Forget everything you thought you knew about dieting.
No calorie counting, no macro tracking, and unlimited portions of select foods—yet the results are staggering.
In a recent YouTube experiment, fitness researcher Jeremy Ethier put two already-fit subjects through a radical 30-day eating protocol that sounds almost too simple to work.
What happened next challenges conventional wisdom about fat loss and might just revolutionize how we think about restrictive eating.
Jump to:
- The Subjects: Already Fit, But Stuck
- The CPB Diet: Simplicity Taken to the Extreme
- The Science Behind Food Monotony
- Week One: The Mental Battle Begins
- Adding Strategic Flexibility
- The Treat Meal Strategy
- Navigating the Menstrual Cycle
- Max Hits the Wall
- The Final Week: Mental Fatigue Sets In
- The Results: Beyond Expectations
- Long-Term Takeaways and Practical Application
The Subjects: Already Fit, But Stuck
Max, a personal trainer and train conductor, started the experiment at 19% body fat according to his DEXA scan. Isabelle, a legree coach, came in at 31% body fat—actually better than the US average.
Both were already athletic and committed to fitness, but struggled with stubborn fat and problematic eating patterns.
I think just with the tracking is something that I kind of struggle with mostly with just having a busier schedule. I don’t always take the time to kind of, you know, weigh everything out.
Max had developed a particularly troubling habit—visiting all-you-can-eat buffets two to three times weekly, eating until physically sick. This behavior disrupted his sleep and created an unhealthy relationship with food.
The CPB Diet: Simplicity Taken to the Extreme
Ethier’s protocol, dubbed the CPB diet, operates on just three rules.
- Rule One: Eat only chicken breast, potatoes, broccoli, and carrots—but consume unlimited quantities
- Rule Two: One tablespoon of olive oil permitted per meal
- Rule Three: Zero liquid calories, diet sodas, or artificial sweeteners allowed
When presented with their final unrestricted meal before the challenge, both subjects showed immediate concern.
I think I can do it, but it’s going to be kind of sad. I love eating avocados and chicken for breakfast will be weird.
To boost compliance, Ethier offered significant incentives. Isabelle would receive a professional photo shoot for her website, with one catch—she’d have to use whatever photos resulted. Max earned ten fully compensated buffet meals if he completed the challenge.
The Science Behind Food Monotony
Dietary variety triggers overconsumption through what researchers call sensory-specific satiety. Even when stuffed at a buffet, people find room for something new because novel tastes activate the brain’s reward system.
When foods remain simple and repetitive, that reward mechanism stops firing as intensely. Research shows people naturally consume 20-30% fewer calories without consciously restricting portions.
One study found participants eating identical mac and cheese daily consumed roughly 100 fewer calories per meal by week’s end—simply because the food became less exciting.
Why Potatoes Dominate the Satiety Index
In a landmark 1995 study, researchers measured the fullness factor of 38 different foods by giving participants 240-calorie portions and tracking satiety over two hours.
Plain white bread served as the baseline with a score of 100. Potatoes absolutely crushed every other food tested.
For identical calorie amounts, potatoes proved three times more filling than white bread and eight times more satisfying than croissants. However, preparation matters enormously—frying potatoes eliminates most of this advantage.
The supporting cast of chicken breast, broccoli, and carrots amplifies these effects. Fiber-rich vegetables and lean protein add tremendous volume for minimal calories while requiring more energy to digest, creating a thermic effect that burns additional calories during digestion.
Week One: The Mental Battle Begins
Early days proved predictably difficult. Both subjects experienced intense cravings and psychological resistance to eating chicken for breakfast.
Chicken for breakfast. It just I don’t know. It just makes me feel very trapped. I’m not someone who really likes to eat a lot of meat and I just really want to make sure that I get enough protein in.
Max developed an unusual fixation on his limited food options.
Every time I think about food, it just images of a potato just pop in my head. Like potato, like I would be at work, I’d be thinking about what I’m going to eat. That’s all like just potatoes.
Despite eating unlimited quantities, neither subject complained about hunger. In fact, they struggled to consume enough food. Weight tracking through the Built with Science Plus app revealed Max averaged only 1,800 calories daily while Isabelle consumed approximately 1,300 calories.
By week’s end, both reported unexpected mental clarity and energy stabilization.
I feel a lot better. I feel like I’ve kind of settled down all my emotions, and I’m focused now. I have mental clarity, good energy, consistent energy, and no crashes throughout the day.
First Week Results: Rapid Physical Changes
After just seven days, measurements revealed dramatic shifts. Max dropped five pounds with his waist shrinking over 3 centimeters. Isabelle lost 1.5 centimeters from her waistline despite daily weight fluctuations.
Adding Strategic Flexibility
Ethier introduced modifications at the two-week mark, particularly for breakfast—Isabelle’s biggest struggle point.
She chose eggs as an additional protein source. Max, seeing strong results, declined any additions and committed to the original strict protocol for the full duration.
This decision splitting the experiment into two distinct paths revealed something crucial about sustainability versus extreme adherence.
The FOMO Factor: Social Isolation
One unexpected challenge emerged around social situations. The experiment occurred during the holiday season, amplifying feelings of missing out.
