Important: Fasting is not for everyone. Always consult with a qualified medical professional before making dietary or lifestyle changes. This information is intended to serve as educational material only and not to be relied upon for medical diagnosis or treatment.
What is Intermittent Fasting?
Intermittent fasting is the practice of cycling between periods of eating and periods of intentional fasting, or abstaining from food. Humans have fasted for millennia, whether for religious or cultural purposes or out of necessity during times of scarcity.
However, it’s a rare occurrence for most modern people to skip a meal when there are convenience stores on every corner.
Researchers are beginning to investigate how fasting intermittently affects weight loss and body composition. Unlike traditional “diets” that dictate what you eat, intermittent fasting focuses on when you eat, and it can be a powerful practice for better health.
Benefits of Intermittent Fasting
The benefits of fasting are similar to those of calorie restriction, which has been shown to have positive effects on weight loss and potentially even longevity. The problem is that for most people, counting calories is extremely tedious, requires a lot of guesswork, and is not sustainable. It tends to create a vicious cycle of losing weight only to gain it all back. Long-term calorie restriction without regular refeeds can be catastrophic for your hormones and lead to lower energy levels, loss of muscle or leave you feeling hungry and cold. Not fun.
That’s where intermittent fasting comes into play.
Intermittent fasting has been shown to mimic the benefits of calorie restriction without the potential drawbacks and the need to intentionally restrict food intake. Studies suggest that intermittent fasting is as effective as traditional calorie-restricted diets for weight loss due to specific benefits that occur during the fasting window:
Improved Fat Oxidation: Human studies have shown that fasting for periods of 12 or more hours can improve fat oxidation and induce mild ketosis.
Increased Metabolic Rate: Short-term fasting has been shown to lead to increased energy expenditure and metabolic rate in human studies.
Blood Sugar Regulation: Fasting can improve insulin sensitivity, lower overall levels of blood sugar, and reduce systemic inflammation, all of which are crucial factors for appetite regulation and metabolic health.
Normalized Appetite: Fasting has been shown to help regulate ghrelin, the “hunger hormone”. Ghrelin antagonizes leptin, the hormone responsible for telling us we’re satiated, so balancing the two is key to regulating appetite.
Better Muscle Retention: Intermittent fasting stimulates the production of growth hormone and testosterone, especially in overweight populations. These hormones help you maintain muscle mass while losing weight, and the more muscle you have, the more calories you burn at rest.
In addition to its benefits for fat loss, intermittent fasting has a host of other health benefits:
Autophagy: A repair process wherein cells dispose of damaged proteins and replace them with new ones. This process has been linked with anti-aging, longevity, and improved metabolic health because it keeps cells young and functioning optimally.
Improved Gut Health: Fasting can make your gut stronger by giving it a break from digestion, protecting it from the negative impacts of stress, increasing levels of good bacteria, and killing off harmful microbes.
Improved Blood Lipid Profiles: Fasting has been shown to improve a number of blood lipid markers including blood pressure, cholesterol, blood sugar, and triglycerides.
Improved Energy Levels: Most people equate hunger with lethargy, but fasting tends to lead to increased energy levels and cognitive function. This is due to increased fat metabolism and ketone production.
Intermittent fasting is a simple way to regulate energy intake without the need to weigh, measure, track, and count every morsel of food you consume. Many people find fasting to be an easier alternative to calorie-restriction for losing fat, increasing energy levels, and improving metabolic health.
Different Types of Intermittent Fasting
There are several different methods for intermittent fasting, each of which consists of different fasting and feeding windows to support different goals. Here are some of the most common types of intermittent fasting:
Time-Restricted Eating: This is a great approach for beginners. Time-Restricted Eating simply involves not eating between dinner and breakfast the next day. If you’ve ever gone to bed a few hours after dinner, gotten a full night’s sleep, and waited a few hours to eat breakfast, you’ve already done this type of fast!
- Fasting Duration: 10-14 hours
- What This Looks Like: If dinner ends at 8 PM, bedtime is at 10 PM, wake up at 6 AM, breakfast would be eaten between 8 and 10 AM. Only water is consumed during the fasting window – no other beverages and no supplements.
- Frequency: Daily
16:8 Fasting: Also known as the LeanGains Method, 16:8 fasting involves fasting for 16 hours each day – as simple as skipping breakfast. This method is popular because a full day’s worth of food could be fit into the feeding window, making it easy to sustain long-term.
