Intermittent Fasting: What Is It And How Does It Work?

Track your mealtimes and stick to your fasting phase to make the most of this practice.

Medically Reviewed by Merlin Annie Raj, RD (Registered Dietitian)
By Charushila Biswas, MSc (Biotechnology), ISSA Certified Fitness Nutritionist

Intermittent fasting has many health benefits (1). It is said to be a healthy way to lose weight. Research shows that it can help protect brain function as well (2), (3). If you are new to it, check out our beginner’s guide to intermittent fasting. It talks about how to practice intermittent fasting correctly, what to eat, how it benefits you, and any side effects of not eating for a prolonged period of time. Scroll down!

Intermittent Fasting 101 – A Beginner’s Guide

  1. What is Intermittent Fasting?
  2. How To Do
  3. Ways To Do
  4. What To Eat
  5. IF Diet Chart
  6. Does It Work For Weight Loss?
  7. Can You Try With Keto Diet?
  8. Can You Build Muscle On IF?
  9. Other Health Benefits
  10. When To Avoid?
  11. Side Effects
  12. Expert’s Answers

What Is Intermittent Fasting?

Intermittent fasting is a process of eating and fasting alternately. This type of eating helps restrict calorie consumption and/or use the stored calories in the form of usable energy. This has shown to have various health benefits. How to do intermittent fasting? Find the quick, comprehensive guide below.

How To Do Intermittent Fasting For Beginners 

To begin intermittent fasting, follow these 5 rules: 

#1  – There is no calorie restriction in intermittent fasting. But you can easily consume fewer calories by breaking down your food intake to 6 meals per day. Skip one of the meals, and you will reduce your calorie intake.

#2 – Test the waters first. Fast for 6 hours and then gradually increase your fasting duration. Fast once or twice a week before trying to fast intermittently every alternate day or every day. 

#3  –  Try to schedule your fasting phase in a way that you get 7 hours of sleep during that time. Go to bed 3-4 hours after a big meal, get your sleep, and you are already into 11 hours of fast! Wait it out for 1-4 hours (depending on the type of intermittent fasting you do), and you have successfully fasted intermittently.

#4 – Keep yourself hydrated by drinking enough water. 

#5 – Talk to your doctor or a registered dietitian. If they allow you to do intermittent fasting, move ahead!

There are various ways you can do intermittent fasting. Listed below are the types of intermittent fasting. Choose the one that suits you.

6 Ways To Do Intermittent Fasting 

  1. 16/8 Intermittent Fasting –It requires you to fast for 16 hours and space out your meals within a short window of 8 hours. This type of intermittent fasting is also known as the 8-hour Diet, 16/8 diet, or Time-Restricted Feeding. For instance, if you have your breakfast at 9 in the morning, your last meal of the day will have to be at 5 in the evening. You will then have to fast until the next morning.
  1. 5:2 Intermittent Fasting – 5:2 fasting involves consuming food without any restrictions for five days in the week and being on a calorie-restricted diet (500-Calorie Diet) for two non-consecutive days (4).
  1. Alternate Day Fasting– This fasting pattern consists of alternating feasting and fasting days. You can consume anything on the feasting days. But on the fast days, you can consume only about 20% of your body’s total energy needs (2). If you consume 2000 calories on the fasting day, you can only consume 400 calories on the fasting day.
  1. 24 Hours Fast – Go on a 24-hour fast for 1 or 2 days a week. Choose the day according to your schedule and convenience. Do this only if your doctor approves it.
  1. Warrior Diet – Fasting during the day and feasting during the night is a lifestyle that the warriors followed. Consume protein-rich foods and a heavy dinner at night. You must also include exercising in your routine. This balance of fasting and exercising will keep you active and fit without an inch of extra body fat. Read more about the warrior diet plan.
  1. Skip A Meal –Skip any of the major meals – breakfast, lunch, or dinner. That way, you can reduce the number of calories consumed and also remained in a fasted state.

Note: Skip a meal only if you had a heavy meal and are not very hungry.

Intermittent Fasting Diet – What To Eat

During Feasting Hours Or Days – Eat foods that satiate your hunger and keep your taste buds alive. You may take the liberty to eat anything.But if you are going on intermittent fasting for health reasons or to lose weight,  avoid foods that nullify your effort. Also, avoid foods that you are allergic to.

During Fasting Hours Or Days – Consume a total of 500 calories per day (for women) or 600 calories per day (for men). Foods rich in dietary fiber will keep you full. Drink water, coconut water, and freshly pressed juices. Consume raw/grilled vegetable salad with lime juice, a pinch of Himalayan pink salt, a tablespoon of olive oil, and a dash of smoked paprika.

