Imagine that you can kick-start your metabolism, feel more energized and enjoy an assortment of health benefits without having to count calories or stick to strict meal plans. Say hello to just some of the benefits of fasting.
What makes fasting seem so novel is that, with all the diet advice out there, the easiest might be to simply not eat. Of course, fasting isn’t the same as starving yourself, which is what many people think when they hear “fasting.” Yet, it isn’t a diet, either.
The literal definition of fasting is to abstain from food and drink for a specific period of time. It’s been around for thousands of years, as spiritual fasting is a part of many religions, and in this context, you can look at it as simply a change in eating patterns.
In place of three square meals a day or a handful of smaller meals throughout the day, you have a specific window of time when you eat, whether it’s a few hours a day or certain days of the week. During that time, you can eat whatever you want — of course, within reason.
If you eat processed foods and potato chips, it’s unlikely you’ll reap the benefits of fasting. If that’s you, you should examine your diet before trying a fast.
However, if you practice fasting and stick to a mostly whole food diet, rich in fruits, veggies, lean proteins, healthy fats and raw dairy, you will see changes — and those occasional splurges on chocolate or cheese won’t have as big of an impact as they might if you were on a calorie-restrictive diet.
The beauty of fasting is that there isn’t one “right” way to do it. In fact, there are several types that are popular and plenty of benefits of fasting.
Benefits of Fasting
1. Aids Weight Loss
There have been studies that support fasting as an excellent tool for weight loss. One 2015 study found that alternate day fasting trimmed body weight by up to 7 percent, while whole day fasting reduced body weight by up to 9 percent..
Another study, this one out of the University of Southern California, discovered that when 71 adults were placed on a five-day fast (eating between 750 and 1,100 calories a day) once every three months, they lost an average of six pounds, reduced inflammation levels and their waistlines, and lost total body fat without sacrificing muscle mass. If you want to lose weight and lose belly fat, fasting even irregularly could be the key.
2. Promotes Secretion of HGH
Human growth hormone (HGH) is naturally produced by the body but remains active in the bloodstream for just a few minutes. It’s been effectively used to help with obesity and building muscle mass, important for burning fat, and fasting helps enhance HGH secretion.
HGH also helps increase muscle strength, which can help improve your workouts. Combine these, and you have an effective fat-burning machine on your hands.
3. May Help Athletic Performance
Fasting has been found to have positive effects on body mass as well as other health markers in professional athletes. This is because, as previously mentioned, it can effectively help shed excess fat while optimizing muscle growth due to HGH production.
Traditionally, athletes are advised to consume high-quality protein a half hour after finishing their workouts (post-workout nutrition) to simultaneously build muscle and reduce fat. Fasting is advised for training days, while eating is encouraged on game days.
4. Helps Normalize Insulin Sensitivity
When your body gets too many carbs and sugar, it can become insulin-resistant. That often paves the way for a host of chronic diseases, including type 2 diabetes.
If you don’t want to go down this route, it’s critical to keep your body sensitive to insulin. Another one of the benefits of fasting is it’s an effective way to do this.
A study published in the World Journal of Diabetes found that intermittent fasting in adults with type 2 diabetes improved key markers for those individuals, including their body weight and glucose levels. Another study found that intermittent fasting was as effective as caloric restrictions in reducing visceral fat mass, fasting insulin and insulin resistance.
5. Balances Ghrelin Levels
What is ghrelin? It is actually also known as the hunger hormone because it is responsible for telling your body that it is hungry.
Dieting and really restrictive eating can actually increase ghrelin production, which will leave you feeling hungrier. When you fast, though you might struggle in the first few days, you actually help normalize ghrelin levels.
Eventually, you won’t feel hungry just because it’s your usual meal time. Instead, your body will become more adept in discerning when it actually needs food.
6. Protects Heart Health
When you consume too much bad cholesterol, your triglyceride levels may shoot up, increasing your risk of heart disease. Intermittent fasting actually helps lower those bad cholesterol levels, decreasing triglycerides in the process.
Several studies have also found that lowering blood pressure is another one of the many benefits of fasting.
All of these play a huge role in heart health, proving protecting the heart is one of the top benefits of fasting.
