The debate surrounding ultra-processed foods (UPFs) often lacks scientific nuance, with many assuming that any processed item is inherently dangerous. However, American nutritional scientist Kevin Hall, originally a physicist, challenges these oversimplifications.
Hall frequently enjoys red lentil pasta with a tomato sauce containing preservatives to maintain its red color, both of which fit the technical definition of UPFs. Yet, he notes that these are not the products people should worry about, as their nutritional profile is perfectly fine and they do not trigger overeating.
For decades, Hall investigated diabetes and obesity by placing groups of people in metabolic laboratories for weeks at a time to examine their metabolism. This rigorous method allowed him to isolate the exact effects of fats, carbohydrates, and UPFs. Alongside journalist Julia Belluz, Hall addresses why we eat what we eat in his book Food Intelligence.
The Myth of Macronutrients and the Role of UPFs
Years of laboratory research into carbohydrates and fats revealed a surprising truth: the human body adapts remarkably well. Swapping massive amounts of carbohydrates for fats in a diet produces minimal differences in the number of calories burned or the amount of fat stored in the body. This efficient system is often overlooked in popular dietary debates, but the laboratory data shows that choosing a low-carb or low-fat diet matters very little for weight management.
This realization shifted the focus of Hall’s research to a different question: what actually determines why some people maintain their weight more easily than others, and what specific dietary patterns drive the high prevalence of obesity? The answers emerged when studying food environments. Individuals in an environment rich in ultra-processed foods consumed an average of 500 kilocalories more per day than those presented with minimally processed meals. Current research now aims to better understand how the modern food environment influences appetite and body weight.
The Overvaluation of Protein
Protein is frequently glorified as the ultimate nutrient, a phenomenon that prompted Hall to dedicate an entire chapter to it. He discovered that modern discussions about high-protein diets and supplements closely mirror the late 19th-century ideas of Justus von Liebig, a renowned German chemist who invented synthetic fertilizer before becoming a diet guru. Liebig generated significant profit by selling meat extracts based on intriguing hypotheses about protein that were largely incorrect, yet his ideas persist today.
Most people believe they need to consume more protein, whereas the majority already consume more than their bodies require. While the optimal amount may be slightly higher for older adults or those building muscle, people often forget that the effect of extra protein is minimal compared to the intensive strength training required to gain muscle mass.
Furthermore, biology demonstrates a classic trade-off between reproduction (cell growth) and lifespan. Animal studies show that higher protein intake enhances reproductive capabilities but shortens lifespan, while reducing protein extends the lifespan of mice. How this translates to humans remains unknown, raising questions about whether this effect applies to all protein or only to specific amino acids.
Misconceptions About Ultra-Processed Foods
Hall’s findings are frequently misunderstood, with many concluding that ultra-processed food is inherently toxic. Some critics mistakenly believe his work attributes a mysterious, inherent danger to meals simply because they carry the UPF label. Conversely, others use his research as a weapon against the food industry without seeking to understand the underlying mechanisms. Hall emphasizes that understanding these mechanisms is essential to explaining why individuals in countries like the United States derive so many calories from UPFs. This knowledge is crucial for governments to implement effective regulations and compel manufacturers to reduce salt, fat, and sugar contents.
When evaluating why UPFs are so compelling, the explanation goes beyond taste. In clinical studies, participants rated unprocessed and ultra-processed meals as equally delicious. Instead, researchers use the term “hyper-palatability” to describe combinations of sugar, salt, and fat, or carbohydrates and salt, that do not occur naturally. This includes items ranging from industrial snacks to a grandmother’s homemade apple pie or cheese sauce on broccoli.
This hyper-palatable food may trigger subconscious signals in the gastrointestinal tract that regulate appetite. Texture also plays a significant role; many industrial products are easy to chew because processing breaks down the physical structure, allowing nutrients to be absorbed much earlier in the digestive tract. Additionally, energy density is a major factor. To extend shelf life, water is removed from these foods, resulting in a high concentration of calories per bite.
Biology versus Environment
While biology, hormones, and metabolism explain how hunger works, the surrounding environment remains the primary driver of consumption. Hall hypothesizes that an interplay exists between seductive, ubiquitous food and fundamental bodily processes, specifically via signals traveling from the gastrointestinal tract to the reward center of the brain. The mere sight of food, or the anticipation of eating, can trigger a release of dopamine. This anticipation encourages eating, which induces a second dopamine peak that sustains the behavior, sometimes overpowering the brain signals indicating that the stomach is full.
Despite these mechanisms, Hall hesitates to label ultra-processed food as truly addictive. Brain imaging studies examining whether milkshakes cause dopamine spikes comparable to nicotine or cocaine showed that they do not. Interestingly, individuals with obesity exhibited a higher baseline level of dopamine, contradicting the common assumption that they possess fewer dopamine receptors. While this does not completely rule out the possibility of food addiction, attributing the issue entirely to dopamine spikes hijacking the brain is an oversimplification.
The Rise of Pseudoscience in Wellness
The wellness industry faces sharp criticism in Hall’s book, particularly regarding the trend of “precision nutrition,” which includes continuous glucose monitors and personalized diet programs. Influencers frequently make bold claims based on minimal scientific evidence to market products. However, these programs can cause real harm. For instance, Hall’s coauthor, Julia Belluz, developed high cholesterol after receiving advice to increase her fat intake.
Furthermore, consumer glucose monitors are highly unreliable and deliver inconsistent results. Creating anxiety around eating a banana due to potential blood sugar spikes does not improve quality of life. The false promises of this pseudoscience ultimately undermine public trust in legitimate nutritional science.
Politics and Scientific Censorship
The Make America Healthy Again movement, led by figures like Robert F. Kennedy Jr., initially embraced Hall’s research as proof that UPFs are harmful. However, political dynamics shifted when the scientific outcomes no longer aligned with the movement’s agenda. While the current administration pays closer attention to the science behind UPFs, data that contradicts their narrative is often dismissed.
When Hall sought to publish the results of his milkshake experiment, officials appointed to the National Institutes of Health blocked the press release. A journalist’s interview request was denied because the findings conflicted with the views of RFK Jr. Later, another paper accepted for publication was censored because it contained the phrase “health equity,” a term that had been restricted. Finding it impossible to continue his work under these conditions, Hall closed the laboratory where he had worked for 21 years and chose to retire from the institution.
A New Chapter in the Obesity Fight
Hall now works with AstraZeneca on the development of obesity medications. While the pharmaceutical industry focuses heavily on creating safe, effective drugs, relatively little is invested in researching eating behavior. Patients starting GLP-1 medications experience a notable decrease in food intake, making it crucial to study how these drugs alter long-term eating habits and dietary quality. This is an area of study that the food industry should investigate even more aggressively than pharmaceutical companies.
This shift in focus does not mean Hall views weight-loss medications as merely treating symptoms rather than the root cause. Instead, he views obesity as the direct consequence of an agricultural system that produces an excess of calories. The global challenge is no longer an inability to feed the population, but rather that the population is overfed.
Medications can provide vital support for individuals who are biologically most vulnerable to this environment. As global systems face the challenge of feeding nearly ten billion people without driving disease or depleting the planet, these medical and scientific tools are essential to managing public health sustainably.