Fasted training has been debated for decades. Does it really increase fat burn? Will my muscles really waste away? Will I have any energy if I haven’t eaten?
In reality, I’ve been training fasted for years. After diving into the real research behind what it actually does to your body, the conclusion remains: the benefits of fasted training are substantial, and most of the “dangers” of fasting are only seen after days or weeks of eating nothing.
Below I break down why I train fasted, why you might consider it, and how you can easily try it out too.
Benefits of Fasted Training
1. Enhances Fat Burn
It’s no secret we’d all like some type of shortcut to boost fat loss. And while there technically are no “shortcuts,” when it comes to losing fat in the long term, fasted training is probably the closest thing you’ll find as a “trick” for boosting pure fat loss quicker.
Studies find that doing cardio sessions in particular while fasted increases 24-hour fat burn by 50 percent. [*] That’s quite a significant increase just by, say, jogging fasted in the morning before breakfast. Other similar studies have found that people who for a run in a fasted state experience a lower respiratory quotient, which indicates they are burning more fat instead of glucose during the training period. [*]
The reason training in a fasted state is proving so efficient for fat burning is because when you train fasted, you rapidly deplete your stored glucose levels. When we eat (especially carbs) our body stores a certain amount of glucose (carbohydrate molecules) to fuel our bodies with energy. When we aren’t eating, our body is using this glucose to run normal operations such as breathing, walking, working, etc…
Normally, we eat every few hours, so this glucose “tank” is constantly being refueled. When we exercise, we use the fuel in this tank as well, and it takes a pretty intense workout to deplete it. However, if we exercise when this tank is empty, our body is forced to search for another source of fuel: your body fat.
When glucose is gone, your body converts stored body fat into ketones for energy, which is why researchers get measurements of fat being burned in a fasted state versus glucose. And no, your body isn’t starving or hurt by burning ketones, especially in the short term – it’s simply using stored body fat for energy, which is technically what extra body fat is designed to do if we were in a starvation scenario during ancient times.
2. Boosts Testosterone
If you know anything about building muscle and leaning out, you’re probably aware of the importance of testosterone. Testosterone increases muscle synthesis so that when we work out, our muscles grow back larger and stronger. [*] Studies also show that testosterone therapy in men with testosterone deficiency also produces significant and sustained weight loss, significant reduction in waist circumference and BMI, and improvement in body composition. [*] (Yep, it’s a fun hormone when we have enough!)
One of the best natural ways to boost test levels is to, dun dun dun: fast and/or train fasted. One theory as to why testosterone may be boosted by fasting is due to survival: when our ancestors hadn’t eaten in a while, they needed the energy and strength that testosterone could provide to find and/or hunt food. [*]
Another benefit of boosting your testosterone, whether you’re a man or woman, is that it may also benefit your mood and therefore your mindset for training. Research has found increasing testosterone levels improves mood by reducing irritability, sadness, and depression. [*] It may also give your energy levels a boost, which will indirectly lead to improved training. [*]
3. Boosts HGH (Human Growth Hormone)
Or, to put it in simpler terms: training fasted boosts your muscle gains. A common misconception when it comes to fasting or not “fueling” our muscles with protein-rich meals every hour, is that our muscles will start to rapidly break down and waste away.
While long-term fasting can result in muscle breakdown, we usually won’t see significant muscle wasting for at least a few days or weeks of no food at all. [*]
Short-term fasting, however, has shown the opposite effect: it increases levels of Human Growth Hormone (HGH), the hormone responsible for muscle growth. One study even found found that, compared to athletes who lifted weights after breakfast, athletes who lifted weights in the morning before eating experienced more of an anabolic (growth) response in their muscles. [*]
Others have found that ketones, those molecules we spoke of earlier that your body burns for energy when it runs out of glucose, have muscle-sparing effects, meaning they help prevent them from breaking down. [*]
How to Start Training Fasted
Getting into the fasted training game is simple: if you haven’t tried it before, ease yourself into it by doing your daily cardio session in the morning, before breakfast. Just grab a water and go. Even if a 20-30 minute session is all you can fit in in the morning, most of these studies hover around that mark of time, so you should see a difference.
For full training sessions, you can basically do it as a try-and-see game. Fasted training isn’t for everyone, and if you feel lightheaded at any time, or just feel too “off,” try eating a few more healthy fats the night before (think a drizzle of olive oil, or a few more slices of avocado, or a handful of nuts). You can also try mimicking fasting by eating a pure fat “breakfast” with no carbs, like coconut oil in your coffee, or a handful of almonds.
The important thing is to follow your training session with a healthy, clean, substantial meal with plenty of protein, clean carbs, and healthy fats to encourage your muscles to use them for growth after you’ve boosted your hormones.
Have you ever trained fasted? How did it work for you?