In this section, the author continues to explore The Impact of Environment on Eating Habits, presenting the modern obesity crisis as the inevitable outcome of a culture designed to encourage constant consumption. Chapter 9 develops this argument through the analogy of a classroom in which 70 out of 100 children fail. Comparing this situation to the high levels of obesity in the American population, Fung argues that failure must reflect the system rather than the individuals within it. This comparison redirects attention away from personal willpower to external factors that insidiously affect dietary choices. Presenting evidence such as the dramatic weight gain in immigrants after moving to the U.S. and the clustering of obesity within social networks, Fung methodically dismantles the idea of obesity as a purely individual concern. By identifying the “obesogenic environment” as one characterized by cheap, ultra-processed food, aggressive marketing, and constant prompts to eat, the author situates obesity within a broader critique of modern society’s cultural norms. 

Chapter 10 explains how the obesogenic environment influences behavior by introducing the concept of “conditioned hunger.” Drawing on Ivan Pavlov’s classical conditioning experiments, Fung argues that much of what people experience as hunger is a learned response to external cues rather than an authentic signal of biological need. This distinction reframes hunger from an inevitable physiological drive to a behavioral pattern that can be modified. The book’s discussion of the hunger hormone ghrelin supports this interpretation by presenting fluctuations in the hormone as evidence that appetite is often a conditioned response that anticipates regular mealtimes. The observation that ghrelin levels exhibit a “spontaneous decrease after approximately 2 hours without food consumption” (170) encourages readers to question the authority of their own appetites. By framing hunger as a habit reinforced by clocks, locations, and social rituals, the author transforms it from an uncontrollable drive into a behavior that can be unlearned.

Fung further develops this behavioral model by arguing that cognitive and sensory expectations can manipulate the body’s physiological responses to food, effectively hijacking natural satiety signals. The author cites studies such as the milkshake experiment to demonstrate that beliefs about calorie content can influence hormonal response independently of nutritional composition. This example strengthens Fung’s claim that eating behavior is shaped as much by perception as by metabolism, allowing him to argue that food manufacturers exploit psychological expectations alongside biological reward systems. His critique of foods marketed as “healthy” or “lite” extends beyond their nutritional content by suggesting that such foods create a deprivation mindset that intensifies hunger and undermines willpower. The author argues that this psychological conditioning creates a self-fulfilling prophecy where diet foods, by their very nature, fail to satisfy. This line of reasoning connects the widespread availability of ultra-processed foods with a more insidious form of manipulation—one that targets our perceptions and expectations to drive overconsumption.

The final chapters of this section transition from diagnosing the problem of conditioned hunger to proposing a solution, presenting fasting as a behavioral reset. The author frames fasting not merely as a method for calorie restriction but as a strategic tool to break the learned association between environmental cues and the impulse to eat. The case studies of Jamal, Sarika, and Barb are presented as narrative evidence for this approach. Their stories are structured to emphasize a common theme: that lasting weight-loss success depends on reshaping established habits through structured practice and support. These accounts reinforce the idea that overcoming obesity requires a fundamental shift in one’s habits and mindset. By emphasizing behavioral change alongside hormonal regulation, Fung broadens the scope of The Hunger Code beyond conventional dieting to a more comprehensive model of weight management. This synthesis reflects the growing popularity of intermittent fasting, habit formation, and behavioral psychology within contemporary health culture, while also distinguishing Fung from the calorie-counting and macronutrient-focused advice often associated with mainstream fitness.

By treating fasting as a therapeutic practice to unlearn conditioned hunger, the author presents a comprehensive strategy that addresses both the psychological and physiological dimensions of weight management.