Why Cutting Calories Triggers Weight Regain | Dr. Jason Fung

This discussion between Dr. Jason Fung and Nick Norwitz challenges the conventional understanding of weight loss, arguing that calories are not the root cause of obesity but rather a dependent variable controlled by hormones and hunger. The conversation explores three types of hunger—homeostatic, hedonic, and conditioned—and offers practical strategies for addressing each. The key takeaway is that sustainable weight loss requires working with your body's hunger signals rather than fighting against them through sheer willpower.

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1. The Provocative Truth: Calories Don't Really Cause Obesity

The conversation kicks off with a bold statement that might raise some eyebrows: calories don't really cause obesity, at least not in a biological sense. 🤯

Nick Norwitz shares his personal frustration from medical school, where he observed countless patients struggling with chronic metabolic diseases centered around obesity. What struck him most was how the entire system—medical, economic, and social—seemed designed to make it harder for people to lose weight and maintain a healthy weight.

"It seems like the entire system, medical, economic, and social, seemed designed to make it harder for people to lose weight and then maintain a healthy weight, which is something from an evolutionary perspective, our body should just do."

Dr. Jason Fung, a nephrologist best known for his pioneering work in intermittent fasting and carbohydrate-restricted diets, has dedicated his career to giving patients real tools. His new book, The Hunger Code, doesn't just question dietary dogma—it kicks it in the teeth.

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2. The Historic Overfeeding Experiment That Changed Everything

Dr. Fung describes a fascinating experiment where lean individuals were fed 10,000 calories per day. The results? Most people didn't gain nearly as much weight as expected. Researchers had to keep increasing the calories just to get participants to gain a certain amount of weight.

But here's the kicker: after the experiment stopped, these people immediately lost all that weight without any effort.

"If you gain 25 pounds experimentally by being forced to overeat, you'll lose that 25 pounds naturally without any effort in two months. If you're normally that weight and trying to lose 25 pounds, you almost can't do it."

Nick shares his own experience eating 6,000 calories a day for up to three weeks:

"I didn't even gain one pound. What happened? Oh yeah, my body temperature went up. My heart rate was crazy. I was sweating all the time. I had to literally sleep with ice packs on me."

This demonstrates that when you increase calories, your body doesn't necessarily store them as fat—it can simply burn more. Different people respond differently, but the point remains: the body actively resists weight change in both directions.

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3. The Misunderstanding of the Energy Balance Equation

The energy balance equation states: Body Fat = Calories In – Calories Out. This is always mathematically true, but it doesn't mean what most people think.

"Most people think it means that if you simply eat 500 fewer calories, you're going to lose a pound of fat per week. The thing is that it almost never creates that weight loss."

Why? Because there are three variables that must balance:

1. Calories in (what you eat)
2. Calories out (what you burn)
3. Body fat stores

When you reduce calories, your body can respond by either:

• Releasing calories from body fat (what you want), OR
• Burning fewer calories (what actually happens)

"Virtually every scientific study of weight loss has shown that metabolic rate goes down when you simply cut calories. Every study."

Dr. Fung emphasizes this doesn't break any laws of thermodynamics—it's just basic algebra with three variables. The energy balance equation isn't a model of obesity:

"It's not a wrong model. It's not a model at all. It's simple arithmetic."

Nick offers a helpful analogy: if you took a millisecond video of someone jumping and caught them at their apex, you might conclude they can fly. But they're coming back down—you just didn't see the whole arc.

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4. The Rudy Leibel Experiment and Dr. Bray's Self-Experiment

Dr. Fung references a classic study by Rudy Leibel where participants were given a liquid diet and force-fed until they gained 10 pounds. The findings:

• Participants required far more calories than expected to gain weight
• As they gained weight, their bodies burned about 500 calories more than normal
• When returned to normal weight, metabolic rate immediately normalized
• When made to lose weight, metabolic rate dropped again

"As you eat more, you burn more. As you eat less, you burn less. And that happens all the time."

