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Ultra-processed foods lead to overeating, weight gain
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Adults without obesity who ate a diet of ultra-processed foods for 2 weeks consumed on average 500 kcal more per day and gained an average 0.9 kg vs. when they ate a diet of unprocessed foods for 2 weeks, according to findings published in Cell Metabolism.
“The perpetual diet wars between factions promoting low-carbohydrate, keto, paleo, high-protein, low-fat, plant-based, vegan and a seemingly endless list of other diets have led to substantial public confusion and mistrust in nutrition science,” Kevin D. Hall, PhD, section chief of the integrative physiology section at the National Institute of Diabetes and Digestive and Kidney Diseases, and colleagues wrote in the study background. “While debate rages about the relative merits and demerits of various so-called healthy diets, less attention is paid to the fact that otherwise diverse diet recommendations often share a common piece of advice: Avoid ultra-processed foods.”
Hall and colleagues analyzed data from 20 weight-stable adults admitted as inpatients to the Metabolic Clinical Research Unit at the NIH Clinical Center, where they resided for 28 days (10 women; mean age, 31 years; mean BMI, 27 kg/m²). Researchers randomly assigned participants to an ultra-processed or unprocessed diet for 2 weeks, followed immediately by the alternate diet for an additional 2 weeks. For both diet phases, participants received three meals daily plus snacks, designed to be well-matched across diets for total calories, energy density, macronutrients, fiber, sugar and sodium, although widely differing in the percentage of calories derived from ultra-processed foods.
“While we attempted to match several nutritional parameters between the diets, the ultra-processed vs. unprocessed meals differed substantially in the proportion of added to total sugar ([approximately] 54% vs. 1%, respectively), insoluble to total fiber ([approximately] 77% vs. 16%, respectively) saturated to total fat ([approximately] 34% vs. 19%) and ratio of omega-6 to omega-3 fatty acids ([approximately] 11:1 vs. 5:1),” the researchers wrote.
Researchers found that energy intake was on average 508 kcal per day greater during the ultra-processed diet phase vs. the unprocessed diet phase (P = .0001), with no effect observed based on order of the diet assignment (P = .75) or sex (P = .28). The increased energy intake observed during the ultra-processed diet resulted from consuming greater quantities of carbohydrates (mean, 280 kcal per day; P < .0001) and fat (mean, 230 kcal per day; P = .0004), but not protein (mean, –2 kcal per day; P = .85), when compared with the unprocessed diet phase, according to researchers.
“The remarkable stability of absolute protein intake between the diets, along with the slight reduction in overall protein provided in the ultra-processed vs. the unprocessed diet, suggests that the protein leverage hypothesis could partially explain the increase in energy intake with the ultra-processed diet in an attempt to maintain a constant protein intake,” the researchers wrote.
Researchers found that participants gained a mean of 0.9 kg and experienced a mean 0.4-kg increase in body fat mass during the ultra-processed diet phase (P = .009 and .0015, respectively) and lost a mean of 0.9 kg and experienced a mean 0.3-kg decrease in fat mass during the unprocessed diet phase (P = .007 and .05, respectively). Individual differences in weight change between diets were not correlated with baseline BMI, but did correlate with energy intake (P < .0001), according to researchers.
“Despite the ultra-processed and unprocessed diets being matched for daily presented calories, sugar, fat, fiber and macronutrients, people consumed more calories when exposed to the ultra-processed diet as compared to the unprocessed diet,” the researchers wrote. “Furthermore, people gained weight on the ultra-processed diet and lost weight on the unprocessed diet. Limiting consumption of ultra-processed food may be an effective strategy for obesity prevention and treatment.”
The researchers noted that the inpatient environment of the metabolic ward makes it difficult to generalize the results to free-living conditions; however, current dietary assessment methods are insufficient to precisely measure energy intake outside the lab. – by Regina Schaffer
Disclosures: One of the authors reports he 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, Danone and Nestec.
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