You might be surprised to learn that you’ve probably gone into ketosis before, even if you weren’t on a ketogenic diet. That’s because your body naturally goes into this state anytime it doesn’t have enough glucose for fuel[*]. No glucose from carbohydrates? Your body flips into ketosis and begins burning fatty acids as fuel instead. But a ketogenic diet takes this metabolic state to the next level. People who follow a low-carb or keto diet to get into a more permanent state of ketosis report health benefits like mental clarity, weight loss, and better performance at the gym. But what is ketosis, exactly? How does it work and is it safe? What about for the long-term? This guide will answer those questions and more. What Is Ketosis? Ketosis is your body’s metabolic process of using fat as the primary source of energy instead of carbohydrates. Carbohydrates fall into two categories: Starchy foods like bread, pasta, potatoes, and other high-carb vegetables Sugar from things like candy, cakes, pastries, and ice cream Get a full list of carb-heavy foods here. On a higher-carb diet, or Standard American Diet, the body runs almost exclusively off of glucose. You have glucose in your blood and stored glucose (aka glycogen) in your muscles and organs such as your liver. On a low-carb or ketogenic diet, dietary fat and fatty acids from stored body fat are released into your bloodstream. From here, your body can use these fatty acids as fuel or they get transformed into molecules called ketones. Ketones are produced when liberated fatty acids (from dietary fat and broken-down body fat) make their way to your liver. In your liver, they’re oxidized and turned into ketones to provide energy for your body and brain. Fatty acids make great fuel, but ketones are even more powerful. Your body uses them efficiently as fuel. What’s more, ketones can cross the blood-brain barrier to provide quick energy for your brain. But this only true in the absence of glucose[*]. Health Benefits of Ketosis The ketogenic diet is one of the best-studied diets in the nutrition sciences. Its effects on physical performance and brain health is especially impressive. Many people use the keto diet to lose unwanted body fat while maintaining muscle mass. Listed below are just a few known benefits of the keto diet. #1: Weight Loss Probably the most widely discussed benefit is weight loss. Because you’re using fat as fuel, ketosis can help you burn through fat stores more quickly[*]. You may also shed more pounds while in this state because of its effects on blood sugar and insulin, cravings, and energy. #2: Blood Sugar Balance Ketosis stabilizes blood sugar and helps prevent insulin resistance. Studies show that restricting your daily carbs may improve insulin sensitivity, obesity, and triglyceride levels[*][*]. In one study, insulin levels in the ketogenic group decreased three times more than the low-fat dieters[*]. Keeping blood sugar and insulin stable won’t just stave off metabolic syndrome and type 2 diabetes, it may also result in fewer cravings, which can help you keep the weight off for the long-term. #3: Fewer Cravings Another way keto helps you lose weight is by reducing cravings. Research into low-carbohydrate diets vs. low-fat diets has shown that low-carb diets significantly reduce food cravings, where low-fat diets increase them[*][*]. With keto, you can stop relying on your willpower and self-control and instead rely on balanced hormones and naturally fewer cravings[*]. Keto might also suppress your appetite, so you’ll be more satisfied with smaller portions[*]. #4: Better Brain Health Ketones can cross the blood-brain barrier and provide clean mental energy without the crash that comes with carb-heavy meals[*]. Although glucose is your body’s default form of energy, your brain can also use ketones as fuel. Ketosis has also been used to help control seizures in children with epilepsy[*]. And it’s been shown to have benefits for people with degenerative brain diseases such as Parkinson’s and Alzheimer’s[*]. #5: Higher Athletic Performance During long periods of exercise, the body uses both what you’ve recently eaten and stored glycogen to power you through. But when those glycogen stores have been used up and you still need fuel, the body must turn to protein or fat for more energy. This is not a very efficient process — unless the body has adapted to a ketogenic state. When you’re in a ketogenic state, your body quickly converts dietary fat or stored fat into usable fatty acids or ketones for quick fuel. This process helps prevent muscle wasting over time. #6: Longevity and Disease Prevention Ketosis has been shown to decrease inflammation, which is at the root of many chronic diseases, including a number of autoimmune diseases[*]. Blood glucose and insulin levels are directly related to brain health. It’s no wonder that many researchers are looking at ketosis as a treatment option for degenerative brain diseases like Alzheimer’s and dementia[*]. Ketosis can help balance blood sugar and make your cells more sensitive to insulin. This is why many researchers are looking at a ketogenic as an alternative treatment for type 2 diabetes patients[*]. Cancer cells thrive off of glucose from carbs. So, there are some theories that getting into ketogenic state can help starve cancer cells and may be a good complementary therapy for cancer patients. Most studies on keto and cancer are done in animal models, but one 2007 study found that the ketogenic diet was helpful in managing brain cancer[*]. How to Get Into Ketosis There’s only one real way to get into ketosis and that is to cut your carb consumption. The general carb limit for the keto diet is around 30 grams per day. If you’re an athlete, this may increase to 50-80 