Sip on detox water made with watermelon, kiwi, cucumber, and a pinch of salt. It will keep your body from missing out on essential micronutrients and electrolytes. Mint leaves tend to increase hunger, so avoid using them.

Here’s a sample intermittent fasting diet schedule if you choose the 16/8 intermittent fasting method:

Sample Intermittent Fasting Diet Chart 

You can eat anything you want in the 8-hour window. This diet chart is a generic diet chart, and it is not specifically meant for weight loss or any other health issue(s).

 Day 1Day 2Day 3Day 4Day 5Day 6Day 7
Breakfast

(8:30 a.m.)

Eggs or oatmealSmoothieAcai bowlEgg and bacon or pancakesMultigrain flakes with milkProtein smoothieWaffles or pancakes
Lunch

(12:00 p.m.)

Chicken or mushroom saladDahl soup + grilled veggies + 1 piece dark chocolatePasta/sandwichNoodlesGrilled fish and saladShakshukaSmoked fish fillet + herbed rice + 1 cup chocolate ice cream
Snack

(3:30 p.m.)

Any snack of your choiceAny snack of your choiceAny snack of your choiceAny snack of your choiceAny snack of your choiceAny snack of your choiceAny snack of your choice
Dinner

(6:30 p.m.)

Mushroom risottoCrab cakes and herbed rice + 1 cup warm milk before bedSoup + 1 piece of dark chocolateChicken tikka masala or mushroom and peas masala and flatbreadTofu and rice noodles + 1 cup vanilla ice creamGrilled chicken, hummus, and pita breadSpaghetti and meatballs + 1 cup warm milk before bed
FastFastFastFastFastFastFastFast

Clearly, intermittent fasting doesn’t keep you from eating what you want in a window of time. But what if you want to lose weight? Will intermittent fasting work? Find out next.

Does Intermittent Fasting Work For Weight Loss?

Yes, intermittent fasting works for weight loss. Here’s how:

  • Lowers blood glucose and improves insulin sensitivity – Studies show that intermittent fasting helps lower blood glucose levels and reduces body weight. It does so by lowering insulin levels and improving insulin sensitivity (5), (6), (7).
  • Uses fat stores as an energy source – When you are in a fasted state (not had food for at least 6-8 hours), it becomes easier for your body to burn fat, irrespective of what you have eaten. Instead of drawing fuel from glucose, your body starts converting glycogen and/or protein to glucose. When the protein reserve is fully utilized, fat is used as a source of fuel.
  • Increases number of good gut bacteria – Intermittent fasting also increases the number and variety of gut microbes, which aid proper digestion (8). It also helps lower inflammation and inflammation-induced weight gain (9).
  • Fasting prompts growth hormone-induced fat loss – Scientists have found that fasting induces the secretion of growth hormone (10). This, in turn, aids fat loss (11).

When it comes to weight loss, the keto diet is quite the trend these days. Can you be on keto and intermittent fasting together? Let’s find out.

Can You Do Intermittent Fasting On A Keto Diet?

Yes, you may continue being on the keto diet while intermittent fasting. But here’s the catch. Intermittent fasting does not restrict carb consumption. Fasting for long might make you want to consume foods rich in carbohydrates, which may throw you off ketosis. But if you can load up on fat and protein and limit your carb consumption according to the keto diet guidelines, you can successfully be in ketosis.

What if you want to build muscle and not just lose fat? Can you build muscles while following intermittent fasting? Find your answer below.

Can You Build Muscle On Intermittent Fasting? 

Yes, you can build muscle while on intermittent fasting. Intermittent fasting will help shed the extra pounds. You must include strength training in your routine to build muscle. You may choose to hit the gym in the morning in the fasted state or in the evening before dinner.  There are many benefits of lifting weights or strength training that you can reap whether you want to build muscle or not.

Other than weight loss, intermittent fasting has other health benefits. Here’s a list. 

Other Health Benefits of Intermittent Fasting

  • Intermittent Fasting Is Easier Than “Dieting”

Fasting intermittently is easier than going on a restrictive diet. Intermittent fasting breaks the monotony of consuming the same foods in the same quantities and makes dieting fun and interesting.

  • Aids Weight Loss

Intermittent fasting is one of the most effective ways to lose weight and maintain weight loss (12). The alternating low-calorie and high-calorie food intake keep your cells functioning well, which, in turn, boosts metabolism.

  • Protects Heart Health

Intermittent fasting is a great way to shed fat and, consequently, help improve your heart health. American scientists found that by practicing alternate-day fasting, obese patients were able to lose weight and reduce the risk of coronary artery disease (CAD) (13).

