Whether you enjoy cardio or not, you probably know that it helps you lose fat faster. I’m often asked whether fasted cardio is the best way to burn fat. Over the years I have successfully implemented fasted cardio with over 3000 of my clients, producing 19 pro cards and over 300 top 3 finishes and countless transformations with lifestyle clients. However, when it comes to the biochemistry of the human body, nothing is as simple. Does fasted cardio help you burn fat faster? What are the benefits of fasted cardio and is it safe?
Fasted cardio is a cardiovascular activity performed after not eating for at least 4-8 hours, typically most people do it in the morning. Many people think that training fasted simply refers to not having any food in their stomach when they exercise. However, that’s not correct. You might not feel as though you have anything in your stomach, but your body may still be digesting the meal you ate up to 3 hours prior. During this time, insulin levels are elevated, which means the body is more in a nutrient storage mode and less of a “fat burning” one. Training fasted would mean that insulin levels are at baseline. The body enters this fasted state approximately three to six hours after eating, depending on the food volume, total calories and macronutrient composition of the meal.
The main benefits of fasted cardio include weight loss, priming your body for optimal nutrient absorption, increase in insulin sensitivity (lowered insulin levels), increased lipolysis, and fat oxidation. Increased lipolysis is when the body breaks down fatty cells to use them as energy, and fat oxidation is when the body burns the energy from fat cells when the body’s glycogen (the body’s storage form of energy) is low. When the body is resting, especially during sleep, blood insulin levels begin to drop. This means the body turns to using fat as energy instead of carbohydrates. Insulin is a hormone made by the pancreas that’s responsible for controlling your blood sugar levels. Insulin shoots up anytime you eat and helps convert the sugar in your blood into energy for immediate use or into fat for future use. When you exercise in the morning before eating, your insulin levels are low. This means you’ll burn fat easier and faster because your body doesn’t have to worry about depleting your blood sugar levels before burning the fat stored in your liver and muscles.
In a fasted state, your body is primed for optimal nutrient absorption. After fasted cardio, your body’s net balance of protein is negative. Muscle protein is partially used for energy. Since the body strives for balance, it transitions from a catabolic state, where molecules are broken down for energy, to an anabolic state, where molecules are built up. The body is ready to better absorb nutrients when anabolic activity is higher than catabolic activity. These nutrients are used to build muscle, and in order to build muscle, energy is also needed. This is why a good combination of carbohydrates, proteins, and fats are essential after a fasted cardio workout.
As mentioned above, fasted cardio may increase fat burning since blood sugar and insulin levels are low after a 4-8 hour fast. Yet this can be tricky if your goal is to build muscle as fasted cardio breaks down fat stores but may also use amino acids to fuel your body. This is where diet plays a huge role in your progress. You can increase your amino acids to reduce these effects and its also important to ensure your body gets enough protein, carbs, and fat ratios to maintain regular and optimal functioning.
Starting your day immediately with a fasted workout eliminates the possibility of potentially skipping it all together. This can increase motivation and productivity that will translate to having an overall better state of mind throughout the day. So unless you have blood sugar control issues that would make it unsafe to exercise without a proper meal or snack, it’s typically safe for most people to perform a low to moderate intensity fasted cardio workout. Often, burning fat for energy without a carbohydrate source can make us crave more calories for refueling, so choose your post workout snack carefully and quickly. Aim for a post-workout meal of around 40% protein, 30% carbs, and 30% fat. It’s important to ensure your body gets the right amount of protein, carbs, and fats because you don’t want to create any sort of nutrient deficiency while reaching your fitness goals. The ratio varies based on your goals so what works for one person may not work for you. Go with what feels good for you, your body, and your fitness goals.