Fasting on Keto – How to Do It and Why You Should

Fasting on Keto

On its own, a keto diet focuses on the food that you eat, particularly your macronutrient intake. You end up with a diet that is high in fat, moderate in protein and low in carbs.

As a general rule, when you eat doesn’t matter. You might have many small meals per day or three main meals.

But, many people follow a different angle – the idea of fasting on keto.

This is based on intermittent fasting, which places a greater emphasis on when you eat. Fasting mightn’t sound appealing at first.

But, there are some considerable advantages. Plus, keto and fasting complement one another.

What is Intermittent Fasting?

Intermittent fasting isn’t a diet because there is no focus on what you eat. Instead, the emphasis is when you eat. This means that intermittent fasting can be combined with most eating approaches, including keto.

The idea is simply that you’re fasting on a regular basis. This means that there are some periods where you’re eating and others where you are abstaining from food.

There are various types of intermittent fasting, which use different fasting periods and approaches.

Fasting is a critical concept. Our bodies behave differently when we’re not eating or digesting, which includes a process called autophagy (we’ll come back to that). Because of this, fasting can have many health benefits. It can improve weight loss too.

 Intermittent fasting involves periods of eating and fasting

Key Fasting Concepts

Fasting on keto

To begin with, let’s define some important terms that relate to fasting.

The Feeding Period or Feeding Window

This is the time where you can eat. The duration will depend on your fasting approach and your overall goals.

It doesn’t matter how many meals you have during this period. The important aspects are your macronutrient and calorie intakes. For example, if you plan to consume 1,800 calories in a day, you need do to that in the window.

You might choose to have two large meals (many people do). Or, you might have smaller meals and some snacks. The choice is yours.

It’s important to hit your macronutrient and calorie goals. Some people find that their appetite decreases over time as their body adjusts. You might also be tempted to eat less, to try and boost weight loss.

But, undereating isn’t effective in the long run. This makes it much harder to stick to intermittent fasting and may mean that you get hungry sooner. Undereating could also mean that you don’t get enough nutrients, which is never a good idea.

The Fasting Period

The fasting period is where you’re not eating. In most cases, you won’t be consuming any food or any significant sources of calories. All you’re allowed is water, unsweetened tea and black coffee, that’s it.

Some forms of fasting are slightly different. For example, if you are fasting every second day, you might just eat 500 calories on those fasting days. This is particularly important for people who need to be active while they are fasting.

Fasting Schedule

This refers to your plan about when you eat and when you don’t. For example, someone following a 16:8 approach might eat between 12 pm and 8 pm and then fast until 12 pm the next day.

Your fasting schedule would normally be fairly consistent. But, some people do adjust it periodically based on social commitments and other factors.

Important concepts focus on when you fast and when you eat

Different Fasting Approaches

Intermittent fasting is a large topic, with many individual styles and techniques. But, most can be broken into these general areas:

  • Extended fasting. This involves fasting for 24 to 48 hours, often without any food at all.
  • Eating windows. With this approach, you eat for specific hours of each day and fast for the rest. 16:8 is a particularly common approach, where all your food is consumed within an 8-hour window. Other variations include 17:7, 19:5 or even 21:3.
  • Alternate day fasting. Here, you’re fasting every other day. Some people choose to eat nothing at all on fasting days. Other people still eat but they keep their calories very low.
  • Skipping meals. Some people also take a less strict approach to fasting. This can involve simply missing meals when they don’t feel hungry or don’t want to eat. The idea still offers many benefits, but isn’t as consistent as the other options.

For most people, the eating window style is the best place to start. This is the easiest approach and it fits well with normal eating patterns.

  • For example, a 19:5 approach might involve having lunch at noon and dinner at 5 pm. That basically means you’re skipping breakfast, then not having anything after dinner.
  • Or, you might design your schedule so that lunch is the meal you miss. Intermittent fasting is flexible like that. You get to choose which pattern works for you and the precise timing that you follow.

Many people begin with a relatively large eating window, such as a 14:10 approach, which gives a 10-hour eating window. It becomes easy to simply shrink that eating window over time. 

The site Mindful Keto offers a guide on how to start intermittent fasting, without the process being overwhelming. Once you’ve been fasting for a while, you might try a longer fast, like 24 hours.

Common approaches include alternate day fasting, extended fasting, eating windows and skipping meals

What’s The Best Approach?

Recommendations vary about the ideal way to fast.

