Kristen Fleming holds a Master of Science in Nutrition. Over her 8 years of experience in dietetics, she has made significant contributions in clinical, community, and editorial settings. With 2 years as a clinical dietitian in an inpatient setting, 2 years in community health education, and 4 years of editorial experience focusing on nutrition and health-related content, Kristen's expertise is multifaceted.
If you’re looking for the ideal weight loss plan, you may be wondering –keto vs intermittent fasting, which is better? Both offer exceptional benefits with regard to weight loss and may be linked to other health benefits. Choosing between the two can be a challenge; however, combining them is also possible. But which choice is the best? When deciding on either keto, intermittent fasting, or both, you should evaluate your weight loss goals and determine if you’re physically and emotionally capable of handling one or both plans.
Combining the two might boost the effects of each diet plan, making your weight loss goals more readily achievable. In this read, we’ll discuss the differences between keto and intermittent fasting, if one is better, and whether they’re safe. Then we’ll discuss whether it’s beneficial and safe to perform intermittent fasting on keto. We’ll also consider reasons why you may not be losing weight on intermittent fasting and keto and how long you should fast while on the keto diet. Read on for everything you need to know about keto, intermittent fasting, and the combination of the two.
Keto Vs Intermittent Fasting: What’s The Difference?
Before you can decide on the keto diet vs intermittent fasting, you need a solid understanding of each one. Both are growing more and more popular as weight loss options. But, if you’re unsure of what they are, that can make your decision so much harder. So, let’s look at what each one is.
What Is Intermittent Fasting?
There are several variations of intermittent fasting, which is a process that restricts when or how much you eat; however, in some cases you can use it to do both. One of the most basic versions is time-restricted eating. During this approach you will eat only during a specific time window over a single day. Generally, this window covers eight hours, leaving you to fast for the remaining 16 hours.
The other variations, whole-day and alternate-day fasting, don’t strictly govern fasting. Instead, you’ll focus on two or more days throughout the week where you severely reduce your food intake. The idea is to limit yourself to roughly 400 to 600 calories daily. You can follow a normal eating routine for the remaining days of the week.
One popular version is the 5:2 diet, which involves normal eating for five days a week and then restricting your calories on two non-consecutive days of your choice. If you choose alternate-day fasting, you’ll restrict your calories every other day of the week (12).
Intermittent fasting works by causing the body to exhaust its sugar stores after hours without food. Once this occurs, the body switches over to burning its fat stores in a process called metabolic switching.
This is in direct contrast with many people who eat throughout their waking hours. Consider someone who eats three meals a day and includes snacking in between. Because there is no extended period without food, the calories from the meals and snacks are used instead of the fat stores. Instead, with intermittent fasting, your body will burn through the calories of your last meal and move on to your fat stores (8).
The ketogenic (keto) diet is a fat-rich, low-carbohydrate diet. While it’s a popular weight-loss choice, it’s been used for centuries in treating specific medical conditions. In the 19th century, it was a common solution to help maintain diabetes. Then, in 1920, it was identified as an effective treatment option for children with epilepsy when their medication was ineffective. More recently, keto has been researched for possible benefits in treating polycystic ovarian syndrome, diabetes, cancer, and Alzheimer’s disease.
In addition to its many possible medical benefits, keto is most well-known for its weight-loss strategy in relation to the popularity of other low-carb diets. Their popularity began in the 1970s with primarily the Atkins diet but has since expanded to include the Paleo and South Beach diets, among others. The primary difference between keto and all these diets is in the focus on the fat proportion. While these other diets are high protein and moderate fat, keto requires an exceptionally high-fat content. Generally, it ranges from 70 to 80% of the total calorie intake, while protein remains moderate.
