The Reason It Works

Originally designed for morbidly obese patients to qualify for surgery. Extremely low calories and carbs force weight loss but spare muscle by keeping protein. About 1000-1200 calories of pure essentials. These are essentially the core foods.

You can do intermittent fasting or not when you eat core foods. The main benefit is logistics. Less time eating means less time to overeat. Not eating a meal is easier than eating an unsatisfyingly small meal. I don't recommend women immediately do this because a subset potentially get cortisol/hormone issues with it.

The core foods approach is not a low carb or ketogenic diet. But part of the day it is. The benefit you get is very smooth focus and energy levels as well as appetite suppression. That's because your insulin sensitivity improves.

Every good nutrition strategy has one thing in common: high protein. It blunts appetite, spares muscle, and supports a bigger caloric deficit. 0.7g/lb bodyweight is sufficient for muscle building. Your core foods hit this mark regardless of what you eat after. You can eat even more protein if you want to have an even higher daily calorie deficit.

Counting calories rarely works beyond a few days. The calculations are inaccurate and people end up gaming the system to their own detriment. Hand measurements are sufficiently accurate at a fraction of the time and focus required.

Core foods fulfill the minimum optimal macronutrients in the smallest calorie package. That leaves a huge daily allotment to spend however you like. Dessert, normal dinner, whatever. Before it was "nail it all or fail it all." Now it's "who cares."