The answer to that question is “it depends.” Some people may find it works well for them while others feel sluggish and lightheaded decreasing their performance during their workout.
Studies show that your body’s response to exercise can differ based on whether or not you eat before exercise. Your body’s primary sources of fuel are body fat and carbohydrates. When you eat before exercising your body will use carbohydrates which will provide you more energy for the exercise. But what if you decide to work out before breakfast? 
When you work out on an empty stomach it is called, fasted cardio and your level of insulin is low or at the baseline level. If insulin is low, there isn’t available energy in your bloodstream in the form of glucose. Your body must rely on stored energy like glycogen and fat to fuel your muscles. If your goal is to do fasted cardio, it can be done any time of day your body is in a fasted state.
What Happens if You Exercise Before Eating? 
As mentioned, if you exercise prior to having a meal your body will use the stored fat for energy that may lead to higher levels of fat loss. However, there is no concrete evidence to support this and this doesn’t necessarily mean that it’s ideal.
When you exercise on an empty stomach, you may burn valuable energy sources and have less stamina. Completely depleting your glucose and glycogen can result in muscle being used as protein. This would do more damage than good as muscle gives your body it’s shape and tone. Usually, if you are burning protein at this stage, you are not feeling too well either.
Low blood sugar levels may also leave you feeling lightheaded, nauseous, or shaky. Another negative effect is that your body can adjust to continually using fat reserves for energy and start to store more fat than usual.
It would be great to have a definite prescription for fat burning, but it depends on how your body works. Try it out for 14 days and see if the scale gives you better results.
When Should You Eat Before Exercising?
Generally speaking, it isn’t recommended to have a large meal within an hour of your workout. If you are hungry try a light snack that is easily digestible such as a piece of fruit or a handful of nuts.
If you prefer working out after your evening meal you should wait at least 2 hours before beginning your workout. Another option is to break your evening meal down into 2 smaller meals.
If your exercise routine requires a lot of strength, energy, and endurance you should eat beforehand. It’s especially important if you plan to work out for longer than an hour. Foods high in protein eaten at least 2 hours prior to intense exercise gives your muscles fuel and improves performance.
Here are some food options you’d want to consider:
- Carbs such as fresh fruits and vegetables, whole grains, and legumes.
- Healthy fats, such as olive and coconut oil, ghee, and avocados.
- Protein-rich food like lean meats, eggs, and low-fat dairy products.
- Nuts, seeds, and sprouts
- Foods are rich in iron such as fish, cooked beans, and green vegetables.
- If you don’t have enough time you can snack on an energy bar, peanut butter sandwich, or fresh or dried fruit.
Light snacks like this can be helpful but a large meal can actually hinder your workout because a portion of your blood is being diverted away from your working muscles to your digestive system to help process your food. This leaves less oxygen available for your muscles and can leave you feeling sluggish.
Should I Try Fasted Cardio?
At the end of the day, the answer is, if it works for you, and you can do it consistently, go for it. What is ultimately going to give you the most results is training on a consistent basis regardless of whether or not you eat first.
Lasting results will happen over time as you continue to train and follow a healthy lifestyle. We all wish there was a firm “this will work for you” answer with a plan we could follow. Weightloss is highly individual and many times it is a process of trial and error before you know what will work best for your body.