Carb bars are bars that contain about 70% or more calories from a carbohydrate source. Typically, this is high fructose corn syrup, maltodextrin, sugar, dextrose, barley malt, or brown rice syrup, to name a few. Therefore, these bars are very high glycemic index foods and will tend to disrupt blood sugar levels. This is especially important for non-athletes who have some degree of carbohydrate intolerance or insulin resistance.
The protein and fat content of carbohydrate bars is usually low. They contain many of the same sources as the ingredients in protein bars. Carb bars can be helpful during long-term exercise such as a marathon or a long bike race. However, it really depends on how fit the person is and what they burn for fuel. In other words, the more aerobic during a workout, the less he will rely on carbohydrates for fuel. Eating a high-calorie bar as a snack during the work day can make you sleepy by the middle of the day.