You can drink 4000 calories of ethanol and not gain weight though! It's the only macronutrient with no storage form. From this was derived the infamous lean chicken breast and tequila diet. Biologically impossible to gain fat on that diet. Dietary protein is used as such, very little is converted into glucose and of that virtually none becomes lipids[1].

Never said it's healthy, but you will lose fat. If you're not keen on the ethanol poisoning aspect of the diet, you can substitute complex fibrous carbs like broccoli or some such and get similar results.

Of course if you really don't care about health you could poison yourself with Dinitrophenol. It's the fat burning drug. Literally. Users routinely die from their bodies cooking them to death.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3636601/

The people that die have an obsessive behavior (like anorexia or body image issues) that cause them to ignore the side effects.

If you were taking a drug and it made you feel horrible would you take more? Most likely you would stop or at least forego increasing the dosage.

These people didn't die because of dinitrophenol. They died because of an underlying condition. It's an accidental suicide.

The wording is a bit awkward, but if you re-read what he wrote, it's not what he's saying at all.

Because a ketogenic diet depends the amount of carbohydrate restriction that will cause your body to physiologically be generating ketone bodies (eg, say less than 20g of net carbs), even at a constant formulation that doesn't change (as your TDEE changes) you will still be in the same state of ketosis - eg, if you measured your mmol concentration of BHB, it would likely remain the same. However, your caloric deficit of course would change (and you would need to lower it to match that to maintain your rate of weight loss).

In your hypothetical example, if your TDEE were 2000kCal and you were able to eat and absorb 4000kCal of butter a day, you would gain weight (although slower than the expected 0.57lb/day due to increased TDEE; this expenditure change (up to +50%!) was shown in the Vermont State Prison overfeeding experiments in the 60s). But despite that, due to the complete lack of carbohydrates, this diet would definitely stimulate ketogenesis (and would do so regardless if your TDEE were a 2000kCal surplus or deficit).

Due to the complete lack of proteins, you would eventually start consuming some lean body mass to produce some of the glucose (a percentage of glucose would be provided by the glycerol molecule holding together each triglyceride) required by the brain (~30%) and RBCs. I'd expect a pure butter diet to have about the same physiologic effect on protein-sparing as an extended fast (eg, you'd probably last a couple months before eventually expiring).