Citation needed. I personally know people who've lost weight long term with quite brief periods of intermittent fasting.
Anecdote alert, but I started doing alternate day fasting after I read the study, then 22 hour a day fasts after I read that people were having results with that. Went from 235 to 185 in 2 years (6' tall, fairly large build.) I'm not strict, and I go off it whenever I'm bored or severely tempted.
I count any drink other than water as a snack, and watch the bread, potatoes, and cornstuffs when I am eating. Who knew it could be this easy? I hadn't really been an overeater for years, I just had never had time to starve.
Yup, I got that and I'm challenging it.
I can't say anything about the people you mentioned. I myself had absolutely no progress when IFing for some days, only dizziness and irritability.
Also, what about tribes that lived in places with cold winters? There are no plants to eat when the ground is covered with snow.
I agree that Cheerios are a bad idea generally, but I'm not pro fasting or skipping meals for weight loss. Fat is stored as an emergency reaction to high blood sugar levels, and you get exactly that when eating more between the fasts (you have to). You constantly expose your brain to too much and too low sugar levels, resulting in highs and lows in your ability to focus (and also your mood).