Posted on May 16, 2019, 4 p.m.
Those eating highly processed foods gained more weight then when eating minimally processed foods, even when the diets had the same number of calories and macronutrients according to results from a National Institutes of Health study published in Cell Metabolism.
The small scale randomized controlled trial examined the effects of ultra processed foods as defined by the NOVA classification system, which are those containing ingredients predominantly found in industrial food manufacturing such as high fructose corn syrup, hydrogenated oils, flavoring agents, and emulsifiers.
Studies conducted in the past looking for associations between health problems and processed food diets have not randomly assigned participants to eat specific foods to measure results, thus scientists were not able to say for certain whether processed foods were a problem on their own or whether those eating them had health problems for other reasons.
"Though we examined a small group, results from this tightly controlled experiment showed a clear and consistent difference between the two diets. This is the first study to demonstrate causality -- that ultra-processed foods cause people to eat too many calories and gain weight." says Kevin D. Hall, Ph.D.
The NIH Clinical Center admitted 20 healthy participants for an uninterrupted month, and in random order participants were provided meals for each two week diet made up of meals that were either ultra processed foods or minimally processed foods. As example an ultra processed breakfast may have consisted of a bagel with cream cheese and turkey bacon, and the unprocessed breakfast may have consisted of oatmeal with bananas, walnuts, and skim milk; both meal types had the same amount of calories, fat, carbohydrates, fiber, and sugars, and participants could eat as much or as little as they choose to.
While on the ultra processed diet participants consumed about 500 calories more per day, and ate faster while on this diet and gain on average 2 pounds, whereas they lost the equivalent amount of weight on the unprocessed diet.
"We need to figure out what specific aspect 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.”
"Over time, extra calories add up, and that extra weight can lead to serious health conditions. Research like this is an important part of understanding the role of nutrition in health and may also help people identify foods that are both nutritious and accessible -- helping people stay healthy for the long term."
Slight differences in protein levels between the diets may explain some of the differences in calorie intake. Ultra processed foods can be difficult to restrict even though this study highlights and adds more weight to the benefits of unprocessed foods.
"We have to be mindful that it takes more time and more money to prepare less-processed foods. Just telling people to eat healthier may not be effective for some people without improved access to healthy foods."
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