Intermittent fasting (IF) is going for long periods of time through out the day where you are not eating or drinking anything that has any caloric impact. The way I first thought about it was the time when I am sleeping. After you wake up from a long night of sleep, you eat your morning meal that we call breakfast. Breakfast is a term that was derived from “break the fast” meaning that you ended a time of fasting. If you think about it, that is exactly what you are doing when you are sleeping, you are fasting. Unless you are one of those people that sleep walk and are able to make a sandwich in your sleep. So intermittent fasting is just extending your normal fasting period.
Instead of eating breakfast, lunch and dinner which is spread throughout the entire day, you will be eating during a shorter window of time. You may eat 2 meals a day or even 1 meal a day and you will fast the rest of the time. While that sounds horrible to skip a meal when you are first starting the keto diet or intermittent fasting, it becomes fairly easy after some time.
I personally eat 2 meals a day, and try to eat them within 6 hours of each other. So if I eat breakfast at 6:00 am, I want to eat my lunch/supper before 12:00 pm. I will not eat anything else for the rest of the day until 6:00 am the next morning. That means that I will be fasting for 18 hours a day.
It does not matter which meals you eat. You can choose to eat lunch and dinner or breakfast and lunch. The key is to eat all of your meals within a fairly small window of time. You will want to have all of your meals (anything that has an insulin response) so that you will have the majority of your day when you do not have anything affecting your insulin. Since this website is written to help people with the ketogenic diet, I will focus my attention to intermittent fasting as part of the ketogenic diet. There may be other factors to consider if you are on a different diet.
Some people have taken intermittent fasting to another level and only eat one meal a day. For those people, they are essentially fasting for about 23 hours a day. While there are some good benefits of fasting for longer periods of time, it just doesn’t work well for me. Maybe someday I will graduate to 1 meal a day, but for the time being I am happy with 2.
How long to fast?
The amount of time that you fast is up to you. There are a lot of differing opinions as to how long you should fast to get the most benefit. I have read some reports that recommend 16 hours and others that say you should fast at least 18 hours. While I can not say for any certainty how long you should fast for the most benefits, I would say that if you are able to fast for 16 hours or more, you should be getting some benefit.
Some reports say that the longer you fast the more benefits you can get from it. There are studies that report that fasting for more than 24 hours can be a great tool for improving your health. These longer fasting periods are not recommended to be done regularly (meaning several times in a week).
Fasting considerations
Three things to consider if you are contemplating adding intermittent fasting to your routine. The first is what meal(s) you want to skip. Consider when would work best to skip a meal or meals. Everyone lives on a different schedule and has different jobs. You will need to decide which meal or meals you want to skip. The second is how long you intend to fast. If you want to fast for 20 hours, you would know that you would need to eat all of your meals within 4 hours. Where as if you want to fast for 16 hours, you would want to eat your meals within 8 hours. These first two considerations need to work together, so look at your work/life schedule to see what works the best for you. The third is can you consistently keep that routine of when to eat and when you are fasting. If you can’t be consistent, you will not be getting the most benefit from it.
Can I fast for more than 23 hours?
Certainly you can fast for more than 1 day. Many people will incorporate 24-72 hour fasts into their lives. These longer fasts can have great benefits, but should not be consistently used. What I mean is that you can do these longer fasts a couple times a year, not once or twice a week. Remember, you still need vitamins, minerals and energy, so too much fasting can be detrimental. These longer fasts can be a great way to “cleanse” if you are wanting to.
How does intermittent fasting work?
By implementing intermittent fasting we are achieving two main things. The first is we are extending our fasting period. The second is we are reducing our caloric needs, meaning that we can eat less. Both of these will help you lose weight or to be able to maintain your weight easier.
So, if we are reducing our caloric needs, we are going to be able to eating less. I think everyone can agree that if we are eating less that that will assist us in losing weight. By eating less, our bodies will be forced to look for another fuel source. The fuel that our bodies are going to be using will be our stored fats. If you consumed any food that was high in sugars or carbs, then you would need to use those up first before you will start burning your fat.
Assuming that you are eating a low sugar and carb diet (keto) then when you are fasting your body will be burning your own fats. Since you are fasting, you will utilize any fats you recently consumed, then body stored fats. The longer we fast the more of our fats will be used up. Those fats will be broken down into ketones that will allow us to have energy and for our bodily functions to keep working. If you are eating too many fats (or calories), it will take longer to use up the food calories, and you may never actually start burning stored fats before you end your fast.
