Can Fasting Reset Metabolism?

When you fast, you stop consuming calories for an extended period of time. When you fast, your body loses its primary energy supply and this initiates a process called metabolic switching.

When you fast, you stop consuming calories for an extended period of time. Since calories are your body’s energy source, changing your caloric intake affects the way that your body processes energy — also known as your metabolism.  

Some studies indicate that your metabolism speeds up when you’re fasting. But the exact way that your metabolism is affected depends on a variety of factors — like the length of your fast. 

Fasting is the process of stopping your caloric intake. People have been intentionally fasting for centuries. It’s part of many religious practices and plays a role in a lot of human cultures. 

The fed-fast cycle describes the different states of your body in terms of energy consumption. There are four stages to the fed-fast cycle. These are: 

• The fed state. This is when you’ve just recently eaten. 
• The post-absorptive state or early fasting state. This is when you’ve finished digestion and your body is waiting for new inputs. 
• The fasting state. This is a shift that occurs about 12 hours after you stop consuming calories. It’s accompanied by a wide range of bodily changes, including significant alterations to your metabolism.
• Starvation or long-term fasting. This is a severe state of caloric restriction. Over time, it can lead to serious health problems, even death. 

Your metabolism is responsible for providing your body with a consistent, balanced energy supply. It specifically refers to the chemical process of converting the energy in the food we eat into usable forms for your body.

This process regulates a wide variety of bodily functions, including: 

• The breakdown of sugars
• The creation of proteins
• The creation of fats
• Mitochondrial activity — this is the organelle that converts sugar into usable energy in your cells

Your metabolism needs caloric input to sustain all of these functions. 

The typical Western diet includes three meals a day plus snacks. This provides your body with a constant supply of fresh energy. So you never need to turn to the reserves stored in your fat tissue. 

But when you fast, your body loses its primary energy supply. So it needs to figure out other ways to metabolize energy and keep your organs in working order. This initiates a process called metabolic switching. 

After you eat, glucose is your main source of energy. Extra calories are converted to fat. But about 12 hours after consuming food, your body needs to find new energy sources. Instead of creating and storing fat and cholesterol, your body mobilizes fat and uses it for energy. This is specifically in the form of fatty acids. 

Your liver breaks down fatty acids into ketone bodies. These ketones are a major energy source for your fasting organs — especially your brain. 

Your body also switches its primary metabolic hormones around the same time. Insulin is your primary metabolic hormone when you’re well-fed. This switches to glucagon during fasting. 

The process of metabolic switching can: 

• Improve your overall metabolism
• Increase your longevity
• Lead to better overall health

This means that you’re likely better off if you give your body enough time to initiate metabolic switching. It’s essentially how our bodies evolved to function. 

In general, everyone goes through daily periods of time when they’re not eating — especially when they sleep. But there are many different ways to safely incorporate longer bouts of fasting into your life. 

Some religions require you to fast for certain periods of time. These practices have been around for centuries so they shouldn’t be dangerous for a healthy adult. But make sure to talk to your doctor if you have any concerns or are looking for advice on the best way to prepare for a religious fast. 

Another form of fasting that’s rapidly growing in popularity is called intermittent fasting (IF). This is a weight loss technique that focuses on when you can eat instead of what you can eat. Studies have shown that IF is just as effective as traditional calorie-cutting methods in terms of the amount of weight you’ll lose. 

There are a few different ways to fast with IF. If you’re thinking about giving it a try then you should find the method that works best with your routine. Examples of IF methods include:

• Alternate day fasting. With this dieting method, you severely restrict your caloric intake every other day. You may eat one meal on this alternate day or nothing at all. Then you eat normally on nonfasting days. 
• Other periodic full-day fasts. You can alter the pattern of fasting so that you’re only not eating on Tuesdays and Thursdays, for example. 
• The 16/8 method or the 18/6 method. These methods of IF only allow you to eat for a set number of hours every day. You have to fast for the rest of the time. With the 16/8 method, you fast for 16 hours straight and then let yourself eat whatever you want for eight hours. Just make sure that you don’t eat unusually large amounts of food during those eight hours. With the 18/6 method, you only let yourself eat for a six-hour window each day. It’s generally better to have this window fall earlier in the day than right before you go to sleep. 

A lot of research on the benefits of intermittent fasting is still ongoing. But current research indicates that the effects of this diet can have widespread positive effects on your health. Examples include: 

• Losing weight, particularly from fat
• Lowering your blood pressure
• Lowering your blood sugar
• Decreasing inflammatory markers throughout your body

IF may also help lower your risk of developing type II diabetes and heart disease.

You may experience some new health problems when you first start fasting or fast for a longer time than normal. These include: 

• Dizziness
• Low blood sugar
• Weakness and fatigue

Studies have also shown that short-term fasting can increase your negative emotions, like anger, depression, and anxiety. On the other hand, other data indicates that people feel more accomplished and experience a greater sense of reward when they do things while fasting. 

Overall, you’ll need to decide for yourself whether or not fasting is worth it for you. Everyone’s bodies are different, so the same techniques aren’t guaranteed to work for everyone. 

You should be wary about fasting if you fall into one of a handful of high-risk categories. This doesn’t mean that you can’t fast. But you should definitely talk to your doctor before you do. This way they can provide personalized advice that’s specific to your condition. 

High-risk groups for fasting include people who: 

• Are still growing — namely if you’re under 18
• Are pregnant or breastfeeding — you don’t want to deprive your child of essential nutrients
• Have diabetes or other blood sugar problems
• Have a history of an eating disorder — this dieting method could lead to unhealthy eating habits if it gets out of hand