We’ve longed been told that calorie restriction, increasing exercise and reducing dietary fat intake are the keys to weight loss. But, if you’ve ever attempted to control your weight by subsisting on fewer calories — especially from mostly bland “diet foods”— you’re already probably aware that this typically produces minimal results and is extremely hard to stick with long-term or consistently.
Considering the high rates of obesity now facing most developed nations — along with an increased risk for health conditions like diabetes or heart problems as a result — researchers have been anxiously working on how to suppress appetite and achieve weight loss in a healthy, sustainable manner. The keto diet has emerged over the past several decades as one potential answer to this large-scale weight loss problem. (1)
While there are some differences in opinion, depending on who you ask, regarding the best approach to very low-carb dieting, studies consistently show that the ketogenic diet (also called the keto diet) produces not only substantial weight loss for a high percentage of people who adhere to it, but also other important health benefits such as reductions in seizures, markers of diabetes and more.
The keto diet revolves around eating foods that are high in natural fats, consuming only moderate protein and severely restricting the number of carbs eaten each day. Even if you don’t have much weight to lose, entering into a state of ketosis can be helpful for other reasons — such as for improved energy levels, mental capabilities and mood stabilization.
Related: Beginner’s Guide to the Keto Diet
What Is Ketosis?
Ketosis is the result of following the ketogenic diet, which is why it’s also sometimes called “the ketosis diet.” Ketosis takes place when glucose from carbohydrate foods (like grains, all sources of sugar or fruit, for example) is drastically reduced, which forces the body to find an alternative fuel source: fat. Although dietary fat (especially saturated fat) often gets a bad name, provoking fear of weight gain and heart disease, it’s also your body’s second preferred source of energy when carbohydrates are not easily accessible.
Because it also requires drastic carbohydrate restriction, complete or intermittent fasting can also induce states of ketosis. (2) However, total fasting, which would result in a level of ketosis comparable to the ketogenic diet, isn’t easy to maintain beyond a few days.
In the absence of glucose, which is normally used by cells as a quick source of energy, the body starts to burn fat and produces ketones instead. Once ketone levels in the blood rise to a certain point, you enter into a state of ketosis— which usually results in quick and consistent weight loss until you reach a healthy, stable body weight.
Let’s go through that again, step by step. What is ketosis? Here’s how it works:
1. Consumption of glucose from carbohydrate foods — grains, starchy vegetables, fruit, etc. — is cut way down.
2. This forces your body to find an alternative fuel source: fat (think avocados, coconut oil, salmon).
3. Meanwhile, in the absence of glucose, the body also starts to burn fat and produces ketones instead.
4. Once ketone levels in the blood rise to a certain point, you enter into a state of ketosis.
5. This state results in quick and consistent weight loss until you reach a healthy, stable body weight.
To sum up a complex process, ketosis happens when the the liver breaks down fat into fatty acids and glycerol, through a process called beta-oxidation. There are three primary types of ketone bodies that are water-soluble molecules produced in the liver: acetoacetate, beta-hydroxybutyrate and acetone.
The body then further breaks down these fatty acids into an energy-rich substance called ketones that circulate through the bloodstream. Fatty acid molecules are broken down through the process called ketogenesis, and a specific ketone body called acetoacetate is formed which supplies energy.
The end result is staying fueled off of circulating ketones (which are also sometimes called ketone bodies) — which is what’s responsible for altering your metabolism in a way that some people like to say turns you into a “fat-burning machine.”
The goal of the ketogenic diet is to keep you in this fat-burning metabolic state of ketosis. This is achieved by following a very low-carbohydrate, high-fat diet that includes only moderate amounts of protein. Foods like bread, cereal, processed snacks and sugary drinks are therefore off the table, while fattier foods like butter, grass-fed beef, fish and also non-starchy veggies take center stage, providing the majority of daily calories (as much as 70–80 percent).
How long does it take to get into ketosis? This will depend on a few factors, including how strictly you limit your carb intake and also certain variables that are mostly out of your control, like your genetics, medical history, body composition and energy needs. If you’re consistently eating from food list, you should be able to see results and improvements within a short couple of weeks.
