Before I gave up grains, sugar and other foods which I used to believe were healthy (or at least not harmful), I had breakfast every single day. At least that's what all kinds of TV ads were claiming, promoting whole grains and cereals and other "healthy" breakfast options often loaded with sugar. Just the thought of skipping a meal made me feel guilty. Doing a full day fast seemed unnecessary and impossible to follow. But all this has just been part of the big high-carb, low-fat campaign.
Myth #1: Breakfast is the most important meal of the day.
As you will learn in this post, nothing can be further from the truth. I rarely eat breakfast - that's the meal I skip almost every day.
Myth #2: You have to eat regularly, ideally 5 small meals a day.
Once you get keto-adapted and not depended on glucose, this will change. Since your insulin levels will not spike, you won't have the need to eat regularly or in small portions (apart from diabetics which I discuss later in this post).
Myth #3: You need to eat most of your carbs for breakfast because that's when your body uses them most effectively.
You should try to eat your carbs throughout the day and not just in one meal. Furthermore, since our body is in fat-burning state in the morning, eating carbs in the second half of the day is more beneficial for weight loss.
Myth #4: Never exercise on an empty stomach. It's bad for your performance and you'll lose muscles instead of body fat.
As described below, for most people Intermittent Fasting is ideal for maximising the benefits of exercise for several reasons.
What is Intermittent Fasting (IF)?
Compared to calorie restriction, IF is not restricted in calories - it simply limits your eating windows to just a few hours a day. In effect, you usually fast for 14-20 hours or even up to 36 hours.
The idea is that you should be eating ad libitum (as much as you want) during your "feeding" window, but you should not eat or drink anything with caloric value during your fasting window (black coffee or tea sweetened with stevia or Erythritol are allowed). You should be aiming at reaching your daily macronutrient targets and without restricting yourself - simply eat to satiety.
If eating ad libitum means that you may not meet your macronutrient targets, that's just fine. Your appetite is what will determine how much you should eat. Aim for your daily protein intake and use fat as a "filler" to sate your appetite while keeping carbs low (20-30 g net carbs). Remember, if you eat less protein than required over a long period of time (not just a day or two), you may lose muscles, decrease your basal metabolic rate and therefore burn less body fat. That's why losing muscle mass is what you really want to avoid.
If you need to know how to find your optimal food intake, try KetoDiet Buddy - our online keto calculator.
Just like Fat Fasting (guide is here), Intermittent fasting (IF) is a diet approach that is often used for breaking though a stubborn month-lasting weight loss plateau. Although Intermittent Fasting is not always a guarantee for weight loss, it has proven to have several health benefits.
IF versus Calorie Restriction
Most studies compare Intermittent Fasting to calorie restriction in the sense that both have several health benefits. However, unlike IF, calorie restriction has many downsides: it's difficult to stick with and can be frustrating. It leads to muscle loss, loss of bone mineral density and may also cause severe micronutrient deficiencies. This is, of course, relative and depends on the scale of the calorie restriction. Another study of mice compared IF and calorie restriction and found that IF exceeded the beneficial effects of calorie restriction. This study compared individuals on IF and calorie restriction and found both to be equally effective for weight loss, although IF was better for the retention of lean mass. So, what if there was a way to improve your healthy and enjoy life without restricting yourself at the same time? It seems that Intermittent Fasting is the best way to achieve both.
Bottom line: Fasting seems to have all the benefits of calorie restriction without its downsides. Fasting leads to natural calorie restriction - without forcing yourself, you will likely eat less. Even if you have a large meal after a fasting period, it will likely not make up for the time you have been fasting.
How Does it Work? Types of IF
When we are fasting on a low-carb diet, our body is using fat stores for energy and we lose body fat. Fasting on a ketogenic diet has more benefits: since our body is depleted from glycogen, we use fat and ketones for energy instead of glucose.
Healthy low-carb eating is great for appetite control and keeps us fuller for longer. As your body gets used to fat and ketones as main sources of energy, you will naturally eat less amount and less frequently. That's the best time to try Intermittent Fasting.
There are several types of IF:
1) Skip a meal every now and then. It is important to note, that you must not force yourself and start feeling too hungry. It should be a gradual process, where you slowly get your body used to it by putting your next meal off slightly every day until you skip it. It's my favourite way to do IF and what I practice 4-5 times a week by skipping breakfast. I'd usually have Monday to Friday with IF and have weekends off. This is, in fact, what most keto-adapted people do - they eat when they are hungry because foods high in fats, moderate in protein and low in carbs induce strong satiety.
2) Break a 24-hour period into 2 segments / windows (e.g. 18/6). This means you fast for 18 hours just drinking water or tea and have a 6-hour period of calorie intake. You can also have 16/8, 20/4 or even 21/3 periods based on what suits you best.