  • Some people suggest the eating window style (like 16:8), as it fits well with regular daily patterns. The site Perfect Keto offers important information about how the 16:8 version fits into a keto diet.
  • Others recommend alternative day fasting, as it can be less stressful on the body.

There are also alternative patterns, that specifically focus on the keto diet.

For example, the Tim Ferriss 3-Day Fast Protocol is promoted as a fasting method to help people get into ketosis quickly. The approach takes advantage of exogenous ketones and/or MCT oil, along with fasting approaches. You can find full details at the site Eat Move Hack.

You may find other recommended approaches too.

Realistically, the best option is the one that works for you. You might find that a 16:8 or an 18:6 diet is easy. Or, you might prefer to fast less frequently for longer periods of time. 

There is no single best way to fast

Benefits of Intermittent Fasting

Long term weight loss success

Fasting for health can sound counterintuitive. But, there are some important reasons to do it.

The Autophagy Mechanism

One key concept is autophagy. This is the process that the body uses for maintenance and repair. Autophagy is important for removing bad cells and helping to build new and healthier cells.

Autophagy is relevant in many areas, including maintaining muscle mass, decreasing aging symptoms and improving overall health. In fact, many of the advantages of intermittent fasting are directly related to autophagy.

The process naturally occurs during fasting and also when carb intake is low (1,2). Fasting while on a keto diet is one of the best ways to increase autophagy. In contrast, being in a fed state most of the time gives the body few chances for autophagy.

Weight Loss

Intermittent fasting promotes weight loss through multiple mechanisms:

  • The process naturally decreases your calorie intake, especially as keto meals tend to be satisfying.
  • The smaller eating window often means that you’re snacking less.
  • Raises levels of norepinephrine, a hormone linked to fat burning (3,4).
  • Increases levels of human growth hormone (HGH) (5).
  • Decreases insulin levels (6,7,8).
  • Fasting may also increase your metabolism (9,10,11).

Mental Clarity

Intermittent fasting has been linked to increased cognition and the ability to think clearly (12). It also raises levels of brain neurotropic growth factor. This compound helps to protect against neurological stress (13).

Fasting may also improve mitochondrial function (14). This action can potentially promote energy, which may improve mental clarity too.

Fitness and Muscle

Fasting also helps you to maintain your muscle mass while losing fat (15). This is a critical outcome, especially as low-calorie dieting often means you lose fat and muscle mass.

Health Benefits

Fasting may also have other implications for health (16).

Research even suggests that not having enough autophagy may contribute to disease development (17). In a similar manner, autophagy may be relevant for disease treatment (18,19) and for the immune system (20).

There are also various other effects, such as improved cellular repair (21), beneficial changes to gene expression (22,23) and protection for the brain (24,25).

Practical Advantages

For many people, fasting isn’t about the biological benefits at all. Instead, it’s a much more practical way to follow a keto diet.

One reason is that you have less to worry about. If you’re doing a feeding window approach, you might only be eating two meals and one snack each day. That’s one whole meal that you don’t have to plan and prepare. You end up with more free time too.

This also gives you more flexibility with your meals. When you’re only having two meals, those meals can be larger and they can contain more calories. This may give you the chance to include more of the foods that you love.

Overeating on Keto

Many people struggle when they start a keto diet. It can be hard to know how much you’re consuming when you’re unfamiliar with listening to your body. Plus, keto foods are often calorie dense. The amount you eat can add up fast, especially if you don’t pay attention to snacking.

As a result, some people end up gaining weight when they start keto, rather than losing it. Others may find their weight plateaus.

Intermittent fasting is a nice ‘hack’ to get around the issue. Because you’re eating less often, it’s easier to keep your calories in check. After all, you can only eat so much food in one sitting.

Intermittent fasting offers various practical and biological benefits

Why Combine Intermittent Fasting and Keto?

Intermittent fasting and keto both are both powerful for health and weight loss. Combining them gives you the advantages of each.

But, that’s not all. There are also clear links between ketosis and intermittent fasting.

  • Fasting helps to decrease your glycogen storage quickly. This makes it easier to enter ketosis. Even just fasting a few days before beginning ketosis can make a large difference.
  • Both approaches have similar impacts, including health implications and relying on fat as fuel. This can mean you increase the strength of the benefits you see.
  • Fasting can help you follow a keto diet, as you have fewer meals and snacks to plan.

The food choice on a keto diet also makes intermittent fasting easier. The high fat content in keto foods helps you to stay satisfied for longer. This can often mean you struggle with hunger less. You may also find the food you eat more enjoyable than with a traditional low-fat diet.