Dr. George Bray, a legendary obesity researcher with 40+ years in the field, conducted a self-experiment. He tried eating more but found he couldn't force himself to overeat regular food. So he switched to cookies and ice cream.

"Then he gained the weight and then he said I started getting uncomfortably hot. I was sweating all the time."

When he stopped the experiment, he lost the weight in just three weeks without any effort—his appetite was completely killed because his body was trying to return to its original weight.

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5. Why Bariatric Surgery Often Fails (A Calorie Paradigm Problem)

The discussion turns to surgical approaches to weight loss, which historically focused on restricting calories:

Failed Approaches:

• Jaw wiring (1960s-70s): People figured out how to get calories through smoothies and soft foods
• Lap bands: The number of procedures has dropped dramatically; most common procedure now is removal
• Roux-en-Y gastric bypass: Peaked in 2010, with most patients eventually regaining weight

"My friend who's a surgeon says the most common lap band procedure we do is removal. People just take them out."

The problem with these surgeries? They enforce calorie restriction while hunger goes up. Eventually, people crack or find workarounds.

"If your problem is hunger goes up, calories are restricted, at some point you're going to crack. You're not going to be able to follow it."

What Works Better:

GLP-1 medications (like Ozempic) work by reducing hunger itself. When hunger goes down, calories naturally follow—and you're working with your body instead of against it.

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6. The Three Types of Hunger 🍽️

This is the core framework of The Hunger Code. Understanding why you eat is crucial because:

"You eat when you're hungry and you stop when you're full. So the problem of overeating is really a problem of over-hunger."

Type 1: Homeostatic Hunger (Physical/Hormonal)

This is the physical hunger most people think about—stomach growling, etc. But it's entirely driven by hormones, not by how long since you've eaten.

Surprising fact about daily hunger patterns:

• Most hungry: Around 7:30-8:00 PM (right after you've eaten lunch)
• Least hungry: 8:00 AM (after 12 hours without food!)

"The idea that hunger is just about the state of having not eaten is not true. It's actually all driven by your hormones."

Morning hormones (cortisol, growth hormone, sympathetic tone) release glucose and suppress hunger as part of your natural circadian rhythm.

The Body Fat Thermostat: Your body tightly regulates how much fat you carry. This makes evolutionary sense:

• Plant-eaters that get too fat get eaten by predators
• Carnivores that get too fat can't catch prey

Dr. Fung mentions the gravistat hypothesis—research showing that osteocytes (bone cells) can sense body weight and send signals to the brain. Studies with weighted vests show people lose approximately the weight of the vest over time!

Type 2: Hedonic Hunger (Pleasure/Reward)

This is hunger driven by pleasure and reward. You don't eat dessert because you're hungry—you eat it because you want to.

"If you think about things like comfort foods, foods that give you comfort, they do because they change these neurotransmitters in your brain."

Key characteristics:

• Driven by dopamine spikes
• Connected to emotional eating
• Exploited by ultra-processed foods
• Can tip over into food addiction

Nick shares a fascinating personal experience: After a strict year of keto with nothing sweet, he accidentally tasted frosting that used to be his favorite—and he abhorred it. The same flavor triggered a completely different response.

"Now, when I have something like a handful of blueberries, just wild blueberries, it tastes sweeter to me and I get more pleasure than like even a full-on ice cream sundae ever used to."

Important insight: Hedonic hunger isn't about actual pleasure—it's about pursuit and habituation. Dopamine is a desire hormone, not a pleasure hormone. As you chase hyper-palatable foods, you need more to get the same response.

There's also biological overlap: insulin spikes can trigger dopamine spikes, and refined carbohydrates both stimulate hedonic hunger AND reduce satiety signaling—a dangerous combination.

Type 3: Conditioned Hunger (The Most Underappreciated)

This is hunger created by pairing food with neutral stimuli—exactly like Pavlov's famous dog experiment. 🔔

"If you ring a bell and give the dog food enough times, the dog will learn that the bell means food. And when you ring the bell without showing the food, it will salivate."

