IT DEPENDS ON THE TYPE OF WORKOUT YOU'RE DOING AND YOUR OVERALL GOAL...

There are a few reasons why you may be wondering if it's a good idea to workout on an empty stomach. One reason could be that you just prefer running more when you feel lighter. I know some people that feel like eating before a run makes them feel sluggish and heavy. Another reason could be that you're short on time and your schedule is more conducive to an afternoon workout then lunch at your desk. Aside from the logistical and preferential reasons for working out on an empty stomach, there's an ongoing debate within the fitness community regarding this very topic. The debate highlights a third reason you may choose to forego food before working out, and that is fasted cardio just may help you burn excess fat.

WHY DO FASTED CARDIO...

The leaner you are, the harder it is to shed body fat. I know, it sucks. However, the reason is that you just don't have a lot of excess fat to spare. Your body is always working to run optimally and sometimes your goals and your body's goals don't easily align. When it comes to your body fat, the body will actively work to preserve a certain amount of fat as it helps regulate brain function, hormones, etc. Therefore, many fitness professionals will implement fasted cardio as a sort of coercion technique to force incremental body fat loss.

The idea behind fasted cardio is that your body is more likely to access fat stores as opposed to glycogen stores. You consume carbohydrates for energy. Those carbohydrates are broken down and stored in the body as glycogen. Your body needs energy every second of the day to perform all functions, and it prefers to get that energy from the glycogen stores FIRST. After there are no remaining glycogen stores, it will burn your body fat for energy. Fasted cardio is thought to force your body's hand to burn more body fat by working out once those glycogen stores are already empty. Remember, no glycogen for your body to burn as energy fuel means your body will need to burn fat. Your glycogen stores typically deplete after 12-16 hours. Therefore, the theory behind fasted cardio is if you have your last meal on Monday at 7 pm then wake up for a workout Tuesday at 7 am you're in optimal fat burning territory. Still, the incremental fat burn is usually not enough to notice if you're overweight. The results tend to be more noticeable if you're working on shedding those last few stubborn pounds.

AVOID FASTED STRENGTH WORKOUTS...

The best fasted cardio workouts are low intensity and steady state. Jogging and walking are great examples of appropriate exercises on an empty stomach. Frankly, your body may not be able to handle more vigorous activities than that without adequate food intake.

I do not recommend fasted strength workouts. Doing so can negatively impact your muscle retention which does help you burn more fat over time. In fact, I'd say just avoid working out on an empty stomach if your overall fitness goal is to build muscle at all.

From a practical standpoint, strength training on an empty stomach is dangerous. If you're the type to get dizzy and disoriented when hungry, then adding heavy weight is a recipe for injury.

If your fitness goal is to burn those last few stubborn pounds of body fat, working out on an empty stomach could be worth a try. However, if you want to add muscle, or improve your performance in any way, you must eat a well-balanced pre-workout meal.