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Medically reviewed by Kayla Girgen, RDMedically reviewed by Kayla Girgen, RD

Ketosis is a metabolic state that occurs when your body uses fat as its energy source instead of carbohydrates. This switch occurs when you drastically reduce your dietary carbohydrates by following a ketogenic (keto) diet, which involves eating foods high in fats and low in carbs. This diet forces your body to employ alternative energy sources instead of the usual carbohydrates your body uses. 

Entering ketosis via a keto diet offers several potential benefits for weight loss and improving your metabolic and cardiovascular health. Before transitioning to a keto diet, it’s important to understand the concept of ketosis and its potential side effects, such as the “keto flu” and nutritional deficiencies that may sometimes occur.

How Ketosis Affects the Body

Ketosis occurs when your body shifts its primary energy source from carbohydrates to fat due to reduced carbohydrate intake. Usually, the body breaks down carbohydrates from the foods you eat into glucose (sugar), which enters the bloodstream and is the energy source for most of your body’s cells, tissues, and organs.

When you reduce your carbohydrate intake to less than 50 grams daily, and the body no longer has enough glucose for energy, it breaks down stored fat into ketones—including acetoacetate, beta-hydroxybutyrate, and acetone. Ketones circulate through your bloodstream, becoming the primary energy source for most of the body’s organs and tissues. 

Entering ketosis leads to several metabolic changes that may promote weight loss, including:

• Increased fat burning: Fat stores become the body’s primary energy source, which may lead to weight loss.
• Appetite suppression: Ketones may have an appetite-suppressing effect by reducing the release of ghrelin—the hunger hormone. This leads to lower calorie intake and contributes to weight loss.
• Blood sugar regulation: Ketosis may help regulate blood sugar levels in people with insulin resistance and lower the risk of type 2 diabetes.
• Muscle mass maintenance: Following a keto diet means about 20% of your daily calorie intake comes from protein, which helps maintain lean muscle mass. Muscle cells also require more energy than fat cells, which may contribute to weight loss.

Benefits of Ketosis

In addition to promoting weight loss, ketosis has several other potential benefits that may improve your overall well-being.

Improves Insulin Sensitivity 

Insulin sensitivity refers to how effectively your body’s cells respond to insulin, the hormone that regulates blood sugar (glucose). In ketosis, the body burns fat and uses ketones instead of glucose, which may improve insulin sensitivity because the body relies less on glucose for energy. This may benefit people with insulin resistance and lower the risk of type 2 diabetes.

Boosts Energy Levels 

Ketones provide a more stable and efficient energy source than glucose, which can help prevent energy spikes and dips associated with carbohydrate consumption.

When the body uses fat as a primary energy source, it may lead to more consistent energy levels throughout the day. As your body adjusts to ketosis, you may initially feel fatigued before you begin to enjoy increased energy levels.

Improves Cognitive Function 

Ketosis may improve cognitive function by providing the brain with a consistent and efficient energy source in the form of ketones. Unlike glucose, which can cause fluctuations in energy levels and contribute to brain fog, ketones supply a stable and sustained energy source.

Evidence suggests ketosis may enhance mental clarity, focus, working memory, and overall cognitive performance and reduce the risk of age-related cognitive decline.

Reduces Inflammation 

Chronic, low-grade inflammation is associated with several health problems, including heart disease, arthritis, neurodegenerative diseases, and some cancers. Evidence suggests ketosis helps reduce systemic (bodywide) inflammation.

While researchers are exploring the mechanisms behind how ketosis reduces inflammation, evidence suggests several factors may contribute to its anti-inflammatory effects, including:

• Burning fat: Adipose (fat) tissue is associated with systemic inflammation. Using the body’s fat stores for energy may help reduce inflammation.
• The nature of ketones: Some evidence suggests that ketones have anti-inflammatory properties that may contribute to reducing inflammation.
• Reducing insulin: Insulin and insulin resistance increase the release of pro-inflammatory cytokines (proteins). Ketosis may reduce inflammation by lowering the body’s need for insulin. 

Signs and Symptoms of Ketosis

The time it takes to enter ketosis varies from person to person. On average, achieving ketosis takes about 3-4 days following a high-fat, low-carbohydrate diet (keto diet) or 72 hours of fasting.  

When you enter ketosis, you may experience flu-like symptoms, known as the “keto flu.” These symptoms typically peak within the first week and gradually subside within four weeks. Being aware of the following signs can help you identify if you are in ketosis:

• Bad breath: Known as “keto breath,” some people report a fruity odor, while others report keto breath smells like acetone (nail polish remover).
• Increased thirst: As the body adjusts to using ketones for energy, it may initially increase how often you pee and make you feel extra thirsty.
• Reduced appetite: Ketones have an appetite-suppressing effect, which means you may feel less hungry and more full after eating fewer calories than usual. 
• Weight loss: Rapid weight loss, particularly in the initial stages, is expected due to the loss of water weight and increased fat-burning.

