Eating highly processed foods is linked to weight gain

At a Glance

  • When people eat a diet full of ultra-processed foods, they consume more calories and gain more weight than when they eat a minimally processed diet.
  • The results suggest the importance of identifying and eating healthy foods.

Eating a healthy diet can help lower your risk of certain diseases and maintain a healthy weight. A healthy eating plan is made up of vegetables, fruit, whole grains, and fat-free or low-fat dairy products. It also includes lean meats, poultry, fish, beans, eggs, and nuts. A healthy diet limits saturated and trans fats, sodium, and added sugars. It also emphasizes eating minimally processed foods.

Previous studies have suggested a link between diets high in “ultra-processed” foods and health problems. Ultra-processed foods have ingredients common in industrial food manufacturing, such as hydrogenated oils, high-fructose corn syrup, flavoring agents, and emulsifiers. They are often cheaper and more convenient than making a meal from whole foods. But they’re usually high in calories, salt, sugar, and fat.

To investigate the impact of eating ultra-processed foods on weight, a team led by Dr. Kevin D. Hall at NIH’s National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) compared body weight changes and calorie consumption for 20 healthy adults—10 men and 10 women—who ate either an ultra-processed or a minimally processed diet for two weeks.

The participants stayed at the NIH Clinical Center for 28 straight days. Each spent two weeks on both of the diets. They received three meals a day, plus snacks, made up of ultra-processed foods or minimally processed foods. For example, an ultra-processed breakfast might consist of a bagel with cream cheese and turkey bacon, while a minimally processed breakfast might be oatmeal with bananas, walnuts, and skim milk.

The ultra-processed and minimally processed meals have the same number of calories, sugars, fiber, fat, and carbohydrates. Participants can eat as much or as little as they want. They reported that the diets both tasted good and were satisfying. Results were published on May 16, 2019, in Cell Metabolism.

On the ultra-processed diet, people ate about 500 calories more per day than they did on the minimally processed diet. These increased calories come from carbohydrate and fat. People also ate faster on the ultra-processed diet and gained 2 pounds on average. When they were on the minimally processed diet, they lost about the same amount of weight.

While the study reinforces the benefits of unprocessed foods, the researchers note that ultra-processed foods can be difficult to restrict. “We have to be mindful that it takes more time and more money to prepare less-processed foods,” Hall says. “Just telling people to eat healthier may not be effective for some people without improved access to healthy foods.”

It’s also not clear what specific aspects of the ultra-processed foods affected people’s eating behavior and led them to gain weight. “The next step is to design similar studies with a reformulated ultra-processed diet to see if the changes can make the diet effect on calorie intake and body weight disappear,” Hall says.

References: Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake. Hall KD, Ayuketah A, Brychta R, Cai H, Cassimatis T, Chen KY, Chung ST, Costa E, Courville A, Darcey V, Fletcher LA, Forde CG, Gharib AM, Guo J, Howard R, Joseph PV, McGehee S , Ouwerkerk R, Raisinger K, Rozga I, Stagliano M, Walter M, Walter PJ, Yang S, Zhou M. Cell Metabolism. 2019 May 10. pii: S1550-4131(19)30248-7. doi: 10.1016/j.cmet.2019.05.008. [Epub ahead of print]. PMID: 31105044.

Funding: NIH’s National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).