The practice of fasting can lead to many metabolic changes within the body. These changes typically begin approximately three to five hours after eating, when the body enters a “post-absorptive” state – rather than the state of ongoing digestion, where eating frequent meals means the body is always involved in some sort of digestive activity.
Why should you practice intermittent fasting?
Whether you practice more long-term fasting for health reasons or spiritual reasons, most people will have to fast at some point for medical reasons. Patients undergoing surgery or other medical procedures that require a general anaesthetic will usually fast before the treatment, but fasting is also practised before several other medical tests, including cholesterol testing, blood glucose measuring, or a lipid panel. This enables doctors to achieve accurate results and establish a solid baseline to inform future testing, if necessary.
#1 Weight Loss
Instead of running on fuel from the food you just ate, fasting allows your body to tap into reserves – fat, which accumulates in the body to be burned whenever the food supply grows scarce. This results in a slow, steady weight loss that can be a huge benefit.
Since fasting is often incorporated as a lifestyle change instead of a temporary fix, this type of diet is much more sustainable than many other “crash diets.” Many studies support the practice as a valuable, reliable tool for weight loss and weight maintenance. Initially, you’ll see a marked weight loss as a result of losing water weight, but according to the author of Eat Stop Eat, each day you fast will show a loss of 0.5 pounds of true body fat.
#2 Improved tolerance of glucose
For diabetics, fasting can be a fantastic way to normalize glucose and even improve glucose variability. Anyone looking for a natural way to increase insulin sensitivity should attempt an intermittent fast. The effects of fasting can make a huge difference in how your body processes glucose.
Generally, insulin resistance is the result of the accumulation of glucose in tissues that aren’t built for fat storage. As the body burns through stored fuel in the form of body fat, that excess accumulation becomes smaller and smaller, allowing the cells in your muscles and liver to grow increasingly responsive to insulin – great news for anyone looking to be less dependent on medications to assist these processes.
#3 Boosts your metabolism
Part of the reason intermittent fasting helps practitioners lose weight is because of the restriction of food. When followed by regular eating, this helps stimulate your metabolism. While long-term fasting can cause a drop in your metabolism, the shorter fasts promoted by intermittent fasting have proven to increase metabolism – by up to 14 per cent, reported by one study.
This is also a more effective tool than long-term calorie restriction, which can often wreak havoc on the body’s metabolism. Weight loss often goes hand in hand with muscle loss. Since muscle tissue is what burns through calories, having less muscle leads to a drop in your body’s ability to metabolize food. Intermittent fasting, though, keeps your metabolism running smoothly by helping you maintain your muscle tissue as much as possible.
#4 Helps contribute to your longevity
Research from University of Chicago scientists revealed that intermittent fasting can “delay the development of the disorders that lead to death.” This suggests regular practitioners can enjoy a longer, healthier life than people who eat a regular three meals a day or follow a traditional restricted-calorie diet.
A theory on this, according to the head of the National Institute on Aging’s neuroscience laboratory Mark Mattson, is that the mild stress that intermittent fasting puts on the body provides a constant threat. Thus increasing the body’s powerful cellular defenses against potential molecular damage. Intermittent fasting also stimulates the body to maintain and repair tissues and has anti-aging benefits, keeping every organ and cell functioning effectively and efficiently.
#5 Establishes a better routine
Unless you’re following a random fast type of diet, having strict eating times followed by periods of fasting can help your body develop a solid routine. You’ll be able to recognize your hunger cycles, you’ll sleep more regularly and soundly, and you’ll start scheduling appointments during convenient hours.
Of course, it can be difficult to establish this routine at first, especially if you have a family or an inflexible work schedule. However, once you’ve developed a consistent plan, you’ll soon start to see all the ways a set routine can benefit your life – and your health.
#6 Stimulates brain function
A study, discussed at a meeting of the Society for Neuroscience in 2015, revealed that intermittent fasting offers “enormous implications for brain health.” According to the study, which was undertaken on both humans and animals, stimulates the brain in several different ways: promotes the growth of neurons, aids in recovery following a stroke or other brain injury, and enhances memory performance. Not only does intermittent fasting help decrease a practitioner’s risk of developing neurodegenerative diseases like Parkinson’s or Alzheimer’s, but there is evidence to show that it may even improve both cognitive function and quality of life for people living with those conditions already.
#7 Boosts your immune system
According to scientists at the University of Southern California, fasting has the power to “regenerate the entire immune system” by boosting the body’s production of new white blood cells, which is how your body fights off infection. Fasting in cycles, as practitioners of intermittent fasting will do on a daily or weekly basis, enables your body to purge the damaged, old, or inefficient parts of the immune system, and replace them with newly generated immune system cells.
