Fasting is an important part of cultural, spiritual and religious traditions around the world and has been for centuries. Intermittent fasting (IF) may seem like a new fad in the health and diet world, but really it isn’t a fad at all. It is what our ancestors naturally did before electricity, refrigeration, food delivery and microwaves! They would go periods of time without food, which is basically what intermittent fasting is.
What is Intermittent Fasting?
Intermittent fasting is an eating pattern in which you cycle between periods of eating and abstaining from food. It doesn’t involve restricting food or calories. It’s all about timing, which is why it is sometimes called time-restricted eating. You’re simply condensing eating hours into a shorter window of time.
Why would you do this?
Digestion is a very energy-intensive process and our digestive systems weren’t meant to be “on” all the time. When we let our digestive systems rest for 12-16 hours in a 24-hour period, they can work on removing metabolic junk and toxins that build up in the body over time.
During fasting, inflammation comes down and your body initiates autophagy, an important cellular cleansing process that breaks down and recycles damaged cellular components. Human growth hormone increases, which helps burn fat, preserve muscle mass and increase growth in muscle, bone and cartilage. Norepinephrine and adrenaline levels also increase which provide energy while you burn fat. Insulin levels decrease to allow you to burn fat instead of store it, and ghrelin (“hunger hormone”) and leptin (“satiety hormone”) levels normalize.
Due to processes activated during the fasted state, we can experience health benefits such as fat loss, more stable energy, reduced oxidative stress, improved cognitive function, prevention and reduction of degenerative disease in the brain, increased longevity and more.
Did your ears perk up with the mention of fat burning? Fasting is great for this because abstaining from food for periods of time trains your body to become fat-adapted, meaning that you burn stored body fat for fuel rather than relying on sugars from food. I went into detail on this in my keto post.
To be an efficient fat-burner, the hormone insulin needs to be as low as possible during the fasting period. Quick recap on insulin’s job in the body: It ushers the circulating blood glucose from the calories you consumed into the cells to be used for energy. When there is excess that can’t be stored in the liver as glycogen, insulin directs the excess to be stored in adipose tissue.
While insulin is necessary for survival, having chronically high insulin levels keep the energy locked away in our fat cells so to free that stored energy and burn body fat, we need to lower insulin. Intermittent fasting is a very efficient way to lower insulin because when there is no food coming in, insulin drops and your body can switch fuel sources from burning glucose to burning fat.
Who should do Intermittent Fasting?
People looking to improve their health and become a better fat-burner! That said, not everyone is a good candidate. Below are some recommended pre-reqs for IF:
- You’re eating a healthy, well-balanced diet which includes adequate healthy fat, protein and fiber from vegetables.
- You can eat three meals a day and no snacks without hypoglycemic symptoms such as light-headedness, confusion, blurred vision, getting hangry, dips in energy, etc.
- You’re getting sufficient sleep (7 – 9 hrs).
- You’re managing stress well and not experiencing adrenal disregulation.
- You’re exercising regularly (not too much and not too little).
- As a woman, you are not experiencing hormone imbalances (sex hormones, thyroid, adrenals).
- You are not underweight, already restricting-calories, have/had an eating disorder.
- You are not pregnant, breastfeeding or trying to get pregnant.
- You don’t have chronic renal disease.
- If you’re an insulin-dependent diabetic, you’re being closely supervised by a doctor.
Before we get into the how-to’s of IF, let me dispel a few common myths:
- Fasting is the same as starvation – INCORRECT. The goal of intermittent fasting is not calorie restriction; it’s time restriction.
- Your muscles will waste away during fasting – INCORRECT. When you’re in a fasted state, your body preserves muscle mass and breaks down fat tissue to meet energy requirements.
- Fasting slows down your metabolism – INCORRECT. While very long periods of time without food (over 72 hours) can cause a drop in metabolic rate, show short term fasting actually increases your metabolic rate by up to 15%!
How do you do IF?
Research suggests that the beneficial metabolic changes associated with fasting start at around the 12-hour mark, though the benefits compound the longer you go. Sixteen hours seems to be the sweet spot for optimal benefits, particularly for men. The fasting window includes sleep so 12 hours should be very do-able! You can pick the fasting and feeding windows that best suit your schedule. If possible, I recommend finishing your last meal of the day 2-3 hours before bed.
