I agree it's not true for most people -- though for someone who has trained themselves to eat a small breakfast, it surely can be. Plenty of people eat nothing

I agree it's not true for most people -- though for someone who has trained themselves to eat a small breakfast, it surely can be. Plenty of people eat nothing for breakfast, and are satiated til lunchtime, but aren't losing weight from it. More interesting to me is why someone would phrase it as a guarantee even if it were true. It suggests that the reader likely hasn't tried it, and would be surprised to discover the result.