If you’re on a weight loss journey, you’ll eventually ask yourself how your body can burn fat more effectively. That question has led many people down a rabbit hole of research, until they stumble across the word keto.

But what is keto, exactly? For one, it’s more than just a trending buzzword: It refers to a natural metabolic state called ketosis, where your body starts using fat stores for energy instead of carbohydrates. This process isn’t new either, as ketosis has been studied for over a century, and was originally used in the 1920s as a medical treatment for epilepsy.

Today, it’s being explored as a tool for weight management and metabolic health. To better understand what it’s about, you’ll find out how ketosis works, how it can support weight loss, and who may benefit from this way of eating.

What Happens in Ketosis?

Think of your body like a hybrid vehicle with two fuel tanks: one for sugar (glucose) and another for fat.

Usually, your body uses glucose from carbohydrates in the diet as its source of fuel. However, if carb intake drops significantly, typically below 50 grams per day, your body needs a backup plan.

This is where your liver steps in and begins breaking down fat into molecules called ketones, hence the name ketosis. These ketones serve as an efficient alternative energy source, especially for the brain, which can’t burn fat directly.

It’s worth noting that the shift won’t happen immediately.

Usually, it takes two to four days of carb restriction to enter ketosis, with variations depending on your metabolism, activity level, and previous diet. Once you reach ketosis, your body prioritizes burning fat for energy, not just from food, but also from stored body fat.

How Ketosis Affects Weight Loss

Ketosis and weight loss don’t just work together because you simply “eat fewer carbs,” but rather due to several physiological changes occurring in your body when it switches fuel sources. 

Appetite Suppression

Ketosis produces several distinct effects, but reduced appetite ranks as one of the most noticeable.

This isn’t just psychological—it’s hormonal, as ketones appear to suppress the hunger hormone ghrelin. In clinical studies, people following a ketogenic diet reported feeling less hungry, even as they lost weight.

This natural reduction in appetite often makes it easier to stick with a calorie deficit, without the constant struggle of willpower or cravings.

Insulin Reduction

Most people are likely familiar with insulin, which regulates blood sugar levels and signals the body to store fat. On a ketogenic diet, however, insulin levels drop significantly, with some studies showing a 53% reduction within the first week.

As your insulin levels decrease, your body has easier access to stored fat, promoting fat burning instead of fat storage. Over time, this enhanced fat-burning state also improves insulin sensitivity, making your body more efficient at managing blood sugar levels in the long term.

Metabolic Advantages

What also stands out about being in ketosis is the slightly increased metabolic rate, especially in the early stages. Put simply, your body works harder to convert fat into ketones than it does to process carbs. Studies comparing ketogenic diets to low-fat diets have documented the positive effects resulting from this shift, where people on keto often lose more fat than their low-fat counterparts. 

Another positive side effect centers on preserving lean muscle mass, a critical component for long-term metabolic health and also indicated to work well when in ketosis.

So, while ketosis isn’t a magic bullet, it creates a metabolic environment that supports sustainable fat loss if you’re able to follow its principles long-term.

How to Know You’re in Ketosis: 7 Signs

So, let’s say you’ve been focusing on a diet that leans into keto. When do you know it’s working? What signs are there that your body has officially flipped the metabolic switch into ketosis? 

Because the transition occurs internally, you may not always be able to spot the changes right away. Still, there are several clear and potentially surprising signals that your body is now relying on fat as its primary fuel source:

You’re drinking more water and urinating frequently

When your glycogen stores (which are bound to water) are used up, you’ll notice a natural diuretic effect. Initially, this can lead to more frequent trips to the bathroom and even mild dehydration, making increased water intake a smart choice. You may also want to consider adding a pinch of salt to your meals to replenish lost sodium.

Your breath smells fruity or metallic

This phenomenon is known as “keto breath” and stems from acetone, a type of ketone released through exhalation. This part may sound off-putting, but it’s a temporary and harmless sign that your body is actively producing ketones. To mitigate these effects, consider brushing your teeth more frequently or chewing on fresh herbs like mint or parsley.

You felt tired at first, but then have steady energy

The “keto flu” might be a familiar term to you if you’ve ever looked into this metabolic state. Essentially, during the initial adjustment, fatigue, brain fog, or irritability are common. These symptoms can last a few days to a week, but begin to fade once your body has adapted. Many people report more stable energy throughout the day, without the blood sugar crashes that come with a high-carb diet.