- Fasting Duration: 16 hours
- What This Looks Like: If dinner ends at 8 PM, eating would resume at 12 PM on the next day. Feeding could be compressed into an even shorter window of 6 hours after fasting for 18.
- Frequency: Daily
Eat-STOP-Eat: Perhaps the simplest fasting protocol, the Eat-STOP-Eat method involves fasting for 24 hours once or twice a week. It’s highly effective for people who have a lot of weight to lose.
- Fasting Duration: 24 hours
- What This Looks Like: If dinner ends at 7 PM, eating would not resume until 7 PM the next day.
- Frequency: 1-2x per week
Intermittent Fasting Guidelines
So, which type of intermittent fasting is best for you? The truth is that there is no one-size-fits-all answer: you must choose which method is the most sustainable for your lifestyle. Here are some guidelines that apply to all types of intermittent fasting.
How Long to Fast: The ideal length of fast depends on your what your body can tolerate.
Start with a short fast of 12 hours and work up from there by adding just an hour at a time.
How Often to Fast: Some people fast for 12-18 hours each day, others prefer less frequent fasts of up to 24 hours. The key is to choose a protocol that’s sustainable and fits effortlessly into your schedule.
What to Eat Before Fasting: Prior to your fast, have a reasonably sized meal with protein for satiety, fiber to slow digestion, and fat to provide you with slow-burning energy.
What to Eat to Break a Fast: You can break a short fast (12-16 hours) with a normal-sized meal comprised of healthy, whole foods. For longer fasts, consider starting with some bone broth and digestifs like lemon and apple cider vinegar to ease the body back into eating.
What to Consume While Fasting: Most experts agree that you should consume water and avoid significant sources of calories during fasting. However, even the top fasting experts can’t come to a consensus on what exactly breaks a fast. Dr. Satchin Panda believes that anything aside from water will break a fast, Dr. Jason Fung believes that zero-calorie beverages like coffee and tea will not break a fast, while Dr. Valter Longo’s Fasting-Mimicking Diet involves consuming small amounts of food while still reaping the benefits of fasting.
All of that conflicting information can feel confusing, but here’s a simple solution: instead of worrying about what “breaks” a fast, consider how what you consume can enhance or inhibit the benefits of a fast.
Here are a few other things you can consume to make intermittent fasting easier and accelerate weight loss:
- Black Coffee and Tea: Caffeine can help suppress hunger and increase fat oxidation. The polyphenols in these beverages might even enhance autophagy during fasting.
- Electrolytes: If you only drink water during your fasting window then you flush out electrolytes, which are vital for basic physiological functions. You can maintain electrolyte balance by simply adding 1 to 2 teaspoons of sea salt or supplemental electrolytes to your first glass of water each day.
- Essential Amino Acids (EAAs): Though EAAs have been shown to inhibit autophagy, they can make fasting easier and more sustainable by suppressing hunger and cravings, improving energy levels, maintaining muscle mass, and supporting training in a fasted state. In other words, if your primary goal for fasting is to lose weight and improve body composition, EAAs will not negatively impact your fast and will likely improve your results. Look for an EAA formula (like Kion Aminos) that has minimal calories and is free of added fillers or sugars, as those components will take you out of a fasted state.
Listen to your body as you experiment with intermittent fasting. If you’re losing fat, feeling good, and performing well during your fasting window, then keep it going! If you find yourself feeling sluggish and see your weight stalling, then modify as necessary. Fasting has many health benefits, but it doesn’t always work for everyone. Remember to consult with your doctor no matter which protocol you choose!
Working Out While Intermittent Fasting
You might be wondering: can you work out while you fast? The answer is yes, and fasted training might even accelerate your fat loss efforts.
Here are some tips to maximize workouts during fasting:
Do the Right Training. If you exercise in a fasted state, opt for workouts that are easily fueled by body fat. Passive aerobic exercise like hiking or high-weight low-rep strength training are great options. It’s best to avoid intense anaerobic, glycolytically-demanding exercise like martial arts and CrossFit as glycogen will be depleted while fasting. This is especially true for women.
Take Time to Adjust. If you’re brand new to fasting, you might see a slight decrease in performance. You will adapt over time as your body gets used to tapping into stored body fat for energy.
Train at the Right Time. Women typically see more fat loss when they eat pre-workout and fast after exercise. Men, on the other hand, are more flexible but tend to see benefits when training fasted and having a post-workout meal.
