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When Does the Body Start Burning Fat During Fasting?

Weight loss is usually the primary motivation behind fasting for many people. Everyone who starts fasting wishes to immediately see the effects of fasting in their bodies, especially weight loss. There is no shame in admitting the fact that you might start wondering about your weight as soon as your start fasting and might start asking the common question that when does the body starts burning fat while fasting.

You have come to the right place as we will try to answer those questions with the help of verified researches.

The brief answer is that fasting for at least 12 hours is essential before the body starts burning fat. In other scenarios, fat-burning might not start until 14 hours of fasting or even more. The duration during which the fat burning process is started is highly dependent on your glucose consumption and the number of glycogen stores in your body.

Burning of Fats

The mechanism of fasting should be clear to you to understand the time needed for burning fat.

A human body constantly needs energy, even during the state of sleep. Glucose is the primary source of energy. Excessive glucose is synthesized into glycogen to use for energy generation. Food sources like meat, fish, fruits, and vegetables are very rich in carbohydrates, proteins, and fats.

When food consumption is stopped during intermittent fasting, fresh glucose is not being provided to your body. As a result, the body has to use glycogen stores for the production of energy. Ultimately, the glycogen levels are also depleted within 12 to 16 hours in usual conditions. After the glycogen stores are completely utilized, the body starts burning fats and proteins simultaneously to obtain the amount of energy required for proper body functioning.

A study by Medical Hypothesis says that short periods of fast are suitable for people who want to maintain heavy muscle mass while losing weight through fasting. The findings of the study show that fasting up to 14 hours a day and exercising for five days a week can aid you in losing fats quickly, without affecting the muscles. A suitable amount of fats should be added to your diet.

Another study by the Journal of the International Society of Sports Nutrition found that if the fasters want to get the optimum results of fasting, they should fast for at least 16 hours, along with exercise to speed the fat-burning process.


As evident from the studies discussed above, the duration in which a human body starts burning fats is dependent on numerous aspects. Typically, 12 to hours of fasting is declared to be the maximum period in which the fat burning process is initiated.

It is important for you to be mindful of your diet during the fasting process. If you restrict your glucose diet outside the fast, it will allow your body to start burning fats immediately during the fasting state. As a result, you can burn a large number of fats and reap a myriad of benefits of fasting.