Intermittent fasting and ketogenic diets have never been so popular for weight loss and improved insulin sensitivity. But should they be combined?
While both eating methods have a growing body of research into the health benefits, is it safe and effective to fast while going keto?
Here we discuss the two diets and the potential benefits and side effects of combining fasting and keto to help determine whether it is a good idea for you.
What is Intermittent Fasting?
Intermittent fasting is an eating method that’s based on limiting your eating window to a specific time. For example on the 16:8 fast, you may consume zero calories for 16 hours during your fast and eat until satiety in the 8-hour feeding window.
While the majority of intermittent fasting protocols don’t call for a restriction of calories or eliminate particular foods, some plans like the 5:2 do focus on your food intake on the fasting days.
The benefits of intermittent fasting have been largely focused on weight loss. However, fasting has also been found to be effective for improving insulin sensitivity, type 2 diabetes management, enhanced cognitive function, chronic disease prevention, and even longevity.
What is Keto?
The ketogenic diet is a diet that focuses on drastically reducing your carbohydrate intake and increasing your fat consumption. While on the diet you maintain moderate protein intake.
Carbohydrates are typically reduced to less than 50 grams of net carbs per day and ideally, under 20 grams. This reduction in carbs puts your body into a metabolic state known as ketosis. This forces it to adapt and use the fat from your diet and body as its main energy source rather than relying on sugar.
As your insulin levels drop very low, your body’s ability to burn fat increases. As a result, it becomes much easier to lose the fat that’s been stored.
Beyond weight loss, the ketogenic diet has been found to be effective at managing epilepsy and type 2 diabetes as well as producing benefits such as increased energy levels, improved health markers, such as cholesterol and blood pressure, and enhanced mental performance.
What Happens When You Combine Fasting and Keto?
Intermittent fasting has the potential to support your ketogenic diet and increase your body’s ability to switch to a state of ketosis.
In a fasted state, your body naturally has to become fat-adapted to maintain its energy balance which is the basis of the keto diet. When you fast, your insulin levels decrease and so do your glycogen stores which help to support the process of using fat as fuel.
However, it only does this during your fast and when you resume your normal eating, your body will simply choose the most convenient way to fuel up. If that means you’re consuming a moderate to high carbohydrate intake, it will be glycogen not fat.
Intermittent fasting can also help to support you to reach ketosis more quickly if you’re already on the keto diet. This is because fasting helps to stimulate your metabolism by inducing thermogenesis in the body. As a result, your body’s ability to burn fat faster enhances and you may see the progress of your dietary modifications quicker.
What are the Advantages of Doing Both?
There are many potential advantages of adopting intermittent fasting while on a keto diet. These include:
- Greater fat loss
As intermittent fasting increases your metabolism through increased heat production, your body is likely to start utilising your body fat stores more quickly. Coupled with the keto diet, this can result in greater fat loss in a shorter period of time.
- Increased weight loss
Beyond fat-adaptation, intermittent fasting aims to decrease your caloric intake by reducing your eating window. On a ketogenic diet, you’re increasing your dietary fat intake and reducing your empty-calorie carbohydrates. There is only so much dietary fat and protein you can eat before you become food. However, you can consume a large number of carbohydrates without feeling completely satisfied. Combining both dietary protocols can help to monitor your portion sizes and overcome your weight loss plateaus.
- Muscle preservation
Studies have found Intermittent fasting may help to preserve muscle mass while you are experiencing weight loss. This can be particularly helpful for keto dieters who have adopted the diet to transform their body shape or enhance their athlete performance.
- Blood sugar level balance
Ketogenic diets have been found to be beneficial in improving blood sugar levels and stability. Intermittent also is known to have a positive effect on insulin sensitivity, however, this can shift dramatically once in the feeding window depending on the type of food you consume. By combining the two and adhering to a low carbohydrate diet inside the eating window, you’re likely to achieve greater long-term blood sugar balance.
- Improved brain health and focus
Both the ketogenic diet and intermittent fasting have found to provide positive effects on mental health and performance. While fasting and on keto, the brain is fuelled by ketones as well as a small amount of glucose that’s synthesised by the liver.This provides a consistent flow of energy for the brain and helps to avoid the large plummets and highs of blood sugar levels. By fasting while on a keto diet, you may see greater improvements in your concentration and mental clarity as well as overcome any brain fog.
- Increased satisfaction
One of the main reasons people fail on any diet is because of the overwhelming feeling of deprivation and hunger. People become frustrated as results are slow to see even though they’ve drastically reduced their portion sizes or cut out all sugar.The benefit of combining fasting and keto is that weight loss can be achieved relatively quickly and without feeling overly deprived. This is because keto diets are high in dietary fat which is much more satisfying than sugar and refined flour foods. You feel full for longer and less likely to snack which means navigating the fasting windows can be much easier.