3) Active individuals, IF combined with exercise. It's an approach similar to the one above but also includes exercise. Martin Berkhan, the author of LeanGains has further described this approach suitable for active people in this guide. Apart from working out in the fasted state (with only 10 grams of BCAA), there are more rules to follow. Your post-workout meal should be the largest one and you should pay attention to the macronutrients on your active vs resting days. Your ideal macronutrients then depend on your goals (fat loss, muscle gain or body recompositioning). In general, on days of your workouts, you should be eating more carbs while on your rest days you should focus on eating fat. Protein intake should be kept high on all days and depends on individual needs. You should also try to keep your feeding window constant as it will help you stick with the plan.
4) Alternate days of fasting with days of unrestricted eating while still eating low-carb food. This approach may be too extreme for most people and I wouldn't recommend you follow it unless you've tried one of the above methods first. You can do this by including one or two fasting days a week.
5) Combination of Fat Fasting with Intermittent Fasting - instead of eating 5 small meals on a traditional Fat Fast, you can try 1-2 regular high-fat meals which makes it easier to follow. I've further described this approach here.
Bottom line: Whether you decide to include one fasting day a week or skip breakfast every day like I mostly do - do what works best for you. Just make sure you don't end up eating too little - you should meet your macros on most days - IF is not about starving!
What Are the Benefits of Intermittent Fasting?
Occasional fasting has been proven to have the same benefits as calorie restriction. Most studies on Intermittent Fasting to date have been focused on its health benefits.
IF improves metabolic syndrome markers
Studies show that IF improves blood lipids, cardiovascular markers, improves insulin resistance & increases insulin sensitivity, reduces blood pressure and inflammation markers (Study 1, Study 2, Study 3).
Several studies that were performed on mice showed increased lifespan when a period of fasting was included in their diet. Most likely reason for that is that fasting affects the ageing process via calorie restriction. Another reason for increased longevity can be the fact that fasting improves the symptoms of metabolic syndrome (obesity, diabetes, etc.) and reduces the risk of cancer. Also, fasting and ketosis has proven to enhance autophagy (body's ability to "repair" itself). Autophagy is required for muscle mass maintenance and has anti-ageing properties. Finally, fasting has shown to enhance production of growth hormone which is known to naturally decrease as we are ageing.
This review of studies shows that metabolic factors are strongly linked to various types of cancer. The strongest risk factors identified in men were high levels of blood pressure and triglycerides, and in women with high plasma glucose. Since IF improves metabolic syndrome markers, it also reduces the risk of cancer. Additionally, this study shows that fasting helps reduce the negative side effects of chemotherapy in cancer patients.
Mental clarity and neurological health
Fasting and ketosis are good for the brain. Once your body becomes keto-adapted and you are no longer glucose-dependent, usually in 3-4 weeks, your body will effectively use ketones, dietary fats and stored body fat for energy. No brain fog and more focus - you can learn more about how ketosis can enhance mental clarity in this post by Dr Bill Lagakos. Intermittent fasting can improve neurodegenerative diseases such as Alzheimer's, Parkinson's, Huntington’s disease and stroke. Scientists at the National Institute on Aging, led by Dr Mark Mattson found that in animal studies Intermittent Fasting can increase the resistance of neurons in the brain to dysfunction and degeneration.
When you exercise in the fasted state, you'll enhance fat burn. Since you have low glycogen stores, your body will use ketones and body fat for energy instead of glycogen. Contrary to common beliefs, fasting does not have a negative effect on performance. Studies show that it can either improve performance or have no effect (Study 1, Study 2). Will you lose muscles if you train in the fasted state? No, you won't - fasting also enhances muscle protein synthesis and recovery after exercise (Study 1, Study 2).
Intermittent fasting is not about starving. When you follow IF, you effectively eat the same amount of food as you would on your non-fasting day, just in a shorter eating window. This by itself usually doesn't help weight loss. The main reason people lose weight on IF seems to be the fact that they naturally eat less. Imagine, if you are already keto-adapted and have just one or two large meals, you will unlikely eat the same amount of food as if you were to have 3 regular meals.
Also, studies show that Intermittent Fasting increases fat oxidation. As mentioned above, it increases the production of growth hormone and decreases insulin levels: all these are factors that help us to lose body fat. Compared to calorie restriction, most studies on IF show that people find IF to be less restrictive, easier to follow and they better adhere to it.
My personal experience: I do IF by skipping meals and found that on days of IF, I naturally eat 20-30% less which I confirmed by using the KetoDiet app. Below is my progress chart where the spikes close to 2000 kcal are either the days I exercise or days without IF (usually weekends) or a combination of both.
