Keto and Intermittent Fasting: How It Works, Benefits, and Risks - Perfect Keto

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Keto and Intermittent Fasting: How It Works, Benefits, and Risks

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Over the past few years, the keto diet has become a very popular way to lose weight and improve health. If you’re on this diet, you may also be hearing about intermittent fasting as an approach that could work well with keto. But are there real benefits of combining keto and intermittent fasting?

In this article, we’ll explain the basics of the keto diet and intermittent fasting, why you might want to do them at once, possible risks, and other important details you should know.

Keto Diet Overview

The ketogenic diet is a very low-carb and high-fat eating plan with the following macronutrient percentages: 5% or fewer carbohydrates, 70-80% fat, and 20-30% protein. Keto has been around since the 1920s as a form of therapy for childhood epilepsy before antiepileptic drugs were introduced (*).

Cutting your carb intake to 50 grams or less per day causes your body to seek an alternative source of energy. Without enough glucose, it breaks down its stored fat, resulting in the production of ketones that now serve as your fuel. These ketones include (*):

To do the keto diet right, you should avoid foods that are typically high in carbs, such as rice, potatoes, cereal, pasta, sweet fruits, bread, and traditional pastries. At the same time, your keto food list includes a variety of meat and seafood, eggs, poultry, non-starchy vegetables, nuts, and zero-calorie sweeteners.

There are many keto diet variations to choose from, such as the standard keto diet (the most common), but all of them involve carbohydrate restriction. Regardless of the type of keto you’re doing, they are beneficial for the following as supported by research:

Other uses of the ketogenic diet include body recomposition (losing fat and gaining muscle) and improving performance among endurance athletes.

Intermittent Fasting Overview

Intermittent fasting, also commonly referred to as IF, involves eating within a specified period and avoiding food and drinks containing calories for the remaining hours.

For example, a popular intermittent fasting approach is the 16:8 in which you fast for 16 hours and eat within an 8-hour window. This would look like having your last meal at 5:00 pm and breaking your fast at around 9:00 am the next day.

Other variations of intermittent fasting include:

  • Skipping breakfast, which is beginner-friendly
  • One meal a day or OMAD
  • 5:2 method where you eat normally 5 days a week and limit calories to no more than 500 or 600 calories on 2 days.

Whether you fast regularly or occasionally, IF is good for you. In fact, you can do intermittent fasting once or twice a week instead of daily calorie restriction, which can be intimidating for some people.

Since you’re consuming fewer calories each week, intermittent fasting results in weight loss. On a deeper level, it helps you lose weight by putting your body in a fat-burning state of ketosis since you don’t have enough glucose.

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Despite circulating myths about fasting, fasting is the body’s natural way to survive and thrive during periods of little to no food. Here are some benefits of IF aside from weight loss:

  • Autophagy, a process by which your body gets rid of damaged cells, bacteria, and viruses (*)
  • Longevity and reducing your risk of aging-related diseases (*)
  • Prevents and manages metabolic diseases, such as diabetes and heart disease (*)

Why Combining Keto and Intermittent Fasting is Becoming Popular

Keeping yourself healthy and fit without putting yourself through any form of restriction is probably everybody’s dream. As a matter of fact, a ketogenic way of eating is already challenging enough. But if you’re already keto-adapted, you might be wondering what keto with intermittent fasting can offer on top of the benefits you’re already experiencing.

Combining both approaches is powerful for increasing weight loss. This is especially true for those who have lost weight initially on keto but are currently experiencing a weight loss plateau. Aside from looking for hidden carbs in your diet and switching up your exercise, adding intermittent fasting to your routine can be a game-changer.

Intermittent fasting makes you consume fewer calories each week. And like the ketogenic diet, IF does not require calorie counting. Moreover, fasting on keto works for decreasing your appetite (*).

You also become more metabolically flexible — in other words, your body easily switches from burning sugar (from glucose) or ketones (from fat) depending on the energy that’s available (*).

Study suggests that metabolic flexibility is linked with better weight management and better exercise performance. You’ll be able to maintain your workouts with the energy you have, which ultimately improves your fat-burning potential.

As long as your keto diet includes sufficient amounts of protein and resistance training, you should not be worried about losing muscle as a result of fasting. A systematic review of human studies found that intermittent fasting paired with resistance training preserves lean body mass while also reducing body fat (*).

Other Benefits of Combining Keto and Intermittent Fasting

While doing each approach alone leads to many benefits, intermittent fasting and keto are even better for several reasons.

One benefit is that it helps you get back into ketosis more quickly.

Let’s say you’ve taken a short break from the keto diet, are following a cyclical keto diet where you eat more carbs during the weekend, or had an unplanned cheat day. Doing intermittent fasting with keto than keto alone allows you to reach ketosis sooner.

Research shows that the metabolic switch from glucose to ketone utilization is triggered between 12 and 36 hours of fasting (*).

