Ultraprocessed foods have become a dominant force in the American diet, making up nearly 70% of the nation's food supply. These industrially manufactured products, laden with refined ingredients and additives, are designed to hit our "bliss point," creating an irresistible allure that is reminiscent of the old Lay's potato chip ads featuring Bert Lahr, where the tagline "Betcha can't eat just one" perfectly encapsulates their addictive nature. The question at hand is whether these foods, with their high levels of sugar, salt, and fat, are universally harmful, and if not, what mechanisms within them drive poor health outcomes.

Sam Srisatta, a 20-year-old volunteer, is dedicating a month of his life to science, participating in a unique randomized clinical trial at the Metabolic Clinical Research Unit of the National Institutes of Health Clinical Center in Bethesda, Maryland. His daily routine is a testament to the rigorous nature of the study: daily weight and vitals checks, bowel movement samples for analysis, and blood draws to monitor his body's reactions to different foods. His meals are timed, weighed, and recorded, with the food either consumed or measured for leftovers, all under the watchful eyes of the research team.

The study, led by Kevin Hall, a senior investigator with the National Institute of Diabetes and Digestive and Kidney Diseases, aims to understand the health impact of ultraprocessed foods. These foods are not just convenience items; they are a category of products that include a combination of artificial flavors, smells, and textures that are beyond the reach of home-cooked meals. Numerous studies have linked the consumption of ultraprocessed foods to an increased risk of obesity, chronic conditions like cancer, cardiovascular disease, type 2 diabetes, and even depression. The impact of these foods on public health is staggering, with diet-related conditions accounting for at least half of all US deaths and contributing to $4.5 trillion in annual healthcare costs.

The debate over the harm caused by ultraprocessed foods is complex and has significant implications for regulatory action. Hall's previous study in 2019 revealed that participants consumed an additional 500 calories per day when on an ultraprocessed diet compared to a minimally processed diet, leading to an average weight gain of 2 pounds per week. A similar study in Japan found an even more pronounced effect, with participants consuming an additional 813 calories per day on an ultraprocessed diet.

The implications of these findings are far-reaching. The World Health Organization has declared obesity a worldwide epidemic, with estimates suggesting that over half the world's population will be overweight or obese by 2035. In the United States, the situation is no less dire, with projections indicating that nearly 260 million Americans will be overweight or obese by 2050 unless immediate action is taken.

The potential role of ultraprocessed foods in the US obesity epidemic is now being investigated as part of the new 2025-2030 US Dietary Guidelines. The Dietary Guidelines Advisory Committee (DGAC) has begun examining the latest science on the health effects of ultraprocessed foods, focusing on their impact on growth, weight gain, and obesity across the lifespan. The committee has set a high standard for the research it includes in its analysis, excluding studies of less than 12 weeks and fewer than 30 people, and prioritizing US-based studies.

However, the committee's analysis has found only "limited" evidence to suggest that ultraprocessed foods could lead to weight gain and obesity in children, adolescents, and adults of all ages. This is due in part to the variance in what is considered ultraprocessed and the serious concerns with the applicability of these foods to the US population given global differences in food supply.

The challenge of studying ultraprocessed foods is not insignificant. Long-term trials are necessary for weight control studies, as weight loss can reverse after the initial period of dietary change. However, such studies are rare due to the expense, lack of funding for nutritional research in the US, and the difficulty in controlling what people actually eat.

The controversy among nutritionists over how to define ultraprocessed foods further complicates the issue. The final advisory report, which will not be delivered to government stakeholders for a few months, has already discussed the scientific findings, which are limited in their ability to make recommendations on ultraprocessed foods.

Despite the limitations, the importance of ultraprocessed foods in nutrition cannot be overstated. Marion Nestle, a leading voice in nutrition, argues that the number of studies linking ultraprocessed foods to health concerns should be enough to tip the balance. She points to the randomized clinical trials, considered the gold standard of research, as providing strong evidence of the harmful effects of these foods.

In the meantime, researchers like Hall continue their work, altering meals to test top theories on why ultraprocessed foods may cause overeating. They hope to understand the mechanisms behind the impact of energy density and hyperpalatability on food consumption, with the ultimate goal of reversing the harmful effects of a highly ultraprocessed diet.

As the study progresses, the impact of these different diets on volunteers like Srisatta will not be known until the study publishes in a few years. In the meantime, the need for more research is clear. By understanding how the food environment shapes our metabolic health, researchers hope to improve the food supply in the future. Each study adds a small piece to the puzzle of understanding, and there is a growing interest in this field of research. The hope is that with more resources, more can be done to unravel the complex relationship between ultraprocessed foods and public health.