What is more effective for weight loss? Calorie restriction or Intermittent Fasting? This review of studies compared the effects of calorie restriction and IF: "these diets are equally as effective in decreasing body weight and fat mass, although intermittent fasting may be more effective for the retention of lean mass." As you know, retention of lean mass is important for long-term weight loss as it plays role in our basal metabolic rate. The more lean mass we have, the more calories we burn at rest.
Being used to IF is great for those who can't always find low-carb foods - either they are travelling, at work with limited options or too busy to cook. Although I would suggest you take low-carb snacks or prepare your meals in advance, this is not always possible. Also, with less meals to prepare, you will save time and money.
Bottom line: Indisputably, there are several benefits of IF. However, the truth remains that there has not yet been a long-term, randomised clinical trial of IF in humans to tell whether or not it extends our life or leads to a sustained weight loss. These potential benefits have only been assessed based on short-term studies and studies in animals.
7 Tips on Getting Started
1) Don't try IF during the first few weeks of a low-carb / ketogenic diet OR if you follow SAD (Standard American Diet). This is very important, as your body has to first get keto-adapted prior to trying IF. You will first need to get used to low-carb eating so that your body can be fully utilising ketones for energy instead of glucose. If you try IF straight away, you won't succeed, as you will initially be glucose-dependent and too hungry to follow it. There is a lot of misinformation on the Internet about IF. Intermittent fasting should be natural and you should not struggle and feel hungry. It's a gradual process and will take time before it can be used effectively. You can learn more about the basics and how to start following a ketogenic diet here: Guide to Keto & Paleo
2) Don't plan IF - listen to your body. IF works best when it's done naturally. It it time for lunch and you don't feel hungry? Skip it and keep the food for dinner. Is it too late to eat? Skip dinner and have a large breakfast instead. I mostly do IF from Monday to Friday by skipping breakfast and sometimes even lunch. In most cases, I would just have my first meal at 1-3 pm and I try to eat at least 3-4 hours before bed to have enough time for my body to digest and avoid sleep disruptions. I don't usually do IF on weekends because I may be going out or simply enjoy having breakfast with others purely from its social point of view :-)
3) Don't force yourself into IF, start slow. As mentioned above, IF should be natural and you should not restrict and deprive yourself. Once you become fat-adapted, you will feel less hungry. Start by avoiding snacking between meals. Then, try skipping "regular" meals but only if you don't feel hungry.
4) Keep yourself busy. I find it easier and more natural to skip meals when I have a busy schedule and don't spend my time near the kitchen. Even if you don't feel hungry, you may be tempted to have a treat or a snack if you are surrounded by food. Based on my experience, I can easily be without food all day when I'm out shopping or meeting people. I may have a coffee, tea or sparkling water but that's about it.
5) Don't expect that IF will fix everything. Although IF can potentially help you lose weight and live a longer life, it's just one of the several factors that will help you meet your targets. Stress levels, sufficient sleep, macronutrients & micronutrients and exercise are just some of the most important factors to consider. Don't use IF as a "quick fix" when you eat more carbs than you planned for, at least not too often. You should do it naturally and should never feel deprived by doing IF.
6) "Bulletproof / butter coffee" will break your fasting period. Ingesting of butter and coconut oil / MCT oil won't maintain your fasted state. Anything with a caloric value will have the same effect and that's why it's called "fasting". What you can do is have a regular BPC or my Ultimate Keto Coffee for breakfast, skip lunch and only have dinner :-)
7) Be warned that IF is not for everybody. According to Dr John Briffa, the author of Escape the Diet Trap, people suffering from anorexia nervosa, bulimia nervosa and Type 1 diabetes should avoid it completely.
Type 2 diabetics should only do it under medical supervision (so they should when following a low-carb diet), because they may need an adjustment to their medication. Others who should avoid IF are those who are generally "stressed" or suffer from chronic fatigue and adrenal disorders, those with lack of sleep or those who overexercise.
Also, studies suggest that pregnant and breastfeeding women should avoid IF. Mark Sisson has a great post in which he explains why IF may not be an effective weight loss tool for pre-menopausal women or even women in general.
No diet plan lots all and you'll have to try how IF works for you. If you experience side effects like sleeplessness, anxiety, irregular periods, or hormone imbalance, you should avoid IF.
Intermittent Fasting: What to Eat
I've been working on easy-to-follow sample meal plans for specific types of IF (skipping lunch, breakfast or dinner, "one meal a day" IF plan and even more). For now, you can check out the recipes on my blog, especially recipes in these categories: Main Dishes and Breakfast - Stay tuned!
Now I'd like to hear from you. What is your experience with IF? Has it helped you lose weight / improve health / feel better?