[awj]

His "side effects" sound like symptoms of low caloric intake, not "removing dietary carbs". With more attention to his diet (yes, I mean counting calories) he could keep up this plan without the headaches/irritability/fatigue.

Also, without knowing other stats (height, age, etc), it's hard to judge if 19 pounds in three weeks is healthy. In general, no, but if he started at 5'5" and 280lb the weight was likely more of a risk than the diet.

These cutesy "rule diets" are a very poor way to manage your health. They're relatively easy to live by, but that's about the only good thing that can be said. There's nothing wrong with eating a low/no-carb diet, but you should educate yourself so you know you're being safe and how/when you'll see the results you want.