A Dietitian’s Take on Keto vs. Intermittent Fasting

March 9, 2021


Culina Health

Positive messages about body acceptance and whole-person health and wellness are part of an incredible movement toward body positivity. However, many Americans are still trying to lose weight, with nearly 50% reporting trying at least one weight loss diet in the past 12 months. Evidence of this is reflected by the weight loss and diet market, which raked in a record-breaking $72 billion in 2018 and is projected to continue increasing over the next 5 years.

With unlimited access to information, finding the perfect weight loss method should be easier than ever without shelling out hundreds of dollars for meal replacements or professional guidance. Instead, we are bombarded with crash diets, anecdotes from under-qualified “experts,” and companies looking to profit from our desperation to lose weight, be healthy, or fit a particular body type ideal. Frankly, it’s exhausting.

For now, let’s focus on understanding the science behind two of the most popular weight loss methods: intermittent fasting and the ketogenic diet, also known as keto.


What is intermittent fasting?

Intermittent fasting is an umbrella term describing any meal pattern where eating and drinking are confined to set times during the day or week. In other words, while many diets focus on what you can eat, intermittent fasting focuses on when you can. There are 3 main types of intermittent fasting: alternate-day, periodic, and time-restricted fasting.

1 – Alternate day intermittent fasting

Alternate day fasting involves switching between “fast” days, where very small amounts of food are eaten, and “feast” days, where eating is largely unrestricted. This style switches every other day and is considered quite restrictive since there are 3-4 days per week where little to no food is consumed.

2 – Periodic intermittent fasting

Periodic fasting involves periods of 24 hours or more of fasting followed by normal, unrestricted eating for a set amount of time. Some may choose to consume up to 25% of their daily requirements during fasting periods, making this style slightly easier to stick to. The 5:2 method is an example of periodic fasting in which you would eat normally for 5 days a week and fast for 2.

3 – Time-restricted intermittent fasting

Time-restricted fasting focuses on restricting eating for a set number of hours during a 24-hour period. The bulk of the fast takes place during sleeping hours. 16:8 is a common method, where a person fasts for 16 hours daily and confines eating to 8 hours daily. Skipping meals or limiting eating to one meal a day are also examples of time-restricted fasting.
Fasting has been practiced throughout human history as a part of religious and cultural traditions. It’s only been during the past 10 years that intermittent fasting has been used as a popular weight loss method.



What makes intermittent fasting so appealing?

Generally speaking, weight loss requires burning more energy than you bring in. Intermittent fasting is helpful because there are substantial periods where no energy is consumed, and the total amount of time spent getting in energy is cut short. Additionally, since the focus of intermittent fasting is time-based, there are no restrictions on what types of food you can eat as long as you maintain a negative energy balance.



What does the research say about intermittent fasting?

According to a 2019 review, intermittent fasting produces “equivalent weight loss when compared to continuous energy restriction” with “no differences between groups in weight or body fat loss.” Basically, this means that when it comes to weight loss, intermittent fasting provides no added benefit compared to just eating fewer calories throughout the day, provided you are burning more calories than you’re eating.

There are also claims that Intermittent fasting can improve insulin resistance, glucose metabolism, and inflammation, decreasing the risk of developing cardiovascular disease and type 2 diabetes. But these effects appear to be due only to calorie restriction and not the fasting pattern.

It’s also important to mention that everyone should not practice intermittent fasting. For pregnant women, children, people with a history of disordered eating, and those with diabetes, intermittent fasting could be dangerous. While intermittent fasting is likely a safe and effective method for weight loss, the results are primarily due to calorie deficit, and this eating pattern can potentially negatively impact blood sugar regulation.



What is the ketogenic diet?

The ketogenic diet, commonly known as keto, is a high-fat, low-carb diet initially used to treat epilepsy in children. Those who follow the diet consume more than half of their calories from fat while consuming only 10-15% of their calories from carbohydrates. This is considered a very low-carb diet; the current Dietary Guidelines for Americans recommend 45-65% of total calories come from carbohydrates.

While many types of low-carb diets exist, the keto diet is unique in that due to the low availability of carbohydrates, the body is forced to shift from using glucose to drive energy production to using fat as the body’s primary fuel source. This metabolic shift generates compounds called ketones, which are then used by cells to create energy. This metabolic state is called ketosis.



What makes keto so appealing?

Some may find the diet easier to stick to than other diets – fatty foods are highly palatable, and their high satiety can keep you feeling fuller longer.



What does the research say about the keto diet?

Like intermittent fasting, weight loss with keto is likely a result of eating fewer calories than you burn, with keto being equally as effective as regular old calorie restriction. Many keto dieters experience rapid weight loss during the first few weeks of adopting the diet. However, most of this is loss of water weight due to the diuretic effect of ketones. After this point, the beneficial effects of keto are unclear.

A study on men who are overweight and obese demonstrated that there was no significant difference in the amount of fat lost while on keto compared to a higher-carb diet with the same amount of calories. Another study found that the diet decreased visceral fat tissue but did not contribute to weight loss in healthy adult men participating in a vigorous exercise regimen.

Conflicting results demonstrate that we need more evidence of the effectiveness of the diet. Furthermore, there are risks associated with the keto diet. Short-term complications related to the diet include nausea, vomiting, headache, fatigue, dizziness, and insomnia. Longer-term side effects include hepatic steatosis, hypoproteinemia, kidney stones, and vitamin and mineral deficiencies. The diet can even induce a life-threatening state known as ketoacidosis.

While keto may be effective at promoting weight loss, diets restricting whole food groups can be challenging to maintain, and the diet has many scary side effects. Good old-fashioned calorie reduction is likely a safer move!


So which is best for weight loss? Intermittent fasting or keto?

There is no best diet for everyone, as everyone has nutrition requirements as unique as they are. With these diets or others, find something you can stick to while still enjoying food. If you are looking for weight loss, calorie reduction is the first step, and it doesn’t have to mean fasting or cutting out whole food groups! The best diet is varied, colorful, sustainable, meets all your nutrition needs, and allows you to have a healthy and joyful relationship with food.

Have more questions about the ketogenic diet and intermittent fasting? At Culina Health, we provide personalized nutrition care with a Registered Dietitian Nutritionist that’s covered by insurance. Schedule a free intro call to get started!

Any general advice posted on our blog, website, or application is intended for reference and educational purposes only and is not intended to replace or substitute for any professional medical advice, diagnosis, treatment, or other professional advice. If you have specific concerns or a situation arises in which you require medical advice, you should consult with an appropriately qualified and licensed medical services provider.

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