The idea behind the keto diet is to deprive the body of glucose to produce an alternative fuel called ketones from stored fat. When you fast or consume very few carbohydrates, the body will obtain glucose from the liver and muscles. After approximately three to four days, the stored glucose will be fully depleted, and insulin will decrease. At this point, the body will switch to using fat as its primary fuel source and the liver will take the fat to produce ketone bodies, which will be used for fuel instead of glucose.
The accumulation of ketone bodies in the blood is called ketosis. A healthy person will naturally experience a state of mild ketosis when fasting, including while sleeping during the night and during strenuous exercise. The time it takes for ketosis to occur differs for everyone, depending on factors such as resting metabolic rate and body fat percentage (2).
The short answer to this question is that it depends. When considering keto vs intermittent fasting for weight loss, you can achieve ketosis with both options; however, keto will be a much more sustained period of ketosis.
Periodic fasting is believed to trigger the same fat-burning process that low-carb and keto diets trigger. Your body can go into a state of ketosis following a 12-hour period with no food, which happens for many overnight before they have their morning meal. However, this process can be affected by snacks in the middle of the night. Keto should maintain this fat-burning process much longer because of your specific avoidance of carbohydrates, forcing the body to use fat as its fuel source (12).
Intermittent fasting will cause the body to produce ketones; however, it will likely not produce as many as needed for therapeutic ketosis. While both options are viable for causing the body to enter into a state of ketosis, it’s a personal choice for how long you want to sustain it. Depending on your total weight loss goals, one option may work better than the other for you. In addition, with the restrictive diet keto presents, you may find it easier to adhere to intermittent fasting. Choosing which one’s right for you is based on many personal factors (6).
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Are Keto And Intermittent Fasting Safe?
Research has demonstrated that the ketogenic diet is safe for most healthy people in the short term, but long-term studies have yet to be completed.
Keto will allow most people to lose weight successfully in a short period; however, research suggests that over the long term it may not be an excellent choice for your health. Whatever diet you choose, incorporating whole, nutritious foods is essential (9).
On the other hand, intermittent fasting must be done correctly and within reason. We discussed a few examples of food consumed at intervals throughout the day. It’s important to note that longer periods are not considered better or even healthy. This includes periods ranging from 24 to 72 hours. Extending fasts this long can prove to be very dangerous (8).
With either plan, it’s best to consult with your doctor before beginning to ensure you will not cause any adverse side effects, as some medical conditions do not pair well with keto or intermittent fasting. It’s always best to be cautious before making a significant diet change to ensure you do it correctly and safely.
Should You Intermittent Fast On Keto?
Intermittent fasting may be beneficial for those on a keto diet. If you’re struggling to get into ketosis, you can participate in intermittent fasting to boost your ketone production. This should help speed up your entry into a state of ketosis (1, 4).
When you start a keto diet it generally takes your body approximately two to three weeks to make the switch from using carbohydrates to fats as its primary energy source. Alternatively, during periods of intermittent fasting your insulin levels and stored glycogen will be low, forcing the body to use stored fat. If you haven’t achieved effective or longer-term ketosis while following the keto diet, adding intermittent fasting might improve your results.
While your keto-based meals are specifically designed to keep your body in a state of ketosis every time you eat, the beneficial effects of fasting will be maintained even if you eat regularly. Combining the two may have a complementary influence on your body’s ability to burn fat.
Greater fat loss may be achieved through this combination than through following intermittent fasting or keto alone. Intermittent fasting can reduce your hunger while increasing your satiety, which is complementary to the keto diet, as high-fat foods are also high in satiety.
When combining the two you will have a good chance of eating less and thoroughly enjoying your food. You’ll avoid overeating and the feelings of disappointment and frustration accompanying it. This will, in turn, make you more likely to maintain your diet (3).
While keto and intermittent fasting have this complementary relationship, you must ease into doing them simultaneously. There can be negative side effects that are challenging to handle for some, including fatigue and irritability. In addition, some medical conditions should not be combined with intermittent fasting or keto, including pregnancy
If it’s too much to do both together, try them one at a time until you’re comfortable, then slowly combine them. Remember, if you find it too challenging or overwhelming, it can lead to negative consequences, such as overeating on non-fasting days and times.