Signs of Ketosis
Beginning the ketogenic diet is different than making most other dietary changes, including many popular low-carb diets, because it involves actually changing your metabolism is pretty significant ways. Most people find that if they ease into the diet, giving themselves about 3–4 weeks to adjust, they experience fewer negative symptoms associated with the early stages.
While entering into ketosis it’s common to notice certain signs and symptoms of your body changing. These have been nicknamed by some “the keto flu.” While implementing the ketogenic diet can be challenging at first, commonly causing some side effects that can last for 1–2 weeks (or potentially more), these typically go away with time. Symptoms usually decrease as your body get’s more accustomed to being in ketosis, but in the meantime you might find that you experience:
- Feeling tired and having low energy despite sleeping well
- Having trouble sleeping
- Increased cravings, especially for carbs or sugar
- Digestive issues like constipation or bloating due to water retention (especially after higher carb days)
- Feeling weaker during workouts and not recovering well
- Being more moody or irritable
- Losing libido
- Bad breath
Most of these side effects happen completely “in your head” — they’re literally caused by your brain. See, every healthy cell in your body except brain cells can derive energy from one of three sources: glucose, ketone bodies and fatty acids (for a short period of time). However, your brain can’t utilize fatty acids since they don’t cross the blood-brain barrier (BBB). When you’ve restricted glucose intake and before your liver starts producing ample ketone bodies, your brain thinks it’s running out of energy, leading to at least a few days of uncomfortable keto flu side effects. (2)
Now that you’re aware of what the initial phase might feel like, here’s the good news: You’re also likely to notice improvements in several health markers, as well as appetite suppression due to keto diet. Below are some positive signs that you’re transitioning effectively into ketosis:
- Weight loss (this can happen quickly due to losing both water and fat)
- Reduced hunger and cravings. You might notice you’re able to “fast” for longer and feel less desire to eat many times per day. In fact, appetite suppression is one of the most meaningful signs of ketosis and often very obvious.
- Potentially improved energy, concentration and mental performance (especially after some time has passed). Initially the opposite might occur, but then you should notice no afternoon “energy dips” and, instead, more sustained energy.
According to most experts on the ketogenic diet, technically nutritional ketosis is defined by serum ketone levels (the amount of ketones in the blood) that fall between 0.5 to 3.0 mM. (3) Some believe that 1.5 – 3 mmol/L is “optimal ketosis,” which might contribute to the most weight loss. Every person is a bit different in terms of what exact macronutrient ratio will keep them in this range, while also allowing them to feel their best in terms of energy levels and other symptoms. You can experiment with different carb amounts while testing to see how this affects your ketone levels, aiming to remain in nutritional ketosis (0.5 to 3.0 mM), as long as you feel well doing so. Try to test at the same time each day for consistency and avoid testing right after exercise.
You can know for sure that you’re in ketosis by measuring ketones in the blood, breath or urine. Several options for doing this include:
- Using a blood ketone meter: These use test trips and provide precise measurements of levels of BHB ketones in your blood. They can be purchased online and sometimes are a bit costly, but are a reliable way to know you’re consuming the right macronutrient ratio to remain in the correct metabolic state.
- Performing urine strip tests: You can measure ketone levels by using inexpensive urine strips, which is cost efficient and simple to do. However, the downside is that only acetoacetate ketone levels are revealed, not levels of BHB. Two popular types are called Ketostix and Uriscan.
- Using a breathalyzer: These measure the ketone called acetone and don’t require strips, however they may not be as accurate as blood tests.
5 Benefits of Ketosis
1. Weight Loss
The ketogenic diet approach to eating is one that can often be maintained and incorporated into a lifestyle, while the same can hardly ever be said for diets that restrict calories and fat, because they simply leave you feeling too hungry.
When you eat more food than your body needs, it’s converted to triglycerides and stored inside your fat cells. The more often you keep consuming large amounts of glucose through carbohydrate foods, the less your body needs to tap into existing sources (your fat cells or stored glycogen in your liver and muscles) for energy, so your newly added fat cells remain intact and, therefore, weight loss is much more difficult.
