Intermittent fasting (IF) is currently one of the world’s most popular health and fitness trends. People are using it to lose weight, improve their health and simplify their lifestyles.
Additionally, many studies show that it can have powerful effects on your body and brain and may even help you live longer (1, 2, 3).
What Is Intermittent Fasting?
Intermittent fasting 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. In this respect, it’s not a diet in the conventional sense but more accurately described as an eating pattern.
Common intermittent fasting methods involve daily 16-hour fasts or fasting for 24 hours, twice per week.
Fasting has been a practice throughout human evolution. Our ancient ancestors didn’t have access to supermarkets, refrigerators or available food year-round making fasting part of survival. As a result, humans evolved to be able to function without food for extended periods of time.
Fasting is also often done for religious or spiritual reasons, including in Islam, Christianity, Judaism and Buddhism.
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 today:
- 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, not eating from dinner one day until dinner the next day.
- The 5:2 diet: With this method, you consume only 500 to 600 calories on two non-consecutive 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.
Intermittent Fasting and Hormones
When you fast, several things happen in your body on the cellular and molecular level.
For example, your body adjusts hormone levels to make stored body fat more accessible.
Your cells also initiate important repair processes and change the expression of genes.
Here are some changes that occur in your body when you fast:
- Human Growth Hormone (HGH): The levels of growth hormones skyrocket, increasing by as much as 5-fold. This has benefits for fat loss and muscle preservation, to name a few. (4, 5, 6, 7)
- Insulin: Insulin sensitivity improves and levels of insulin drop dramatically. Lower insulin levels make stored body fat more accessible. (8)
- Cellular repair: When fasted, your cells initiate cellular repair processes. This includes autophagy, where cells digest and remove old and dysfunctional proteins that build up inside cells. (9, 10)
- Gene expression: There are changes in the function of genes related to longevity and protection against disease. (11, 12)
These changes in hormone levels, cell function and gene expression are responsible for the health benefits of intermittent fasting.
Intermittent Fasting and Weight Loss
Weight loss is the most common reason for people to try intermittent fasting. (13) By making you eat fewer meals, intermittent fasting can lead to an automatic reduction in calorie intake.
Intermittent fasting also changes hormone levels to facilitate weight loss.
In addition to lowering insulin and increasing growth hormone levels, it increases the release of the fat burning hormone norepinephrine (noradrenaline). Because of these changes in hormones, short-term fasting has been shown to increase your metabolic rate by as much as 14 percent, respectively. (14, 15)
By helping you eat fewer and burn more calories, intermittent fasting causes weight loss by changing both sides of the calorie equation.
A 2014 review study found that this eating pattern can cause up to an 8 percent weight loss over just 3 to 24 weeks, which is a significant amount, compared to most weight loss studies. (16)
According to the same study, people also lost up to 7 percent of their waist circumference, indicating a significant loss of harmful belly fat that builds up around your organs and causes disease. (17)
Another study showed that intermittent fasting causes less muscle loss than the more standard method of continuous calorie restriction (18).
However, keep in mind that the main reason for its success is that intermittent fasting helps you eat fewer calories overall. If you binge during your eating periods, you may not lose any weight at all.
Intermittent Fasting and Health Benefits
Many studies have been done on intermittent fasting, in both animals and humans. These studies have shown that it can have powerful benefits for weight control and the health of your body and brain.
