No, that's bullcrap.
I eat about 2 cans of tuna a day, and I work out and I'm seriously Rambo cut without any supplements or steroids. I weigh about 140, 5'7. A couple nights ago I had a whole thing of basically RARE (raw) tuna for a meal at this restaurant. In school back in the day, we even had a f*cking tuna club. LMAO it was a joke but yeah.....
The point is.....
your friend is an idiot.
However- being a pescetarian is not good, because fish lack many of the essential amino acids that we as humans need.
I would suggest eating a lot of eggs as well, like 3 for breakfast; and also eat steak and chicken occasionally, as well.
The point is HOW THEY'RE PREPARED, not the meat- the only "bad" meat, really, is pig or shellfish.
don't ever eat junk food, fast food, candy, chocolate (except pure chocolate which is nasty), microwaved food, soda's, artificial sweeteners, "lite" or "sugarfree" foods or gum, or ever have caffeine or any other artificial drugs.
Don't ever take any kind of drug- no pharmaceutical ones, no narcotics, no illegal or legal ones, nothing.
If you want to lose weight, EXERCISE by running, playing basketball or soccer, and lifting weights reps of 20 to sculpt the body.....
AND eat hot peppers to speed metabolism and burn fat! but NEVER starve yourself or limit your food consumption. That is downright dangerous.
Also- eat all 5 food groups equally. The food pyramid is basically right, but it is a little off in its serving calculations. They are meant to be eaten equally!
Last thing- exercise, exercise, exercise!
Your friend's a bonehead.