Intermittent fasting (IF) is currently one of the world’s most popular health and fitness trends.
People are using it to lose weight, improve health and simplify their healthy lifestyle.
Many studies show that it can have powerful effects on your body and brain, and may even help you live longer.
This is the ultimate beginner’s guide to intermittent fasting.
What Is Intermittent Fasting (IF)?
Intermittent fasting (IF) is a term for an eating pattern that cycles between periods of fasting and eating.
It does not say anything about which foods you should eat, but rather when you should eat them.
In this respect, it is not a “diet” in the conventional sense. It is more accurately described as an “eating pattern.”
Common intermittent fasting methods involve daily 16 hour fasts, or fasting for 24 hours, twice per week.
Humans have actually been fasting throughout evolution. Sometimes it was done because food was not available, and it has also been a part of major religions, including Islam, Christianity, Judaism and Buddhism.
When you think about it, our hunter-gatherer ancestors didn’t have supermarkets, refrigerators or food available year-round.
Sometimes we couldn’t find anything to eat, and our bodies evolved to be able to function without food for extended periods of time.
If anything, fasting from time to time is more “natural” than constantly eating 3-4 (or more) meals per day.
How To Begin Intermittent Fasting
Intermittent fasting has been very popular for many years and several different methods have been used.
All of them involve splitting the day or week into “eating periods” 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, for example from 1 pm to 9 pm. 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: On two non-consecutive days of the week, only eat 500-600 calories. Eat normally the other 5 days. More details here.
By making you eat fewer calories, all of these methods should make you lose weight as long as you don’t compensate by eating much more during the eating periods.
I’ve personally found the 16/8 method to be the simplest, most sustainable and easiest to stick to. It is also the most popular.
There is more detailed information on the different protocols here: 6 Intermittent Fasting Methods.
Intermittent Fasting and Your Body
When you fast, several things happen in your body on the cellular and molecular level.
For example, your body changes 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 hormone skyrocket, increasing as much as 5-fold. This has benefits for fat loss and muscle gain, to name a few.
- Insulin: Insulin sensitivity improves and levels of insulin drop dramatically. Lower insulin levels make stored body fat more accessible.
- 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.
- Gene expression: There are changes in the function of genes related to longevity and protection against disease.
These changes in hormone levels, cell function and gene expression are responsible for the health benefits of intermittent fasting.
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. It may even help you live longer.
Here are 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 .
- Insulin resistance: Intermittent fasting can reduce insulin resistance, lowering blood sugar by 3-6% and fasting insulin levels by 20-31%. This should protect against type 2 diabetes.
- Inflammation: Some studies show reductions in markers of inflammation, a key driver of many chronic diseases.
- Heart health: Intermittent fasting may reduce LDL cholesterol, blood triglycerides, inflammatory markers, blood sugar and insulin resistance. These are all risk factors for heart disease.
- Cancer: Animal studies suggest that intermittent fasting may help prevent cancer.
- Brain health: Intermittent fasting increases a brain hormone called BDNF, and may aid the growth of new nerve cells . It may also protect against Alzheimer’s disease.
- Anti-aging: Intermittent fasting can extend lifespan in rats. Studies showed that fasted rats live as much as 36-83% longer.
Keep in mind that the research is still in its early stages. Many of the studies were small, short in duration or conducted in animals. Many questions have yet to be answered in higher quality human studies.
Who Should Fast ?
If you are underweight, or have a history of eating disorders, then you should not do intermittent fasting without consulting with a health professional first.
In these cases, it can be downright harmful.
Should Women Fast?
There is some evidence that intermittent fasting may not be as beneficial for women, as it is for men.
For example, one study showed that it improved insulin sensitivity in men, but worsened blood sugar control in women.
Although there are no human studies on this, studies in rats have shown that intermittent fasting can make female rats emaciated, masculinized, infertile and cause them to miss cycles.
There are plenty of anecdotal reports from women who became amenorrheic (their menstrual period stopped) when they started doing IF, then went back to normal when they stopped doing it.
For these reasons, women should definitely be careful with intermittent fasting. Ease into it, and if you have any problems like amenorrhea then stop doing it immediately.
If you have problems with fertility and/or are trying to conceive, then consider holding off on intermittent fasting for now. Intermittent fasting is probably a bad idea when pregnant or breastfeeding.
Safety When Fasting
Hunger is the main side effect of intermittent fasting.
You may also feel weak and that your brain isn’t performing 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, then 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 female who is trying to conceive.
- Are a female with a history of amenorrhea.
- Are pregnant or breastfeeding.
All that being said, intermittent fasting does have an outstanding safety profile. There is nothing “dangerous” about not eating for a while if you are healthy and well nourished overall. We always recommend consulting with a doctor about dieting.
Frequently Asked Questions About Intermittent Fasting
Here are answers to the most common questions about intermittent fasting.
1. Can I drink liquids during the fast?
Coffee can be particularly beneficial during a fast, because it can blunt hunger.
2. Isn’t it unhealthy to skip breakfast?
No. The problem is that most stereotypical breakfast skippers have unhealthy lifestyles. If you make sure to eat healthy food for the rest of the day then it is fine.
3. Can I take supplements while fasting?
Yes. However, keep in mind that some supplements (like fat-soluble vitamins) may work better when taken with meals.
4. Can I work out while fasted?
Yes, fasted workouts are fine. Some people recommend taking branched-chain amino acids(BCAAs) before a fasted workout.
5. Will fasting cause muscle loss?
All weight loss methods can cause muscle loss, that is why it is important to lift weights and keep protein intake high. One study shows that intermittent fasting causes less muscle loss than regular calorie restriction.
6. Will fasting slow down my metabolism?
No. Studies show that short-term fasts actually boost metabolism. However, longer fasts (3 days or more) can suppress metabolism.
7. Should kids fast?
That’s probably a bad idea.
How To Start
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 done a 16+ hour fast.
Many people actually instinctively eat this way. They simply don’t feel hungry in the morning.
I personally find that the 16/8 method is the simplest and most sustainable way to do intermittent fasting. I recommend that you try that one first.
If you find that it is easy and you feel good during the fast, then you can 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 (the 5:2 diet).
Another approach is to simply fast whenever it is convenient. As in, 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.
I recommend that you experiment with the different approaches and find something that you enjoy and fits your schedule.