Dr. Jason Fung and Dr. Eric Westman talk about metabolism
Dr. Eric Westman sits down with Dr. Jason Fung to break down one of the biggest misconceptions in modern health: weight loss is NOT just about calories. For decades, we’ve been told that “calories in vs calories out” is the key to losing weight — but what if that idea is completely wrong?
Dr. Fung explains why hormones like insulin play a far more important role in fat storage, hunger, and metabolism than simple calorie counting. They discuss why so many diets fail, why people regain weight, and how your body actually regulates fat through a biological “set point” rather than willpower alone.
The conversation dives deep into intermittent fasting, how it works, and why it can be such a powerful tool for weight loss and reversing metabolic disease. They also unpack the real reasons behind hunger — including emotional eating, food addiction, and the impact of ultra-processed foods that are engineered to keep you eating.
Dr. Fung also shares insights on GLP-1 weight loss drugs, explaining why they work, where they fall short, and why relying on them without changing behavior can lead to long-term failure
::: spoiler summerizer
Core thesis
- Obesity and type 2 diabetes rise together and drive kidney disease.
- Calorie counting and calorie-equivalence miss the mechanism that decides whether energy is burned or stored.
- Weight regulation follows a body-fat thermostat shaped by hormones, with insulin as a central signal.
- Homeostasis governs body fat the way it governs temperature, water, and sodium balance.
- George Bray's self-overfeeding experience shows increased heat production during overfeeding.
- A lean physiology and an obesity-prone physiology do not respond to surplus energy the same way.
Hormones and difficult cases
- A post-bariatric, postmenopausal patient with low body temperature shows that stored fat can remain inaccessible during low intake.
- The barrier is release of stored energy, not absence of stored energy.
- Insulin, estrogen, thyroid hormone, cortisol, sympathetic tone, glucagon, and other hormones influence access to stored fat.
- Perimenopause, androgen deprivation, and prednisone-associated weight gain are examples of hormone-driven body-composition change.
- Very low intake can be useful in hard cases, but the mechanism still runs through hormones and access to stored energy.
- Low-carbohydrate eating lowers the insulin signal that keeps fat stored.
Fasting physiology
- Fasting lowers insulin and shifts multiple hormonal signals, including ghrelin, growth hormone, cortisol, sympathetic tone, and mTOR.
- Overnight fasting of roughly 12 to 14 hours is normal physiology.
- Longer fasts can reach 16 hours, 24 hours, or multiple days when applied appropriately.
- Stored body fat acts as an internal calorie reserve that can cover long periods, while protein and essential fatty acid needs still matter.
- Coffee, tea, herbal tea, small amounts of cream, and bone broth fit many weight-loss fasting plans.
- The 5:2 pattern and the fasting-mimicking pattern preserve many fasting benefits.
- Rising glucose during fasting can come from release of stored glycogen and glucose under counterregulatory hormones.
Insulin measurement and diabetes type
- Glucose alone does not distinguish low-insulin hyperglycemia from high-insulin insulin resistance.
- C-peptide works as a practical proxy for insulin status.
- Many atypical, lean, or older adults with mild hyperglycemia fit slow autoimmune diabetes better than classic type 2 diabetes.
- Low-carbohydrate diets can lower insulin demand in those patients, while insulin therapy fits low-insulin cases better than high-insulin cases.
The Hunger Code
- Physical homeostatic hunger is only one driver of eating.
- Many episodes of eating come from emotional and social hunger more than physical hunger.
- Hedonic hunger uses food for reward, mood change, boredom relief, and emotional soothing.
- Conditioned hunger links eating to cues such as coffee, television, road trips, movies, school schedules, and social gatherings.
- Food noise grows when eating is attached to every routine and every environment.
- Japan is an example of smaller socially accepted portions and fewer eating cues than some US settings.
Ultra-processed food, addiction, and long-term strategy
- Ultra-processed foods are engineered triggers of hedonic hunger through flavors, colors, sweeteners, texturizers, and emulsifiers.
- Food addiction does not fit moderation advice.
- The Yale Food Addiction Scale made food addiction easier to study.
- Cutting ultra-processed food, fasting, and redesigning the social and physical environment are the book's three golden rules.
- Keto, low-carb, carnivore, and fasting lower insulin, reduce exposure to addictive ultra-processed foods, and reduce cue-driven snacking convenience.
Guidelines and GLP-1 drugs
- The new Dietary Guidelines for Americans shift toward real food and away from calorie counting and heavily processed food.
- GLP-1 and GLP-1/GIP drugs work as powerful satiety tools at pharmacologic doses.
- Their risks and benefits depend on how sick the patient is and why the drug is being used.
- Weight regain after discontinuation is likely when emotional, conditioned, and ultra-processed-food drivers stay unchanged.
