Is It Necessary to Reach Ketosis to Lose Weight?

Written and medically reviewed by Katya Meyers, RD

The ketogenic diet is one of the most popular diets in the world. In recent years, it has topped the charts as one of the most often-Googled diets. Fans of the keto diet tout improved energy levels, better concentration, reduced appetite, and weight loss as benefits to being “in ketosis,” or the metabolic state in which your body is using ketones (a byproduct of fat metabolism) for fuel. Sounds pretty great! 

However, getting (and staying) in ketosis does present some hurdles. For one thing, it can take up to 2–4 days to fully get into ketosis. Additionally, even very small amounts of carbohydrates (approximately 20–50 grams, or the amount found in just 1–2 medium apples) can kick you out of ketosis. That may sound pretty strict, but here’s the good news: You do not have to actually be in ketosis to lose weight and burn fat.

Can You Lose Weight without Being in Ketosis?

Although ketosis is a state of accelerated fat burn, your body still uses fat for fuel even when it’s not in ketosis. Your body becomes even more efficient at using stored fats for fuel when you are metabolically flexible, or able to switch easily between using carbohydrates (in the fed state) and stored fat (in the ultra low-carb or fasted state) for energy. 

The ability to easily switch between fuel sources is a sign of good metabolic health and flexibility, and the better your metabolic flexibility, the easier it is to lose weight. So, how can you gain this metabolic flexibility? Follow a few simple practices, like lowering your intake of simple carbohydrates, exercising, and intermittent fasting for 14–16 hours each day, and you’ll become more metabolically flexible — and therefore able to burn fat — regardless of whether or not your body ever reaches ketosis. 

Do You Have to Be in Ketosis to Burn Fat?

Ketosis is a metabolic state where your body primarily uses ketones, which are produced from fat breakdown, as a fuel source. However, your body can also convert fat for energy through a process called lipolysis, which occurs when there is a calorie deficit, even if you are not in ketosis. When you consume fewer calories than your body needs, it starts breaking down stored fat to make up for the energy deficit. This process can happen regardless of whether you are in ketosis or not.

Conversely, when blood glucose (blood sugar) levels are high — say, for example, after a large high-carbohydrate meal — insulin levels will rise, prompting your body to shut off ketosis in favor of lipogenesis (i.e., fat storage).

The human body has evolutionarily adapted to rely on stored fat in between longer periods without food. After all, there were no convenience stores in the caveman days! Unfortunately, easy access to convenient foods encourages frequent meals, with the average person in Western society consuming 5–6 meals and snacks per day. With insufficient time to burn through all these incoming calories, many people constantly store fat without ever giving their body a chance to burn it. Fasting, or intentionally avoiding foods and caloric beverages for a certain length of time, is a simple way to set this right. Research shows that intermittent fasting is one of the most effective ways to encourage fat burning to promote weight loss.

What Is Ketosis?

You might’ve heard of the term “ketosis,” but you may still be wondering what it is. Ketosis is a metabolic state that occurs when the body is primarily using ketones for fuel instead of glucose. Normally, your body relies on carbohydrates as its main source of energy, which are broken down into glucose, which your body uses for fuel. However, when carbohydrates are restricted and in short supply, such as during a low-carb or ketogenic diet, or after 14–16 hours of fasting, the body switches to burning more fat for fuel. After a longer stretch of restricting carbs, or after 18–24 hours of fasting, the body enters ketosis. In this metabolic state, the liver converts fatty acids into molecules called ketones, which can be used as an alternative energy source. These “repackaged” molecules are particularly needed by the brain, which can’t directly use fat for fuel.

Ketosis has been defined as attaining a blood level of the ketone B-hydroxybutarate (BHB) above 0.5 millimolar (mM). Other signs you may be in ketosis include fruity-smelling breath or urine, experiencing suppressed appetite, headaches, and/or a drop in energy and focus in the initial adaptation phase.

What Is the Ketogenic Diet?

The ketogenic diet, often referred to as the keto diet, is a low-carbohydrate, high-fat diet that aims to induce ketosis in the body. It involves drastically reducing your carbohydrate intake and replacing it with fats, which leads to a shift in the body’s primary source of fuel.

Following the ketogenic diet typically involves careful monitoring of carbohydrate intake, prioritizing healthy fats (such as avocados, nuts, and olive oil), moderate protein intake, and avoiding high-carbohydrate foods like grains, starchy vegetables, sugars, and most fruits.