On a keto diet, carbs provide only about 5 percent of daily calories, compared to anywhere between 40–60 percent on a “standard diet.” Reducing carbohydrate consumption this drastically means that the majority of empty calories from highly processed foods must be eliminated from your diet, including things like white bread and rolls, pasta, rice or other grains, sugar-sweetened beverages, desserts, etc. These are the same foods that tend to cause fluctuating blood sugar levels, cravings for more carbs and sugar, low energy and contribute to overeating in general.
With their absence, the body starts burning its own excess fat stores instead, promoting weight loss in a very high percentage of people. (4)
2. Suppressed Hunger & Reduced Cravings
In contrast to most other diet plans, remaining in ketosis doesn’t require counting calories, measuring portions or dealing with hunger pangs for the sake of eating as little as possible. In fact, most people feel satisfied and energized while in ketosis and find that they can go for longer periods without the need to eat (which is why intermittent fasting is commonly practiced with a keto diet).
Compared to meals that mostly contains carbs, high-fat, moderate protein meals are very filling and do a great job of controlling hunger hormones, often for many hours. This results in less need for snacking or grazing throughout the day, especially on junk foods or sweets.
Clinical results suggest both direct and indirect actions of ketones via modifications of various hunger-related hormones concentrations. While it’s not completely clear how ketosis reduces appetite, studies have found that ketosis is effective at lowering food intake and regulating appetite by altering levels of the hunger hormones including cholecystokinin (CCK) and ghrelin. At the same, ketone bodies seem to affect the hypothalamus region in the brain, positively impact leptin signals, and avoid slowing down the metabolism like most other diets do. (5)
3. Improvements in Blood Sugar Control & Heart Health
Aside from its benefits related to weight loss, the keto diet can also drastically improve other health conditions tied to factors like poor blood sugar management, overeating and poor gut health. These contribute to common health problems such as:
- Heart disease
- High blood pressure and unhealthy cholesterol or triglycerides
- Diabetes (6)
- Indigestion, including IBS symptoms or acid reflux (7)
- Cancer and tumor growth (8)
- The keto diet has also been used for decades to help control seizures and symptoms of epilepsy in both children and adults (9)
How can ketosis help reduce your risk various health concerns? It comes down to the benefits of stabilizing your blood sugar and decreasing glucose intake and usage. As glucose enters your blood, your pancreas sends out insulin to pick up the sugar and carry it to your cells so they can use it as energy. However, when your cells have used or stored all the glucose that they can, what remains is converted into glycogen to be stored in the liver and muscles OR converted into triglycerides, the storage form of fat.
4. More Energy & Enhanced Mental Focus
Not only do most people find that excess weight quickly drops off while on the keto diet, but many also experience improvements in terms of sustaining higher levels of energy.
After a period of time, your body becomes adapted to using ketones as fuel instead of glucose. Your muscles begin to learn to convert acetoacetate into a ketogenic substance called beta-hydroxybutyrate, or BHB. BHB then becomes the new preferred ketogenic source of energy, including to fuel all brain activity. What is not needed is expelled from the body as waste.
Another process also happens during ketosis that helps keep your body energized, and it’s called gluconeogenesis. This occurs when glycerol (created during beta-oxidation) get’s converted into glucose that your body can use for energy. Protein in your diet can also be converted to glucose in small amounts. So as you can see, essentially your body is able to create its own source of necessary glucose without getting it from carbohydrate foods. The human body is very efficient, and it knows just how to convert other macronutrients (protein and fat) into useable molecules that can be dispersed throughout the body as needed.
5. Reduced Risk for Other Chronic Diseases (Especially Neurological)
There’s strong evidence that a keto diet can help treat or manage serious diseases including epilepsy, Alzheimer’s disease, Parkinson’s disease and certain types of cancer. Studies show the diet helps to reduce disruptions in nerve and neural activity in the brain.
While it’s still not entirely clear how the keto diet helps treat these conditions, most experts believe that drastically cutting off glucose supply and entering ketosis helps elicit biochemical changes that prevent and eliminate short-circuits in the brain’s signaling system that are responsible for cellular damage, seizure and tumor growth.