I’ve been feeling a lot of FOMO lately, so the fear of missing out here. Um, I was invited to a potluck, a birthday potluck social, and me and my wife couldn’t go. I went to this grand opening of my friend’s bakery, um, baking factory. So, I went and then I realized I couldn’t even sample anything.
Max redirected this energy toward replacement habits—drinking tea, reading books, and planning non-food-centered activities with friends. This shift represents one of the protocol’s most valuable benefits.
Eliminating constant food decisions frees up mental energy and willpower for other aspects of life, including workout consistency and resisting evening junk food.
The Treat Meal Strategy
At week two, Isabelle received permission for one weekly treat meal—what researchers call a “planned hedonic deviation.”
This deliberate temporary break from routine helps maintain social connections while providing mental and physical relief. Studies suggest this approach produces better long-term results compared to rigid daily restriction.
Isabelle worried the treat meal might trigger uncontrollable cravings.
I definitely thought it would spike like more cravings. So, I was a little worried to have it. But honestly, I feel totally fine. I feel like it’s been easy just to kind of get back into routine again today.
Additional ingredients gradually entered Isabelle’s rotation—oranges, tomatoes, avocado, Greek yogurt, and bok choy. These weren’t random selections. Oranges ranked as the most filling fruit in the original satiety research, while bok choy provides massive volume for minimal calories.
Isabelle faced a challenge Max couldn’t relate to—managing the diet through her menstrual cycle when hunger and cravings naturally intensify.
Despite common advice suggesting women need dramatic diet or workout changes during this time, research doesn’t strongly support such modifications. Instead, listening to your body while maintaining overall structure proves most effective.
Isabelle increased meal volume by adding more potatoes and managed cravings with tea and sugar-free gum—simple adjustments that kept her on track without breaking protocol.
Max Hits the Wall
Around week three, Max experienced a severe psychological downturn.
I just can’t take this anymore. Just this chicken breast and potato diet, I just had enough. I got to the gym yesterday. I just laid on the mat for a solid 15 minutes. It’s mostly the thoughts. Every time I stop and think about something, I spiral down this deep hole.
His weight loss pace—nearly double the typically recommended rate—raised serious concerns about muscle preservation. However, research suggests short-term rapid weight loss can spare muscle mass if three conditions are met: high protein intake, consistent resistance training with a solid program, and limited duration.
Still, Ethier worried about what the final DEXA scans would reveal.
The Final Week: Mental Fatigue Sets In
As the 30-day mark approached, both subjects struggled with motivation despite knowing the end was near.
I’m actually finding the last few days quite challenging to be honest. Mostly because I am also in the end part of my cycle, which tends to make me feel more bloated, more puffy. Feeling like I’m comparing that versus day one. I’m just not seeing like a huge difference.
Both had already planned their first post-experiment meals. Max wanted steak and fruit—foods completely absent from his diet. Isabelle craved blueberry pancakes.
The Results: Beyond Expectations
When the final DEXA scans came back, even Ethier—who designed the experiment—appeared shocked.
Isabelle’s Transformation
- Fat loss: 5 pounds
- Body fat percentage: Dropped from 31% to 28%
- Lean mass: Gained half a pound of muscle
For context, typical monthly fat loss results show 1-2% body fat reduction. Isabelle achieved a 3% drop while simultaneously building muscle—an extremely rare outcome.
Max’s Dramatic Changes
- Fat loss: 14 pounds
- Body fat percentage: Plummeted from 19.3% to 12.9%
- Muscle mass: Completely preserved
I didn’t I honestly did not think that was possible. I don’t think you realize 14 lbs of fat and going from 19 to 12.9 in 30 days. In 30 days.
Max reported unexpected improvements beyond body composition, including significantly better sleep quality and duration.
Long-Term Takeaways and Practical Application
Neither subject regained the weight in the weeks following the experiment. Max used his buffet rewards to treat friends and family, making up for social moments missed during the challenge.
Most importantly, Max reported breaking his unhealthy buffet-binging habit completely.
The extreme nature of this protocol isn’t necessary for everyone, and it shouldn’t be attempted long-term without medical supervision. However, applying even basic principles—eating mostly whole foods, reducing dietary variety, choosing highly satiating options—can produce meaningful results.
Key Principles You Can Apply Today
- Reduce decision fatigue: Rotate between three to four go-to meals rather than constantly varying your diet
- Prioritize satiety: Build meals around potatoes, lean proteins, and fiber-rich vegetables
- Limit food reward: Minimize highly palatable processed foods that trigger overconsumption
- Strategic flexibility: Include planned treat meals to maintain social connections and psychological relief
- Listen to hunger cues: When eating whole, filling foods, trust your appetite rather than rigidly tracking every calorie
Isabelle reflected on her journey with pride, acknowledging that comparing female and male fat loss results isn’t meaningful due to physiological differences.
I feel really proud of like losing 5 lbs of fat and I’ve never been on like a weight loss journey or tried to, you know, intentionally lose like weight.
The experiment demonstrates that sometimes the simplest approaches—though not always the easiest—produce the most dramatic results. Unlimited food within strict boundaries created a psychological reset that transformed both subjects’ relationships with eating while delivering exceptional body composition changes.
Whether you attempt the full protocol or simply incorporate its core principles, this experiment reveals powerful truths about satiety, food reward, and the mental liberation that comes from eliminating constant dietary decisions.
