Fungus in the gastrointestinal tract. Dr.Peebles told my friend that this is why he was feeling sluggish.

He said to drink liquid acidophilus (don't eat yogurt instead). He said this would cause gas for the first couple of days, but to not stop taking it, as this was a sign it was working.

It did exactly what Dr.  Peebles said it would do, and my friend has much more energy now.