The primary benefits associated with the ketogenic diet include weight loss, improved insulin sensitivity, potential improvements in neurological conditions, such as epilepsy, and increased satiety.

However, it’s important to note that the diet may not be suitable for everyone. Researchers have shown that the ketogenic diet comes with risks, including nutrient deficiencies and increased muscle breakdown, and studies suggest it may not be as effective as more balanced dietary approaches in the long term. It is advisable to carefully weigh the cost-benefit and consult with a healthcare professional before starting any new dietary approach.

Basic Principles of Weight Loss and Fat Burning

While the keto diet has been linked to weight loss and a reduction in appetite, it can be challenging to maintain in the long term. In fact, low-carb diets like keto have less than a 50% adherence rate, even for those with added motivation, like people with diabetes. The key to successful weight loss is to find a way to not only create a sustainable caloric deficit, but to do so in a way that does not trigger your body to slow down its metabolism or start burning important tissue you want to preserve, like muscle. Regularly fasting for 14–16 hours is one such strategy, especially when paired with a balanced and nutritious diet, regular physical activity, and consistency and patience.

Basal Metabolic Rate

Basal metabolic rate (BMR) refers to the amount of energy expended by an individual at rest to maintain essential bodily functions, such as breathing, circulating blood, and regulating body temperature. BMR can vary depending on factors such as age, sex, body composition, and genetics. During weight loss, it’s important to maintain your BMR to ensure that your body continues to burn calories efficiently and support overall health.

To maintain BMR, aim for a gradual and sustainable weight loss of 1–2 pounds per week. Rapid weight loss can lead to muscle loss and a decrease in BMR. Focus on developing a consistent fasting practice to create a spontaneous, modest calorie deficit, rather than drastically cutting calories. Maintaining muscle through resistance training is another effective strategy. Muscle is more metabolically active than fat, so preserving muscle mass helps to maintain a higher BMR. Incorporate strength training exercises into your routine to preserve and build muscle and ensure that your diet includes adequate protein to support muscle maintenance and repair. 

Finally, get enough sleep. Sufficient sleep is crucial for maintaining a healthy BMR. Inadequate sleep can disrupt metabolic processes and lead to hormonal imbalances that affect metabolism. Aim for 7–9 hours of quality sleep per night.

Caloric Deficit

A calorie deficit refers to consuming fewer calories than your body needs to maintain its current weight. It is a fundamental concept in weight loss because when you create a calorie deficit, your body taps into its energy reserves, primarily stored fat, to make up for the shortfall. This leads to weight loss over time.

Unfortunately, counting calories for weight loss often fails. That is due to a range of factors — both biological (such as the increase in hunger hormones and reduction in RMR) and psychological (the motivation required to measure and weigh all your food) — that make counting calories a diet strategy that is both laborious and unsustainable. Researchers estimate that over 80% of dieters ultimately fail in their attempts to lose weight through traditional dieting. 

Fortunately, intermittent fasting is a simple approach that creates a spontaneous reduction in calories and yields successful, long-term weight loss — no complicated math required. Condensing your eating window by a few hours each day has been shown to be an effective way to lose weight and reduce body fat, with less hunger than chronic calorie restriction (aka “regular dieting”). 


Exercise is a highly effective component of weight loss. Physical activity increases energy expenditure, encourages metabolic flexibility, regulates appetite, and helps control cravings. It may help you feel fuller for longer, making it easier to stick to your fasting window and maintain a healthy eating pattern.

Most importantly, regular exercise offers numerous health benefits beyond weight loss, including improved cardiovascular health, increased strength and endurance, better mood, reduced stress, and enhanced overall well-being. 

To maximize the weight-loss benefits of exercise, aim for a combination of cardiovascular exercises (such as brisk walking, jogging, or swimming) and strength-training activities. Find activities you enjoy and incorporate them into your routine consistently. It’s also important to note that exercise should be complemented by a balanced diet to achieve sustainable weight loss. In particular, pairing exercise with an intermittent-fasting practice can improve your weight-loss and fat-burning efforts. 

