Take a look at some of the qualities that a weight gainer should have and some of the popular types of gainers so you can make an informed decision before you spend your money. Back in the day, weight gainers used to be fairly cheap protein powders loaded with sugar and fat to up the calorie content. The serving size would be something like 128 oz. and the serving would contain 3000 calories. Not exactly a practical serving size, and all that sugar kind of went against the idea of eating clean. Plus, the quality of the protein in the gainer was usually poor. Although many gainers like this still remain on the market, fortunately, the supplement industry has come a long way. The quality of a protein is determined by how well your body can use it, a factor termed "biological value", or BV for short. Basically, it refers to how well and how fast your body actually gets and uses the protein. So a whey protein like whey isolate (BV 159) is the most readily absorbed, while a milk protein like casein (BV 77) is absorbed less readily and is said to be of less quality. Now, sometimes it's good to eat lower BV rated proteins because you want to absorb it slowly, like before you go to bed. But generally, you want protein with a higher BV rating. Another thing to consider is how much sugar is contained in the gainer. Excess amounts of sugar have been shown to give an insulin spike, as well as increase levels of seratonin. This has been shown to give most people a feeling of drowsiness, irritability, and headaches. This doesn't affect everyone, but some people are more sensitive than others. Plus, the insulin spike sets your body to storing fat. Look at the nutrition label on the gainer, and see how much sugar it contains, listed under the carbohydrates. Somewhere in the 30-60 gram range is pretty good. This brings up the question of what you want in the carb/protein/fat ratio. You need carbs to help protein absorption, and you know you need the protein. Fats are definitely your friends in a gainer (though not saturated fat), as they seriously up the calorie content. A general rule of thumb is twice as much protein as fat, and twice as many carbs as protein.