What are the Disadvantages Doing Both?
- It doesn’t guarantee good health
A big misconception of the ketogenic diet is that you can consume a daily diet of mainly eggs, bacon and cheese and be in good health. Introducing intermittent fasting to your regime also doesn’t justify eating anything that fits within the high fat, low carb model. A healthy keto diet consists of whole foods and mostly unsaturated healthy fats of sources such as olive oils, avocado, nuts and seeds.
- It takes organisation and discipline
To get into ketosis takes organisation and discipline as you have to adhere to an extremely low carbohydrate intake. To successfully implement an intermittent fasting regime, you need to commit to a scheduled time of eating and fasting that suits your lifestyle and fits the protocol.For some, the extra constraints of carbohydrate restriction or time limitations can prove too challenging initially. However, with the right organisation and knowledge, you can implement both successfully.
- It may not be right for you
While both diets have a growing body of research into the benefits, the individual models don’t suit everybody, nor will they when combined. For example, some people experience greater weight loss while on a high carbohydrate, low-fat diet. It’s important to understand your health priorities and find a diet or combination of protocols that suit you.
Tips for Fasting and Keto Success
Combining the ketogenic diet and intermittent fasting can be effective for some people. If you’re considering trying both protocols together, here are our top tips for success.
- Start one protocol first
A big reason people can’t sustain a dietary protocol long-term is that they’re too restricted or the changes they’ve made are too big. If you’re new to keto and intermittent fasting, start one method first. Get used to intermittent fasting and find a method that suits your needs and lifestyle before you introduce a keto diet. Once fasting becomes a natural habit, make the next shift of reducing your carbohydrate intake and increasing your healthy fats.
- Keep hydrated
Unless well hydrated, both intermittent fasting and the keto diet can result in unpleasant side effects. Due to your restricted intake of food while fasting, some people can become dehydrated. And the increase in dietary fat and reduction in fibre as part of the keto diet often sees people become constipated, especially initially. Drinking water can help overcome both side effects.
- Reconsider “bulletproof” coffee
Bulletproof coffee is a popular way for keto dieters to start their day. However, adding butter, coconut oil or MCT oil into your coffee each morning does mean you’re consuming calories. Unless your eating window is scheduled for the start of the day, you’re essentially going to break your fast by drinking your fat-packed coffee. In this case, we recommend you stick with plain black coffee.
- Keep busy
Keeping busy is a great way to help you stick to any dietary regime, especially in the beginning. If you’re a keto dieter, but new to fasting, make sure you keep occupied during your fasting window so you don’t spend your time thinking about food and exacerbating your hunger pangs.
- Listen to your body
For those new to the keto diet, you may be surprised about how satisfied you feel after eating a high fat, low carb meal. You’re likely to not need to snack as frequently, or snack at all. Likewise, when you add an intermittent fasting schedule to your regime, you may not have a burning desire to feed during the eating window. Listen to your body and start to eat more intuitively so you don’t overeat and instead you’re providing your body with what it needs.
- Find out if it’s right for you
If you’re overweight with no pre-existing health conditions or type 2 diabetic, you may find intermittent fasting combined with the keto diet is a great option to help you manage and overcome your health issues. However, there are circumstances where this combination is not suitable. If you’re a child, teenager, pregnant or breastfeeding, this is not the diet for you. If you have a sleep disorder or suffer from eating disorders like anorexia or bulimia, this program shouldn’t be tried. If you have a health condition such as type 1 diabetes, you should consult your health practitioner before implementing either one of these diets.
Combining intermittent fasting with the keto diet may help you reach ketosis faster and experience greater results. This combination may help you achieve weight loss and improve your blood sugar balance.
While it may work wonders for some individuals and suit their lifestyle well, for others the combination isn’t as effective or should be avoided. If it has been deemed safe to do so, give it a try and track your progress to see what works for you.
Explore in more detail
- A Beginner’s Guide To Intermittent Fasting
- A Guide To The 16:8 Fast
- A Guide To The 20:4 Fast
- A Guide To The 5:2 Fast
- Intermittent Fasting And Exercise
- Intermittent Fasting And Hormone Balance
- Intermittent Fasting And Keto
- Intermittent Fasting And Type 2 Diabetes
- Intermittent Fasting And Weight Loss
- Intermittent Fasting: Tips To Starting Your First Fast
- Side Effects Of Intermittent Fasting
- Tips For Intermittent Fasting Success
- Top FAQs Of Intermittent Fasting