Those who are trying to combat overeating and achieve a healthy weight often resort to counting calories. This approach, however, is not the best for disease prevention or weight loss, and does not address the negative health implications of eating highly processed foods.

A recent study published online by Cell Metabolism on May 16, 2019, found that when people ate a diet full of ultra-processed foods, they consumed more calories and gained more weight than when they ate a minimally processed diet. The results highlight the importance of educating yourself on healthy foods, and incorporating them into your diet.

Many studies show a correlation between the intake of ultra-processed foods and a wide variety of health issues. The rise in obesity and type 2 diabetes has been linked to an increasingly industrialized food system, which favors large scale production of high-yield, inexpensive, agricultural inputs like corn and wheat, which are refined and processed.

Highly processed foods contain ingredients common in industrial food manufacturing, such as hydrogenated oils, high-fructose corn syrup, flavoring agents, and emulsifiers. They are typically high in calories, salt, sugar and “bad” fats (trans fats and saturated fats). Currently, the majority of calories consumed in America are from ultra-processed foods.

A research project led by Dr. Kevin Hall at NIH’s National Institute of Diabetes and Digestive and Kidney Diseases compared body weight changes and calorie consumption for 20 healthy adults, evenly divided between men and women, who ate either an ultra-processed or minimally processed diet for two weeks. The volunteers stayed at the NIH Clinical Center for one continuous month, were randomly assigned a diet for two weeks, and then switched.

The ultra-processed and minimally processed meals had an equal number of calories, macronutrients, sugars, fiber, fat and carbohydrates. For example, one ultra-processed breakfast consisted of a bagel with cream cheese and bacon, while an unprocessed breakfast was oatmeal with fruits and nuts. Participants could eat as much or as little as they wanted.

On the ultra-processed diet, participants ate an average of 500 more calories per day, ate faster, and gained 2 pounds during the two weeks on average. On the minimally processed diet, they lost about 2 pounds over the same time period.

“Though we examined a small group, results from this tightly controlled experiment showed a clear and consistent difference between the two diets,” said Kevin D. Hall, Ph.D., an NIDDK senior investigator and the study’s lead author. “This is the first study to demonstrate causality — that ultra-processed foods cause people to eat too many calories and gain weight.”

That said, the researchers noted the major lifestyle changes that could be necessary to shift to a less processed diet, as well as the socio-economic limitations.

“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.”

Overall, the study reinforces one common piece of advice recommended by most diets, which is to avoid ultra-processed foods in favor of whole foods as often as possible.