Even if you’re trying to increase your protein intake to build or retain muscle, adding a scoop of protein powder to your smoothie will slow down your digestion. You’ll need up to an hour for your stomach to digest the protein in your smoothie, according to Men’s Health.
While fiber is an important part of a healthy diet, it won’t sit well in your digestive system if you plan a hard workout. According to the American Council on Exercise, high-fiber fruits and vegetables in your smoothie might be better as a snack a little later. Although a medium banana has 3 grams of fiber, you can include one in your pre-workout smoothie. Healthy fats make a smoothie feel more filling, but ACE says to avoid too much fat in a pre-workout smoothie because it takes much longer for your body to convert that fat to energy.
The Mayo Clinic suggests avoiding too many calories before a workout. Even if you can burn 600 calories during your spin class, some pre-made smoothies can be high in calories and sugar. For example, Naked Superfood Machine has 270 calories and a whopping 54 grams of sugar. Meanwhile, Smoothie King’s MangoFest smoothie has 300 calories and 66 grams of sugar.