Can I do low sugar, low carb, and low fat?
You may be thinking that if you ate a low sugar, low carb and low fat diet that your fasting would be more effective. In essence, you are correct, but the cost of doing that is your health. You still need to eat fats in order to get the nutrients and energy needed for your body to function the way it is supposed to. So don’t skimp on the fats (or eat too many), or other foods that have the nutrients that you need daily. Intermittent fasting is an amazing tool to be used with the ketogenic diet, but if your diet is not balanced neither will work as well.
If you reduce your fat intake too much to speed up your weight loss journey, do so with caution. If you are fasting and your body needs energy and there are none easily available, your body may break down muscle. Yes, your body will break down muscle if it is needed. If you are trying to loose weight the healthy way, then take things slowly, it will happen. Eat moderately, learn how many calories you need (for your body type, activity level, etc), and adjust slowly to find the right formula for you. Don’t take shortcuts that can adversely affect your health or goals. You didn’t add all your the weight in a month, you won’t loose it all in a month.
What are the benefits of intermittent fasting?
There are a whole slew of benefits of intermittent fasting and I hope that I can cover most of them.
- IF will help you get into ketosis or fat burning faster. Our bodies will deplete glucose stores at a faster rate, thus helping you to get into ketosis faster.
- Burn more fat. Using intermittent fasting with the keto diet, you can significantly increase your fat burning. One study says you can burn almost twice as much fat if you eat a ketogenic diet and fast for at least 16 hours a day.
- More benefits from your workout. If you work out in a fasting state, you can improve muscle performance, increase muscle gains and will absorb nutrients from post-workout meals. Here is one study that shows that fasting does not have a negative impact on performance. Please keep in mind that there is a limit to this benefit, you still need nutrition, and a usable form of energy. If you don’t have enough stored energy (either carbs in the cells, or stored fat), you will start to brake down muscle. Autophagy is good for your muscles to repair and get bigger, but you don’t want to lose those gains because your body is needing energy.
- Muscle repair. I talk more about autophagy below, but it is necessary for repairing muscles. When our muscle cells get damaged, they need to be repaired or replaced. Autophagy is our bodies way of recycling cells and replacing the old damaged cell with a new one. This is huge when trying to build muscle. By replacing damaged cells, the surrounding cells are able to work more efficiently and in turn give you more performance.
- Increased Human Growth Hormone (HGH) or somatotropin. Studies vary about how much your HGH will increase when you fast. The numbers can range from 1,500%-2,500% increase in men. The amount that it increases is affected by how long you fast. One study showed that in a 24 hour fast, men’s HGH increased 2,000% and women’s HGH increased 1,300%. The HGH is a small protein that is made by the pituitary gland and is secreted into the blood stream. Its production is controlled by a complex set of hormones produced in the hypothalamus and in the intestinal tract and pancreas. Some factors that affect its production are exercise, trauma and sleep. HGH can help produce lean muscle mass, burn fat, stimulates growth, cell production and cell regeneration. HGH will also drive muscle protein synthesis, which speeds up repair and recovery of muscles. There is also evidence that HGH will improve your skin and increase your stem cell production (used for repairing injuries, damaged cells, joints and help with chronic pain). It has also been linked to increasing the production of Brain-derived neurotrophic factor (BDNF), which improves your ability to learn, creates stronger neural pathways, allowing your brain to function much better. (Synthetic HGH does have some negative health affects, so get it naturally with fasting). A good number of studies show that your HGH will increase significantly starting at hour 16 (or so) of your fast.
- Cancer. There have been studies that show that fasting can decrease the size of some tumors and can increase the effectiveness of chemotherapeutic drugs. While there are many more studies currently going on, the ones that have been completed suggest that by adding a fast, it can reduce the risk of cancer or even help the body and pharmaceuticals fight the cancer.
- Mental focus. Fats are considered a very energy efficient fuel. Our brains use a lot of fuel. While our brain does need some glucose to function (which our liver produces from fats) other functions work well on ketones. Because fats are so efficient, your brain can also work more efficiently.
- Reduces inflammation. Intermittent fasting has been shown to decrease oxidative stress and body inflammation markers. Sugar is also inflammatory, so by removing it from our diet, we are reducing inflammation.
