November 22, 2021 6 min read

By Melissa Mitri, MS, RD

Keto and intermittent fasting are two of the most popular diets out there. 

If you’ve been following keto, you may be wondering if you should incorporate intermittent fasting into your routine. Since intermittent fasting has its own unique benefits, many people wonder if combining it with a keto diet plan can yield even bigger results.

When it comes to following a new diet plan, understanding the benefits and potential risks is essential to determine what’s best for you.

If you are thinking of combining keto and intermittent fasting, there are pros and cons to doing so.

What Is the Keto Diet?

The keto — or ketogenic — diet is a very low carb, moderate protein, and high-fat eating pattern. The calorie guidelines for a traditional keto diet are 70% from fat, 20% from protein and 10% from carbohydrate. 

The carbohydrate restriction is typically 20-50 grams per day, which is significantly lower than a traditional low-calorie diet.

Today, the keto diet is used for many other reasons, with the most popular being for weight loss or to help support healthy blood sugar levels.

The basic premise behind keto is that your body utilizes fat for fuel instead of carbs. This brings your body into a state known as ketosis. It can take anywhere from two to seven days to achieve true ketosis by consuming less than 50 grams of carbs per day. However, it may take longer than this for some, depending on several factors such as age, physical activity level and metabolism.

When in ketosis, the thought is that your body will then burn a larger amount of fat, which can result in weight loss and other metabolic benefits such as cellular repair, muscle growth and visceral fat loss. Visceral fat is the fat that accumulates around your organs, and is considered the most dangerous type of fat.

If you are following a keto diet, but are unsure if you have entered the state of ketosis, you can do a test. There are many at-home tests available to determine if you’re actually in ketosis, to confirm that the diet is working.

According to a 2015 study, the keto diet can be an effective weight-loss diet that is also satisfying. Many who follow keto report feeling full with the combination of a high-fat, low-carbohydrate diet. And when you are more satiated on a diet, it can help make it easier to stick to. Many people have reported following keto for months because they feel satisfied and more energetic on it.

What Is Intermittent Fasting?

Intermittent fasting, otherwise known as IF, is not a specific diet like keto, but rather a way of eating. 

Fasting has been common practice in many cultures for centuries, but is more recently gaining attention as a tool to improve health. The theory behind any method of fasting is that you are giving your body and your cells the time to regenerate and repair itself..

With intermittent fasting, there are no foods you have to avoid; instead, you are simply altering your eating schedule. 

However, adhering to a healthy, balanced diet will provide the biggest benefits from fasting. If you are eating mostly unhealthy, processed foods during your eating window, the benefits will be minimal or nonexistent.

There are several popular methods of intermittent fasting: the 5:2 diet, the alternate-day fasting and the 16/8 method:

5:2 Diet 

With this method, you are supposed to consume fewer than 500 calories for two days per week and eat normally the other five days.

Alternate-Day Fasting

With this method, you fast every other day and eat normally on the other days. On fasting days, you consume about 25% of your daily calorie needs.

16/8

With this method, you fast for 16 hours with an eating window of eight hours on a daily basis. Every day is the same with this method, which is considered one of the easiest to follow.

Reported benefits of intermittent fasting include:

  • weight loss.
  • improved brain activity and focus.
  • lower insulin levels.
  • reduced inflammation.
  • promoting heart health

Many of these benefits have been seen more in the short-term, over a few months. There is still more research needed on the long-term health implications of fasting. 

The fasting schedule you choose will depend on your individual goals, preferences and lifestyle. Many people start with the 16:8 method, but may adjust it over time depending on how they feel.

Since there are many potential health benefits of both keto and intermittent fasting, should you combine the two?

Pros of Keto + IF

Could get you into ketosis faster

Adding fasting to your keto plan can help your body get into ketosis more quickly than the keto diet alone. While in a fasted state, your body starts to shift its fuel source from carbohydrates to fats - which is exactly what happens on the keto diet. When fasting longer than 12 hours, your insulin levels also start to decrease, which is a good thing in terms of your metabolism. 

    Combining keto and intermittent fasting can be particularly useful if you struggle to get into true ketosis and stay there. It’s possible that adding fasting to the mix may give you a jumpstart and improve your metabolism more so than doing keto or intermittent fasting alone.

    May lead to more fat loss

    Combining keto and intermittent fasting may help your body burn more fat than either method alone. Intermittent fasting has been shown to be an effective way to burn fat by promoting thermogenesis, or heat production, in the body. A review of 28 different studies was done that showed that those who practiced intermittent fasting lost an average of 7.3 pounds more fat mass than those following a continuous very low-calorie diet. This can support the theory that adding on fasting to an already calorie-restricted keto diet can result in a greater weight loss.

    What is also interesting is that intermittent fasting may preserve muscle mass during weight loss and improve energy levels more than a continuous daily calorie restriction alone. This may be particularly enticing for keto followers looking to build muscle and simultaneously drop body fat. However, it’s important to note that regular strength training is still essential to maintain or increase muscle mass on any diet plan.

    May increase satiety

    Studies have also shown that intermittent fasting can improve satiety, especially when following a calorie-restricted diet such as keto. Feeling full and satisfied is an essential component of any diet plan in order for it to be sustainable. A diet that makes you feel deprived is likely going to backfire and cause weight regain in the long run. If you are struggling to stay satisfied on the keto diet, it’s possible that adding intermittent fasting may help curb your appetite and make it easier to follow. 

    Who Should Avoid Keto + IF?

    Even though there are a few surefire benefits of combining keto and intermittent fasting, it’s not for everyone. Here are a few situations when it may not be a good idea:

    Pregnant or breastfeeding

    If you are in this stage of life, it is not recommended to restrict your calories or avoid certain foods. The most important thing is having a variety of nutritious foods;  limiting your eating window or the type of foods you eat make it harder to meet your nutritional needs.

    History of an eating disorder

    It is not recommended to follow a keto or intermittent-fasting program if you have a history of an eating disorder. This is because the restrictions or rules associated with these diets can be a trigger for eating disorder behaviors, and will likely worsen your relationship with food. 

    If you struggle with an eating disorder, consider an intuitive eating approach, and always speak to your doctor about your concerns.

    History of diabetes or heart disease

    Those with diabetes or heart disease should always speak to their doctor first before considering a keto diet or intermittent fasting. Since a keto diet is very high in fat, it may not be the best plan to support heart health in someone with a history of cardiovascular disease.

    Since both fasting and keto can alter insulin and blood sugar levels, they may require an adjustment in insulin or can put you at risk for hypoglycemia, or low blood sugar. 

    How Keto and Intermittent Fasting Work Together

    Overall, combining keto and intermittent fasting may help you reach ketosis faster than following a keto diet alone. It may also lead to greater fat loss. 

    However, while this combined method may be the magic bullet for some, it’s not for everyone. A diet program and IF schedule should be very individualized, and what may work perfectly for someone may not work for another.

    Ultimately, some trial and error may be needed to determine what’s best for you — practicing fasting and keto alone, or combining the two. 

    Either way, feeling satisfied with how you’re eating is vital to long-term success on a diet. Regardless of your health history or goals, always speak to your healthcare provider first to decide what’s best for you.

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