Other mechanisms that have been suggested include: changes in ATP production making neurons more resilient in the face of metabolic demands, altered brain pH affecting neuronal activity, direct inhibitory effects of ketone bodies or fatty acids on ion channels, alterations in amino acid metabolism, and changes in synthesis of the inhibitory neurotransmitter GABA. (10)
How to Get Into Ketosis
Inducing ketosis requires severely limiting your carbohydrate consumption, this way you cut off supply of glucose to your cells. In addition to severely restricting carbs, you also need to limit your protein consumption, since protein can be converted into glucose in small amounts. This is the exact reason that most low-carb diets (such as Atkins or the Paleo diet) do not result in ketosis, because they allow a high intake of protein that keeps supplying the body with enough energy that it doesn’t need to burn fat.
- If you intend to follow a “strict” ketogenic diet, aim to get 60–80 percent of your daily calories from sources of fat. Between 15–25 percent of calories should be from protein sources, and only about 5–10 percent from carbohydrates.
- Based on the fact that most authorities recommend getting 45–65 percent of your calories from carbohydrates and only 20– 35 percent of your calories from fat, this will likely be very different than what you’re used to.
Transitioning Into Ketosis:
- For optimal results and the quickest improvements in terms of blood sugar and weight loss, it’s recommended you aim to eat between 20–30 grams of net carbs (total grams of carbs minus grams of fiber) a day.
- It’s usually best to include more carbs to begin with during your transition into ketosis, in order to help you adjust and avoid strong side effects (more on this below). Aim for around 50–60 grams net carbs daily in the beginning while you work towards decreasing to 20–30 grams if you wish.
- Keep in mind that the ketogenic diet takes into account net grams of carbohydrates, not simply total grams. Net carbohydrates are the amount of carbohydrates left over after you subtract grams of fiber from total grams of carbohydrates. For example, if vegetables you’re eating have 5 grams of carbohydrates total, but 3 grams come from fiber, the total number of net carbohydrates is only 2 grams, which is the number you add to your daily total.
- To figure out how many calories you need from each macronutrient group, first figure out how many calories you should be eating in total for weight maintenance or loss. You can use an online calculator to help determine your energy/calorie needs. Then split up your calorie intake into fats, proteins and carbs.
- Make sure to drink plenty of water throughout the day and also increase your intake of electrolytes, especially potassium from things like leafy greens and avocado.
- Exercise might also help you get into ketosis faster, although in the initial stages this may be hard due to low energy levels.
Remember that as your body changes — for example, you lose weight or increase muscle mass — your calorie needs and macronutrient ranges may also need to change. Always monitor your own biofeedback to make sure you’re fueling your body in the best way possible.
Risks and Side Effects
Before starting the ketogenic diet, it’s always best to consult with your physician if you have a history of existing health conditions including diabetes, kidney disease or damage, heart problems, a hormonal imbalance, or history with an eating disorder.
The ketogenic diet may not be safe for people with certain metabolic conditions or health conditions, especially:
- Gallbladder disease
- Impaired fat digestion
- History of pancreatitis
- Kidney disease
- Impaired liver function
- Previous gastric bypass surgery for weight loss
- Type 1 diabetes or impaired insulin production
- History of alcoholism or excessive alcohol
One particular concern to be aware of is the risk for ketoacidosis, which especially applies to diabetics. Ketoacidosis is a dangerous metabolic state in which excessive amounts of ketones are produced. In mostly healthy individuals, ketosis is regulated by insulin, which is the hormone that controls the creation of ketone bodies and regulates the flow of fatty acids into the blood.
People with type 1 diabetes do not produce enough insulin, so their bodies are unable to regulate ketones, which can lead to a dangerous environment. Always consult with your doctor if you have diabetes before changing your diet, and look out for warning signs of ketoacidosis including: excessive thirst, increased urination, nausea, vomiting, abdominal pain, shortness of breath, weakness, fatigue and confusion.
- Ketosis is the result of following the ketogenic diet (sometimes called “the ketosis diet”).
- While entering into ketosis it’s common to notice certain signs and symptoms of your body changing, which can be both pleasant or uncomfortable. These include reduced appetite/suppressed hunger, weight loss, changes in energy levels and sleep, bad breath, digestive issues or moodiness.
- The unwanted side effects of ketosis (nicknamed “the keto flu”) usually go away within a couple of weeks and can commonly be managed by eating more fat, drinking enough water, getting more electrolytes, resting and being patient during the transition.