A popular training method many fitness enthusiasts encourage is called fasted cardio. The basic premise of this type of workout is the notion that when you exercise during a fasted state, the body must rely on its reserves. The body pulls energy from body fat to be able to perform, thus, the rationale would be that more total body fat is burned when doing cardio when you are fasted. The term “fasted” refers to having an empty stomach or not having had any food for an extended period. Ultimately, it is up to you if this approach works for you or not. There are pros and cons to this type of training, and it remains a debated subject. The founder of fasted cardio (who coined the term in his book “Body-for-LIFE”) was Bill Phillips who was a bodybuilder.
People who do fasted cardio typically get their workout in first thing in the morning before breakfast. Moderate intensity cardio for 30-45 minutes is usually the protocol. Bill Phillips believes that the most effective way to burn fat is in a fasted state. This is because the body had reduced glycogen levels at that point, so the body relies on fat stores for energy.
On the other hand, exercising when fasted can make working out challenging in terms of energy levels. You might not be able to exercise as long as you could if you had the energy from foods you had eaten prior to the workout. Instead of crushing your workout, you might be dragging through it. Another potential danger is really working up an appetite from the fasted workout, so you might become ravenous and overeat following the workout.
Ultimately, no matter if in a fasted state or haven eaten before, the body does benefit from the act of exercising in and of itself. It is a personal decision. For those who like afternoon/evening workouts, fasted cardio might be hard to do. Someone lifting weights might not have the force to push and pull objects. A long-distance runner might not have the stamina to complete their run. There are many variables to consider, and your goal(s) as well as how your body responds to working out on an empty stomach, are all determinants of your exercise routine. Hey, some people wake up and just don’t have time for breakfast, so they inevitably do fasted cardio anyways. Some people are just breakfast eaters. Again, plan your exercise selection based on you and only you. That will set you up for consistency, reaching your goals, and sustaining your healthy habits.
Body composition changes associated with fasted versus non-fasted aerobic exercise – PMC (nih.gov)
