Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake

“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. 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. [..]

The rise in obesity and type 2 diabetes prevalence occurred in parallel with an increasingly industrialized food system characterized by large-scale production of high-yield, inexpensive, agricultural “inputs” (primarily corn, soy, and wheat) that are refined and processed to generate an abundance of “added value” foods. Ultra-processed foods have become more common worldwide, now constitute the majority of calories consumed in America, and have been associated with a variety of poor health outcomes, including death. [..]

As compelling as such theories may be, it is important to emphasize that no causal relationship between ultra-processed food consumption and human obesity has yet been established. In fact, there has never been a randomized controlled trial demonstrating any beneficial effects of reducing ultra-processed foods or deleterious effects of increasing ultra-processed foods in the diet. [..]

We admitted 10 male and 10 female weight-stable adults aged (mean ± SE) 31.2 ± 1.6 years with BMI = 27 ± 1.5 kg/m2 as inpatients to the Metabolic Clinical Research Unit (MCRU) at the NIH Clinical Center, where they resided for a continuous 28-day period. Subjects were randomly assigned to either the ultra-processed or unprocessed diet for 2 weeks followed immediately by the alternate diet for the final 2 weeks.

During each diet phase, the subjects were presented with three daily meals and were instructed to consume as much or as little as desired. Up to 60 min was allotted to consume each meal. Menus rotated on a 7-day schedule, and the meals were designed to be well matched across diets for total calories, energy density, macronutrients, fiber, sugars, and sodium, but widely differing in the percentage of calories derived from ultra-processed versus unprocessed foods as defined according to the NOVA classification scheme. [..]

The weekly cost for ingredients to prepare 2,000 kcal/day of ultra-processed meals was estimated to be $106 versus $151 for the unprocessed meals as calculated using the cost of ingredients obtained from a local branch of a large supermarket chain. Snacks appropriate to the prevailing diet and bottled water were available throughout each day. The meals plus snacks were provided at an amount equivalent to twice each subject’s estimated energy requirements for weight maintenance as calculated by 1.6× resting energy expenditure measured at screening. [..]

[..] participants gained 0.9 ± 0.3 kg (p = 0.009) during the ultra-processed diet and lost 0.9 ± 0.3 kg (p = 0.007) during the unprocessed diet. [..]

Body fat mass increased by 0.4 ± 0.1 kg (p = 0.0015) during the ultra-processed diet and decreased by 0.3 ± 0.1 kg during the unprocessed diet (p = 0.05), whereas fat-free mass tended to increase during the ultra-processed diet (0.5 ± 0.3 kg; p = 0.09) and decrease during the unprocessed diet (0.6 ± 0.3 kg; p = 0.08). [..]

Despite substantial differences in energy intake and body weight change between the ultra-processed and unprocessed diets, oral glucose tolerance tests performed at the end of each diet period indicated no significant differences in glucose tolerance. Therefore, insulin sensitivity as measured by the Matsuda index was not significantly different between the ultra-processed and unprocessed diets (3.9 ± 0.2 versus 4.5 ± 0.2, respectively; p = 0.1). Furthermore, there were no significant differences in either average daily glucose concentrations or glycemic variability between the diets as measured by daily CGM [continuous glucose monitoring]. [..]

Until such reformulated products are widespread, limiting consumption of ultra-processed foods may be an effective strategy for obesity prevention and treatment. Such a recommendation could potentially be embraced across a wide variety of healthy dietary approaches including low-carb, low-fat, plant-based, or animal-based diets. However, 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 classes.”

Full article, KD Hall, A Ayuketah, R Brychta, et al. Cell Metabolism, 2019.5.16