I have to agree with this. However it's not because it's aggressive. It's because he's recommending eating at all. When you eat very little, your body's metabolism drops to match the new standard energy intake.
A much preferable recommendation would be to simply water fast for the same time. Lose even more weight (mostly water weight), then eat normally. Much more natural in the context of evolution. Periods of eating, periods of fasting. The practice is as old as time itself.
I've found that I can manage a day without taking in any calories, if I'm willing to feel really tired and have a moderate headache by ~1pm, and be horribly brain-fogged and useless by ~2pm. I've got a job and kids to take care of—I can't afford to have days like that very often. The hunger's not a problem—it's that I feel rather ill by mid-afternoon.
FWIW I rarely eat breakfast, so I guess I'm usually doing the (lame, IMO) "16/8" fasting pattern, though I'm skeptical that has any benefit.
The reason you feel sick is because you're body isn't used to the shift from carbohydrates for energy and ketones as energy (body fat). You get brain fog because only fat in the form of ketones can cross the blood brain barrier. So adaptation to ketones are vital. You need to work into it. No different from exercise, or climate adaptation.
Having cold showers shifts your body into using ketones more and more.
Regarding not eating breakfast, watch these videos from FoundMyFitness:
Dr. Satchin Panda on Time-Restricted Feeding and Its Effects on Obesity, Muscle Mass and Heart Health
Time restricted eating, AKA your 16/8, is VERY important. Even if you don't immediately notice changes. Those changes could begin to occur 2 to 8 years later. Depending on adherence. Also based on Dr. Ruth Patterson's advice, skipping breakfast leads to eating late into the night, which is not good for your health generally.
Of course you will gain the weight back, if your eating above your daily calorie burn - that has nothing to do with aggressive weight loss. You just need to keep your weekly average low enough to not gain the weight back. Depending on your metabolism and your bodies "set point" you might only need 3-5 days a month of this to maintain your current weight.
Late response, but: My point was not that the mechanics are flawed, rather that most people don't have the discipline to maintain their weight loss when it comes from a short, extreme intervention rather than a holistic lifestyle change.