Studies showed that a 72 hour fast was even enough to help protect cancer patients from the harmful and toxic effects of chemotherapy treatments – which generally causes significant damage to the patient’s immune system.
Further clinical trials are needed, but many researchers are confident that intermittent fasting could be incredibly helpful for immunocompromised individuals and the elderly.
#8 Rejuvenates your skin
Acne sufferers know that one of the best ways to control bothersome skin conditions is through diet – eating only unprocessed foods and limiting consumption of dairy products. It’s no surprise, then, that regular intermittent fasting can offer impressive benefits that can be seen all over a practitioner’s glowing, radiant face. Many of these conditions are caused by food sensitivities, which can lead to inflammatory conditions and acne. After a fast, introduce foods one at a time and note any changes to your skin, to accurately pinpoint which foods should be avoided.
Intermittent fasting also has a positive effect on your hair and nails, helping them grow healthy and strong. Not only will you feel good after incorporating intermittent fasting into your lifestyle, you’ll look great, too.
#9 Reduces oxidative stress
Oxidative stress is caused by an imbalance in the body’s production of reactive oxygen and its antioxidative defenses and may lead to chronic diseases and cancers. Unstable molecules, known as free radicals, can react with important molecules like DNA and protein – damaging these molecules and creating an imbalance.
The weight reduction brought on by regular intermittent fasting can lead to a reduction in the body’s level of oxidative stress, helping prevent the development of these unpleasant conditions. A greater antioxidant capability is a huge benefit that comes with intermittent fasting and one that shouldn’t be overlooked by anyone looking to pursue improved health and well-being.
#10 Triggers Autophagy
During a fast, the body’s cells begin to undertake a process called autophagy. Over time, dysfunctional or damaged proteins can build up within cells, and this waste-removal process helps the body filter out this excess material. This process is an important part of the body’s ability to repair and detoxify, and some researchers assert that increased autophagy offers a boost in protection from many diseases, including cancer and Alzheimer’s disease.
Autophagy helps cells overcome stresses brought on by external causes like the deprivation of important nutrients, as well as internal issues like pathogens or invading infectious organisms.
You can read more about autophagy in this article here:
https://longevitylive.com/anti-aging/can-autophagy-cells-reverse-aging-and-boost-longevity/
Suggested meals
Generally, intermittent fasting means you can eat whatever healthy foods you like – within specific feeding windows, and as long as you are getting the nutrients you need. If your goal is to achieve the benefits of intermittent fasting, you won’t get there by indulging on fast food and candy. Use these meal ideas to help come up with some nutritious ways to fuel and nourish your body during your specific eating windows or periods of partial fasting.
Under 300 calorie suggestions
- one serving of oatmeal: approximately 250 calories
- roasted vegetables with balsamic vinegar and a squeeze of lemon: approximately 260 calories
- pesto salmon with kale: approximately 290 calories
- sausage with roasted ratatouille: approximately 260 calories
- prawn and squash curry: approximately 290 calories
Under 200 calorie suggestions
- light salad with spinach, feta cheese, lemon, and beetroot: approximately 150 calories
- sliced apple with 1 tbsp of nut butter: approximately 145 calories
- 100g serving of low-fat yogurt, 1sp of raw honey, 2 sliced plums: approximately 150 calories
- omelette with spinach: approximately 160 calories
- 40g of hummus and a bowl of raw vegetables: approximately 175 calories
Under 100 calorie suggestions
- one serving of miso soup: approximately 40 calories
- one soft boiled egg: approximately 70 calories
- lightly salted edamame beans: approximately 85 calories
- handful of almonds: approximately 90 calories
- one chopped and peeled kiwi: approximately 45 calories
These meals can be combined and altered to suit your taste, but it’s a good idea to try and keep each meal small and easy for your body to process. Focus on eating raw fruits and vegetables, unprocessed whole grains, organic lean protein, plenty of fibre, and lots of healthy fats to ensure that during your scheduled eating windows, you’re getting all the nutrients you need to keep your energy level up and satisfy you through your periods of partial or complete fasting.
Types of fasts
People practice fasting for a wide range of reasons, so there are several types of fasts to accommodate this variety of needs. Most will offer similar benefits, so no type of fasting is necessarily superior to others – it comes down to what works for an individual’s lifestyle, faith, or general well-being.