Plus, intermittent fasting works best when people are also following a healthy diet. Keto works well for this reason and you’re heavily relying on whole foods and healthy fats.

Keto and intermittent fasting naturally complement one another

Challenges of Intermittent Fasting

Of course, fasting has its limitations too. These can be overcome, but they’re still worth considering.

It Doesn’t Work for Everyone

Intermittent fasting can be powerful – but, it isn't always the best choice.

If you find that fasting means you’re low in energy, miserable and irritable – then it probably isn’t for you.

Forcing yourself to fast anyway simply isn’t a good idea. The process would make you unhappy, which is horrible for long-term health and weight loss. Instead, you need a balance that works for you physically and emotionally.

In contrast, others find that fasting is liberating. For many, the approach provides more flexibility with food and time, without having a noticeable impact on energy. Even the associated hunger decreases over time.

Fasting is also unsuitable for some groups of people. This includes anyone who:

  • Is pregnant or nursing
  • Experiences difficulties sleeping
  • Is sensitive to hormonal changes
  • Has previously had an eating disorder (or is sensitive to disordered eating)
  • Is under significant stress

You should also talk to your doctor first, especially if you have a medical condition or are taking medication.

Makes You Hungry

The hunger tends to decrease over time. But, most people still experience periods where they are hungry. This can be frustrating and is sometimes impractical.

Can Decrease Energy

Some people find that their energy levels decrease when they miss a meal. For example, if your eating window was 12 pm to 8 pm, you might find that you struggle some mornings. This can be a problem for people who work at that time.

This effect doesn’t always happen. You can also adjust your eating window so that when you eat suits your lifestyle. But, if you find a strong connection between energy and when you eat, intermittent fasting may not be the right approach.

What About Refeeding Syndrome?

A related area is refeeding syndrome. This is a medical term. It relates to metabolic disturbances that occur after a person has been malnourished and is then fed (26). The concept mostly applies to hospital settings, but it can also occur with extended fasts.

To avoid this, you need to ensure you’re not malnourished. You should be certain that you’re consuming enough minerals. This includes focusing on nutrient-dense foods when you do eat and getting sufficient salt.

This issue is only relevant if you’re fasting for five consecutive days or more. Short fasts, particularly those less than 24 hours, won’t put you at risk. You also won’t experience problems with an eating window approach.

Intermittent fasting can be challenging, especially at first. But, many people find that it gets easier over time.

What About Metabolism Slowdown?

We’re often told that having many small meals per day is critical for weight loss and metabolism. So, dropping down to a small eating window sounds like a bad plan.

But, the small frequent meal idea is a myth. You don’t need to eat like that for weight loss. For that matter, short-term fasts can even speed up your metabolism (27,28,29) and they help you lose weight.

The main metabolic impact actually comes from weight loss. Your metabolism may decrease when you lose weight – especially if you lose a large amount (30,31,32). That effect occurs regardless of how you lose the weight

Plus, intermittent fasting can help you retain muscle. This can be beneficial for your metabolism and is a key advantage.

Despite the myths, intermittent fasting doesn’t slow down your metabolism

Intermittent Fasting for Women

Many women are able to follow intermittent fasting fine, but that’s not always the case. For some, intermittent fasting can have a significant negative impact, which includes hormonal imbalances.

This happens because female bodies are much more sensitive to starvation and will often respond strongly. Attempting to push through this response can sometimes lead to binge eating. Some women also find that they stop ovulating or that their health suffers in other ways.

Because of this, women should pay close attention to how they feel when fasting. Watch out for significant mood swings, fatigue or extremely strong hunger. These can all be indications of hormonal changes.

It may also be worth relying on a longer eating window (such as a 14:10 approach) or trying an alternative to intermittent fasting. Some women switch to alternative day fasting and find that this is more effective. Dr. Axe also talks about the idea of Crescendo Fasting, which many women find effective. 

A Variation on a Keto Fast

Some people take a different approach, where they have a Bulletproof coffee (or a keto coffee) instead of breakfast. This isn’t a true fast, as this type of coffee is relatively high in fat and calories. It doesn’t offer the same autophagy benefits either.

Even so, it can be an alternative for people who struggle with traditional intermittent fasting and for women. After all, a keto coffee can still be lower in calories than a full breakfast and is more satisfying than no food at all.

Some women can experience hormonal problems with intermittent fasting, so it’s important to be careful

Do You Need to Fast?

Absolutely not! You can lose weight and be healthy on a keto diet alone, without ever fasting. Many keto dieters don’t fast. Others do. The choice is yours.

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