Some fitness experts will tell you to do cardiovascular exercise first thing in the morning before you eat breakfast. The reason? When you’re in a fasted state and your glycogen stores are low, your body has to draw on fat stores for energy. Thus, you’ll theoretically burn more fat as fuel when you exercise before eating. In addition, when you consume carbs before working out, it boosts insulin levels, and insulin is a hormone that promotes fat storage. Based on this, it would seem that eating a meal or snack before working out, particularly if you eat carbs, would reduce the amount of fat you burn. But recent research has called this idea into question.
The Downsides of Doing Cardio before Breakfast
Research shows that if you eat a carb meal before doing low-intensity exercise you’ll burn less fat than you will if you fast beforehand. On the other hand, the effects seem to be different in trained individuals who work out at a moderate-intensity or greater compared to less fit people.
When fit individuals train at 65% V02 max or greater, research shows it doesn’t interfere with the body’s ability to use fat as fuel, while in untrained individuals it may have a fat-sparing effect. This suggests that once you reach a certain level of fitness and are working out at a moderate-intensity, eating a modest breakfast before you start working out won’t have a negative impact on your body’s ability to use fat as a fuel during exercise.
Why It’s Better to Eat Breakfast Before Your Workout
There are some upsides to doing cardio after eating a carb meal. Recently a study was carried out by researchers at the University of Padua in Italy. They found that individuals who ate before working out burned more total energy including fat for a full day after they had completed their workout.
Eating before a morning workout makes even more sense if you’re doing high-intensity exercise or interval training. When you do high-intensity exercise, your body is anaerobic for periods of time. This forces it to use carbohydrates as a fuel source. If your glycogen stores are low, you won’t be able to push yourself as hard. This means you’ll burn fewer overall calories and less overall body fat if your glycogen stores are depleted.
High-intensity exercise where the body is forced to tap into carbohydrates as a fuel source creates an oxygen deficit. This means your body will burn greater amounts of energy for hours and even days after you stop working out. But if you’re carb-depleted, you’ll struggle to work out at this intensity and won’t get the benefits.
What does this mean? Unless you’re doing cardio at a low-intensity like walking on the treadmill, there are few benefits to not eating before your workout. Quite the opposite. If your goal is to work out hard, carbohydrates improve your performance and allow you to maximize the intensity.
The Bottom Line?
If it’s a rest day for you, and you’re doing low-intensity exercise, do it in a fasted state. In this case, you’ll use more fat as fuel. If you plan on increasing the intensity, especially if you’ll be doing high-intensity exercise, have a small pre-exercise meal of lean protein and complex carbohydrates about an hour or two before your workout. Good choices are a bowl of oatmeal with low-fat milk or an egg on whole grain toast. You’ll feel better, and you’ll be able to exercise harder too.
References:
J. Applied Physiology. 1986; 6: 165-72.
Am. J. Physiol. 1999 May; 276(5).
J. Appl. Physiol. 1976; 41:683-88.
Shape Magazine. August 2011. page 106.
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