Dr. Carlos Monteiro is a Brazilian epidemiologist and public health researcher at the University of São Paulo. Fung introduces him as a revolutionary figure in nutrition science whose work provides an important framework for understanding the modern diet. Monteiro is credited with developing the NOVA food classification system, which categorizes foods based on their level of industrial processing rather than their nutrient content. Fung asserts that “[t]his insight would ultimately transform the world of public health nutrition” (100).

Fung highlights Monteiro’s key insight, which arose from a paradox: in the 2010s, Brazilians were gaining weight even as they were buying less table sugar and cooking oil. Monteiro discovered they were swapping traditional foods for packaged, ready-to-eat products. This led him to conclude that the problem was not a single nutrient but the industrial manipulation of food itself. As Fung summarizes, “It wasn’t the calories or the macronutrients… that defined these fattening foods. It was the ultra-processing” (99). 

Monteiro’s work serves as the scientific foundation for Fung’s first Golden Rule: avoid ultra-processed foods (UPFs). The NOVA system gives readers a practical tool to identify foods that are engineered to be hyper-palatable, low in satiety, and hormonally disruptive. By detailing Monteiro’s focus on UPFs, Fung underscores The Impact of Environment on Eating Habits and makes his argument for The Bioengineering of Addiction via Ultra-Processed Foods. Shifting the blame for obesity away from individual failure and toward the food environment, he suggests that the system, not a failure of willpower, is the primary problem in weight management.

Ivan Pavlov was a renowned Russian physiologist whose experiments on classical conditioning in dogs in the 1890s laid the groundwork for modern behavioral psychology. Fung uses Pavlov’s research as the primary scientific analogy for understanding “conditioned hunger,” the third and final type of hunger he identifies as a driver of obesity.

Fung explains that just as Pavlov’s dogs were conditioned to salivate at the sound of a bell, humans have been conditioned to feel hungry in response to external cues. These triggers can include the time of day (e.g. lunchtime), a specific location (e.g. a movie theater), or an activity (e.g. watching television). This response is not merely psychological; Fung emphasizes that these cues trigger a physiological release of the hunger hormone ghrelin. Thus, much of the hunger people experience is a “learned, or conditioned, response” (166) rather than a true signal of the body’s need for energy.

Pavlov’s work is essential to Fung’s exploration of The Impact of Environment on Eating Habits. It provides a scientific explanation for why people eat when they are not physically hungry and why willpower often fails in obesogenic environments saturated with food cues. For Fung, understanding this conditioning is the first step toward breaking unhealthy habits and reclaiming control over eating behavior.

Fung presents Dr. George Bray as a “legendary obesity researcher” (24) whose work provides critical evidence against the simplistic “Calories In, Calories Out” model of weight gain. Bray is known for his self-experimentation with overfeeding in the 1970s, which Fung uses to introduce the concept of the “body fat thermostat,” or the body’s natural tendency to maintain a specific weight.

Fung recounts how Bray deliberately gained 22 pounds by eating high-sugar, high-fat foods every day. Bray noted that his body fought the weight gain by increasing its temperature to burn more calories. After the experiment, he “quickly dropped back to his original weight” (25) with no conscious effort. This phenomenon, along with similar findings from Dr. Ethan Sims’s Vermont State Prison studies, demonstrated that the body has a homeostatic mechanism to regulate its fat stores.

Bray’s research is key to Fung’s argument about homeostatic hunger. It serves as evidence that obesity is not a simple problem of overeating but rather “a disorder of the body set weight being too high” (29). Fung uses Bray’s experiment to establish that weight is primarily regulated by hormones that control this internal thermostat, not by the conscious counting of calories. This shifts the focus of treatment from calorie restriction to hormonal regulation.