Whey protein is a highly used supplement among bodybuilders, fitness enthusiasts and weight loss adherents. Whey comes from milk which is 20% whey and 80% casein. Casein is a protein found in cheese for instance in cottage cheese where it's plentiful. During the cheese making process, whey protein is collected. Whey protein contains essential amino acids and branched chain amino acids(BCAA's) which are effective for building lean muscle mass and shedding body fat as well. The great thing about protein is it's low in calories, only 4 calories per gram of protein but can keep hunger pangs at bay, hence should be effective for weight loss. But there are people who use whey protein and are gaining fat, this is why the question "can whey protein make you fat?" is raised. To be honest, there are a few reasons why people are getting fatter while using whey protein. Here are some of them:

No Proper Diet In Place

Some people think that whey protein is a shortcut for losing weight. Hence they don't pay attention to their diets thinking just by consuming whey protein will ensure rapid weight loss. This is wrong. Whey protein is simply protein and it builds muscles which in turn speed up your metabolism. A fast metabolism helps burn fat and aids weight loss. But if you're not eating the right foods, your progress can become stagnant or you can become fatter. Eating solid nutritious foods should still be the core of your nutrition while taking whey protein.

Not Training Hard Enough/Wrong Exercise Routine

If you're not exercising hard enough or following the wrong exercise routine and taking whey protein while still adhering to the wrong diet, you can still get fatter. Your goal is to build muscle and burn excess calories and fat so if you're not performing high-intensity workouts, you can't expect whey protein to lose weight for you. Whey protein is highly effective to repair and rebuild your depleted muscle tissues after a grueling workout. So take advantage of your whey protein notably post-workout. Focus on compound exercises and high-intensity interval training(HIT) which is short bursts of intense exercise sessions for instance 20 push-ups then another 20 push-ups with only 30 seconds rest in between or fast-paced running for 15 minutes instead of slow-paced running for 60 minutes. You'll burn more calories with these strategies.

Poor Metabolism

Your metabolism is slow. People with a sluggish metabolism have a tendency to store body fat as compared to burning it. Your poor metabolism has to do a lot with an improper nutrition routine. But if you eat muscle-building and fat-burning foods, your metabolism will skyrocket. Whey protein can help boost your metabolism but you can't rely on it alone, you still need a wide array of nourishing foods.

As mentioned earlier, protein is low in calories and it's no different for whey protein. But anything in excess whether it's carbs, fats or protein can lead to excess body fat although it's more difficult for protein. Apart other functions, amino acids from protein are usually used to build new muscle tissues or maintain your muscle mass but any excess will either be converted to glucose and used up as energy(notably when your carbs intake is low), stored as body fat or mostly excreted in the urine. It's highly unlikely that whey protein will make you fat so don't worry about that. 1 single scoop of whey protein contains like 110 grams of calories which isn't much. And the ideal time to take it is post-workout as a protein shake, other times, just focus on whole foods. If you are looking for a whey protein supplement, I recommend you to get a whey protein isolate. Whey protein isolate is a high quality protein and has the highest biological value(BV). It is 154 on the BV ladder. The higher the BV is means the protein is most efficiently broken down, absorbed and utilized for protein synthesis.