7. Helps Slow Signs of Aging
While more human research is needed, studies in rats seem to link intermittent fasting with increased longevity. One study found that intermittent fasting decreased body weight and increased the life span in rats.
Another found that a group of mice who fasted intermittently actually lived longer than the control group, although they were heavier than the non-fasting mice. Of course, it’s not clear that the same results would happen in humans, but the signs are encouraging.
In fact, there is a plethora of evidence that it can in fact slow signs of aging and promote longevity.
8. Combats Inflammation
Another one of the benefits of fasting is that it’s been shown to help decrease unhealthy inflammation levels, which in turn helps stave off chronic diseases and improve overall health. A meta-analysis of randomized, controlled trials published in 2020 found that fasting may help reduce C-reactive protein levels, which is a marker of inflammation.
Meanwhile, a patient with ulcerative colitis reported feeling better after eight weeks of intermittent fasting, and at the same time, inflammation markers like C-reactive protein and calprotectin levels were significantly reduced in the patient as well. This anti-inflammatory effect makes it an effective way to eat to beat disease.
9. May Protect Brain Health
Research published in Nutrition Reviews in 2023 examined available data on the potential benefits of fasting and caloric restriction on cognition and their effects on Alzheimer’s disease. The researchers concluded: “These observations lead to a hypothesis that intermittent fasting over the years will potentially reverse or delay the pathological process in Alzheimer’s disease.”
10. May Help With Cancer Prevention and Treatment
There is evidence that the benefits of fasting extend to cancer treatment and prevention. As one study put it: “Fasting or fasting-mimicking diets (FMDs) lead to wide alterations in growth factors and in metabolite levels, generating environments that can reduce the capability of cancer cells to adapt and survive and thus improving the effects of cancer therapies.”
Meanwhile, detailed research on the benefits of fasting for cancer prevention from 2020 found that periodic fasting and fasting -mimicking diets “have the potential to play an important complementary role in medicine by promoting disease prevention, enhancing disease treatment, delaying the aging process, and stimulating stem cell-based regeneration.”
Types of Fasting
Intermittent Fasting
This type of fasting is also known as cyclic fasting. Intermittent fasting is a catch-all phrase for eating (and not eating) intermittently. In fact, almost all of the methods below are types of intermittent fasting!
Typical intermittent fast times range from 14 to 18 hours. The longest period any one of these plans would require you to abstain from solid food would be about 32–36 hours.
Time-Restricted Eating
If you practice time-restricted eating, you abstain from food for anywhere between 12–16 hours. During your eating window, you can eat as much of your favorite healthy foods as you’d like. This is one of the most common methods of fasting.
Time-restricted eating is pretty simple to implement. If you finish dinner at 7 p.m., for instance, you wouldn’t eat anything again until 7 a.m. at the earliest. If you wanted to take it further, you can extend the no-eating time until about 11 a.m. or 12 p.m.
Because you’re sleeping for a large chunk of the “no eating” time, this is a good way to introduce fasting into your lifestyle and experiment without any major changes.
16/8 Fasting
Basically another name for time-restricted eating, here you fast for 16 hours a day and then eat the other eight.
Alternate Day Fasting
Another type of intermittent fasting, alternate day fasting has you severely restricting the amount of calories you eat during fast days, then eating to your stomach’s content on non-fast days. Food isn’t completely off the table, but you stick to about 25 percent of your normal caloric intake. Someone eating 2,000 calories would cut back to 500, for example.
Alternate day fasting isn’t necessarily a long-term plan, because it can become difficult to stick to, but it can be helpful to get a healthy habit in motion.
5:2 Diet
It’s very similar to alternate day fasting except you eat normally for five days of the week. On the other two, calories are restricted to about 500–600 calories a day.
The Warrior Diet
Here, you’ll stick to fruits and veggies during the day and then eat a well-rounded, larger meal in the evenings.
The Daniel Fast
Based off of Daniel’s experiences in the Bible’s Book of Daniel, the Daniel fast is a partial fast where vegetables, fruits and other healthy whole foods are featured prominently, but meat, dairy, grains (unless they’re sprouted ancient grains) and drinks — like coffee, alcohol and juice — are avoided.
Most people follow this fast for 21 days in order to experience a spiritual breakthrough, have more time to reflect on their relationship with God or just to feel closer to what Daniel would have experienced in his time.
