In this first of its kind study, scientists have found that consuming ultra-processed foods cause weight gain in human volunteers in just 2 weeks.
Many studies in mice have linked processed foods to problems like intestinal inflammation and obesity. But mice are not human beings, as critics of such studies always point out.
In human, researchers have found links between processed foods and health issues like increased risk of developing autoimmune conditions, cancer, obesity and even death.
Unfortunately, the same ultra-processed foods make up 57.9 percent of energy intake in the U.S.
According to NOVA food classification system, ultra-processed foods are meat nuggets, soft drinks, frozen meals, packaged snacks and foods high in additives and low in unprocessed ingredients.
In this study, Kevin D. Hall, of the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, MD compared the effects of ultra-processed foods versus unprocessed foods on human in the journal Cell Metabolism.
The finding is surprising
The research team recruited 10 females and 10 male volunteers who stayed at the NIH Clinical Center for 28 days.
They gave ultra-processed food to half of the participants for the first 2 weeks and the other half were given unprocessed foods. After the 2-week period, the two groups switched food to ensure each participant consume both the unprocessed food and ultra-processed food for 2 weeks.
All of the participants eat three meals per day and eat as little or as much as they wanted. They also had access to bottled water and snacks all day.
Hall says, “We hypothesized that ultra-processed foods might lead to an increase in calorie intake because they are often high in fat, salt and sugar while being low in fiber.” “Therefore, when we matched the unprocessed and ultra-processed diet for these nutrients, we expected the ultra-processed food to result in similar calories intake and little differences in body weight.”
The participants ate an average of 508 calories more each day when on the ultra-processed food than when on the unprocessed diet. As a result, they put on an average of 0.9 kilograms (2 pounds) during the time, mostly in the form of body fat.
Kevin D, Hall says, “I was surprised by the results from his study because I thought that if we matched the two diets for components such as sodium, carbohydrates, sugar, protein and fat, there wouldn’t be anything magical about the ultra-processed food that would cause people to eat more.”
Participants in the group that eat unprocessed food lost an average of 2 pounds (0.9 kg) during the 2 week study period. This group also saw an increase in their gut hormone peptide YY, which suppresses hunger and decreases in the hunger hormone ghrelin.
What might be the problem?
Hall and his colleagues think several reasons must have lead the participants in the ultra-processed food study group to gain weight.
Although the study volunteers rated the familiarity and pleasantness of the diets as the same, they ate significantly faster in the ultra-processed food group.
In fact, they ate an extra 17 calories (7.4 grams) of food per minute than those in the group of unprocessed food.
Hall comments, “There may be something about the sensory and textural properties of the ultra-processed food that made them eat more quickly.” He says, “If you are eating very quick, perhaps you are not giving your gastrointestinal tract enough time to signal to the brain that you are full. When this happens, you might easily overeat.”
Hall comments, “Despite a close match in the macronutrient composition of both diets, the unprocessed diet contains slightly more protein. “It could be that people consumed because they were trying to reach certain protein targets.”
The team discovered that the ultra-processed food group ate more fats and carbohydrates than the unprocessed food group, but not protein.
The meal in the ultra-processed food group had a higher energy density than in the unprocessed group, which Hall proposes ”Likely contributed to the observed excess energy intake.”
Can we say ultra-processed foods are a social problem?
The researchers identified many limitations in their studies, which include “the impatient environment of the metabolic ward makes it hard for generalize our results to free-living conditions.”
They also said they didn’t take into consideration how cost, skill and convenience influence consumers to choose ultra-processed food over unprocessed foods.
Hall comments, “Ultra-processed foods contribute over half of the calories consumed in the USA, and they are convenient and cheap options.”
“So, I think it may be hard to substantially reduce ultra-processed food’s consumption, especially for those in the lower socioeconomic brackets who may not have the equipment, resources, time or skill to buy and safely store unprocessed food ingredients and then plan and prepare a tasty, unprocessed meal.”
Hall concludes, “Policies that discourage eating of ultra-processed foods should be sensitive to the expense, skill, time and effort needed to prepare a meal from minimally processed foods – resources that are often in short supply for people who are not members of the upper socioeconomic classes.”
Of course, Hall is not the first person to suggest a link between socioeconomics and food choices. One recent, large-scale study suggests that n high-income countries like the U.S., rural populations are gaining weight than people in the city.
The authors in the study say that this may partly due to social and economic disadvantage, including lower availability, lower income and education, and higher price of healthful and fresh foods.