Dry Fasting
This type of fasting is done without food or water. A soft dry fast allows the individual to shower and brush their teeth, but an absolute dry fast, or a black fast, requires no contact with water whatsoever. This type of fasting is the most extreme and is typically practised as a spiritual act rather than for health reasons.
Liquid Fasting
While fully abstaining from solid food, a liquid fast allows individuals to consume water or juice – and has become quite trendy since the “Master Cleanse” or Lemonade Diet was introduced in the 1970s. This type of fast is typically short-lived, lasting between one to three days, and can include the use of laxatives and enemas to ensure full cleansing of the body’s lower digestive tract.
Partial Fasting
Also referred to as “selective fasting,” this type of fasting is incorporated into many cleanse diets or mono-diets. This means either limiting the amount of solid food consumed, or limiting consumption to specific types of food, like eating only brown rice, grapefruit, or apples.
Intermittent Fasting
This type of fasting involves sticking to a diet that cycles frequently between a period of fasting and a period of non-fasting. There are various ways to incorporate intermittent fasting into your lifestyle – alternate day fasting, one-day-per-week fasting, or 24-hour plans – but all provide similar benefits.
Planning an intermittent fast
Intermittent fasting is one of the easiest ways to see the benefits of fasting without making huge lifestyle adjustments – but it certainly takes a bit of planning. Luckily, there are tons of recommended schedules to help you figure out when to eat and when not to eat, which means that there is an intermittent fast plan that can accommodate pretty much any schedule or lifestyle.
Before embarking on a specific plan, consider what you want from the fast – are you looking to lose weight? Support a training plan? Make it a part of your regular healthy lifestyle? These factors will all play a role in helping you choose an intermittent fast schedule that will work for you.
16/8 Fast (also known as Leangains)
Fitness expert Martin Berkhan popularized this method of fasting, requiring practitioners to fast for 14 to 16 hours each day, with a restricted eating period of only eight to 10 hours – typically, you’d finish dinner at around 8 p.m. and then not eat again until noon the following day. Women sometimes have a more difficult time with longer fasts, so many women adjust this schedule to include a fast period of 14 to 15 hours, instead of the recommended 16.
For people who don’t eat breakfast, this type of fast will feel incredibly natural, but big breakfast eaters will have a harder time waiting all morning before eating their first meal. However, during your feeding window, practitioners are encouraged to fit in 2 to 3 healthy meals. Water, coffee, and other calorie-free beverages are allowed during fast periods, to help curb excessive hunger.
Possible 16/8 Fast (Leangains) Schedule
Sunday night, 8 pm: finish eating the last meal of the day
Sunday night, 11 pm: go to bed (fast time – 3 hours, so far)
Monday morning, 7 am: wake up (fast time – 11 hours, so far)
Monday morning, until noon: continue fasting, drinking only calorie-free beverages
Monday, noon: Fast time – 16 hours!
Monday afternoon, until 8 pm: enjoy one or more meals, sticking to healthy choices
Monday night, 8 pm: restart 16 hour fast
5:2 Fast
This would be considered more of a partial fast, as practitioners never truly abstain from solid foods. The diet encourages normal eating for five days of the week, with two days of restricted calorie intake, generally between 500-600 calories per day.
Popularized by British doctor and journalist Michael Mosley, this diet allows for an easier adjustment for people who have never counted calories before – but to achieve the benefits of the fast, it’s important to eat healthy, nutritious foods both during the fast days and on regular diet days, as well.
Possible 5:2 Fast Schedule
Sunday: eat normally, choosing healthy foods
Monday: follow reduced calorie diet – throughout the day, consume only 500-600 calories
Tuesday: eat normally
Wednesday: eat normally
Thursday: reduce calories again, staying between a daily total of 500-600 calories
Friday: eat normally
Saturday: eat normally – continue to fuel your body with nutritious foods
24-hour Fast
Whether you decide to begin fasting after breakfast, lunch, or dinner, under this diet plan, you wouldn’t eat again until the same meal the next day – after 24 hours of straight fasting. This method has been quite popular for the last few years, after being touted by fitness expert Brad Pilon.
It’s important to ensure that your diet remains healthy and that you’re not overeating during your feeding periods – especially if one of your goals is to lose weight. It can be difficult to adjust to this type of fast, so experts recommend starting with 14 to 16 hours and working your way up to a full 24-hour fast. One day per week is challenging enough, and those who plan to attempt to have 24-hour fasting periods each week should take care to get enough rest and limit physical activity during the fasts.
Again, during the 24-hour fasting period, non-caloric beverages like water or coffee are permitted.