Alternatives to Ketosis for Weight Loss and Fat Burning

Ketosis is far from the only option if your goal is to lose weight and burn fat. There are plenty of other tried-and-true methods, including intermittent fasting, caloric restriction, fast-mimicking diet (FMD), and even simply focusing on maintaining a healthier diet and moving your body more vigorously and often. 

Intermittent Fasting

Intermittent fasting has gained significant attention as a dietary strategy for weight loss and fat loss in recent years and can be a good substitute for or addendum to following a ketogenic diet. Intermittent fasting involves alternating between periods of fasting and eating within specific time windows. Specific physiological benefits of intermittent fasting — namely enhanced fat burning and improved insulin sensitivity — contribute to effective fat loss, which is the true goal of weight loss. Improving your metabolic flexibility can also help you get into ketosis (and stay there) more efficiently, if that is your goal. Finally, intermittent fasting is shown to produce a spontaneous caloric deficit, which further contributes to weight loss.

Many different intermittent-fasting methods exist, such as the 16:8 method (fasting for 16 hours and eating within an 8-hour window) or alternate-day fasting. Your fasting goals determine what you can consume during your fasting window. Typically, water and very low-calorie beverages, such as unsweetened coffee or tea, are allowed during any fast, while many — but not all! — forms of sweetened beverages are not. 

People often find intermittent fasting appealing due to its flexibility and compatibility with busy schedules. If you are looking to amp your results even further, maintain a balanced diet during your eating periods and focus on nutrient-dense foods to ensure proper nutrition. In particular, what you eat before and after a fast can make your fasting practice both easier and more effective by reducing the swings in blood sugar and energy levels that you might otherwise experience.

Caloric Restriction

The purpose of caloric restriction is to create a calorie deficit by consuming fewer calories than your body needs. By reducing your overall caloric intake, you can achieve weight loss regardless of the specific dietary approach you follow. Research shows that intermittent fasting is one of the simplest ways to lower your calorie intake spontaneously. In other words, by committing to a shorter eating window each day, it is likely that you will naturally reduce your calorie intake, no calorie counting required!

Fasting-Mimicking Diet (FMD)

The Fast-Mimicking Diet (FMD) is a dietary approach that involves consuming a specific low-calorie, plant-based meal plan for a designated period, typically 3–5 consecutive days. It aims to provide some of the benefits associated with fasting while still allowing for some calorie intake. The FMD promotes a mild form of fasting, which can create a calorie deficit and potentially lead to weight loss. Compared to the ketogenic diet, the FMD permits a slightly wider variety of plant-based foods.

However, most people following the FMD rely on prepackaged foods, which are expensive, high in sodium, and do not provide sufficient nutrients to be a suitable long-term diet solution.  In addition, when compared to the large body of research supporting intermittent fasting, the studies examining FMD are relatively small and based primarily on rodent models. 

Another diet that seeks to mimic the benefits of fasting while allowing for some calories to be consumed is the “Fat Fast”, which is a low-calorie diet (usually 1,000 calories per day) that involves even further increasing the fat proportion (roughly 90%) and decreasing carbohydrate and protein proportions. However, due to the caloric and nutrient restrictions, this approach is neither sustainable in the long term nor well-researched enough to recommend.

Healthy Diet and Exercise

Combining regular exercise with a healthy diet is a great alternative to the ketogenic diet when it comes to weight loss and fat loss. Adopting a balanced and nutritious diet that focuses on whole foods, including lean proteins, fruits, vegetables, whole grains, and healthy fats, can support weight-loss goals. This approach provides essential nutrients while controlling portion sizes and promoting a calorie deficit.

Regular exercise incorporating both cardiovascular activities and strength training helps burn calories, build muscle, and boost metabolism. It contributes to overall energy expenditure and fat loss. Exercise also offers additional health benefits, such as improved cardiovascular fitness, increased strength, and enhanced well-being. This approach is sustainable, flexible, and can be tailored to individual preferences and dietary needs. Plus, combining intermittent fasting with either (or both!) a healthy diet and regular exercise can help you reach your goals even faster. 

It’s important to note that successful weight loss and improved body composition require consistency, patience, and adherence to a balanced lifestyle. While following the ketogenic diet is one approach to weight loss and improved body composition, there are many other approaches that can work and may be more sustainable. And no matter which dietary approach you follow, combining it with 14–16 hours of intermittent fasting each day can help you lose weight and burn fat more effectively.

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Katya Meyers, RD
Posted in Health & Science

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