The ketogenic diet, or the "keto" diet, as it is more commonly called, is a high fat, moderate protein and low carbohydrate diet that is a very popular diet for many reasons but mostly because it has been found to be effective for weight loss.
Studies show that a ketogenic diet can help treat obesity and diabetes, and in fact, may even have health benefits for other diseases associated with insulin resistance as well as cancer and neurodegenerative conditions.(1)
The keto diet works because it forces your body to enter nutritional ketosis that helps with fat loss that leads to weight loss. To understand how the keto diet works, it is important to know what is ketosis and how you can tell if you are entering ketosis.
Ketosis is a metabolic state when your body uses fat rather than carbohydrates as a source of energy. A typical diet contains high amounts of carbohydrate, which your body uses effectively as the preferred source of energy. But when you go on the keto diet, you drastically reduce the amount of carbohydrates you eat and replace them with higher amounts of fat. To meet energy needs on a low carb diet and after glycogen stores have been depleted, your body enters into the metabolic state of ketosis. Ketosis increases your body's ability to use both dietary fat as well as stored body fat as fuel. The liver produces ketones from fatty acids that become source of energy for nearly every cell in the body. (2)
In general, it can take 2 to 4 days for a person to reach ketosis if the keto diet is strictly followed and carbohydrate intake is restricted. (3) For some it may take several days or longer on a keto diet to achieve ketosis. (4)
However, the time it takes to enter into ketosis varies from person to person, and largely depends on how rigorously you follow the keto diet. Additionally, your typical diet before starting on the keto diet, exercise routine and metabolism also determine how long it will take you to enter ketosis.
If you are wondering, how can I speed up ketosis? There are some studies that show you may be able to speed up the time it takes to reach ketosis by fasting (3,4) or by supplementation with MCT oil or Medium Chain Triglycerides (5) such as coconut oil. In addition to sticking to low carb intake, you may want to try intermittent fasting, increase intake of healthy fats or supplement your high-fat diet with exogenous ketones, which may help speed up ketosis.
Signs that your body is entering ketosis
You will notice several changes as your body adapts to the keto diet and will be able to tell that your body is entering ketosis when you notice the following common signs.
A fruity smell to your breath may very well be one of the side effects you experience when your body is in ketosis. Also known as the "keto breath", this bad breath has nothing to do with your oral hygiene, but it is, in fact, a good indicator that the keto diet you are diligently following is working!
As your body starts to burns fat stores for energy, it produces three ketone body by-products: acetoacetate, beta-hydroxybutyrate and acetone, which circulate in the bloodstream. As ketone levels in the body increase, acetone, due to its small size, diffuses easily in the air spaces of the lung and is exhaled through your breath, giving it a fruity smell. (6) Breath acetone concentration can be measured using a breath acetone analyzer to check if a person is in ketosis and monitoring fat loss. (6)
The good news on bad breath when you are on the keto diet is that you have entered ketosis and your body is burning body fat stores!
When you start on the keto diet, your body first turns to using glucose and glycogen stores for energy before burning stored fat. Most of the initial weight loss you experience may be due to the diuretic effect of the keto diet, when you lose water weight. However, as you continue to follow the high-fat keto diet and your body enters ketosis, you will notice a steady loss in weight. (6)
If you do hit a weight loss plateau, watch this video for common mistakes that you may not realize you’re making.
Weight loss on the keto diet is well studied and documented. A recent study on US military personnel shows that the weight loss when on a keto diet was accompanied with loss of body fat without impacting physical activity levels. (7) Meta-analysis of 14 randomized controlled trials (RCTs), with a total of 734 obese or overweight participants, found that in addition to weight loss, the keto diet improved lipid profile and glycemic control in participants with diabetes. (8)
Another sign that your body is entering ketosis is if you feel less hungry and have fewer cravings between meals while on the keto diet. This loss in appetite and feeing of satiety on ketogenic low-carb diets appears to be due to ketosis, according to a systematic review and meta-analysis study. (9) A low carbohydrate diet may increase satiety and suppress appetite by altering hunger related hormones. (10)
Brain fog, keto flu and tiredness are some of the first signs you may experience when you enter into ketosis. Although this is disheartening, these symptoms are short-term as your brain responds to the low carb intake and using ketones instead of glucose as fuel source. As you continue with the keto diet and the fat-burning process continues, your brain adapts to using ketones effectively, which may increase focus and improve brain function. Keto dieters have reported improved attention, less confusion and better memory function. (11,12)
The most accurate way of knowing if your body is entering ketosis is by a blood test to measure blood ketone levels. A reading of blood beta-hydroxybutyrate levels at or above 0.5 mmol/L using a specialized blood ketone meter confirms that you are in ketosis. (13) Although it is the most accurate method of testing ketosis, it requires a pinprick to draw blood from your finger to a test strip similar to that for testing blood sugar levels.
The bottom line
Just remember that the time it takes to reach ketosis varies from person to person. The key is keep following the keto diet and not be impatient as you will probably experience some or all the above symptoms when you enter ketosis.