Other ways to fast include:
How to Fast
Ready to try a fast? Here’s how to make it easier.
1. Decide what type of fast you’re going to do.
A good way to start with a fast is to ease in with time-restricted eating, starting with 12 hours of fasting. If that feels good after a few days, you can increase the fast to 14 hours and up to 18. It’s not recommended to fast for longer than that.
Have you fasted before? Then you might want to try a more ambitious fast, like alternate day fasting.
2. Set some goals.
What do you want to accomplish from a fast: lose weight, be healthier, feel better, have more energy? Write it down, and put it in a place you’ll see frequently during your fast.
3. Make a menu and stock the fridge.
Before beginning your fast, decide when you’re eating and what you’ll eat then. Knowing this in advance takes the pressure off, especially if you feel like you may eat everything in sight “because you can.”
As you become more used to doing a fast, you might find it’s unnecessary to sort out meals beforehand, but having a range of healthy food waiting for you in the fridge makes fasting a lot easier.
4. Listen to your body.
Fasting can take some time to get used to as your body sheds old habits and learns new ones, but it’s important to listen to your body!
If you’re in hour 10 of 16 hours of fasting and feel like you absolutely need a snack, then have one. If your fast time is up but you’re not hungry yet, wait until you are.
There are no hard and fast rules here. You’re not “messing up.”
You might find it helpful to jot down a sentence or two each day about how you felt. You might find that during certain times of the month or year, different types of fasts work better for you.
How long should I fast?
There’s no concrete amount of time to fast, although as mentioned earlier, the typical intermittent fast ranges from 14–18 hours. Instead of focusing on how long you should fast for, it’s better to keep a few things about fasting in mind instead:
- If you’re genuinely hungry, eat something. If you don’t, you’ll spend your time hungry, stressed about being hungry, and hungry and stressed (or even hangry!).
- If you’re still in the early stages of eating better and choosing whole foods, perhaps wait some time before beginning a fasting routine so it’s not one more thing to worry about. Concentrate on eating whole, good-for-you foods first.
- Are you training for a big event, like a marathon or triathlon? This is probably not the right time to try fasting. Speak with your coach and doctor first.
- Again, listen to your body!
What liquids am I allowed to consume?
This depends. If you’re on a time-restricted fast and you’re in no-eating hours, it’s best to stick to no- or low-calorie drinks like water, coffee (with no milk) and tea.
If you’re on an alternate day diet or something similar, even during low-calorie hours, you can technically drink whatever you’d like — but remember, this will count against your calories. Would you rather spend 100 calories on an apple or a glass of milk? It’s your call.
Abstaining from alcohol during a fast is a good idea.
Can I exercise while fasting?
Generally, you can exercise while fasting. You might even find that on time-restricted eating, you feel more energetic in the mornings to get your workout in.
On more restrictive fasts, however, your low-calorie days might leave you feeling too sluggish. If that’s the case, you might consider squeezing in a gentle yoga session or going for a walk.
As usual, check in with yourself. You can always scale back or up depending on how you feel.
Risks and Side Effects
The health benefits of fasting are extremely appealing, but I do want to stress that fasting isn’t always for everyone. People who suffer from hypoglycemia and diabetics should probably avoid fasting, up until blood glucose and insulin levels have been normalized.
Pregnant and breastfeeding women should absolutely not fast, as it can have negative effects on the baby.
Additionally, if you take certain medications or have other health conditions, it’s best to consult your doctor about introducing fasting into your lifestyle. However, for most of the population, it can be a really helpful tool in managing your weight and health.
Final Thoughts
- Fasting is a change in eating patterns. Instead of set meals and meal times, you have a window of eating.
- There are many types of fasting. “Intermittent fasting” is the most common catch-all phrase and encompasses a few different types, including alternate day and time-restricted eating.
- Deciding what type of fast you’re doing, what you hope to get out of it and stocking the fridge with the foods you’ll eat will go a long way in a successful fast.
- The health benefits of fasting range from increased weight loss to normalizing insulin sensitivity and possibly even slowing down the aging process.
- While fasting is healthy for most people, if you’re pregnant or breastfeeding, you should avoid it entirely. If you have diabetes, a serious medical condition or take prescription medication, it’s best to consult with your doctor before embarking on a fast.
