Intermittent Fasting Vs. Keto – Which Is The Better Diet?

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By Thomas Youngerman

Reviewed by Juliana Tamayo, MS, RDN - Last Updated

Intermittent Fasting Vs. Keto

Diets come into vogue and then gradually lose popularity. There have been the Atkins Diet, the Scarsdale, the Beverly Hills, and the South Beach. Leading us to the Paleo, the low-carb, no-carb, slow-carb, and the Ketogenic Diet. Then there is the IIFYM (If It Fits Your Macros) and CR, the Calorie Restriction Diet. With so many options, and many with contradictory principles, how do you determine which is best for you?

This guide will focus on two top trending eating plans, the keto diet and intermittent fasting. Note we refer to these as eating plans; Intermittent Fasting (IF) is not a diet per se, although it is a popular technique among dieters and health enthusiasts. Both methods aim to mimic a calorie restriction diet’s effects, yet neither plan emphasizes your caloric intake. We’ll explain the calorie restriction concept and describe the physiological changes it induces. We will also look at the types of intermittent fasting and their goal of metabolic switching, followed by the keto diet, its principles, and objectives. Finally, we attempt to answer the question, “which is better, keto vs. intermittent fasting.” We think you will find our assessment interesting. Let’s get started!

Intermittent vs keto

The Calorie Restriction Diet – Proven To Extend Lifespan

Okay, perhaps a bit misleading. However, severe calorie restriction, reducing caloric intake by 30% – 40% while still obtaining optimal micronutrients, has been proven to extend the lifespan of various species in laboratory studies. If CR worked as well in humans as in rodents, we could increase the average life span to 120 years and maximum life span to 150. It’s unlikely anything approaching these gains will be attained as there is no scientific proof to date that humans would respond to CR like rodents.

The many benefits of CR observed in the lab have led to exploring CR mimetic drugs and other eating plans that produce similar physiological responses. CR creates changes in the operation of metabolism, increasing cell repair and recycling, autophagy. It reduces oxidative damage and chronic inflammation, both of which play a significant role in aging and the onset of age-related diseases. Calorie restriction improves insulin resistance, and ketone body concentrations are produced. 

Ketone bodies, D-beta-hydroxybutyrate (D-BHB), it seems, are increased during exercise, fasting, or when on a low carbohydrate diet. Time to enter ketosis. Let’s first see how intermittent fasting can help you enter ketosis faster as your body burns through its glycogen stores more quickly.

Calorie Restriction

Intermittent Fasting

IF is not a diet; it is a time-restricted feeding pattern that features a fasting period and time for meals. Fasting for a minimum of twelve hours is known to mimic the effects of calorie restriction. When in a fasted state, your body flips the “metabolic switch” from glucose to fatty acid-derived ketones for your primary fuel. Your body exhausts its sugar stores and starts burning fat. 

When fasting, you give your body time to repair cells and produce beneficial hormones. Your insulin levels drop, which facilitates fat burning. Human growth hormone (hGH) levels increase, essential for muscle gain and fat burning. Autophagy activity, which helps destroy unwanted or damaged cells to regenerate newer and healthier ones, increases. Additional intermittent fasting benefits include less free radical damage and reduced inflammation. 

Intermittent Fasting

There are several popular forms of IF that can fit nearly any personal preference or routine. Each method is defined by a fasting period or a fueling window. For example, the 16 / 8 Method indicates a sixteen-hour fast, followed by eight hours for your meal. The 12 Hour Method allows eating 12 hours during the day, followed by a 12 hour fast – the shortest fasting period, which will enable you to enter a fasted state. There is a Fast 5 Method meaning you can only fuel up in that 5-hour window and fast the other 19, the One Meal a Day Method, and the Alternate Day Method. 

Finally, there is a 5:2 Method, sometimes referred to as a time-restricted feeding fast. In the 5:2, you eat as you normally would for five days and practice two days per week of restricted-calorie intake.

Intermittent fasting is flexible, complements any eating style you choose (be it keto, vegan, vegetarian, or Paleo), and amplifies weight loss while enhancing your metabolic fitness.

Keto Diet

The keto (or ketogenic) very-low-carbohydrate, high-fat diet was developed to mimic the same beneficial effects of fasting by eliminating the glucose found in carbohydrate foods. The diet works by depleting the body of its sugar reserves, once again flipping the metabolic switch to burning fat for energy. When in a state of ketosis, your body’s energy comes from ketones rather than glucose. 

We refer to the classic keto diet as high fat, moderate protein, and very low carbohydrates. Carbs are reduced to 10% or less of your calories. Typically, fats make up 70% of your intake, and the remaining 20% is from protein. A word of caution when discussing macronutrient ratios, too much protein can stall your progress, even kick you out of ketosis. Excess protein gets converted to glucose and stored as fat.