How To Measure Ketone Levels

There are a few ways to determine whether you’ve reached ketosis. Consider the following measurement scales:

• Blood tests: A healthcare provider can order a blood test and send your blood sample to the lab to measure ketone levels. Alternatively, you can use a blood ketone monitor at home to measure your levels. If you have a home monitor, you can prick your finger, place a drop of blood on a ketone test strip, and insert the strip into the meter. The meter will provide a reading that shows your ketone levels. 
• Urine strips: Ketone urine test strips are available at many drug stores and pharmacies. You can urinate on the test strip or collect your urine in a sterile cup and dip the test strip into the collection cup to test for ketosis. 
• Breath meters: Breath ketone meters detect acetone levels in your breath by blowing into a handheld device. Though breath meters offer a noninvasive way to monitor ketosis, they may not provide as accurate results as blood tests. 

Side Effects and Risks

While ketosis may offer some health benefits, it is important to approach it with caution. Ketosis has potential short and long-term side effects and risks and is not safe for everyone. Work with your healthcare provider before starting a keto diet to ensure it’s right for you.

Potential short-term side effects of ketosis include:

• Keto flu: Many people report flu-like symptoms in the first few weeks of ketosis, including headache, fatigue, nausea, and dizziness. These symptoms are manageable if you drink enough water and increase your electrolytes.
• Digestive discomfort: As your body adjusts to a high-fat, low-carb diet, you may experience diarrhea, constipation, and stomach pain.
• Dehydration: When adapting to ketosis, the body releases more fluids through urination, increasing the risk of dehydration. Symptoms of dehydration include dry mouth, dark-colored urine, dizziness, and fatigue.
• Electrolyte imbalance: Increased urination and water loss can lead to electrolyte imbalances. You can replenish your body’s electrolytes through a nutritious diet or supplemental electrolytes. 

Following a keto diet for a longer period can increase the risk of: 

• Nutrient deficiencies: A strict keto diet can restrict your intake of essential vitamins and minerals from foods like fruits, vegetables, and whole grains.
• Kidney stones: Adhering to a high-fat, high-protein, low-carb, low-fiber diet long-term may increase the risk of developing kidney stones.

A keto diet and ketosis may be unsafe for people with certain health conditions, including: 

• Type 1 diabetes
• Type 2 diabetes (if taking insulin)
• Liver failure
• Kidney disease
• Arrhythmias (irregular heartbeats) 
• Eating disorders
• Pregnancy and breastfeeding 
• Older adults

Tips for Achieving and Maintaining Ketosis

Reaching and staying in ketosis requires careful planning and a commitment to specific dietary strategies and healthy lifestyle habits. A healthcare provider can guide you on adopting a ketogenic diet safely and effectively and offer you a personalized meal plan that helps meet your needs.

Here are some additional tips for achieving ketosis: 

• Restrict carbs: The cornerstone of achieving ketosis is drastically reducing carbohydrate intake. Aim for 20-50 grams of carbs daily. 
• Focus on healthy fats: A keto diet requires most of your calories from fats, so it’s important to increase your intake of healthy fats like avocados, nuts, seeds, olive oil, and fatty fish. 
• Eat moderate amounts of protein: Limit your daily protein intake to 1 gram per pound of your body weight. For example, if you weigh 150 pounds, eat no more than 150 grams of protein daily.
• Stay hydrated: To prevent dehydration, it’s essential to drink at least eight glasses of water daily.
• Replenish your electrolytes: Your body may lose electrolytes during the initial stages of ketosis. Consider drinking more electrolytes or incorporating electrolyte-rich foods like bone broth into your diet. 
• Get regular exercise: Moderate exercise can help promote ketosis. However, it’s important to listen to your body and avoid overexertion, especially when you first start.

Mistakes to Avoid

As with any diet, the keto diet has a learning curve, and it may take some time to adjust to your new eating plan. Making mistakes with a specific diet is common, but here are some things you may consider avoiding to ensure that you’re going into ketosis safely and correctly:

• Not eating enough fats: At least 70% of your calories should come from healthy fats, which are crucial for energy production, reaching ketosis, and satiety (feeling full). 
• Eating the wrong fats: While fats are the mainstay nutrient on the keto diet, it’s important to limit your intake of unhealthy fats, such as vegetable oils, and instead eat healthy fats in foods like eggs, avocados, nuts, oils, cream, and butter. 
• Consuming too few or too many calories: The keto diet promotes weight loss, but as with any diet, eating too many calories can lead to weight gain. But, eating too few calories can cause fatigue and excessive weight loss. To help achieve a proper balance for your body, consider talking to your provider or using an online ketosis calorie calculator.
• Accidentally consuming hidden carbs: Hidden carbohydrates are common in sauces, salad dressings, and condiments. Foods labeled “low carb” do not mean they are keto-friendly. If you have difficulty reaching ketosis, ensure your foods don’t contain hidden carbohydrates. 

A Quick Review

Ketosis offers a range of health benefits, from weight loss and improved blood sugar control to enhanced cognitive function and higher energy levels. However, ketosis has downsides, including uncomfortable side effects and risks for people with certain medical conditions.

Talk to a healthcare provider if you are considering fasting or adopting a keto diet. They can provide guidance and monitor your progress to ensure a safe and successful ketosis journey. 

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