Peo­ple eat­ing ultra-processed foods ate more calo­ries and gained more weight than when they ate a min­i­mal­ly processed diet, accord­ing to results from a Nation­al Insti­tutes of Health study. The dif­fer­ence occurred even though meals pro­vid­ed to the vol­un­teers in both the ultra-processed and min­i­mal­ly processed diets had the same num­ber of calo­ries and macronu­tri­ents. The results were pub­lished in Cell Metab­o­lism.

This small-scale study of 20 adult vol­un­teers, con­duct­ed by researchers at the NIH’s Nation­al Insti­tute of Dia­betes and Diges­tive and Kid­ney Dis­eases (NIDDK), is the first ran­dom­ized con­trolled tri­al exam­in­ing the effects of ultra-processed foods as defined by the NOVA clas­si­fi­ca­tion sys­tem. This sys­tem con­sid­ers foods “ultra-processed” if they have ingre­di­ents pre­dom­i­nant­ly found in indus­tri­al food man­u­fac­tur­ing, such as hydro­genat­ed oils, high-fruc­tose corn syrup, fla­vor­ing agents, and emul­si­fiers.

Pre­vi­ous obser­va­tion­al stud­ies look­ing at large groups of peo­ple had shown asso­ci­a­tions between diets high in processed foods and health prob­lems. But, because none of the past stud­ies ran­dom­ly assigned peo­ple to eat spe­cif­ic foods and then mea­sured the results, sci­en­tists could not say for sure whether the processed foods were a prob­lem on their own, or whether peo­ple eat­ing them had health prob­lems for oth­er rea­sons, such as a lack of access to fresh foods.

“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.”

For the study, researchers admit­ted 20 healthy adult vol­un­teers, 10 male and 10 female, to the NIH Clin­i­cal Cen­ter for one con­tin­u­ous month and, in ran­dom order for two weeks on each diet, pro­vid­ed them with meals made up of ultra-processed foods or meals of min­i­mal­ly processed foods. For exam­ple, an ultra-processed break­fast might con­sist of a bagel with cream cheese and turkey bacon, while the unprocessed break­fast was oat­meal with bananas, wal­nuts, and skim milk.

The ultra-processed and unprocessed meals had the same amounts of calo­ries, sug­ars, fiber, fat, and car­bo­hy­drates, and par­tic­i­pants could eat as much or as lit­tle as they want­ed.

On the ultra-processed diet, peo­ple ate about 500 calo­ries more per day than they did on the unprocessed diet. They also ate faster on the ultra-processed diet and gained weight, where­as they lost weight on the unprocessed diet. Par­tic­i­pants, on aver­age, gained 0.9 kilo­grams, or 2 pounds, while they were on the ultra-processed diet and lost an equiv­a­lent amount 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,” Hall said. “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.”

For exam­ple, slight dif­fer­ences in pro­tein lev­els between the ultra-processed and unprocessed diets in this study could poten­tial­ly explain as much as half the dif­fer­ence in calo­rie intake.

“Over time, extra calo­ries add up, and that extra weight can lead to seri­ous health con­di­tions,” said NIDDK Direc­tor Grif­fin P. Rodgers, M.D. “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.”

While the study rein­forces the ben­e­fits of unprocessed foods, 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 said. “Just telling peo­ple to eat health­i­er may not be effec­tive for some peo­ple with­out improved access to healthy foods.”

Sup­port for the study pri­mar­i­ly came from the NIDDK Divi­sion of Intra­mur­al Research.

Source link