Keto & Intermittent Fasting: Should You Combine Them 2024?

Intermittent fasting and the ketogenic diet have been around for many years, each with its own history. Fasting has long been a staple in many religions, and the ketogenic diet was first developed as part of a neurological treatment for children with epilepsy. Lately, though, they both have taken the diet world by storm and have intrigued researchers regarding their effectiveness for weight loss and other potential health benefits. 

Obesity is increasing in our population, leaving more people vulnerable to heart disease, diabetes, inflammation, and other health conditions. Today, more people rely on intermittent fasting and the ketogenic diet to make changes in their health through weight loss. In this article, we will explore what’s involved in keto and intermittent fasting, their effects on the body, and the implications associated with combining them. 

Can You Do Keto And Intermittent Fasting Together?

If your goal is losing weight, combining keto and intermittent fasting would most likely give you the results you’re looking for, but it’s important to remember that it may not work for everyone. Fasting intermittently while following a high-fat, low-carb diet may help you lose weight faster, but it is unnecessary to reach actual ketosis. 

Both diets are incredibly restrictive and challenging to follow long-term. If you decide to try keto fasting weight loss, it is not recommended to start both diets simultaneously. If adding IF to the keto diet, consider beginning with a small fasting window while you sleep to avoid skipping meals. Consider following a modified keto diet that allows for healthy carbohydrate foods such as fruits, whole grains, and starchy vegetables. 

As with any nutritional changes, it is important to monitor your food intake and not lose sight of its role in your day-to-day functions. Adequate nutrition is more than just a tool for burning fat; it is necessary for your body to function. 

What Is Intermittent Fasting?

Intermittent fasting (IF) is best described as an eating pattern that cycles between calorie restriction and normal food consumption. Intermittent fasting doesn’t restrict the types or amounts of foods you eat but instead specifies a time you are allowed to eat. Studies have found that IF diets have the potential to help with a myriad of health conditions, but its recent increase in popularity is due to their perceived success as a weight-loss tool. 

IF originates from the idea that the human body has evolved to function on limited or no energy intake. Many supporters of the trend emphasize prehistoric times when hunters and gatherers survived for an extended time without eating between hunts or harvests. Now that we have the luxury of grocery stores, fasting is no longer a forced lifestyle but rather a choice to be made. 

Prehistoric hunter-gatherers were hunkered down for the night by sunset. Today, however, we’ve socially evolved to incorporate nightlife into our circadian rhythm. Times that were once set aside for rest and sleep are now spent at entertainment venues, movies, restaurants, night shift work, and even doing homework and studying. Since eating and resting functions are so intimately entangled in our circadian rhythm, the lives we lead today are no longer based strictly on night and day. This upsets our energy intake/output ratio, making it difficult to maintain consistent body weight.

How Does Intermittent Fasting Work?

Furthermore, gastric emptying and circulation to the digestive organs are greater during the day. Metabolism of sugars is slower in the evening,^[1] so weight gain or even fat accumulation could be more likely to occur when calories are consumed at night. Also, the gut “microbiome” is affected by disturbances in the circadian rhythm, which can affect their net energy absorption.

When you fast, your body adjusts its hormone levels to make stored body fat more accessible and help facilitate fat loss. IF specifically increases the release of norepinephrine, a fat-burning hormone, which may increase metabolic rate. Another study^[2] found that participants following IF lost 4-7% of their waist circumference, reducing the dangers associated with harmful belly fat that can build up around organs, as is seen with the insulin resistance associated with metabolic syndrome.^[3]

There are several different methods of fasting, each with an assigned fasting window and eating window. Common forms of IF include:

The 5:2 Fasting Regimen

Under the 5:2 fasting method,^[4] you eat regularly for five days of the week and then eat a very small percentage of your nutrition needs the other two days. During these two days, which should be nonconsecutive, you consume no more than around 500-600 calories each day.  

Alternate Day Fasting

Those that practice intermittent fasting under the alternate-day fasting^[5] (ADF) method will eat normally one day with their regular calorie intake and then fast the following day. Then the pattern continues through the planned intermittent fasting schedule.

The 16/8 Protocol

The 16/8 protocol,^[6] also referred to as the lean gains protocol,^[7] involves skipping breakfast and eating during an eight-hour window. Then, during the remaining 16 hours of the day, you are supposed to fast and avoid any caloric intake. (This is the closest thing to how human beings’ dieting habits were like in our hunger-gathering prehistory.) 

Eat Stop Eat

The Eat Stop Eat method requires you to abstain entirely from eating for two nonconsecutive days within one week, and then you can eat freely the remaining days of the week. On fasting days, you can drink water, coffee, and any other calorie-free drinks. Consider this the nuclear option to the 5:2 Method.

