Updated: May 16
Fasting has been a practice throughout human evolution. It's perhaps the oldest and the most powerful dietary intervention imaginable. Ancient hunter-gatherers didn’t have supermarkets, refrigerators or food available year-round. Sometimes they couldn’t find anything to eat. As a result, humans evolved to be able to function without food for extended periods of time. In fact, fasting from time to time is more natural than always eating 3–4 (or more) meals per day.
Intermittent fasting (IF) is an eating pattern that cycles between periods of fasting and eating. It doesn’t specify which foods you should eat but rather when you should eat them.
Fasting differs from starvation in one crucial way: control. Fasting is the voluntary avoidance of food for spiritual, health, or other reasons. Food is easily available, but you choose not to eat it. It’s done by someone who is not underweight and has enough stored body fat to live off. Fasting is also often done for religious or spiritual reasons, including in Islam, Christianity, Hinduism, Judaism and Buddhism. In addition to religious and spiritual reasons, many cultures throughout history have used fasting as a tool to improve health.
Anytime you are not eating, you are intermittently fasting. For example, you may fast between dinner and breakfast the next day, a period of approximately 12-14 hours. In that sense, intermittent fasting should be considered a part of everyday life. Consider the term “break fast.” This refers to the meal that breaks your fast – which is done daily.
Intermittent fasting is not something unusual but a part of everyday, normal life. It is perhaps the oldest and most powerful dietary intervention imaginable. Yet somehow we have missed its power and overlooked its therapeutic potential. Learning how to fast properly gives us the option of using it or not.
Intermittent Fasting Methods
There are several different ways of doing intermittent fasting — all of which involve splitting the day or week into eating and fasting periods. During the fasting periods, you eat either very little or nothing at all.
These are the most popular methods:
The 16/8 method: Also called the Leangains protocol, it involves skipping breakfast and restricting your daily eating period to 8 hours, such as 1–9 p.m. Then you fast for 16 hours in between.
Eat-Stop-Eat: This involves fasting for 24 hours, once or twice a week, for example by not eating from dinner one day until dinner the next day.
The 5:2 diet: With this method, you consume only 500–600 calories on two nonconsecutive days of the week, but eat normally the other 5 days.
By reducing your calorie intake, all of these methods should cause weight loss as long as you don’t compensate by eating much more during the eating periods. Many people find the 16/8 method to be the simplest, most sustainable and easiest to stick to. It’s also the most popular.
Figuring out what works for you takes some trial-and-error, and a professional can help you tweak and troubleshoot. If you go it alone, I suggest starting with a 12-hour daily fast and easing into a 16-hour fast. Leave alternate-day and 20-hour fasts to people who've done it for a while.
How intermittent fasting works
Fasting for at least 12 hours changes how your metabolic system works. Most of the time, your body gets its energy from a sugar called glucose. Glucose is found in the foods you eat and beverages you drink. When you eat three meals during a day, your body maintains a steady glucose level because you’re eating and drinking frequently.
However, when you fast for more than 12 hours, your body’s glucose levels start to dip because you’re not eating as frequently. When your body doesn’t have the glucose it needs for energy, it taps into your body’s fat for energy. When this happens, the fatty acids in your body are absorbed into your blood. They produce a chemical called ketones. Your body then uses the ketones as its energy source. This is called a metabolic switch. Your body is switching from glucose to ketones. When your body uses ketones instead of fat, you may lose weight. But, behind the scenes, the ketones also may be having a positive effect on your body’s organs and cells.
To get the benefits of intermittent fasting, you need to fast for at least 12 hours. That’s how long it takes your body to switch from using glucose for energy to using fat for energy. Additionally, it will take your body a while to get used to this new eating schedule. So don’t expect results right away. You may need to wait between 2 and 4 weeks to see or feel any results.
That translates to a few key intermittent fasting benefits:
Weight management: Everything from your hormones to your blood sugar affects what shows up on the scale. Intermittent fasting has been shown to help prevent insulin resistance and leptin resistance, which may assist with weight management.
Fat burning: Your body preferentially uses glucose (carbohydrates) for energy. When you fast, your body uses up available glucose, and then transitions to burning fat for fuel—aka a metabolic state called ketosis. Break your fast with keto-friendly foods to help your body stay in ketosis and reap those fat-burning, brain-powering benefits.
Helps remove cellular waste: Over time, your cells naturally accumulate damaged cells and waste. This junk can interfere with cellular function. Intermittent fasting has been shown to promote a process called autophagy, which is what happens when your body clears out the junk so your body can work even better.
Supports healthy aging: Studies show that intermittent fasting can help protect your cardiovascular system and your insulin sensitivity to support healthy aging. It even helps promote feelings of tranquility and alertness.
What is the best way to break a fast?
While intermittent fasting is not a diet per se, it is still important to emphasize healthy foods during your eating window, especially what you eat to break your fast. It's completely counterproductive—and even dangerous for insulin and blood sugar balance—to fast and then immediately binge on unhealthy foods.
In other words, don't break your fast by going through the drive-thru or eating a bunch of carbs like white bread or sugar. A meal too high in carbohydrates will result in an unpleasant glucose crash. Your best bet: something with protein, healthy fats, and vegetables.
Related : What Can Ruin My Metabolism?
Safety & Side Effects
Hunger is the main side effect of intermittent fasting. You may also feel weak and your brain may not perform as well as you’re used to. This may only be temporary, as it can take some time for your body to adapt to the new meal schedule. If you have a medical condition, you should consult with your doctor before trying intermittent fasting.
This is particularly important if you:
Have diabetes, low blood pressure or problems with blood sugar regulation.
Are underweight or have a history of eating disorders.
Are pregnant or breastfeeding.
Take-aways for Better Health
Avoid sugars and refined grains. Instead, eat fruits, vegetables, beans, lentils, whole grains, lean proteins, and healthy fats (a sensible, plant-based, Mediterranean-style diet).
Let your body burn fat between meals. Don’t snack. Be active throughout your day. Build muscle tone.
Consider a simple form of intermittent fasting. Limit the hours of the day when you eat, and for best effect, make it earlier in the day (between 7 am to 3 pm, or even 10 am to 6 pm, but definitely not in the evening before bed).
Avoid snacking or eating at nighttime, all the time.
Intermittent fasting can be a safe and effective weight loss strategy. intermittent fasting of all types can help slow aging and reduce the risk of some diseases, including cancer, diabetes, and heart disease. To start, you may want to try a simple form of the 16/8 plan or even a 14-10 plan, which limits the hours of the day when you eat.
However, this newly popular approach is not a magical cure that will work for everyone. Studies show a success rate for intermittent fasting that is about the same as other diets. A lot of people have found it effective, but it’s very personalized. Like most diets, the effectiveness is based on how well the plan fits the individual. Overall, we recommend just having a healthy lifestyle that includes a healthy dietary pattern and being physically active.
About the authors:
Madur & Anitha Jagannath are certified Nutrition Consultants, in addition to their professions in technology and human resources. When Madur started feeling lethargic and slowing down, he started exercising regularly, became conscious of healthy eating habits and nutrition. He is an avid runner and does half-marathons often. At Voyage to Wellness, they attribute our reputation to the lasting customer relationships they have developed throughout the years. They believe in health & wellness and being fit, at all stages of people's lives.
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