The two food supplements I've been using since high school, to both gain weight and increase cerebral capacity are; Pizza and Beer.

The Pizza will put weight on you quickly. If on Friday night you find out it's going to be blowing on Saturday, Eat UP! You'll be 10lbs. heavier by morning!

And the beer will make you super intelligent, even quicker!

Just ask anyone, after their 5th beer...

But be careful, too much beer and you'll lose your Pizza weight!