grams. You’ll replace those calories from carbs with fat and protein, but if you plan on losing weight, you’ll also need to cut your overall calorie consumption. You’ll have a unique macronutrient ratio that works best for your body and goals, but the general rule is: Carbs: 5-10% of daily calories Protein: 20-25% of daily calories Fat: 70-80% of daily calories Notice that your fat intake is much higher on this diet than in most other ways of eating. That’s because your body will be using fat as fuel to the exclusion of carbohydrates. Use this keto macro calculator to find the macros ratio you should start with. If you find that you’re not able to reach ketosis with your ratio, you might need to make adjustments. It takes some time to become fat-adapted — often at least a week if you’re doing this diet for the first time. Be patient as your body makes this shift. A dramatic change in your eating habits all at once can have some troublesome side effects, especially for fertile women, so make sure you’re transitioning at a pace that works for you. Fat-adaptation simply means that you’ve run through your stored glucose and your body is now used to running off of fatty acids and ketones. Here’s how it works: Step #1: Cut Carbs When there isn’t a sufficient level of available glucose, and glycogen levels are depleted, blood sugar levels and insulin levels decrease, and your body looks for an alternative source of fuel (fat). The transition from a regular diet to this extremely low-carb way of eating can be rocky for some. As you make the switch, you might notice some foggy-headedness, lethargy, muscle cramping, and maybe even a few brutal headaches. These are all symptoms of the keto flu, and they will go away once your body becomes fat-adapted. Consider going easy on the exercise during the initial transition. Step #2: Your Body Breaks Down Fatty Acids When your body begins to burn fat for energy, this process is known as beta-oxidation. This is when there is an increase in acetyl-CoA, which turns into acetoacetate. Acetoacetate then shifts to beta-hydroxybutyrate, also known as the ketone body, which floats around in your blood and eventually provides energy to the body and brain. Step #3: Ketones Become Fuel Once you’re fat-adapted, your body and brain are able to use ketones as a quick and efficient source of fuel. Your keto flu symptoms should be completely gone by this point, and you’ll likely notice a spike in your energy levels. You might also notice some temporary sleep disruption as your body revs its engines. It’s at this point that your first pounds usually begin dropping. How Many Carbs? The number of carbs you have to cut to get into ketosis varies from person to person. This depends heavily on: How much fat you have to lose Your activity level Your metabolism Many people have to cut down to 30 grams of carbs per day or fewer to start the fat-adaptation phase. Others — like athletes who burn a lot of energy throughout the day — can get away with more carbs, from 50-80 grams. Again, use the keto macro calculator to determine your carb goals. If you’ve gone three to four weeks on the keto diet and you’re still not in ketosis, you may want to lower your carb intake even more. If you’re super low on energy after the first week or so on a keto diet, you may want to add some carbs back to your meal plan. How Long Does It Take to Get Into Ketosis? This transition could take anywhere from 48 hours to one week, depending on your activity level, lifestyle, body type, and carbohydrate intake. It also depends on whether or not you’ve become fat-adapted before. Many people report being able to get back into ketosis quickly once they have previously done it. There are several ways you can speed up this process, like intermittent fasting, drastically cutting your carb intake, trying a carnivore diet, or cutting carbs while upping your exercise routine to burn through stored glucose faster. Can You Get Into Ketosis in 24 Hours? The average person may enter a mild state of ketosis during an overnight fast. Fasting causes your blood sugar and insulin levels to drop. These metabolic changes signal your liver to turn fatty acids into ketones, causing your blood ketone level to rise[*]. But that doesn’t mean that you’re fat-adapted or that you’ll get the benefits overnight. It’s highly unlikely you’ll get into a steady state of ketosis in 24 hours. It’s even less likely if you’re doing a ketogenic diet for the first time. Your body has been burning sugar for fuel your entire life. It will need time to adapt to burning ketones for fuel. Remember: Once you get into ketosis, there is no guarantee you will remain in this state. The levels of ketones in your blood changes with every meal, so if you eat a carb-laden meal, practice carb cycling, or increase your carb intake for athletic performance, your body may start burning glucose again. To get back into a fat-burning state, follow the same methods you did in the first place. How to Stay in Ketosis To maintain a ketogenic state, continue restricting carbohydrates and focusing on low-carb vegetables like leafy greens and crucifers, high-quality protein like wild fish and pasture-raised eggs, chicken, beef, and pork, and healthy fats like grass-fed butter and coconut oil. Other tips include: Intermittent fasting Make sure you’re not overeating calories (keto doesn’t have to be a low-calorie diet, but you do need to be in a calorie deficit if you want to lose weight) Commit to a fitness plan to keep your glycogen stores low Check out these helpful tips to getting into and staying in ketosis. How to Tell if You’re in Ketosis You might be wondering, what does ketosis feel like? Do you have to test your ketone levels? The first phase of ketosis is called