- The magic anti-aging tool. While fasting our bodies will use a process called autophagy to actually “eat” old or damaged cells and replace them with new cells. Autophagy basically recycles the parts of the cell that are able to be reused, and will get rid of anything unhealthy in the old cell. This only takes affect when you are on a reduced protein, low carb diet and you are fasting. Autophagy has been linked to stopping the aging process, reversing disease and even preventing cancer. Autophagy can used by the majority of cells or systems in your body to replace cells that are not working properly.
Should I use intermittent fasting?
The only people that can answer that are you and your doctor. Assuming that your doctor does not have any reason for you to not intermittent fast, the decision is solely yours. It can be a good tool to help you lose weight. But, if you are not able to stick to your fasting window or are miserable when you are fasting, then don’t.
Intermittent fasting obviously is not necessary for the ketogenic diet or needed to lose weight. It can definitely speed up weight loss, but just by following the keto diet, you will still lose weight. My thoughts are that if you don’t have the self discipline to keep to the schedule you create, or are having trouble being strict with keto (cheating), then you will probably not get much in the way of benefits from intermittent fasting. On the other hand, if you are able to stick with your schedule and are true to your diet, then you will reap the benefits.
Combining intermittent fasting and keto
I combined IF with keto and lost weight fairly quickly, but I was strict with my diet and eating windows. Even now that I am to a weight that I am happy with, I am still intermittent fasting. For me it has just become routine. Some days I only eat 1 meal a day because I am just not hungry when it is time for my first meal. While I plan to eat 2 meals a day, I feel that if I am not hungry then I wont eat just because I am scheduled to. But, I am done eating when my window is supposed to end.
If you decide to give intermittent fasting a try, just remember that you will most likely be hungry until your body adjusts. It may take almost no time at all to adjust, or it may take you a couple of weeks. One thing that I discovered was that if I was getting hungry before my next eating window, I was not consuming enough fats in my previous meal. Once I adjusted my fat intake, it was much easier to implement my fasting routine. If you need to have a snack while you are getting started IF, it’s ok during your adjustment period. The only deadlines are the ones you implement, but remember that life happens.
I would recommend starting out with daily intermittent fasting. If you are motivated to do so, try a couple of longer term fasts. Dr. Dom D’Agostino (ketogenic researcher) suggests doing a 3 day fast, 3 times a year. I have not done a fast for more than 24 hours, so I don’t have any pointers for you on this one. Just read my words of caution below and you should be fine.
If you read all of the reasons to implement intermittent fasting above, hopefully you are starting to see why so many people are adding it to the keto diet. There are a lot of great benefits to adding a fasting routine to your diet. While there is no fountain of youth, this is about as close as we can get to keep ourselves young and healthy.
Words of caution
If you are going to start intermittent or longer term fasting, there are a few things that you should know. If you aren’t sure if it is safe, you start feeling bad while fasting, or want more information, consult your doctor or a nutritionist that practices fasting.
- Stay hydrated. Drink plenty of fluids (possibly with electrolytes, pink Himalayan salt or sea salt work well). When
you are on a keto diet, your body does not retain fluids very well. It is very important that you keep hydrated. Especially if you are working out regularly.
- Before you start an extended fast (more than 48 hours), eat nutritious foods beforehand. If you are going to fast, you want to make sure that your body has proper nutrition to sustain your fast.
- Refeeding syndrome. Refeeding syndrome is when our body can potentially shift the balance of fluids and electrolytes in a fatal manner once you break your fast if you were not properly nourished before your fast. This is typically only an issue if you are going to be fasting for more than 5 days. Because our bodies do not retain water well when you are on a ketogenic diet, there is the potential to lose too much sodium and potassium (essential electrolytes). If you are doing daily intermittent fasting you should not need to worry about refeeding syndrome.
- Extended fasts have the potential for muscle loss. If you are not bringing in any protein for an extended period of time, your body will start to break down your muscles. This is especially true if you are working out a lot or have a very active job.
- If you are not on the keto diet and you start a fast, your body can potentially switch from using glucose to fats and back to glucose when you end your fast. I am not aware of any serious health risks here, but you may experience the keto flu when transitioning back and forth. Depending on how long your fast is, you may not even get into ketosis (depends on how much glucose you have stored). You may also experience more intense hunger pains, blood sugar fluctuations, mood swings and low energy.
