A delicious kind of malnutrition though.

Makes me wonder how much of the weight loss was more due to water loss rather than body fat. I remember reading something about people who are on the verge of starvation lose weight after getting access to food again due to water loss from the water required to digest food.

The meaning of that rule is generally "if you consume less calories than you use, it is physically impossible not to lose weight". Which is definitely true.

You can eat more than you use and not gain weight if you are not metabolising the food efficiently, but you can't eat less than you use and not lose weight. The former is limited by how badly you are able to mess up your body, the latter is limited by the fundamental laws of physics.

If you're at a calorie deficit, you will lose weight no matter what you're eating or what state your body is in.

Nothing in the Second Law of Thermodynamics prevents your body from turning some of your heart muscle into fuel, as bad of a plan as that may be.

That would still be losing weight(mass). The problem in this thread is that people are considering fat loss and weight loss to be the same thing. They're not. The simple truth is that a caloric deficit will always result in a net decrease in mass. This is fundamentally true of any system. Energy being removed from a system always results in a decrease in mass of that system. This is physics 101. Eating a caloric deficit will always cause a reduction in mass, though it may not be the mass you want to reduce. Eating at a caloric deficit without providing the body with the proper balance of macro-nutrients and exercise could lead to reductions in muscle, bone, and connective tissue mass. Reduction of carbohydrates in one's diet generally has a net positive effect in a caloric deficit due to the fact that there is essentially "more room" in the diet for higher quality nutrients such as proteins and fats. That said, cutting carbohydrates out entirely is a terrible idea as they are the body's primary source of short term energy.

I'm not sure it does. He said he weighed 340 pounds when he did this. His daily break even calories might be well above 4K. IIRC 2500 is recommended for the average male, who certainly does not weigh 340 pounds.

It doesn't, because exercise isn't the only way of getting 'calories out'.

Some amount of bacon a lot less than that provides all the nutrition to be gained from any amount; anything further is just waste.

It doesn't. If you maintain a fully rounded meal while also scaling calories in/out it holds.

I can straight up eat sugar only too for a month and have the same weight loss results, also diabetes.

That's the point, isn't it? If the roundness of the meal matters, it's not just calories in/out.

This is what happens all the time when calories in/calories out comes up, it becomes an exercise in pedantry. "It's just calories in/calories out" is not read by any normal person to mean "I should just cut my calorie intake by 500 for the day, and then drink that as olive oil 'cause that's easier to measure" It's there to convey "you can still eat french fries: just not as many."