For some, using intermittent fasting is not essential for a keto diet. They can maintain a good state of ketosis without the added benefits of fasting just from cutting their carbohydrates back. You’ll have to decide if intermittent fasting vs fasting keto is better for you (3, 5).
Intermittent fasting and keto can both work well, depending on your personal circumstances and dedication to the diet plan. Whether alone or in combination, you can see tremendous results as your body switches from using its glycogen stores to its fat stores.
When deciding on intermittent fasting keto vs non keto, you’ll need to weigh the pros and cons of a ketogenic diet in combination with your intermittent fasting plan. While the two can present dramatic results, it may be too challenging and overwhelming for you mentally and physically to incorporate them simultaneously.
Alternatively, you can consider low carb and intermittent fasting vs keto. In this version, intermittent fasting is combined with a low-carbohydrate diet but not the traditional very low-carb, high-fat diet that keto presents. All these options are viable and have been proven successful for weight loss. The important thing is choosing the plan that will work best for you and your current circumstances and health (1, 3, 5).
How Many Hours Should You Intermittent Fast On Keto?
Generally, most who incorporate intermittent fasting with a keto diet choose the 16:8 fasting schedule. During this schedule you permit yourself to eat during a designated eight-hour window. However, all meals and snacks must be keto-approved. The remaining 16 hours of the day are reserved for fasting. This process is intended to speed up ketosis and help sustain it longer (11).
Why Am I Not Losing Weight On Keto And Intermittent Fasting?
If you’ve tried keto, intermittent fasting, or a combination of the two and you’re not losing weight, several reasons could be behind this. Both diet plans require a careful balance of nutrition and dedication to ensure optimal results.
With keto, if you don’t achieve ketosis, the diet might not work. The primary reason someone would not achieve ketosis is a failure to cut back far enough on carbohydrate intake. With this diet, the goal is generally between 20 and 50 grams of carbohydrates per day, which equals approximately 5 – 10% of the total caloric intake.
Remember, keto is also a moderate protein diet, which means you should not consume the bulk of your calories from protein-rich foods. The body can take excess protein, break it down into amino acids, then convert them into sugars. Protein should be restricted to approximately 35% of the diet to avoid this.
In addition to counting your macros on a keto diet, you’ll also need to count calories. Just like with any other diet, if you consume more calories than you burn in one day, you’ll gain weight instead of losing it, making it essential to keep an eye on how much you are eating on a daily basis (10).
On the other hand, with intermittent fasting, it’s essential to plan your meals appropriately to avoid overeating or binging. When you withhold food from yourself, it may lead to undesirable behavior when it’s time to eat, causing you to consume more calories than you should or would in a normal setting.
Additionally, choosing appropriate foods is essential. If you pick all high-calorie foods to eat when you break your fast, there’s the potential that you could eat more calories than you’ll burn in a day (7).
The same principles apply when you are combining keto and intermittent fasting. You’ll need to adhere to all the keto diet rules while monitoring your caloric intake and preventing binging when not fasting.
Final Thoughts
Keto vs intermittent fasting is a question many dieters ask when setting out on their weight loss journey. While both offer the benefits of ketosis, keto provides it on a much more sustained level than intermittent fasting. However, combining the two plans is thought to be an effective way to boost one’s entry into ketosis and help sustain it.
To make this combination effective, you must ensure you eat the right calories, carbohydrates, and protein. When you’re off your fast, you must not binge or eat excessively high-calorie foods that will ruin all your progress.
Intermittent fasting and keto can make a great combination when done safely. Choosing the 16:8 plan is the most common, with an eight-hour window for eating keto-friendly meals and snacks. Making the decision between keto, intermittent fasting, or both is based on several personal factors, including your current health and ability to cope with the potential side effects.
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