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Study Finds Ultra-Processed Foods Drive Weight Gain: The Salt: NPR



An example of one of the study's ultra-processed lunches consists of quesadillas, refried beans and lemonade diets. Participants on this diet ate an average of 508 calories more per day and gained an average of 2 pounds over two weeks.
                
                
                    
                    Hall et al. / Cell Metabolism
                    
                

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Hall et al./Cell Metabolism
        
    

An example of one of the study's ultra-processed lunches consists of quesadillas, refried beans and lemonade diets. Participants on this diet ate an average of 508 calories more per day and gained an average of 2 pounds over two weeks.

Hall et al./Cell Metabolism
            
        

Over the past 70 years, ultra-processed foods have come to dominate the U.S. diet. These are foods made from cheap industrial ingredients and engineered to be super tasty and generally high in fat, sugar and salt

The rise of ultra-processed foods has coincided with growing rates of obesity, leading many to suspect they've been playing and a big role in our growing waistlines. But is it something about the highly processed nature of these foods itself that drives people to overeat? A new study finds the answer is yes

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 to a diet made 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 over a two-week period.

"The difference in weight gain for one [group] and weight loss for the other during these two periods is phenomenal. We have not seen anything like this, "says Barry Popkin, a nutrition professor at the University of North Carolina, who has studied the role of ultra-processed foods in the American diet

Dariush Mozaffarian, dean of Tufts University's Friedman School of Nutrition Science and Policy, agrees that the findings are striking. He says what was so impressive was that NIH researchers documented this weight gain even though each meal offered on the two different diets contained the same total amount of calories, fat, protein, sugar, salt, carbohydrates and fiber. Study participants were allowed to eat as much or as little as they wanted, but ended up eating more of the ultra-processed meals, even though they did not rate them as being tastier than the unprocessed meals

"These are landmark findings that the processing of food makes a huge difference in how much a person eats, "says Mozaffarian. That's important, because most of the foods now sold in the U.S. – and increasingly, around the globe – are ultra-processed.

And ultra-processed foods include more than obvious suspects, such as 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. Popkin says 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.

The new research, which appears in the journal Cell Metabolism was led by Kevin Hall, senior scientist at the National Institute of Diabetes and Digestive and Kidney Diseases. Hall says he was surprised by his 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 "when you match the diets for all of those nutrients, something about the ultra-processed foods still drives this big effect on calorie intake," Hall says.

To conduct the study, Hall and his colleagues recruited 20 healthy, stable -weight adults – 10 men and 10 women – to live in a NIH facility for a four-week period.

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 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

Even though the study was small, it was also highly controlled. Researchers knew exactly how many macronutrients and calories participants were eating and burning because they took detailed metabolic measurements. The researchers also tracked other health markers, including blood glucose levels and even hormone levels. Hall notes that this makes these types of studies extremely difficult and expensive to carry out. But the study design makes the findings much more significant, Popkin and Mozaffarian both say.

"Putting people in a controlled setting and giving them their food lets you really understand biologic what's going on, and the differences are striking," says Mozaffarian.

For one thing, previous studies have linked an ultra-processed diet to weight gain and poor health outcomes, such as increased risk for several cancers and early death from all causes. But these studies were all observative, which means they could not prove that these ultra-processed foods caused these outcomes, only that they were correlated.

Hall says the new study was not designed to see what exactly it is about ultra-processed foods that drive overeating, but findings suggest some mechanisms. that was kind of intriguing that some of the hormones that are involved in food intake regulation were quite different between the two diets compared to baseline, "Hall says.

For example, when participants were eating the unprocessed diet, they a higher level of an appetite-suppressing hormone called PYY, which is secreted by the gut, and lower levels of ghrelin, and hunger hormone, which may explain why they ate fewer calories. On the ultra-processed diet, these hormonal changes flipped, with participants having lower levels of the appetite-suppressing hormone and higher levels of the hunger hormone.

Another interesting finding: Both groups ate about the same amount of protein, on the ultra-processed diet ate a lot more carbs and fat. There is a concept called protein leverage hypothesis that suggests that people will eat until they have met their protein needs. Hall says that this seems to be the case in this study and it partly explains the difference in calorie consumption they found. Even though the meals were matched to calories and nutrients, including protein, the ultra-processed meals were more calorie-dense per bite. In part, that's because ultra-processed foods tend to be low in fiber, so researchers have added fiber to beverages served as part of these meals to match the fiber content of the unprocessed diet. This means that participants on the ultra-processed diet may have had to work through more carbs and fat to hit their protein needs

And one last finding of note: People ate much faster – both in terms of grams per minute and calories per minute – on the ultra-processed diet. Hall says it could be that, because the ultra-processed foods tended to be softer and easier to chew, people devoured them more quickly, so they did not give their gastrointestinal tracts enough time to signal their brains that they were full and ended up overeating

Hall says his findings have implications for diet wars – vegan versus low-carb or low-fat diets. "They all have something in common." "People who cut out ultra-processed foods."

Popkin says the take-home message for consumers is, "We should try to eat as much real food as we can. "It's a good food, it's a good food, it can be beef, chicken, fish or vegetables and fruits, and one has to be very careful once it starts to go into other kinds of food."

But Popkin says the findings also present a challenge for the global food industry: how to preserve convenience, abundance and low cost of food without sacrificing health. "Let's see if they can produce ultra-processed foods that are healthy and that will not be so seductive and will not make us eat so much extra," he says. "But they have not yet."


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