Intermittent fasting has now become one of the best ways to improve your health and lose body fat. All you need to do is abstain from food and drinks with calories for a certain period depending on your tolerance and what your schedule allows.
That said, there are different fasting methods to try, and all of them share similar benefits. In this article, you’ll learn the science and benefits of intermittent fasting. We’ll also discuss safety concerns and tips to keep in mind.
What is Intermittent Fasting?
Intermittent fasting is a practice in which an individual follows a schedule that alternates between fasting and eating. A typical fasting protocol lasts anywhere from 12 to 24 hours. Popular examples include fasting for 16 hours and resuming your meals and snacks for the remaining 8 hours.
Note that intermittent fasting isn’t technically a diet but rather a pattern of eating that has been practiced throughout human history.
Hunter-gatherers, for instance, ate at irregular intervals depending on the availability of food. These people rarely, if ever, suffered from obesity and metabolic disorders like Type 2 Diabetes, heart disease, and non-alcoholic fatty liver (NAFLD) disease (*).
The Greek physician Hippocrates recommended fasting as far back as the 5th century B.C. for patients exhibiting certain symptoms of illness. According to Hippocrates, “To eat when you are sick, is to feed your illness.”
This goes to show how intermittent fasting results in improved health, especially when done properly. Unlike what many people think, intermittent fasting isn’t starvation, which is an involuntary act.
Rather, it follows a specific pattern, and those who fast have full control over when to start and stop fasting. It all depends on your experience level, tolerance, and other factors.
How Does Intermittent Fasting Work?
Intermittent fasting works this way:
By avoiding food and drinks containing calories within a set period, your blood sugar drops and this causes your body to burn through your glycogen stores (the stored form of glucose in your liver and muscles). As your fasting hours increase, you eventually enter a metabolic state of ketosis. This is when your body uses fat to produce compounds called ketones — an alternative source of energy where glucose isn’t readily available (*).
For those who are on a keto diet, intermittent fasting is sometimes used as a strategy to re-enter ketosis following a few days of increasing their carbs. This could be a cheat day, the holidays, or the remaining 1-2 days of a cyclical keto diet.
Meanwhile, people who are interested in trying the keto diet can use fasting as one of the ways to achieve ketosis for the first time.
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For others, intermittent fasting is part of their lifestyle (regardless of the diet they’re on) for weight loss purposes without counting calories, to allow their digestive system to rest, and get through an extremely busy work day.
Anyone can do fasting, especially if they do not feel hungry. Just keep in mind that if you have a medical condition or are underweight, you will need guidance from a healthcare provider.
Intermittent Fasting Methods
Shorter fasts are the best place to start if you’ve never tried intermittent fasting before. As you get used to fasting, you may try increasing your fasting hours or doing multiple shorter fasts in a week. Choose your intermittent fasting plan below:
- 16/8 fasting – This is a popular fasting method where you eat within an 8-hour window and fast within a 16-hour window. It can look like eating dinner as early as 5 pm and eating at 9 am the next day. It’s simple and allows for flexibility according to your preferred mealtimes.
- Skipping a meal – Simply skipping a meal daily (breakfast, lunch, or dinner) works for most people. If you feel overwhelmed by the idea of fasting, this is a good entry point to know what fasting feels like. Instead of having a meal, you can replace it with another activity, such as taking a walk, doing meditation, or finishing a project.
- The 5:2 diet – This fasting plan includes five days of eating normally with two days of intermittent fasting. For example, fasting during Mondays and Tuesdays, which are probably your busiest days at work, then eating normally from Wednesday to Sunday.
- Alternate-day fasting – ADF for short, alternate-day fasting involves alternating between a full day of fasting and a full day of eating (resuming your normal meals). For example, eating on Mondays, Wednesdays, and Fridays and fasting on Tuesdays, Thursdays, and Saturdays.
- 24-hour fasting – Eating no food for 24 hours is a more advanced intermittent fasting plan, although it still falls under the category of short-term fasting. (Longer-term fasting is a fasting duration of more than 36 hours.) During this fast, you’re not allowed to consume anything with calories except for plain black coffee, unsweetened tea, and zero-calorie electrolytes.
- 20/4 fasting – Also known as the Warrior Diet, this approach means fasting for 20 hours followed by a 4-hour eating window. If you’ve done the 16/8 fast successfully multiple times and would like to proceed to a 24-hour fast, try the 20/4 plan first.
- Fat fasting – If you want to get back on track with intermittent fasting or you still haven’t made the choice of whether to fast or not, fat fasting is the way to go. Unlike a “true” fast, this method involves eating foods, except that these foods should be mostly high-fat. Examples are eggs, bacon, avocados, butter, ghee, and fatty fish.
Intermittent Fasting Benefits
Before learning how to do intermittent fasting, it’s important to understand its benefits. Fasting for weight loss is a common reason for doing it, but what about the rest? Here are some of them.
- Increases fat loss while maintaining muscle mass: For some people, losing body fat is enough to meet their goals. However, others (particularly those who do body recomposition) are worried that fasting might lead to muscle loss. The good news is that fasting is unlikely to cause it, and research shows that fasting may increase human growth hormone levels (HGH), which spares muscle (*).
- A good combination with the keto diet: Doing keto and intermittent fasting at the same time may lead to bigger benefits than doing each method alone. Both approaches lead to ketosis, which has many benefits for your brain and body.
- Improves blood sugar control: Fasting for periods can lower your blood sugar levels and make your body more sensitive to insulin. If you have a higher-than-normal blood sugar reading but you’re still not diagnosed with Type 2 Diabetes, fasting will help.
