Louise, he probably should talk with his doctor about this. If he has hereditary cholesterol issues, he can control it to some point with diet, but the rest simply does its thing.
Bad cholesterol runs in my family. My four year old cousin had a choleterol level of 300+
There is no way he could have eaten enough fried food for that to happen...
That said, yes, this diet usually helps lower cholesterol, but you need to make sure you are eating the good fats that lower cholesterol. The saturated fat in lunch meats and cheese could definitely be doing it. The walnuts are fine, but try to eat some veggies with a small amount of cheese or or a protein packed dip like hummus or bean dip rather than just cheese and meat, okay? The more veggies, the better.