Proteins are the main building blocks for muscles, bones and skin, so it's no wonder protein shakes are so beneficial.
Protein helps build muscle and muscle burns more energy than fat. However, getting your protein solely from food sources usually means it's mixed with fat or carbohydrates, which isn't ideal for those looking to lose weight. With a whey protein shake, you can get all the protein your body needs (and stay fuller longer) without the additional calories you're trying to avoid. That is what makes whey protein shakes effective post-workout drinks and meal replacements.
Also, as you build muscle, you won’t just burn calories during your workout. Those muscles will continue to burn calories throughout the day. That is why weight loss programs encourage participants to incorporate strength training and protein shakes into their weight loss regimen.
While the majority of people get enough dietary protein, people on low or very low calorie diets are at risk for protein deficiency. If you're significantly restricting calories, a whey protein shake will provide you with protein, keep your energy levels up, and keep your calorie count down.