The issue is not lack of knowledge about appropriate amounts to eat, it's the physical sensations and mental state of being satiated at those amounts and the self control to limit yourself when you are not.

I’m hungry right now. I should be working, but all I want to do is to eat. I have already eaten more than enough today, and I would like to lose weight.

I could take more caffeine to reduce my desire for food, but it is already too close to bedtime. I could try to focus on work (I am) but I keep getting intrusive thoughts about the fact that I could just get ice cream/cookies/chicken fingers/burrito/quesadilla/insert food here in just a few moments.

I wish I could take these drugs, unfortunately I cannot. Terrible side effects.

Strangely, after visiting Japan I found it quite easy to eat a healthy low calorie diet for about two weeks. Now I’m back to constant food noise, despite trying to stick to a Japanese-style diet (lots of fish and vegetables and fermented foods).

The people who say “just eat less” don’t understand what the actual problem is.

I was on a GLP-1 a few years ago and lost 70 lbs. After I got off, I kept a ton of diet changes (no more Pepsi or Gatorade and a lot of water instead, switching to whole grains and fiber/protein variants on pasta, etc.) and gained the weight back in a year and a half. The literature backs this up: keeping up weight loss is hard.

All research points to a "no" answer - weight is regained, and quickly. Which helps explain why obesity is so prevalent - it is something in the brain's chemistry.