People eating a diet of ultra-processed food consumed more calories and gained more weight than those on a minimally-processed diet, despite meals being matched, shows a small randomized controlled trial (RCT) by the US National Institutes of Health (NIH).
The results of the study suggest that limiting consumption of ultra-processed foods may be an effective strategy for obesity prevention and treatment, write the authors, led by Kevin Hall, PhD, from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) in Bethesda, Maryland.
Twenty inpatients at the NIH Clinical Center took part, equally split between men and women, and the authors note that this small-scale study is the first randomized controlled research of its kind.
“Though we examined a small group, results from this tightly controlled experiment showed a clear and consistent difference between the two diets,” said Hall in a press release from NIH, adding that, “this is the first study to demonstrate causality — that ultra-processed foods cause people to eat too many calories and gain weight.”
Participants gained nearly a kilogram during the ultra-processed diet (0.9 kg; P = .009), which is around 2 lb, and lost a similar amount of weight (0.9 kg; P = 0.007) while on the unprocessed diet.
Also, on the ultra-processed diet, people ate about 500 calories more per day, and ate faster compared with those on the unprocessed diet.
The research is published online in the May 16 edition of Cell Metabolism.
Ultra-processed Foods Common Worldwide: Driving Obesity Epidemic?
The rise in obesity and type 2 diabetes has occurred in tandem with large scale, inexpensive production of corn, soy, and wheat that are processed to generate so-called ‘added-value’ to food, write the authors.
“Ultra-processed foods have become more common worldwide [and] now constitute the majority of calories consumed in America, and have been associated with a variety of poor health outcomes,” they add.
They point out that, to date, there have not been any RCTs demonstrating any deleterious effects of ultra-processed foods in the diet, or potential benefits of reducing ultra-processed foods.
Against this background, the authors decided to investigate the causal role of ultra-processed foods on energy intake and body weight change.
Upon entry to the NIH Metabolic Clinical Research Unit (MCRU), 20 adults (10 men, 10 women, average age, 31 years) with stable weight, and an average body mass index (BMI) of 27 kg/m2 were randomly assigned to consume either an ultra-processed, or minimally processed, diet for two consecutive weeks before immediately switching to the alternate diet.
All participants received three daily meals and were free to eat as much or as little as desired within 1 hour. Meals were designed to be well matched across diets for total calories, energy density, macronutrients, fiber, sugars, and sodium, but differed widely in the percentage of calories derived from ultra-processed vs unprocessed foods.
As an example, an ultra-processed breakfast might consist of a bagel with cream cheese and turkey bacon, whereas the minimally processed breakfast was oatmeal with bananas, walnuts, and skim milk.
Energy expenditure, and average energy expenditure, respiratory quotient, sleeping energy expenditure, body composition, and liver fat were measured.
Reasons for Increased Energy Intake With Processed Food Unclear
In the article, Hall and colleagues note that the study was not designed to identify the reasons for the observed differences in energy intake.
But there are hypotheses suggesting that the detrimental effects of processed food result from their elevated sugar, fat, and sodium content, in tandem with the fact that they are low in protein and fiber.
The authors attempted to match these nutritional variables in the presented meals to investigate whether other aspects of ultra-processed diets contribute to excess energy intake.
“Had the experimental diets used in our study allowed for greater differences in sugar, fat, and sodium content more typical of differences between ultra-processed versus unprocessed diets, we may have observed larger differences in energy intake,” they observe.
They also highlight the fact that their study was conducted in an ‘inpatient’ environment, noting that “current dietary assessment methods are insufficient to accurately measure energy intake outside the laboratory, and adherence to study diets cannot be guaranteed in free-living subjects.”
So the findings are likely not generalizable to the ‘real world,’ they stress.
Nevertheless, “Our data suggest that eliminating ultra-processed foods from the diet decreases energy intake and results in weight loss, whereas a diet with a large proportion of ultra-processed food increases energy intake and leads to weight gain,” the authors write.
Whether reformulation of ultra-processed foods could eliminate their deleterious effects while retaining their palatability and convenience “is unclear,” they add. But until such reformulated products are widespread, limiting consumption of ultra-processed foods “may be an effective strategy for obesity prevention and treatment.”
However, the authors caution, “policies that discourage consumption of ultra-processed foods should be sensitive to the time, skill, expense, and effort required to prepare meals from minimally processed foods — resources that are often in short supply for those who are not members of the upper socioeconomic class.”
Cell Metabolism. Published online May 16, 2019. Full text
The study was supported by the Intramural Research Program of the National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases .
Hall has disclosed no relevant financial relationships. Another author, Ciaran G. Forde, has received reimbursement for speaking at conferences sponsored by companies selling nutritional products, serves on the scientific advisory council for Kerry Taste and Nutrition, and is part of an academic consortium that has received research funding from Abbott Nutrition, Nestec, and Danone. The other authors have disclosed no relevant financial relationships.