  • Improves Insulin Sensitivity

Intermittent fasting may also help improve insulin sensitivity (14). When your body becomes insulin sensitive, your glucose metabolism improves, and you stop feeling hungry all the time.

  • Promote Cellular Repair And Autophagy

Intermittent fasting may also improve cellular repair and autophagy. Autophagy is your body’s natural process of degrading the dysfunctional components of the cells and recycling them. The upregulation of autophagy may be neuroprotective and act as a treatment for Alzheimer’s disease (15).

  • Inhibits Cancer Cell Growth

Rat studies showed that intermittent fasting might help reduce the risk of cancer by increasing the antioxidant effect and inhibiting cancer cell growth (16). However, more human studies are needed for further confirmation.

  • Protects Brain Function

Intermittent fasting (IF) helps improve cognitive function and protect the brain from an inflammatory response (17). Scientists have found that IF can help ameliorate neurodegeneration in mice with induced Alzheimer’s disease (18). IF can also help increase the production of brain-derived neurotrophic factor (BDNF), which has been found to protect the brain from degeneration and dysfunction in animal models (19).

  • Reduces Inflammation And Blood Pressure

Intermittent fasting may also help reduce inflammation and pro-inflammatory cytokines. Additionally, if you are hypertensive, fasting intermittently may help reduce your blood pressure (20).

  • Lowers Bad Cholesterol Levels

Intermittent fasting can help in lowering LDL cholesterol (bad cholesterol) (21). It also reduces triglyceride levels. Triglycerides are fats found in blood, and their elevated levels can lead to cardiovascular problems (22). 

There is no reason you shouldn’t fast intermittently. But are you wondering if you should be fasting at all? Let’s find out in the next section. 

When To Avoid Intermittent Fasting?

As per the John Hopkins University, kids and adolescents under the age of 18 should avoid intermittent fasting (23). Other than that, you should avoid intermittent fasting in the following cases:

  • Avoid intermittent fasting if you are underweight, have an eating disorder, or have been advised against it by your doctor.
  • A few studies have shown that women tend to miss their period, and their blood sugar levels go up when they practice intermittent fasting (24), (25), (26). Therefore, avoid intermittent fasting if you are pregnant, breastfeeding, or have fertility issues.
  • If you do not sleep well and have chronic stress, do not fast intermittently.
  • Avoid intermittent fasting if you have low blood pressure and blood sugar regulation problems.

Note: Always consult your doctor before practicing intermittent fasting.

Before we come to a close, take a quick look at the side effects of IF. 

Side Effects of Intermittent Fasting

  • You may feel irritated.
  • When practiced long-term, it may lead to an eating disorder.
  • It may hinder athletic performance.
  • It may cause muscle loss.
  • It may cause amenorrhea and infertility in women.

Intermittent fasting is a method of alternately eating and fasting. It aids in calorie restriction and/or the utilization of stored calories as useful energy. Intermittent fasting also aids in weight loss. Some people benefit from intermittent fasting, while others do not. However, it is an effective strategy to reduce weight and improve health if you combine it with healthy eating, exercise, and sleep. You can fast on occasion, but not regularly. Consult your doctor before following this method to understand if it will work for you or not.

Frequently Asked Questions

Can I drink lemon water during intermittent fasting?

The intermittent fasting method permits plain lemon water containing solely lemon juice. The beverage does not break your fast as it has nearly no calories. When practicing intermittent fasting, drinking 1 or 2 glasses of lemon water can also aid in fat loss and hunger control.

Can you take vitamins during intermittent fasting?

Regular vitamin pills and capsules are safe to take while fasting because they are unlikely to alter insulin levels. However, vitamins sold as liquids, chewable tablets, or gummies are often flavored with sweeteners. They can provoke an insulin spike, so take them within your meal period if you use them.

Key Takeaways

  • Intermittent fasting involves eating and fasting alternately to restrict calorie consumption.
  • There are many ways to do intermittent fasting, and this method can lower blood sugar, promote gut health, and improve heart health.
  • If you balance it with proper nutrition, exercise, and sleep, intermittent fasting can greatly facilitate weight loss and improve health.

Sources

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author
Charushila is an ISSA certified Fitness Nutritionist and a Physical Exercise Therapist. Over a span of 5 years, she has... more

Merlin Annie Raj

(Registered Dietitian Nutritionist)
Merlin Annie Raj is a Registered Dietitian based out of Hyderabad, India. She has vast experience in Clinical Nutrition as... more

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