Most of us are aware of fasting, either for religious or health purposes. You might have considered it for weight loss. But how does fasting work? Why does it work? What are the benefits? Is it safe? All of these questions are answered below, so read on.

What is Fasting?

Fasting is the voluntary avoidance of eating food for religious, health, weight loss, or other reasons. It differs from starvation because of intent. Starvation is the involuntary avoidance of eating food for a long period of time. Fasting is intentional.

A fast usually lasts between 12 and 24 hours. Extreme fasting programs require you to go without food for days or weeks. There are various methods used to fast. Some diets only allow you to drink liquids like water or tea, while others allow you to eat small portions of food.

History of Fasting

Fasting has been used therapeutically since at least the 5th century BCE, when Greek physician Hippocrates recommended abstinence from food or drink for patients who exhibited certain symptoms of illness (Britannica).

Many religions throughout history have used fasting as a sacrifice, requirement to approach deities, or cleansing of the mind, body, and soul. Fasting is also done as a sacrifice or initiation ritual in tribes and secret societies.

Benefits of Fasting

Aside from religious aspects, fasting has a number of health benefits. The most popular reason for fasting is weight loss. Research has also shown that restricting your food intake for long periods of time have health benefits such as improved cholesterol, blood pressure, glucose levels, inflammation, and more.

Fasting for Weight Loss

The #1 reason people fast is to burn fat and lose weight. Intermittent fasting is proven to be the most effective method for weight loss. There are various methods, but the general goal is to abstain from eating for short periods of time. For example, the 16/8 intermittent fasting plan restricts food consumption and drinking beverages containing calories to 8 hours per day. The remaining 16 hours requires abstinence from food.

Obviously, intermittent fasting helps you lose weight because you’re eating less overall. Additionally, the absence of food causes your body to use fat as an energy source instead of glucose. You’ll be burning fat instead of the glucose your body produced from food. This metabolic shift is similar to ketosis and what happens on the ketogenic diet. It takes place after 12-24 hours for most people.

Fasting for Improved Health

A number of studies have shown that intermittent fasting helps prevent and improve health conditions such as insulin sensitivity, high blood pressure, high cholesterol, and inflammation. Studies done on animals have also shown disease-modifying benefits on chronic disorders including diabetes, cardiovascular disease, cancer, and neurodegenerative brain diseases.

Health benefits can be linked to evolution and our human ancestors. Early humans were hunter-gatherers who would often go long periods of time without food. As a consequence, their bodies adapted and allowed them to overcome this feast-or-famine environment. The body learned to protect itself and function without using food as an energy source. During a fast, the body produces few new proteins. The cells then take protein from nonessential sources, break them down, and use the amino acids to create new proteins that repair the body. Once the body is replenished with food, new proteins are produced in vital organs.   

Is Fasting Safe?

For healthy people, fasting for a few days is normally safe. Intermittent fasting allows you to eat during set time periods, so the risk of side-effects is not as great. However, those with conditions such as diabetes and heart disease should avoid this ritual or consult with their physician first. If you’re pregnant, breastfeeding, or have a history of eating disorders, avoiding fasting is advised.

Side-Effects of Fasting

People react differently to changes in diet. Those who fast may develop symptoms such as irritability, fatigue, dizziness, dehydration, constipation, and inability to concentrate. These side-effects usually disappear once the body is used to the process.

Of course, the most obvious side-effect of not eating is hunger. You may experience intense hunger at times during your fast, but these usually subside after long periods without food.

Lastly, there is a risk of overeating during scheduled mealtimes. Since you’re going long periods without food, you may feel like you’re able to binge to make up for it. You may also have sugar cravings or salt cravings. Eating more than normal will lead to weight gain, despite long periods of fasting.


Fasting and intermittent fasting has many benefits for weight loss and health. Done safely, it is proven to be one of the most effective replacements for a normal diet. If you’re still unsure, give it a try and decide for yourself. The only thing you have to lose is more fat.