- Gives your digestive system a break: Perhaps the most obvious benefit of any fasting protocol is that it lets your gut rest from constantly digesting food. For instance, if you’ve overindulged during the holidays or a vacation break, you might want to fast first before resuming a healthy diet.
What Does Research Say About Intermittent Fasting?
Studies on intermittent fasting have been conducted on both animals and humans. If you’re looking for more science-backed reasons to incorporate fasting into your lifestyle — whether or not you have a medical condition — here’s what the research says:
When it comes to your intestinal microbiota (or gut microbiome), intermittent fasting can increase Akkermansia muciniphila, an oval-shaped bacterium with the following benefits (* , *):
- Maintains the intestinal epithelial barrier, which prevents gut problems
- May improve metabolic syndrome and obesity as a probiotic
- Keeps bad bacteria out
Did you know that intermittent fasting may also help prevent and fight cancer? According to a clinical trial done on 101 patients with different types of cancer (breast cancer, colorectal cancer, lung cancer, etc.), fasting caused their immune system “to recognize the cancer as something it should attack.” (* , *)
It may be a good idea to include intermittent fasting in addition to chemotherapy treatment to slow cancer progression. Additionally, fasting starves cancer cells of glucose, while the ketone bodies produced during ketosis feed normal cells (*).
Another reason to use fasting is Type 2 Diabetes reversal. As you probably know, Type 2 Diabetes increases your risk of complications and comorbidities, such as (*):
- Heart disease
- Kidney disease
- Nerve damage
- Liver disease
A study recently published in The Journal of Clinical Endocrinology and Metabolism found that a 3-month intermittent fasting plan achieved diabetes remission (meaning, blood glucose levels are normal and there’s no need for diabetes medication) for at least 1 year (*).
Safety, Precautions, and Drawbacks
While intermittent fasting is generally safe and natural, some people need to consult with their health professional before giving it a try. This is important if you are or have:
- Taking any medication that lowers your blood sugar levels (for example, insulin and sulfonylureas)
- Trying to get pregnant, are pregnant, or breastfeeding
- A history of an eating disorder like anorexia or bulimia
- Underweight or struggling with weight gain
- Low blood pressure or are taking medication that reduces BP
As for the drawbacks, longer periods of fasting (or depending on the person) can cause symptoms similar to the keto flu. This includes headaches, dizziness, nausea, and fatigue.
People who are metabolically inflexible — meaning that they’re not used to burning ketones for fuel instead of glucose — are more likely to feel the negative symptoms of intermittent fasting.
You can help your body adjust by doing it more often (along with properly planned meals), staying physically active each day, and following a keto diet.
How to Get Started with Intermittent Fasting
In this section, we’ll explore some helpful ways to start fasting in the easiest possible way.
The first and most important tip is to start slowly. For example, you might want to begin with a 12-hour fast and then increase that duration to 16 hours after a few weeks of getting used to it. You can also start by skipping one meal, like breakfast, or try delaying breakfast for a few hours. So, if you usually eat at around 7 or 8 am, push it to 10 or 11 am.
During a fast, make sure that you stay hydrated. If you want, have sparkling water or add some slices of lemon to a pitcher of water for flavor. Zero-carb and zero-calorie electrolyte powders also keep you hydrated while preventing electrolyte imbalances.
You might ask whether exercising is fine during fasting. In reality, there is no reason to quit exercising on your fasting days. Lifting weights, cardio, and HIIT are fine as long as you feel comfortable doing them. Some people prefer doing more intense workouts after their pre-fast meal so they have enough fuel to push through the workout.
Remember that a successful fast also starts by eating a healthy pre-fast meal. Fill up with healthy fats from avocados, fatty fish, and nuts. Make sure you also have quality animal-based or plant-based protein, such as eggs, beef, pork, chicken, tofu, mushrooms, and lupini beans.
Below are common questions and answers on the topic of intermittent fasting:
Can I drink liquids during intermittent fasting?
Plain water, sparkling water, and other non-caloric beverages like black coffee, tea, and zero-calorie electrolyte powders are allowed. These options won’t break a fast. Water and electrolytes, in particular, allow you to stay hydrated. They also fill you up!
Can I take supplements while on intermittent fasting?
Supplements are fine as long as they are calorie-free and sugar-free. Just keep in mind that some supplements work better with food, such as fat-soluble vitamins A, D, E, and K.
Can I work out while on intermittent fasting?
Yes. There’s no reason to forgo a workout while intermittent fasting unless you feel very tired or choose to have that workout after you break the fast.
How long should I do intermittent fasting?
You can fast intermittently from 12-36 hours. We would recommend starting with a 12-hour fast or skipping a meal, and then bumping it up to a 16-hour fast.
The Bottom Line
From increasing fat loss to reversing Type 2 Diabetes, breaking up your regular eating pattern can have a positive impact on your overall health. Do it as part of a healthy lifestyle or use it together with a keto diet since each can enhance one another’s benefits.
Unlike starvation, intermittent fasting allows you to have full control over how long you fast and when to end a fast, which you can do when it’s too uncomfortable to push through!
Remember that just because you’re fasting, doesn’t mean you can overindulge in unhealthy foods during your eating window.
Hollstein T et al. Effects of Short-term Fasting on Ghrelin/GH/IGF-1 Axis in Healthy Humans: The Role of Ghrelin in the Thrifty Phenotype. 2022 August 18
Luo Y et al. Rational consideration of Akkermansia muciniphila targeting intestinal health: advantages and challenges. 2022 October 17
DePolo J. Intermittent Fasting May Help Cancer Treatments Work Better, Small, Early Study Suggests. 2021 November 30
Vernieri C et al. Fasting-Mimicking Diet Is Safe and Reshapes Metabolism and Antitumor Immunity in Patients with Cancer. 2022 January 1