the fat-adaptation phase or keto-adaptation phase. This is when you’re making ketones, but your body isn’t 100% used to producing them or using them as fuel. When you begin to produce ketones on a more regular basis, you’re fat-adapted. Your body has fully shifted over to burning fat as its primary fuel source, to the point where you have metabolic flexibility: you can eat carbs and fall out of ketosis, and your body will snap right back into keto once it processes the carbs. This may take a month or more. Testing your urine throughout the day is a good way to gauge the impact of the food you’re eating on your ketone levels. Getting into ketosis — even on the keto diet — does not guarantee fat-adaptation. That’s why it’s important to stick to strict keto for at least a few weeks when you’re just starting out if you want all the biggest benefits of the ketogenic diet. What Does Ketosis Feel Like? Many people report feeling differently when they’ve become fat-adapted. A few noticeable positive effects could include: More stable energy Reduced cravings Mental clarity More endurance Weight loss Still not sure? You may want to test your ketone levels. How to Measure Your Ketone Levels A great way to be sure you’re in ketosis is by measuring the ketone levels in your body, and you can do this at home. When your body makes ketones, it won’t use all of them as energy. Excess ketones will spill into different areas of your body. There are three different ways you can measure ketone bodies: in your urine, blood, or breath. Blood Testing You can use a blood glucose meter to test for levels of the ketone BHB. Since there are very few factors that alter results found through this method, it’s an accurate way to measure levels. It’s pricey though and will set you back about $5-$10 for each test strip. Urine Testing Use a urine strip. Package instructions might vary slightly, but generally, after around 45-60 seconds you should be able to see the color that indicates the measure of ketones in your urine. This is the least expensive testing option, but the least reliable. Your body becomes more efficient at using ketones when you’ve been in ketosis for a while, so the strips might show a lower ketogenic state than you’re actually in. Plus, other variables like hydration level and electrolyte levels can change the readings. It’s better to use this method if you’re brand new to keto. Breath Testing This method is best used as a supplement to a blood or urine test to help confirm ketone levels. You can use a Ketonix meter to test breath acetone, or BrAce, levels. The advantage of this method is that you can purchase a meter once and use it as many times as needed — no strips required. Is Ketosis Safe? What Are The Long-Term Effects? Ketosis is 100% safe. In fact, low-carbohydrate diets help many people shed unwanted fat, avoid metabolic disease, and perform better at work and at the gym. When this question comes up, it’s likely because of a few common misconceptions: High-fat diets are a heart health nightmare and will kill you A keto diet means starving your body of important nutrients Ketosis is the same thing as ketoacidosis, a deadly condition that can occur in uncontrolled diabetes None of these things are true. It Does Not Cause Heart Disease We’ve all been told that fat, especially saturated fat and dietary cholesterol, causes the hardening of arteries and heart disease. The most current research on this topic debunks this myth. In fact, four large meta-analyses in the last decade (looking at more than 500,000 participants) have found that there’s no link between saturated fat and heart disease[*][*][*][*]. It Won’t Starve You of Micronutrients If you do keto the wrong way (eating bacon and cream cheese at every meal without vegetables or fruit), you may end up deficient in certain vitamins and minerals. But do keto correctly by eating real, whole foods, and you shouldn’t have a problem. The fact is: meat, vegetables, and healthy fats are the most nutrient-dense food groups on the planet. High-sugar processed foods, grains, and potatoes pale in comparison. Ketosis vs. Ketoacidosis People also often confuse ketosis with diabetic ketoacidosis (or DKA). But they are two entirely different things. DKA occurs when the amount of ketones in the blood is extremely high and can turn the blood acidic. People with diabetes can get DKA if they don’t take enough insulin, become dehydrated from not drinking enough fluids, or become hurt or sick. Other causes may be starvation, alcoholism, or an overactive thyroid. Symptoms of DKA may include: Nausea or vomiting Excessive urination or thirst Hyperglycemia Fruity-smelling breath Gasping or breathlessness Ketoacidosis is a dangerous state that can be deadly if not treated. It’s not the same as nutritional ketosis, which is a safe state achieved through a healthy low-carb diet. Ketosis is a normal metabolic function in which your body is using ketones efficiently and safely. When you adopt a keto diet, you’ll only produce a low level of them in your blood. Enough to give you energy — not nearly enough to cause ketoacidosis or create health problems. How Long Is It Safe to Be in Ketosis? Low-carb, high-fat diets are far from dangerous in the short-term. To date, there isn’t much research showing the long-term effects of a ketogenic diet over the course of several years. But there’s no research to suggest that long-term keto is bad for you, either. Being in ketosis for more than a year shows improvements in[*][*][*][*]: Blood glucose Triglycerides Cholesterol Weight BMI Blood pressure If your body didn’t like ketones, it’s highly unlikely you’d see so many positive effects. So give the keto diet a try and discover for yourself why it can be good for your health.