The problem in modern America: We've paired food with everything.

• Sitting in the car? 🚗 Eat something
• Watching TV? 📺 Eat something
• At your desk? 💻 Eat something
• Reading a book? 📖 Eat something
• Walking on the street? 🚶 Eat something

Even opposite emotional states trigger eating:

• Good thing happened → Celebrate with food! 🎉
• Bad thing happened → Treat yourself with food! 😢

"Society is pushing you in the direction of eat, eat, eat."

Dr. Fung points out that other cultures handle this differently. In Japan, eating while walking is heavily frowned upon. Eating is meant to happen at a table, not everywhere all the time.

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7. Obesity Spreads Like a Virus 🦠

A remarkable study from the New England Journal of Medicine examined how obesity spreads through social networks:

"If your best friend becomes obese, your own risk of becoming obese goes up by like 117%."

This isn't about genetics—it's about social influence:

• If your friend eats salad, you eat salad
• If your friend plays squash, you play squash
• If your friend eats French fries, you eat French fries

Environmental impact examples:

• A Japanese person in Japan has very low obesity risk
• Move that same person to America → obesity risk increases sixfold within a generation and a half
• Military families moved to high-obesity counties see their own obesity risk increase

"It's not simply an individual thing. The environment actually plays a huge massive role."

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8. Practical Tools to Fight Conditioned Hunger

Tool #1: Change Your Mindset (Food Propaganda Works!)

The most powerful tool is changing how you perceive things. You can deliberately choose what you want to believe and repeat it until it becomes true.

"You can see cookies as a rewarding treat that you enjoy, or you can see it as poison. You choose."

Dr. Fung's example with ultra-processed foods: Years ago, he started thinking "sugar is poison" and repeating it to himself. Over time, his perception genuinely changed.

"So now I look at something and I go, 'Whoa, this is gross. Look at all this stuff that's in here.' But it changed with the mindset because I'm not seeing this as something I want but can't have. I see it as something I don't want."

This is targeted, intentional internal propaganda—and it works.

Tool #2: Use Mantras

Mantras are lessons you repeat until they gain power—like Nike's "Just Do It."

Dr. Fung's fasting mantra: When he gets hungry during a fast, he pats his tummy and says:

"Burn baby burn."

This reframes hunger as a positive signal that fat is being burned, rather than a negative feeling of deprivation.

"Every time I do that, my hunger is manageable because I'm reminded of the benefits."

Tool #3: Rebuild Habits

Habits don't require willpower but provide benefits day after day—like brushing your teeth.

Dr. Fung has made eating twice a day a habit. Now when he does a 24-hour fast, he only has to skip one meal instead of two plus snacks.

"Once you have that habit, you're at a huge advantage."

Tool #4: Control Your Environment

While you can't always change your environment, you can:

• Set rules about where you eat (only at the kitchen table, never at desks or in cars)
• Practice fasting regularly to set the opposite expectation—that you're not going to eat most of the time
• Be aware of how your physical space affects eating (studies show patterns like having cereal on the counter or entering your house through the kitchen correlate with obesity)

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9. Final Thoughts

The conversation wraps up with Dr. Fung explaining why The Hunger Code fills an important gap:

"I've read a lot of diet books. I've read a lot of nutrition books, and like 90% talk about calories. But nobody really talks about hunger. What is it? What are the types of hunger? How can you impact those types of hunger?"

The book includes:

• Three golden rules for weight loss
• 50 practical tips
• Lessons from cognitive behavioral therapy
• Strategies for breaking bad habits and creating healthy ones

The bottom line: If you think losing weight is just about the diet, you've probably already lost. It's about eating behavior—which includes the foods you eat, but also hedonic pleasure, mindset, conditioning, and behavioral psychology.

"It's actually eating behavior that you need to impact, not just the foods that you eat."

The goal isn't to see a cookie and want it but resist it (that's torture). The goal is to genuinely not want the cookie in the first place. That's the real freedom. 🎯