH) study has just been released that links highly processed foods to weight gain in a rather dramatic way.  The reason is because the study was highly controlled and results were obvious.

*Highly processed/ultra-processed foods include more than just the obvious suspects, like chips, candy, packaged desserts and ready-to-eat meals. The category also includes foods that some consumers might find surprising, including Honey Nut Cheerios and other breakfast cereals, packaged white bread, jarred sauces, frozen sausages and other reconstituted meat products, and yogurt with added fruit…ultra-processed foods usually contain a long list of ingredients, many of them made in labs. So, for example, instead of seeing “apples” listed on a food label, you might get additives that re-create the scent of that fruit. These are foods designed to be convenient, low cost and requiring little preparation.  -Dr. Barry Popkin, nutrition professor, University of North Carolina (source)

Highly-processed/ultra-processed foods are “formulations mostly of cheap industrial sources of dietary energy and nutrients plus additives, using a series of processes” and containing minimal whole foods (.   (source)




Study overview and results


The study, conducted by researchers at the National Institutes of Health, is the first randomized, controlled trial to show that eating a diet made up of ultra-processed foods actually drives people to overeat and gain weight compared with a diet made up of whole or minimally processed foods. Study participants on the ultra-processed diet ate an average of 508 calories more per day and ended up gaining an average of 2 pounds over a two-week period. People on the unprocessed diet, meanwhile, ended up losing about 2 pounds on average over a two-week period…(source / source)

…each meal offered on the two different diets contained the same total amount of calories, fats, protein, sugar, salt, carbohydrates and fiber. Study participants were allowed to eat as much or as little as they wanted, but ended up eating way more of the ultra-processed meals, even though they didn’t rate them as being tastier than the unprocessed meals.

-Dariush Mozaffarian, Dean of Tufts University’s Friedman School of Nutrition Science and Policy

The results point to chemical additives as the culprit

The lead scientist on the study was surprised by the findings, because many people have suspected it is the high salt, sugar and fat content in ultra-processed foods that drives people to gain weight. But the results of the study revealed something else is triggering weight gain…

“When you match the diets for all of those nutrients, something about the ultra-processed foods still drives this big effect on calorie intake.”

-Dr. Kevin Hall, senior scientist at the National Institute of Diabetes and Digestive and Kidney Diseases

Study Methods

This small pilot study/clinical trial was highly controlled. Twenty healthy, stable-weight adults — 10 men and 10 women — were recruited to live in an NIH facility for a four-week period. All their meals were provided for them.

Participants were randomly assigned to one of two diets for two-week stretches: One group was fed an unprocessed diet full of whole or minimally processed foods like stir-fried beef with vegetables, basmati rice and orange slices. The other group ate an ultra-processed diet of meals like chicken salad made with canned chicken, jarred mayonnaise and relish on white bread, served with canned peaches in heavy syrup. When the two weeks were up, the groups were then assigned to the opposite diet plan.

Besides tracking daily intake of calories and nutrients, the researchers also took detailed metabolic measurements, and measurements of blood glucose levels and hormone levels.  (source / source)

Additional Findings

“One thing that was kind of intriguing was that some of the hormones that are involved in food intake regulation were quite different between the two diets as compared to baseline.”

–Dr. Kevin Hall, senior scientist at the National Institute of Diabetes and Digestive and Kidney Diseases

Participants eating the unprocessed diet had higher levels of an appetite-suppressing hormone called PYY, which is secreted by the gut, and lower levels of ghrelin, a hunger hormone, which might explain why they ate fewer calories. On the ultra-processed diet, these hormonal changes flipped, so participants had lower levels of the appetite-suppressing hormone and higher levels of the hunger hormone. (source / source)

Study Takeaway/Solution

Consumers should avoid or significantly reduce the amount of highly processed foods in their diet and create their own meals of natural, whole foods (organic where possible).


Journal Reference:  Hall, Kevin D., et al. (2019). Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake, Cell Metabolism, Clinical and Translational Report,