There are numerous IF approaches. Consider these options to determine which plan will work best for you.
- 12-hour fast – This is the plan I recommend for newbies interested in experimenting with IF, as it is the easiest and gentlest. Most people have no issues creating a 12-hour fasting window between dinner and breakfast (for example, finish dinner by 7pm and have breakfast at 7am) because they are sleeping for most of it!
- 16/8 cycling – This is essentially the same strategy as the 12-hour fast, only you’re limiting your eating window to eight hours and extending your fasting window to sixteen. In my experience, it is a more difficult transition than the 12-hour fast, however the results are more profound. With this plan, you may stop eating by 8pm and have lunch at noon, thereby creating a 16-hour daily fasting window. Otherwise, you could stop eating at 5pm and eat breakfast at 9am. Try experimenting different windows as I find it depends on the individual! Women may have a harder time with 16/8 (more on that later!) so, for women, I recommend modifying to 14/10.
- Alternate-day fasting – This plan involves a “fast day” in which you consume only 25% of your normal caloric intake (around 500 calories of protein, fat and veggies – no sugar or starches), alternated with a “feed day” when you eat whatever you want. This is not the IF plan I tend to recommend as I think the calorie-restricted days may be a challenge and the feed days can be a slippery slope (think: binging on junk).
- 5:2 plan – Similar to Alternate-day fasting, the 5:2 plan allows you to eat normally five days a week while limiting calories to 500-600 calories on the other two days.
- Warrior Diet – this plan involves eating small amounts of raw fruits and veggies during the day, then eating one big meal at night.
- Eat WHEN (When Hunger Ensues Naturally) – As the name suggests, eat when you’re hungry and abstain when you’re not. For example, if you aren’t hungry in the morning, don’t eat breakfast. Or if you’re not hungry at noon when all your co-workers are going out for lunch, don’t just eat because it’s “lunchtime.” This is more of an anything goes type of approach which works well for some but not for others who prefer more of a structured regimen. This plan’s flexibility is useful in times such as when your plane gets delayed and you’re stuck in an airport with no decent food options, you can elect to fast and avoid the wilted salad or Kudos bar.
Tips for easing into IF
- Go slow – start by finishing your evening meal 3 hours before going to bed. If you’re not already getting a 12-hour fast, aim for that for 2-4 weeks before moving on.
- Next, increase your fasting window to 13 hours for 2 weeks. Once that feels easy, try 14. You get the drift.
- If you feel hungry, take a few deep breaths and realize that it is OK to have an empty stomach and feel hungry. Drink some water, coffee, or tea. If that’s not doing it for you, add 1-2 tablespoons of MCT oil to your beverage and go on a walk. If you’re really miserable or experiencing hypoglycemic (low blood sugar) symptoms, eat something. It’s ok to break your fast earlier than planned. Try again the next day.
People with steady IF schedules seem to have more success with it than those with erratic schedules. Once your body adjusts to the IF routine, your hunger hormones adapt to the new schedule and fasting gets easier.
Some people fast every day. Some people fast 2-3 days each week. You can try different patterns and find what works for you and your schedule. It takes time for your body to get used to this way of eating. Once you train your body to burn fat for fuel, you will begin reaping the benefits of stable energy and mood, improved mental clarity, loss of excess body fat and no longer feeling like a slave to food and hunger.
Intermittent fasting is not for everyone so, if you’re happy with the state of your health, don’t feel like you need to engage in IF! It’s just another tool in the toolbox for those trying to take things to the next level. If you decide to try, it is important to make sure you’re eating healthy. Food quality is still crucial for maintaining vibrant health, controlling inflammation and reducing the risk of nutritional deficiencies.
Food quantity is also important while practicing IF because you need to eat enough at meal times to elongate your satiety curve and prevent the urge to snack. How you break your fast is key. I recommend a balanced meal containing 4-6 ounces of protein, a serving of healthy fat such as 2 tablespoons of olive oil or ½ avocado, 2-3 cups of vegetables, plus a tablespoon of fermented veggies.
What can you have while fasting?