Possible 24-hour Fast Schedule
Saturday night, 8 pm: finish eating the last meal of the day
Saturday night, 11 pm: go to bed (fast time – 3 hours, so far)
Sunday morning, 7 am: wake up (fast time – 11 hours, so far)
Sunday, all day, until 8 pm: continue fasting, using non-caloric beverages to curb hunger
Sunday night, 8 pm: Fast time – 24 hours! Enjoy a healthy meal, you’ve earned it
Alternate-Day Fast
This is a rather extreme type of fast, which can be undertaken in varying degrees of intensity. Some practitioners don’t eat at all during the fasting period, while others do a partial fast with a drastically reduced intake of calories, around 500 for the day.
Since this type of fasting is difficult, it’s not recommended for beginners or people who are looking to introduce a sustainable lifestyle change. However, it has proven to be very effective in helping practitioners gain a wide range of health benefits.
Possible Alternate Day Fast Schedule
Sunday: eat normally, choosing healthy foods
Monday: eat sparingly, sticking to a 500-600 calorie limit
Tuesday: eat normally
Wednesday: partial fast, consume no more than 500-600 calories
Thursday: eat normally
Friday: limit intake to 500-600 calories for the day
Saturday: eat normally – focus on nutrition
Warrior Diet
After fasting or eating small amounts of raw produce throughout the day, practitioners of this type of partial fast end the day with a huge meal in the evening, within a four-hour feeding window. This style of fasting rose to notoriety in recent years thanks to fitness guru Ori Hofmekler, and was one of the first popular diets to incorporate intermittent fasting.
The Warrior Diet is based on the theory that “ancient warriors” ate lightly during the day, if at all – and feasted in the evening after bringing home their “hunt.” With this diet, your food intake will consist primarily of one evening meal, and won’t require any calorie counting.
Possible Warrior Diet Fast Schedule
Saturday night, 6 pm: finish eating last meal
Saturday night, 11 pm: go to bed
Sunday morning, 7 am: wake up
Sunday, 7 am to 5 pm: enjoy calorie-free beverages, snacks of raw fruits and vegetables
Sunday, 5 pm: enjoy a large, healthy dinner
Random Fast
This type of fasting is something we all do from time to time. Skipping a meal on occasion, when you’re not hungry enough to eat or when you’re too busy to take the time to prepare a meal and sit down to eat it. There is a misconception out there that if you don’t eat every few hours, your body will go into “starvation mode” and start burning muscle, but this kind of eating is fairly typical of how our ancestors lived.
Before we learned how to preserve foods for later consumption, meals were eaten whenever food was available. Following this kind of eating schedule can provide similar benefits to any other type of fasting, but is much easier to accommodate into a busy lifestyle. A Paleo-type diet is recommended when practicing a spontaneous type of fasting and can be a challenge for people who need structure and routine.
Possible Random Fast Schedule
Sunday: eat normally, choosing healthy foods
Monday: skip breakfast, eat a healthy lunch and healthy dinner
Tuesday: reduce calorie intake to 500-600 for the day
Wednesday: eat normally
Thursday: eat normally
Friday: skip breakfast and lunch before eating a large, healthy dinner
Saturday: snack throughout the day, limit to 500-600 calories
If none of these types of fasts can work with your lifestyle, don’t lose hope. Fasting doesn’t have to follow strict rules or schedules – find a fasting style that works for you. Experts recommend making one small change at a time and maintaining that adjustment for at least two weeks, to give yourself a chance to evaluate whether the change works for you or not. Then, continue to introduce further small changes as needed, until you’ve reached your ultimate goal.
Keep in mind that no matter what kind of schedule you decide to follow for your intermittent fasting, you should never go more than 36 hours without eating. When you do eat, make sure you’re eating healthy, nutritious meals – not enjoying “cheat days” by bingeing on junk food. Fasting isn’t just about not eating, it’s about helping your body function in a more effective, efficient way, and filling it with empty calories and various chemicals isn’t conducive to the process.
Can I exercise while fasting?
Since food provides your body with the fuel necessary to get through a tough workout, it is beneficial to exercise during your fast – as long as you do it correctly. Your body generally uses stored carbohydrates in the form of glycogen to power you through your workout. During a fast, when your glycogen reserves are depleted, your body will be forced to turn to other energy sources for fuel – like fat. However, experts recommend that if you’re fasting, keep your workouts short.