- Poor long-term adherence is tied to nausea, reduced food pleasure, social friction around meals, and failure to build a real-food pattern.
- Cleaning up ultra-processed food first and moving people toward real food is the long-term path, with or without medications.
:::
Dr. Fung explains why hormones like insulin play a far more important role in fat storage, hunger, and metabolism than simple calorie counting. They discuss why so many diets fail, why people regain weight, and how your body actually regulates fat through a biological “set point” rather than willpower alone.
The conversation dives deep into intermittent fasting, how it works, and why it can be such a powerful tool for weight loss and reversing metabolic disease. They also unpack the real reasons behind hunger — including emotional eating, food addiction, and the impact of ultra-processed foods that are engineered to keep you eating.
Dr. Fung also shares insights on GLP-1 weight loss drugs, explaining why they work, where they fall short, and why relying on them without changing behavior can lead to long-term failure
::: spoiler summerizer
Core thesis
- Obesity and type 2 diabetes rise together and drive kidney disease.
- Calorie counting and calorie-equivalence miss the mechanism that decides whether energy is burned or stored.
- Weight regulation follows a body-fat thermostat shaped by hormones, with insulin as a central signal.
- Homeostasis governs body fat the way it governs temperature, water, and sodium balance.
- George Bray's self-overfeeding experience shows increased heat production during overfeeding.
- A lean physiology and an obesity-prone physiology do not respond to surplus energy the same way.
Hormones and difficult cases
- A post-bariatric, postmenopausal patient with low body temperature shows that stored fat can remain inaccessible during low intake.
- The barrier is release of stored energy, not absence of stored energy.
- Insulin, estrogen, thyroid hormone, cortisol, sympathetic tone, glucagon, and other hormones influence access to stored fat.
- Perimenopause, androgen deprivation, and prednisone-associated weight gain are examples of hormone-driven body-composition change.
- Very low intake can be useful in hard cases, but the mechanism still runs through hormones and access to stored energy.
- Low-carbohydrate eating lowers the insulin signal that keeps fat stored.
Fasting physiology
- Fasting lowers insulin and shifts multiple hormonal signals, including ghrelin, growth hormone, cortisol, sympathetic tone, and mTOR.
- Overnight fasting of roughly 12 to 14 hours is normal physiology.
- Longer fasts can reach 16 hours, 24 hours, or multiple days when applied appropriately.
- Stored body fat acts as an internal calorie reserve that can cover long periods, while protein and essential fatty acid needs still matter.
- Coffee, tea, herbal tea, small amounts of cream, and bone broth fit many weight-loss fasting plans.
- The 5:2 pattern and the fasting-mimicking pattern preserve many fasting benefits.
- Rising glucose during fasting can come from release of stored glycogen and glucose under counterregulatory hormones.
Insulin measurement and diabetes type
- Glucose alone does not distinguish low-insulin hyperglycemia from high-insulin insulin resistance.
- C-peptide works as a practical proxy for insulin status.
- Many atypical, lean, or older adults with mild hyperglycemia fit slow autoimmune diabetes better than classic type 2 diabetes.
- Low-carbohydrate diets can lower insulin demand in those patients, while insulin therapy fits low-insulin cases better than high-insulin cases.
The Hunger Code
- Physical homeostatic hunger is only one driver of eating.
- Many episodes of eating come from emotional and social hunger more than physical hunger.
- Hedonic hunger uses food for reward, mood change, boredom relief, and emotional soothing.
- Conditioned hunger links eating to cues such as coffee, television, road trips, movies, school schedules, and social gatherings.
- Food noise grows when eating is attached to every routine and every environment.
- Japan is an example of smaller socially accepted portions and fewer eating cues than some US settings.
Ultra-processed food, addiction, and long-term strategy
- Ultra-processed foods are engineered triggers of hedonic hunger through flavors, colors, sweeteners, texturizers, and emulsifiers.
- Food addiction does not fit moderation advice.
- The Yale Food Addiction Scale made food addiction easier to study.
- Cutting ultra-processed food, fasting, and redesigning the social and physical environment are the book's three golden rules.
- Keto, low-carb, carnivore, and fasting lower insulin, reduce exposure to addictive ultra-processed foods, and reduce cue-driven snacking convenience.
Guidelines and GLP-1 drugs
- The new Dietary Guidelines for Americans shift toward real food and away from calorie counting and heavily processed food.
- GLP-1 and GLP-1/GIP drugs work as powerful satiety tools at pharmacologic doses.
- Their risks and benefits depend on how sick the patient is and why the drug is being used.
- Weight regain after discontinuation is likely when emotional, conditioned, and ultra-processed-food drivers stay unchanged.
- Poor long-term adherence is tied to nausea, reduced food pleasure, social friction around meals, and failure to build a real-food pattern.
- Cleaning up ultra-processed food first and moving people toward real food is the long-term path, with or without medications.
:::