Another benefit is mental clarity and brain health. Periods of fasting combined with eating high amounts of carbohydrates can cause swings in your blood glucose levels, which can contribute to brain fog.

On the contrary, ketosis ensures that your brain relies on a consistent fuel source, resulting in better mental performance.

In one study, older participants with mild cognitive impairment (which includes memory and thinking problems) were assigned to either a high-carb diet or a low-carb diet for 6 weeks. Those in the low-carb group experienced cognitive improvements within a short period (*).

Sticking to a keto diet, especially when combined with intermittent fasting, can stop the progression of mild cognitive impairment.

For those looking to control their blood sugar levels to prevent prediabetes or reverse type 2 diabetes, incorporating an occasional fast to your keto diet regimen will improve your results.

In a 2018 study, researchers placed adults with type 2 diabetes on a keto diet for 1 year. Results showed that the participants who remained on the diet were able to reduce their HBA1C, weight, and medication (other than metformin) (*).

A 2018 case report discussed three cases in which insulin requirements were reduced in type 2 diabetes patients that fasted. Interestingly, these patients had the disease for at least 10 years (*).

Last but not least, for anyone on keto, intermittent fasting gives people a break from food planning, prepping, and cleaning up after meals.

It’s no secret that being on this diet requires choosing foods carefully. But with a fasting schedule, you can save time and effort — and instead, spend them on other things.

Potential Risks of Combining Keto and Intermittent Fasting

Intermittent fasting with keto can present some risks if done incorrectly or without the supervision of a healthcare provider (for those with a medical condition).

For example, someone with type 2 diabetes will have to discuss with their doctor regarding adjusting their medications. This is because blood glucose meds, combined with carb restriction and fasting, can cause your blood glucose levels to drop too low (also known as hypoglycemia).

On the other hand, those with type 1 diabetes may be at risk of ketoacidosis, characterized by dangerously high ketone levels. A 2020 case report mentioned a 58-year-old woman with type 1 diabetes admitted to the emergency room with severe metabolic acidosis and ketosis after starting an intermittent fasting keto diet 9 days ago (*).

This case emphasizes the importance of consulting with your physician before starting a diet plan if you’re receiving treatment.

For people who are generally well, there is a risk of micronutrient losses or electrolyte deficiencies. This happens when you do not consume enough nutrients during your eating window.

Since the keto diet cuts out carbs, it’s important to ensure you eat a varied diet. Also, avoid eating too little fat because not enough fat can lead to vitamin deficiencies. Remember that dietary fat helps with vitamin absorption, including vitamins A, D, E, and K (*).

Losing so much weight due to keto (and possibly fasting) can lead to loose skin — although this doesn’t happen to everyone. Generally, the greater and quicker the weight loss, the greater the risk of having loose skin.

How to Approach Intermittent Fasting Keto Safely

If you’re just experimenting with intermittent fasting, especially when combined with a keto diet, start slow. For those who’ve never fasted before, a shorter fast will do, such as a 12- or 13-hour fast. From there, you can gradually transition to a longer 16-hour fast.

Alternatively, beginners can do a “fat fast” for 2-5 days, which isn’t technically a fast, although it mimics fasting by putting your body in ketosis. There’s no need to abstain from food in a fat fast. You simply need to eat mostly dietary fats, such as eggs and fatty cuts of meat, high-fat nuts, and high-fat dairy.

While fat fasting isn’t supported by research, it can help you ease into fasting without feeling restricted. However, we do not recommend going more than 5 days in a fat fast to avoid nutrient deficiencies or muscle wasting due to a lack of protein.

The bottom line is to avoid shocking your system by going from having three full meals per day to none at all.

Before starting any fasting plan, speak with your doctor. Ask about the medications you’re currently taking (if any) because some medications may break a fast if they contain added sugar and starch. Moreover, if you’re fasting and taking diabetes or blood pressure medications, your doctor may need to lower their dosages.

Keto and Intermittent Fasting Sample Meal Plan

Below is a plan showing what your meals would look like if you did a 16:8 intermittent fast. Note that you can eat anything you would like during your 8-hour window as long as these foods are keto-friendly and nutritious.

Day 1

  • 9:00 am – Omelet with cheddar cheese and mushrooms, black coffee
  • 1:00 pm – Avocado salad and a keto-friendly protein shake
  • 5:00 pm – Air fryer chicken wings with broccoli and cheese

Day 2:

  • 9:00 am – Coconut and almond flour pancakes, black coffee
  • 1:00 pm – Ground beef and cabbage, sugar-free lemonade
  • 5:00 pm – Tuna patties, avocado slices or berries, and cauliflower florets

Day 3: 

  • 9:00 am – Breakfast casserole (Italian sausage, cheese, broccoli, heavy cream, and spices), black coffee
  • 1:00 pm – Pork tenderloin wrapped in bacon, keto-friendly smoothie
  • 5:00 pm – Salmon with garlic and butter sauce

Work with a registered dietician to determine your keto macros and the best meals to meet these macros. You can also use our keto calculator and check out our recipe section for meals, snacks, and dessert ideas.