Keto Diet

Ketosis has a proven track record for fast weight loss. Other benefits include:

  • Reduced risk of type-2 diabetes
  • Improved cognitive function
  • Better hormone regulation
  • Cardiovascular health
  • Reduced risk of metabolic syndrome
  • May reduce the risk of some cancers

Both IF and the ketogenic diet have an impressive list of benefits and produce similar physiological processes. As previously stated, intermittent fasting may help you reach ketosis faster. But which is better? The hunger experienced during fasting is a non-issue on the keto diet. The regimented eating plan required on the keto isn’t necessary during fueling windows on IF. We suggest you experiment with both methods, see which works best and is easiest for you to maintain as compliance is the key to any diet. 

Or, perhaps the best plan is a combination of intermittent fasting AND the keto diet.  

Intermittent Fasting And The Keto Diet

There is no reason these two strategies need to be mutually exclusive. Many, if not most people who practice intermittent fasting combine the eating pattern with a low-carb, slow-carb, or no-carb diet to accelerate their results. By practicing intermittent fasting while on keto, you can take advantage of the benefits that both offer. Both methods help people drop weight without restricting calories while improving blood sugar, cholesterol, and blood pressure.

As discussed, being in a fasted state helps raise your ketone levels by keeping insulin low – and being in ketosis while fasting allows you to burn fat for fuel. Another benefit of using them in tandem is that following the keto diet during fueling windows promotes satiety and can decrease hunger and cravings allowing you to fast for extended periods. 

Benefits Of Combining Intermittent Fasting And Keto

The benefits of intermittent fasting and keto, as calorie restriction mimetics, are well documented. We contend the synergistic effect of combining the two may enhance the benefits of both. This seems obvious when weight loss is the objective; however, changes in metabolism, hormones, and cell function may also slow the aging process and reduce the risk of age-related diseases.

There are several practical benefits of fasting while on the Keto Diet:

  • Fasting speeds the onset of ketosis
  • Keto Fasting may help you burn more fat and lose more weight than either strategy alone
  • Keto Fasting helps retain more lean muscle 
  • Adding fasting to keto can help you break through plateaus
  • Fasting may help avoid keto flu

Other benefits of keto fasting:

  • Reduces your risk of type 2 diabetes
  • Positive effects on cholesterol levels and lowered blood pressure improves cardiovascular health 
  • Reduces oxidative damage and chronic inflammation 
  • Initiates “autophagy” – cleaning out damaged cells
  • Promotes brain function
  • May reduce the risk of some types of cancer 

How To Combine Intermittent Fasting And Keto

Combining IF and keto is not at all difficult. The flexibility of IF allows you to choose your eating pattern, 16/8, the 12 Hour Method, even the 5:2. Then during your fueling window, you adhere to the macronutrient ratios of Keto; 70% of calories from fat, 20% from protein, and 10% or less from carbohydrates. The combination of protein, which provides the greatest satiety of any macro, and fat will reduce hunger and cravings during your fasting period.  

Keto Supplements

One potential issue when keto fasting is the possibility of creating nutritional deficiencies. To address this concern, we recommend several dietary supplements you may want to add to your regimen:

  • A Multivitamin/Mineral  
  • Exogenous ketones
  • MCT Oils
  • Digestive Enzymes
  • Omega 3 Fatty Acids
  • Fiber
  • Vitamin D3 
  • B Complex 
  • BCAAs (Branched-chain amino acids)

There are also quite a few supplements out there designed specifically for the Ketogenic diet. Some options worth checking out include Kiss My Keto Exogenous Ketones, Real Ketones Prime D+, Orgain Keto, and KetoFire.

Keto Supplements

Who Should Try Combining Keto And Intermittent Fasting?

Combining keto and IF is likely safe for most people. Others may find keto fasting simply too challenging or may experience adverse reactions. The most obvious issue when fasting is hunger. If you become hungry, have some water, tea, or black coffee. If the craving is intolerable, eat. Although fasting while on keto helps to minimize the keto flu, you may experience its symptoms:

  • Brain Fog
  • Headaches
  • Fatigue
  • Dizziness
  • Dehydration
  • Irritability

Although most people usually eat less when intermittent fasting, some overeat when they finally break their fast. Combining IF with keto is an excellent strategy to offset this tendency. 

Pregnant or breastfeeding women, people with pre-existing health conditions, such as diabetes or heart disease, and those with a history of eating disorders should probably avoid keto fasting.

As with any new diet regimen, we highly recommend you check with your medical professional before initiating a fast.

Our Take – Intermittent Fasting Vs. Keto  

So, we dodged the question, which is better. Both are effective ways to lose weight and be healthier without severe calorie restriction. The answer will be personal, each person and their lifestyle is different, and each person’s body will respond uniquely. Experiment with both methods and see which works best for you, or as we propose in this article, use them in tandem. 

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Thomas Youngerman

Thomas Youngerman is an entrepreneur and author in the health and wellness space with extensive experience in the supplement industry. He has owned multiple sports nutrition stores and served as the Category Manager and Director of Business Development for a regional chain of nutrition stores. Thomas created a successful line of men’s healthy aging supplements that was distributed in GNC, The Vitamin Shoppe, and Kroger, and later sold to a West Coast corporation. Thomas was previously a certified nutrition coach. He has a strong understanding of nutrition, supplement formulations, DSHEA, cGMP, and FDA regulations.