The obvious answer is nothing but water. Rest assured, though, you can have black coffee, plain black or green tea and unflavored sparkling water. You’ll notice all these options are zero calories. There is a grey area among IF experts regarding add-ins such as fresh lemon slices or juice, apple cider vinegar, spices like cinnamon and turmeric and some herbal teas. I personally think fresh lemon and herbal teas are fine while fasting.
The next question, then, might be: “what about non-caloric sweeteners like stevia or monk fruit?” These are all a NO because the sweet taste (regardless of whether it’s a zero-calorie sweet) primes your body to expect calories and release insulin in anticipation of those calories coming in. Rising insulin stops the fat burning process.
Protein is a definite NO as it turns off autophagy (the mechanism for clearing cellular debris). This includes bone broth, collagen peptides, BCAA’s, etc.
The other big grey area in the research is whether adding pure fat (i.e. MCT oil or coconut oil) to your black coffee or green tea will break a fast. Within the fasting adjustment period, adding MCT oil to your beverage might help you adjust to fasting by encouraging your body to switch to fat burning. For those trying to lose body fat, keep in mind that you’re going to be burning the fat from the MCT oil, rather than your own stored body fat, but it can definitely help you make the transition. For that reason, you may want to include it during the adjustment period and then gradually wean yourself off (switching to black coffee or plain green tea) as your body adapts to burning its own fat.
What about exercise?
When you exercise in a fasted state, like first thing in the morning before breakfast, it activates your sympathetic nervous system (SNS). Since your body’s fat burning processes are controlled by your SNS, fasted exercise forces the breakdown of fat and glycogen for energy. Studies have shown that fasting before aerobic training leads to reductions in both body weight and body fat. For most people, this is one of the main reasons they’re exercising in the first place so it’s worth a try!
There are a variety of factors that play a role in whether it’s suitable for an individual to exercise while fasting, such as age, pregnancy, medications, medical history, hormone imbalances, level of fitness, type of exercise, etc. I believe the best approach is to listen to your body!
Many people report feeling great working out on an empty stomach, others may feel weak, lightheaded, nauseous, etc. without some food first. Experiment with what works best for you. For more info on what to eat before and after workouts, check out this post.
Are gender differences a factor in IF?
While there aren’t enough studies on the subject to draw firm conclusions, it seems that men and women respond differently to IF based on inherent metabolic and hormonal differences.
At its core, abstaining from food, whether intentional (in the case of IF) or unintentional (in the case of starvation), is a stressor. It is sending a message of scarcity to your body. Daily long fasts (14-16 hours of fasting) could run the risk of becoming chronic stressors so should be approached with caution by women, particularly pre-menopausal and peri-menopausal women and those with adrenal and thyroid problems.
I recommend starting to experiment with IF slowly and cautiously, be self-aware of how your unique physiology is responding and only continue if it comes naturally and you feel good doing so. For women, I typically recommend a 12-hour fast most nights (7pm – 7am) and, if it feels right, add in two or three 14-hour fasts (7pm – 9am) during the week. If your sleep quality decreases, your menstrual cycle becomes wonky or stops altogether, or you start getting any other weird symptoms, that is certainly a sign from your body to stop IF and go back to your normal eating habits.
What works for me?
If you’re thinking “Whoa! Information overload!” and don’t know where to begin, I’ll share what I do personally.
As a thin woman with polycystic ovary syndrome (PCOS) and hypothyroidism, I have to be particularly careful to keep my hormones balanced (so I can have regular cycles) and not make my body think I’m in starvation mode (which slows down my thyroid and thus my metabolism). Every day, I do at least a 12 hour fast. This is no problem for me as I like to eat breakfast a little later (9am-ish) anyway.
This 12-hour fast is usually more like a 13-14 hour fast, as long as I can finish dinner by 7-8pm, which depends on how late I stay at the office. One day a week, I do a 15-16 hour fast in which I wait to eat breakfast or lunch until 11am-12pm or finish dinner by 5:30/6pm. On that day, I do not do my usual morning workout, which is either HIIT, running, weight training or reformer pilates, etc. as a harder workout makes me too hungry to sustain a fast without feeling annoyed by hunger pains.
Instead, I opt for a gentle walk or restorative/yin yoga practice which takes my mind off the fact that I’m fasting and makes me feel grounded and calm. As I mentioned above, from personal and clinical experience, I find that women do better on shorter fasts (12-14 hours) and therefore I don’t push it more than that.184