Here are some of the main health benefits of intermittent fasting:
- Weight loss: As mentioned above, intermittent fasting can help you lose weight and belly fat, without having to consciously restrict calories. (19)
- Insulin resistance: Intermittent fasting can reduce insulin resistance, lowering blood sugar by up to 6 percent and fasting insulin levels by as much as 31 percent, which all protect against type 2 diabetes. (20)
- Inflammation: Some studies show reductions in biomarkers of inflammation, a key driver of many chronic health issues. (21, 22, 23)
- Heart health: Intermittent fasting may reduce “bad” LDL cholesterol, blood triglycerides, inflammatory markers, blood sugar and insulin resistance — all risk factors for heart disease. (24, 25)
- Brain health: Intermittent fasting increases the brain hormone BDNF and may aid the growth of new nerve cells. It may also protect against Alzheimer’s disease. (26, 27, 28, 29)
- Anti-aging: Intermittent fasting can extend lifespan in rats. Studies showed that fasted rats lived from 36 to 83 percent longer. (30, 31)
Keep in mind that research is still in its early stages. Many of the studies were small, short-term or conducted in animals. Therefore, many questions have yet to be answered in higher quality human studies. (32)
Intermittent Fasting and Lifestyle
Eating healthy can become simple, but incredibly hard to maintain for some folks.
One of the main obstacles is all the work required to plan for and cook healthy meals. Intermittent fasting can make things easier, as you don’t have to plan, cook or clean up after as many meals.
For this reason, intermittent fasting is extremely popular among the life-hacking crowd, as it improves your health while simplifying your life at the same time.
Intermittent Fasting Side Effects and Precautions
Hunger is the main side effect of intermittent fasting. You may also feel weak and have slight brain fog as well. However, for most people this is only 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.
- Have problems with blood sugar regulation.
- Have low blood pressure.
- Take medications.
- Are underweight.
- Have a history of eating disorders.
- Are a woman who is trying to conceive.
- Are pregnant or breastfeeding.
With that said, intermittent fasting has an outstanding safety profile. There is nothing dangerous about not eating for a while if you’re healthy and well-nourished overall.
Getting Started
Chances are that you’ve already done many intermittent fasts in your life.
If you’ve ever eaten dinner, then slept late and not eaten until lunch the next day, then you’ve probably already fasted for 16 plus hours. Some people instinctively eat this way. They simply don’t feel hungry in the morning.
Many people consider the 16/8 method the simplest and most sustainable way of intermittent fasting, therefore, you might want to try this practice first.
If you find it easy and feel good during the fast, then maybe try moving on to more advanced fasts like 24-hour fasts 1–2 times per week (Eat-Stop-Eat) or only eating 500–600 calories 1–2 days per week (5:2 diet).
Another approach is to simply fast whenever it’s convenient, simply skip meals from time to time when you’re not hungry or don’t have time to cook.
There is no need to follow a structured intermittent fasting plan to derive at least some of the benefits.
Bottom Line:
While intermittent fasting has been proven to have some great health benefits it is not something you have to or even need to do.
It’s simply one of many lifestyle strategies that can help improve your health.
At the end of the day the best diet for you is the one you can stick to long term.
Eating real food, exercising regularly and getting enough sleep are still the most effective and important factors to focus on when it comes to a leaner, healthier, happier YOU!
Frequently Asked Questions
1. Can I Drink Liquids During the Fast?
Yes, water, coffee tea and other non-caloric beverages are fine. Do not add sugar to your coffee. Small amounts of milk or cream may be okay.
2. Isn’t It Unhealthy to Skip Breakfast?
No, the problem, statistically, is that most people who skip breakfast typically have unhealthy lifestyles. If you make sure to eat healthy food for the rest of the day then the practice is perfectly healthy.
3. Can I Take Supplements While Fasting?
Yes, however, keep in mind that some supplements, particularly fat-soluble vitamins work better when taken with meals.
4. Can I Work out While Fasted?
Yes, fasted workouts are perfectly fine. However, some people prefer taking Branch Chain Amino Acids (BCAAs) before a fasted workout.
5. Will Fasting Cause Muscle Loss?
All weight loss methods can cause some muscle loss, which is why it’s important to lift weights and keep your protein intake high. However, studies show that intermittent fasting causes less muscle loss than regular calorie restriction. (33).
6. Will Fasting Slow Down My Metabolism?
No, studies actually show that short-term fasts actually boost metabolism. (34) However, longer fasts of 3 or more days suppress your metabolism (35).
7. Should Kids Fast?
Allowing your child to fast is probably a bad idea.