FAQs

Discover more answers to questions about keto and intermittent fasting below.

How many hours should you intermittently fast on keto?

That depends on the type of fast you feel most comfortable with. Intermittent fasting hours range from 16 hours to 24 hours. You can also do one meal a day (OMAD plan) or limit your calories to 500-600 two days a week (5:2 plan).

How much weight can you lose in a week with keto and intermittent fasting?

Weight loss will vary from person to person. Different factors play a role, such as your metabolism, sleep habits, muscle mass, exercise, etc. on top of doing keto and intermittent fasting. However, we can assume that combining keto and IF will lead to greater weight loss than keto or fasting alone.

Who should not combine keto and intermittent fasting?

It’s best for pregnant and breastfeeding women to avoid both approaches. This is because the keto diet and intermittent fasting limit your calories and micronutrients, which may negatively affect fetal development and milk supply.

The Bottom Line

Since intermittent fasting naturally depletes your glycogen stores, it’s a great complement to a keto diet. Combining them helps with overcoming a weight loss plateau, speeding up ketosis, increasing mental clarity and brain health, and improving metabolic flexibility.

Intermittent fasting can shock your system, so make sure you allow your body to adjust. Prioritize nutrient-dense foods during your eating window. Check with your healthcare provider if you’re undergoing treatment.

Both keto and intermittent fasting will work for you if you do them correctly.

20 References

Wheless J. History of the ketogenic diet. 2008 November

Dhillon K et al. Biochemistry, Ketogenesis. 2022 February 10

Dashti H et al. Long-term effects of a ketogenic diet in obese patients. 2004

Alarim R et al. Effects of the Ketogenic Diet on Glycemic Control in Diabetic Patients: Meta-Analysis of Clinical Trials. 2020 October 5

Sullivan M. Can a Ketogenic Diet Reduce Alzheimer’s Risks and Symptoms?. 2021 June 7

Shalaby J et al. Ketogenic Diets and Cancer: Emerging Evidence. 2017 February

Luukkonen P et al. Effect of a ketogenic diet on hepatic steatosis and hepatic mitochondrial metabolism in nonalcoholic fatty liver disease. 2020 March 16

Brietzke E et al. Ketogenic diet as a metabolic therapy for mood disorders: Evidence and developments. 2018 July 31

National Cancer Institute. Autophagy.

Longo V et al. Intermittent and periodic fasting, longevity and disease. 2021 January 14

Endocrine Society. Intermittent fasting can help manage metabolic disease. 2021 September 22

Ravussin E et al. Early Time-Restricted Feeding Reduces Appetite and Increases Fat Oxidation But Does Not Affect Energy Expenditure in Humans. 2019 August

Ravussin E et al. Early Time-Restricted Feeding Reduces Appetite and Increases Fat Oxidation But Does Not Affect Energy Expenditure in Humans. 2019 August

Keenan S et al. The Effects of Intermittent Fasting Combined with Resistance Training on Lean Body Mass: A Systematic Review of Human Studies. 2020 August 6

Anton S et al. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. 2017 October 21

Altayyar M et al. The Implication of Physiological Ketosis on The Cognitive Brain: A Narrative Review. 2022 January 25

Hallberg S et al. Effectiveness and Safety of a Novel Care Model for the Management of Type 2 Diabetes at 1 Year: An Open-Label, Non-Randomized, Controlled Study. 2018 February 7

Furmli S et al. Therapeutic use of intermittent fasting for people with type 2 diabetes as an alternative to insulin. 2018 October 9

Cardona A et al. Intermittent Fasting as a Trigger of Ketoacidosis in a Patient With Stable, Long-term Type 1 Diabetes. 2020 August 22

Albahrani A et al. Fat-Soluble Vitamins: Clinical Indications and Current Challenges for Chromatographic Measurement. 2016 February

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4 thoughts on “Keto and Intermittent Fasting: How It Works, Benefits, and Risks

  1. That’s some great basic information, but I’d like to know something a bit more in-depth… do ingesting exogenous ketones initially inhibit autophagy.
    I’m not sure if you would know this, if for example there hasn’t been sufficient research in this area. However, if they do initially inhibit autophagy then, depending on your goals, the timing of intake may be worth considering; for example BEFORE a fast as opposed to during.

  2. So,a lightbulb is finally appearing over my head. At first, I was drawn to fasting as opposed to the Calorie-deficit model of weight loss, which is yo-yo dieting. However, I’m at a bit of a plateau, so is it correct to say that being on keto in conjunction with fasting makes calorie restriction different? In other words, if I restrict calories for added weight loss (drawing on stored fat for the balance of energy requirement) that I won’t put myself into “starvation mode”, i.e., screw up metabolism and “set point” because there’s a seamless fat burning paradigm between keto and fasting?

    1. Hi Anthony, it’s unique to everyone. Certainly, agree moving from keto to fasting is more comfortable than high carb to fasting.

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