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.
Key Fasting Concepts
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.
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.
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.
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.
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.
Benefits of Intermittent Fasting
Fasting for health can sound counterintuitive. But, there are some important reasons to do it.
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).
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.
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).
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.
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.
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.
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 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.
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.
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.
Want to Improve Your Health?
Better health starts in the kitchen, with the food that you eat and the meals you prepare. Getting the best outcomes involves making good choices about the food and the ingredients that you use.
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