Why Cutting Calories Triggers Weight Regain | Dr. Jason Fung

Core Topic: The biological and hormonal reasons why calorie restriction alone fails for long-term weight loss.
Main Conclusion: Calories don't cause obesity; hormonal imbalances, societal conditioning, and three types of hunger (homeostatic, hedonic, conditioned) drive weight gain and make calorie restriction unsustainable.
Key Point: Sustainable weight loss requires addressing root causes like hunger hormones, food addiction, and environmental triggers—not just "eating less."

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1. The Calorie Myth: Why "Calories In, Calories Out" Fails

Dr. Jason Fung challenges the idea that obesity is caused by overeating. He explains that calories are a dependent variable, not the root cause:

"The energy balance equation (body fat = calories in − calories out) is always true, but it doesn't mean what most people think. When you cut calories, your body fights back by lowering metabolic rate, making weight loss harder."

Historical experiments show that overfeeding people 10,000+ calories daily rarely leads to significant weight gain. When the experiment ends, participants naturally lose the weight without effort. This proves that hormones, not willpower, control body weight.

"Metabolic rate adjusts to minimize fat storage. If you eat more, you burn more; if you eat less, you burn less. This is why calorie restriction backfires."

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2. The Three Types of Hunger: Root Causes of Overeating

Fung breaks hunger into three categories, each requiring a different solution:

Homeostatic Hunger: Physical Hormonal Signals

This is the "stomach growling" type of hunger, driven by hormones like ghrelin, leptin, and insulin.

"Hunger isn't about how long you've gone without food—it's dictated by hormones. Your body's circadian rhythm even makes you least hungry at 8 a.m., despite 12 hours of fasting."

Hedonic Hunger: Pleasure and Reward

This is craving driven by dopamine spikes from hyperpalatable foods (e.g., sugar, processed carbs).

"You don't eat dessert because you're hungry. You eat it for pleasure. Processed foods hijack reward pathways, making you seek more even when full."

Conditioned Hunger: Environmental Triggers

Pavlovian conditioning links neutral stimuli (e.g., TV, stress, social settings) to eating.

"If you always eat while watching TV, your brain associates screens with hunger. This 'conditioned hunger' explains why obesity spreads socially—like a virus."

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3. The Problem with Calorie Restriction: Why It Triggers Weight Regain

Cutting calories without addressing hunger hormones leads to a vicious cycle:

1. Hunger spikes as the body defends its set weight.
2. Metabolism slows to conserve energy.
3. Cravings intensify, making relapse likely.

"Calorie restriction is like fighting your own body. You're working against biology, not with it."

Fung cites bariatric surgery failures as proof. Early surgeries (e.g., jaw wiring, lap bands) worked temporarily but failed long-term because they ignored hormonal drivers. Modern surgeries (e.g., gastric sleeves) succeed partly by altering hunger hormones like GLP-1.

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4. Social Influence: Obesity as a "Viral" Condition

Obesity spreads through social networks. Dr. Fung shares a New England Journal of Medicine study:

"If your best friend becomes obese, your risk of obesity increases by 117%. Environment shapes habits—what's 'normal' to eat or how often you snack."

Cultural norms amplify this. For example:

• In Japan, eating while walking is frowned upon.
• In the U.S., food is paired with nearly every activity (cars, desks, celebrations).

"Moving a Japanese person to America increases their obesity risk sixfold within a generation. Environment is a silent driver."

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5. Breaking the Cycle: Tools to Fight Conditioned Hunger

Fung emphasizes mindset shifts and environmental control:

1. Mantras: Repeat affirmations to reframe food (e.g., "Sugar is poison" or "Burn, baby burn" during fasting).
2. Habit Replacement: Replace conditioned triggers (e.g., snacking while working) with new rituals (e.g., drinking water or taking a walk).
3. Fasting: Regular fasting "resets" hunger hormones and reduces reliance on external cues.

"Fasting isn't about deprivation—it's about relearning how to listen to your body. When I fast, I pat my tummy and say, 'Burn, baby burn!' It reminds me I'm using stored fat."

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6. The Hunger Code: A New Framework for Weight Loss

Fung's book The Hunger Code outlines three golden rules and 50 practical tips to address hunger holistically:

• Rule 1: Reduce homeostatic hunger by stabilizing insulin and leptin.
• Rule 2: Combat hedonic hunger with whole, satiating foods.
• Rule 3: Disrupt conditioned hunger by changing environments and mindsets.

"Weight loss isn't about 'eating less.' It's about working with your biology—hormones, habits, and environment."

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Conclusion: Rethinking Weight Loss

Dr. Fung's message is clear:

"You can't out-willpower biology. Calorie restriction fails because it ignores the real drivers of hunger. Sustainable weight loss requires addressing hormones, rewiring habits, and reshaping your environment."

By focusing on hunger as the root problem, not calories, individuals can finally break the cycle of weight regain. 🌱