Photo by Mathilde Langevin on Unsplash
“When glycogen is in short supply, your body also reverts to breaking down protein – your muscles’ building blocks – for fuel,” said Kelly Pritchett, Ph.D., R.D., assistant professor in nutrition and exercise science at Central Washington University and a board-certified sports dietetics specialist.
This means that even though you will likely burn more fat if you’re exercising on an empty stomach, you could also start burning protein if you work out too hard without fueling your body with carbs – leading to a loss of muscle mass, in addition to fat.
Without food, you’ll also feel the weakening effects of lowered levels of glycogen and blood sugar. As your body adjusts to regular intermittent fasting, you’ll be able to handle this energy loss a bit better, but initially, overdoing it with your workouts could be detrimental. Make sure you’re getting enough rest to compensate for your lowered energy level before you attempt to get on the bike or start pounding the pavement.
Challenges to expect during a fast
Fasting can be a difficult practice to incorporate into a busy lifestyle, especially for individuals who have never monitored meals or counted calories in the past. For people who are newly adopting a healthy diet and exercise program, it’s a good idea to develop a routine and let your body adjust before attempting to bring in an intermittent fast plan.
Working your scheduled fast periods around your family, job, and other commitments can also be a struggle. If you have the support of your workplace and your loved ones as you incorporate fasting into your life, it will be a lot easier to stick to your eating routine. Since you will likely face a brief period of lowered energy and some mood swings initially, it can be beneficial to arrange for your first fasts to fall on weekends, or days with less scheduled activity. Be prepared to feel a bit rundown as your body adjusts to a new eating schedule.
People who have struggled with eating disorders in the past can find that fasting may trigger relapses – particularly binge eaters. The hunger that can develop during a period of fasting could lead you to overeat during your feeding days, but this is generally not a problem for people who have a healthy attitude toward food and eating.
If you’ve experienced food-related mental health issues, a diet that incorporates any period of fasting for longer than eight to 12 hours might not be appropriate.
Finally, fasting is generally not a good idea if you’re pregnant. When your body is growing another human inside it, you’ll need to fuel it frequently and make sure you’re getting all the nutrients you need in regular doses – however, there is no research to show that fasting is a harmful practice for pregnant women. Some Muslim women do choose to practice fasting during Ramadan even throughout a pregnancy, but all pregnant women are encouraged to discuss drastic dietary changes with their doctor to ensure it will be safe for the baby.
Fasting throughout history
For thousands of years, fasting has been promoted as a spiritual healing practice, employed by religions around the world. The widely recognized “father of modern medicine,” Hippocrates of Cos, wrote, “to eat when you are sick is to feed your illness.” Hippocrates regularly prescribed fasting as a way to speed healing from a variety of ailments.
The practice was also adopted by Greek writers and philosophers Plato, Aristotle, and Plutarch, who wrote, “instead of using medicine, better fast today.” Ancient Greeks much preferred using natural healing methods – and since humans, like animals, lose their appetite when suffering from an illness, this universal human instinct is embraced through the practice of fasting.
Even more modern thinkers have recognized the value of fasting as a way to encourage the body’s natural healing process – including Philip Paracelsus and Benjamin Franklin. However, the practice has been primarily utilized by religious groups. Virtually every religion in the world promotes fasting as for spiritual reasons, since the practice has been touted in the scriptures of Jesus Christ, Buddha, and the prophet Muhammed. Cleansing, or purification, has been embraced by a wide variety of religions and cultures throughout history.
Traditional fasting
While modern Western medicine is somewhat reluctant to accept the traditional, natural remedies of the past, the practice of fasting has managed to continue to this day. In the 1970s, the idea of “cleanse diets” emerged as a solution to help people lose weight and detoxify their bodies, and the popularity of yoga has encouraged more modern practitioners to embrace fasting as an Ayurvedic healing therapy. As more people recognize the power of the mind-body connection, the more important these self-healing practices will become – and the fact that many groups and individuals continue to fast to this day proves this ancient practice has earned a place in the modern world.
This article was first published by LongevityLive.com on the 27th of March 2017 and updated and fact-checked again on the 24th of July 2024.
About the author
Jen Miller is a former electrical engineer and product specialist with more than 20 years of product design and testing experience. She has designed more than 200 products for Fortune 500 companies, in fields ranging from home appliances to sports gear and outdoor equipment.
She founded Jen Reviews to share her knowledge and critical eye for what makes consumers tick, and adopts a strict no-BS approach to help the reader filter through the maze of products and marketing hype out there. She writes regularly and has been featured on Forbes, Fast Company, The Muse, The Huffington Post, Tiny Buddha and MindBodyGreen.