Supplement With EAAs. EAAs (like Kion Aminos) increase fat oxidation during workouts and keep the body from cannibalizing muscle when taken prior to fasted training. Taking EAAs, such as Kion Aminos, is also a potent hack for extending a fast post-workout, as they provide muscles with the proteins needed for rebuilding and recovery but allow you to continue burning fat until the next meal.
Intermittent Fasting for Women
Due to different hormonal profiles, women have to take some special considerations when intermittent fasting. For women, fasting creates a major reduction of Kisspeptin, which is a precursor to reproductive hormones. Therefore, fasting can lead to a significant decrease in sex hormone production in women, which can cause a whole host of symptoms including hormonal imbalances, loss of menstrual cycle, infertility, or thyroid issues. Women also produce less leptin than men, which means that they are more sensitive to hunger when food intake is restricted.
So, should women try intermittent fasting at all?
It depends. Fasting is not a good idea for women who are very lean (under 18% body fat) and/or extremely active, have subclinical hypothyroidism, have hormone disorders, have a history of an eating disorder, or are pregnant, breastfeeding, or trying to conceive.
Healthy women typically do best with shorter or less frequent fasts, such as:
The Crescendo Method, which involves fasting for 12-16, hours 2-3 days a week on non-consecutive days. Ideally, fasting would fall on rest days as opposed to training days.
Eat-STOP-Eat, 24-hour fasts once every 1-2 weeks.
Occasional Prolonged Fasting, like a Fasting-Mimicking Diet or an Elemental Diet for 3-5 days, done 1-4 times per year.
Here are some other tips on how women can take advantage of the potent benefits of fasting without sabotaging their hormones:
Avoid intense exercise like CrossFit and long distance running during fasting. Opt instead for low-rep strength training, low-intensity cardio like hiking or swimming, and restorative movement like yoga.
Sleep, ensure you're doing everything possible to get plenty of quality nighttime rest.
Minimize stress, and prioritize relaxing activities.
Eat adequate calories from nourishing foods during feeding windows, including plenty of healthy fats to optimize hormone production.
Intermittent Fasting Mistakes
Fasting can be a great tool in the right context, but it’s ultimately a stressor on the body. When combined with others stressors such as extreme calorie restriction, intense exercise, or stressful life situations, fasting might do more harm than good for your health.
Consider augmenting your fasting routine, or ditching it altogether, if you experience any of the following symptoms:
- Irregular menstrual cycles or loss of period
- Decreased fitness performance or recovery
- Poor sleep
- Negative changes to mood
- Binge eating or uncontrollable cravings
- Inability to lose weight
- Acne or dry skin
- Loss of libido
- Always feeling cold
- Thinning hair or hair loss
Intermittent fasting should be icing on the cake of an overall healthy lifestyle. Make sure you cover your bases by eating nutritious foods, getting good sleep, exercising intelligently, and managing lifestyle stress before incorporating it into your daily life.
Common Concerns of Fasting
Will intermittent fasting make me lose muscle? Remember that intermittent fasting is more muscle-sparing than traditional dieting. You’ll only lose muscle if you don’t consume adequate calories (especially protein) during your feeding window. Strength training and supplementing with EAAs like Kion Aminos will also help support muscle maintenance during fasting.
Will intermittent fasting slow down my metabolism? Fasting has not been shown to reduce metabolism. Your metabolism won’t slow down as long as you eat enough calories during your feeding window.
Will intermittent fasting affect my thyroid? Fasting can cause a temporary reduction in thyroid hormone T3, which plays a role in metabolism and energy production. However, T3 production returns to normal once feeding is resumed. This re-uptake of metabolism and thyroid hormone is a benefit that is unique to fasting, as it doesn’t occur during long-term calorie restriction.
When do I take supplements during intermittent fasting? Most supplements contain insignificant amounts of calories and can be taken during the fasting window. However, some supplements are best consumed with food, including vitamins and fat-soluble nutrients. The best practice is to follow the directions on the packaging.
Safety, Side-Effects, and Special Considerations
Fasting is a great practice, but it’s not appropriate for everyone. Do not fast if you are underweight, under the age of 18, have recently undergone surgery, or currently deal with mental health conditions. If you have gout, diabetes, or are currently taking prescription medication, then only fast under the supervision of your physician.
Intermittent fasting is quickly becoming one of the most popular and profound weight loss practices, and for good reason: it’s simple, effective, flexible, sustainable, and best of all, it’s free. Fasting can be incorporated into nearly any other diet and lifestyle with relative ease. Share your fasting stories, advice or questions below!