Fasted workout burns fat fast! It seems a pun, but it works.
Fasted cardio, in fact, is quite popular in the fitness world and a common practice for many bodybuilders, athletes, and among the I-want-to-lose-fat-quickly people.
But... what is a fasted workout? Many people know it as it sounds: training on an empty stomach or, in other words, exercising when you’re hungry.
Well, it’s a bit more than that and it has to do with your body energy system and storage.
Let’s dig deeper and let’s understand the biochemical process behind it.
Right after you consumed a meal, in the alimentary tract, the food brakes down and it is absorbed into the blood. Blood glucose levels rise and stimulate the release of insulin, a peptide hormone produced by beta cells of the pancreatic islets, which job is to shuttle nutrients into your cells for use.
We are now in a state called “postprandial”, “absorptive” or “well-fed state”, which occurs shortly after eating and lasts three to five hours after the meal.
Once the absorption process has ended, our body enters the “post absorptive” stage, called also “fasted” state. This period is characterized by the drop of the insulin’s blood concentration to a low baseline level.
The special role of the insulin in the Fasted cardio mechanism
The key player is insulin. This hormone helps cells intaking glucose to be used for energy.
If the body has sufficient energy, insulin signals the liver to take up glucose and store it as glycogen. Glycogen is actually the storage form of glucose in animals and humans. It is stored in the liver and muscles as a primary source of energy. When there is no glycogen available, the body will reach for its secondary energy source: stored fat and muscle protein.
Therefore, low insulin levels equal fat burn.
Consequently, after a meal (in the “postprandial state”) your body suppresses its fat-burning mechanisms because energy is readily available from the food you just ate.
On the contrary, after fasting for 8 to 12 hours like overnight, and heading to the gym or running, your body first will tap into the stored glucose for energy to turns, then, to burn stored fat.
In the graph below, from Yodiaries.com, you can understand better the relationship between insulin levels and fat loss between meals.
Pros and Cons
Like most health and fitness theories, fasting cardio workout also has supporters and opponents with pros and cons.
Based on a study published on The British Journal of Nutrition, those who exercise in the morning without having breakfast burn about 20% more fat than those who ate before. Which I would take any day! Doing some kind of aerobic workout in a fasted state, infact, is proven to increase lipolysis and fat oxidation rate.
On the flip side, according to the sport dietetics specialist Kelly Pritchett Ph.D., R.D., exercising without eating before brings your body to adapt to this situation, slowing your metabolism and causing a decrease in the number of calories burned.
Another downside to fasted training is that it can increase muscle loss.
Based on that, I would recommend this kind of workout routine especially to those who need to loose weight, not to those who just need to tone up or gain muscle mass.
You probably are asking yourself how can someone do cardio workout first thing in the morning on an empty stomach and your bewilderment is pretty understandable.
So, if fasted training doesn’t fit your lifestyle or your schedule or if you simply just don’t like it, don’t do it.
You can definitely still reach your goals.