Yes, it can as many protein bars are very high in calories and sugars. In order to lose weight, you must be in a calorie deficit and overeating protein bars can slow weight loss progress. If you are eating protein bars as snacks, look for bars with not more than 250 calories per serving. If you are eating a protein bar as a meal replacement, then choosing a bar closer to 400 calories is a better option as that will fill you up for longer and it’s considered a meal.