By assigning yourself an eating window, you will naturally consume fewer calories. In addition to weight loss, intermittent fasting diets have been found to decrease inflammation (balance your immune system function),^[8] improve brain function,^[9] and improve other metabolic processes,^[10] such as blood sugar control, cholesterol levels, and blood pressure. 

Furthermore, this eating schedule can encourage cells to initiate essential repair^[11] processes and change the expression of genes. Unfortunately, however, when the body alternates between glucose and ketones for energy, you are subjected to the side effects of these swings.

What Is The Keto Diet?

The ketogenic diet, or keto diet as it’s often called, is a low-carb, high-fat diet that induces the metabolic process of ketosis. Originally meant to treat epilepsy and other neurological disorders, the keto diet has evolved into a common weight loss diet known for burning fat. 

The keto diet involves eating a dramatically reduced carbohydrate intake of approximately 20-50 grams daily and consuming foods high in healthy fats and moderate in protein. The recommended dietary allowance for carbohydrates for adults without blood sugar concerns is 130 grams daily. This underfeeding of carbs eventually depletes glucose stores, forcing the body into the metabolic state of ketosis. 

This diet induces what is normally an “escape route” from starvation. Normally, sugar (glucose) is metabolized into energy.^[12] During ketosis, the body relies on fatty acids as its primary energy source through a process called gluconeogenesis.^[13] This alternate biochemistry pathway has helped humans survive intermittent starvation throughout time.

Keto dieters typically follow this eating plan anywhere from two weeks to six to twelve months. In the research available,^[14] the keto diet may offer health benefits in cardiovascular health and insulin sensitivity. However, short-term side effects^[15] of the keto diet can include nausea, headache, fatigue, difficulty maintaining exercise tolerance, and constipation. There is still a need for additional research regarding the long-term effects of the keto diet on the body. Still, potential long-term adverse reactions can include hepatic steatosis, vitamin and mineral deficiencies, and kidney stones. 

Keto Intermittent Fasting Diet: Benefits & Risks

Research has shown results in the short term regarding weight loss when following the keto diet or intermittent fasting. Although more research is needed to observe the long-term effects of the eating plans combined, the intermittent fasting keto diet may offer certain benefits, such as 

A Smoother Path To Ketosis

By including intermittent fasting with your keto diet, you may reach ketosis quicker than on the keto diet alone. When fasting, your body maintains its energy by shifting its fuel source from carbs to fats, which is the exact premise of the ketogenic diet. 

Increased Fat Loss

Studies have shown that IF can help eliminate excess fat mass through a boosted metabolism that metabolizes it into the energy you need. A review of 28 studies^[16] shows an average of 7.3 pounds more fat loss when compared to that of participants only following very low-calorie diets.  

Preserved Muscle Mass

It is believed IF may preserve muscle mass and improve energy levels during weight loss. This is especially helpful to keto dieters who aim to decrease body fat while improving their athletic performance. It’s important to monitor protein intake to avoid consuming too little or too much. Too little will not maintain muscle mass; too much could endanger your kidneys.^[17]

Combining intermittent fasting with keto diets may present attractive potential benefits, but there are also concerning potential risks. Common adverse reactions to fasting while on the keto diet include irritability, fatigue, and overeating on non-fasting days, ultimately leading to unintentional weight gain. Furthermore, combining keto with limited eating windows may create or exacerbate disordered eating.

An important consideration is the time limit placed on your diet. Specifically, what will you do after your diet is over? Temporary diets offer quick short-term results, but research on the long-term effects of both keto and IF is lacking.

The reality is that weight loss is a life choice and therefore involves continued disciplined lifestyle choices; otherwise, no matter how successful a temporary diet is, you may gain your lost weight back. A balanced diet can sometimes feel like “rocket science,” so consulting with a registered dietitian or nutritionist can help you design an eating pattern that will serve you for the rest of your life. 

Who Should Try Intermittent Fasting And Keto?

Combining IF and keto can help accelerate weight loss in the short term, but both diets are very restrictive, so they are not necessarily appropriate for everyone. In addition, if you have a history of particular health concerns such as diabetes, renal disease, or heart health problems, you should consult your medical providers before implementing any dietary changes that can impact these conditions. This is powerful manipulation of your biochemistry, so go into it fully prepared.

Those with a history of disordered eating should avoid these diets. While they may offer potential health benefits, their restrictive nature can trigger or exacerbate complex eating disorders. Those undergoing cancer treatment and pregnant and breastfeeding women should also avoid the restrictions.

Developing the right eating plan with a schedule of healthy foods is essential to our overall health and wellness, but everyone’s balanced diet is unique. If you have questions regarding keto vs intermittent fasting, it is recommended that you speak with your healthcare provider to discuss what steps might be right for you. You might also consider meeting with your registered dietitian nutritionist to discuss your individualized nutrition needs and how to live after your diet.

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