If I eat this stuff will I GAIN weight?

The fat calories will only add FAT and not MUSCLE. If you are wishing to gain weight, but "good" weight (not FAT), you should try drinking cans of "meal substitutes," which are usually used by people LOSING weight, or who have to be on liquid diets due to medical conditions. These "liquid meals" are nutritionally BALANCED, with proteins, carbs, vitamins, minerals, etc. because they are a meal SUBSTITUTION. To use them in a weight GAIN program, the weight is gained from "good" calories rather than fat. What you do is eat your 3 meals each days as usual... your basic food groups, etc. But then, add THREE of these liquid meals as snacks inbetween your usual meals. So a day will consist of: Breakfast Liquid Meal Lunch Liquid Meal Dinner Liquid Meal You are increasing your caloric intake, almost doubling it in fact. But, again, these are "good" calories, and your body will make muscle, skin, bones, blood, etc. from it, and not add it to your waist as FAT.

As long as you don't exceed the calories and fat and protein you need in your diet, you won't gain weight. Be careful of those things, though. Use them carefully and they can be an asset to your health.