Fasting is all the rage right now in the health and fitness world, and there are some great reasons why. If you’re new to fasting and also following (or wanting to follow) a ketogenic diet, read this guide to fasting on keto for beginners.
Basics of Fasting on Keto
Unlike keto, fasting is not a diet; it’s a method. It doesn’t determine what you eat but rather when you eat. Before incorporating fasting into your routine, knowing the basics can be really helpful, including the different options when it comes to fasting.
Types of Fasting
When people talk about fasting on the ketogenic diet, they’re usually referring to intermittent fasting, which is when you only eat within a certain timeframe. There are different versions of intermittent fasting that one might engage in:
Eating within a daily window: This is one of the most common methods. For example, you might only eat between 11am and 7pm each day, giving your body 16 hours to fast and eight hours of calorie intake. Some will shrink that “feeding” window to six, four, or even as little as just one hour a day.
Fat fast plus intermittent fasting: Fat fasting, a period of eating all fats for meals and snacks (eating fat bombs is an example), is popular for helping break weight loss plateaus. Fat fasting combined with intermittent fasting would mean still eating all fat but only during a certain window of time.
Skipping meals: This is a good method for easing into fasting and slowly getting used to not eating for every meal. For example, you could skip breakfast during the weekdays.
Alternating fasting days with non-fasting days: An example would be eating nothing for a few days a week and eating normally the other days. This is less recommended than the other methods and may be too extreme for most people, at least in the beginning. One option that’s more doable is the 5-2 method where you eat normally for five days followed by two days of eating ¼ of your regular calories.
Ketogenic Diet and Fasting
Thankfully, eating keto can actually make fasting easier because the high fat content in ketogenic foods makes you feel full and satisfied with less food!
Remember: it’s important to eat to satiety during your eating window. You still want to get enough calories and macronutrients in your day during this time. Stick to only water, black coffee, or unsweetened tea and no food during your fasting time.
Now, you might be wondering what’s so special about fasting.
Benefits of Fasting on Keto
There are a number of advantages to fasting on keto:
To get into ketosis faster: Fasting can help you deplete glycogen stores more quickly and eliminate carb intake so you can enter ketosis more quickly. You can even plan to fast a few days before starting a ketogenic diet. Taking exogenous ketones can also help with this. Combine them and it’s like magic!
To drop weight faster: Just like with ketosis, intermittent fasting is a popular option for people wanting to lose weight quickly. Not only does the body begin breaking down fat for energy, you’re also more likely to eat less overall from intermittent fasting.
To get the benefits of calorie restriction: Intermittent fasting is often compared to calorie restriction, but they aren’t the same. However, intermittent fasting provides the same benefits and much easier to follow long-term. Plus, intermittent fasting still helps ensure you get proper nutrition and calorie intake each day while still helping promoting weight loss.
To increase mental clarity: Ketosis and fasting are both beneficial for the brain when it’s running on ketones. Most people can expect a boost in mental clarity and less brain fog throughout the day.
To make things more simple: Following a ketogenic diet might seem tricky while traveling or eating out, but not if you plan to fast. It takes away the worry of what to eat and lets you know that you’ll be okay abstaining until you can make yourself a good keto meal.
It can also reduce the need to cook, meal prep, or grocery shop quite as often and open up more time in the day. And we can all use more of that, right?
Improve Your Health
Even if you aren’t interested in rapid weight loss or the other reasons above, fasting is worth it just for the health benefits. Regular fasting has been tied to:
- Support of our muscles through enhanced growth and maintenance, as well as promote anti-aging
- Better metabolism: Not only is fasting good for weight loss, it may also benefit your metabolic health
- Longer life span : fasting can change gene expression that might improve longevity
- Reduced inflammation, even better than a ketogenic diet over the long-term
- Improved insulin sensitivity since you’re giving your body a break from constant insulin spikes from food, which can lead to metabolic problems like type 2 diabetes and more
- Better repair of the body: Fasting has been shown to enhance the body’s ability to heal itself (also known as autophagy)
Combine each of these benefits with the power of the keto diet and you’ll be a healthy, fat-burning machine!
Combining Fasting with the Keto Diet
The main difference between fasting on any diet and fasting while on keto isn’t hard to figure out: when you break the fast, you’ll only eat ketogenic diet foods. This is great because you’ll be able to maintain ketosis (which mimics fasting) and its benefits even when you do eat food.
Here are a few additional points to keep in mind when combining starting fasting with a ketogenic diet:
- Make sure you’re still staying within your macros for keto and eating enough calories for the day during your eating periods.
- Note that simply fasting itself isn’t enough. It’s also important to combine it with optimal nutrition, enough sleep, and work on reducing stress. But that’s why it’s so powerful when combined with a ketogenic diet and wholesome high-fat foods.
- If you find fasting difficult, you make try becoming keto-adapted first before jumping right into fasting. When your body is still dependent on glucose, it’s a safe bet you’ll get hungry much faster, which will make it harder to stick with your fasting schedule. But once you’re in ketosis using ketones for energy, fasting will feel more natural.
- Start slow, if you need to. Some people thrive on jumping right into a change, but most of us need to go more gradually. Start by cutting out any regular snacks, then move on to a full meal, and so on.
Exercise During Fasting
It’s a myth that this type of fasting will make your muscles waste away. Same goes for the ketogenic diet — which is why it’s specifically moderate (not high) protein to preserve muscle mass.
That being said, if you’re someone who is very active, it can be helpful to supplement with 5-10 grams of BCAAs during fasting periods to prevent lean tissue loss. You might also consider a targeted keto diet in between fasting periods and make sure your post-workout meal is the biggest one to help recover.
Take Home Message
Intermittent fasting and the ketogenic diet can be awesome complements to one another, and each provide many benefits for health and weight loss. If you’re healthy and able, try it out for yourself and see what changes you notice!
Sources: Longo, Valter D., and Mark P. Mattson. “Fasting: Molecular Mechanisms and Clinical Applications.” Cell metabolism 19.2 (2014): 181–192. PMC. Web. 26 July 2017.  Brandhorst, Sebastian et al. “A Periodic Diet That Mimics Fasting Promotes Multi-System Regeneration, Enhanced Cognitive Performance and Healthspan.” Cell metabolism 22.1 (2015): 86–99. PMC. Web. 26 July 2017.
Dr. Anthony Gustin is a board-certified sports chiropractor, functional medicine practitioner, entrepreneur, podcast host, and founder of Perfect Keto.
After growing his sports rehab and functional medicine clinics to six locations in San Francisco, he shifted his mission to help as many people as possible achieve optimal health and well-being.