You’re naturally eating less

You may not be actively trying to restrict your calorie intake, but you end up more satisfied with smaller portions. That’s because ketones help regulate hunger hormones, like ghrelin and leptin, leading to earlier satiety (i.e., you’ll feel full more easily). 

Your focus and mental clarity improved

Once the brain fog subsides, many people function well on ketones. Some anecdotal reports indicate that people feel sharper or more mentally focused, especially during tasks that require sustained attention. 

Your ketone levels are measurable

If you’re testing with a blood ketone meter, readings between 0.5 and 3.0 mmol/L typically indicate nutritional ketosis. This is the most accurate way to track your progress, especially if you’re fine-tuning your diet for specific health or weight goals.

Your urine strips show ketones

This method may be less precise than blood testing, but urine strips can detect ketones in the early stages of ketosis. As your body becomes more efficient at using ketones, these results may fade, even while you’re still in ketosis. Therefore, it’s probably best to think of them as a starting tool, rather than a long-term tracker.

Ketosis and Popular Diets Used for Weight Loss

As discussed, ketosis is not a diet but a metabolic state. However, there are several popular dietary approaches specifically designed to help the body reach and maintain ketosis, with plans varying in structure and restrictiveness. 

If you’re wondering which keto diet might suit you, there are pros and cons, all heavily depending on your goals, lifestyle, and dietary preferences. Below are four of the most common diets that promote ketosis, along with their unique characteristics and the individuals for whom they might be best suited.

Standard Ketogenic Diet (SKD)

This ketogenic approach is probably the most well-known and certainly a widely researched version of a keto diet. Typically, it involves:

• Fat: 70–80% of total calories

• Protein: about 15–20%

• Carbohydrates: roughly 5–10% (or under 50 grams per day)

The SKD is structured, measurable, and supported by numerous studies showing effective weight loss, improved blood sugar control, and reduced insulin levels. Due to its precision, it appeals to individuals who enjoy tracking macros and seek a consistent, proven method to achieve ketosis.

Best for: Individuals seeking reliable results with a structured plan, particularly those with weight loss goals or metabolic issues such as insulin resistance.

Effectiveness: HighSustainability: Moderate (requires commitment and planning)

Intermittent Fasting (IF)

This method focuses on timing more than the “what” in your diet. Intermittent fasting can come in a few different versions, some of the most popular being the 16:8 and 18:6. To explain those numbers: During intermittent fasting, you’re eating within a set time window and fasting the rest of the day. As an example, if you set yourself a time frame of 8 hours in which you can eat, you’ll fast the other 16 hours of that day. 

During fasting windows, your body begins to deplete glycogen stores and may enter a mild form of ketosis. So, while not ketogenic by default, IF can complement a low-carb diet or induce short-term ketosis even if your carb intake is moderate.

Best for: People who prefer flexible food choices and want to tap into some of the metabolic benefits of ketosis without fully overhauling their diet.

Effectiveness: Moderate to High (especially when combined with low-carb eating)Sustainability: High (many find it easy to incorporate into daily life)

Carnivore Diet

This more restrictive approach involves eating only animal products: meat, fish, eggs, and some dairy. With virtually zero carbohydrates, ketosis happens naturally and consistently. 

Some people turn to a carnivorous way of eating to reduce inflammation or manage autoimmune symptoms. However, while it is simple, the diet lacks certain essential nutrients, such as fiber. Because of this,  increasing nutrient diversity, navigating social dining, and long-term health impacts should be carefully considered.

Best for: Individuals seeking a strict elimination diet or those with food sensitivities who want a simplified way to enter ketosis.

Effectiveness: High (fast ketosis and reduced cravings)Sustainability: Low to Moderate (highly restrictive, may not suit everyone)

Ketovore Diet

This is a hybrid diet that combines elements of the classic ketogenic and carnivore diets. This plan allows for mostly animal-based foods while still including small amounts of low-carb vegetables (like leafy greens or avocados). If you’re looking for inspiration, here’s a list of zero carb foods perfect for low-carb diets to get you started. 

Compared to the carnivore diet, it strikes a middle ground, keeping carb levels low enough for ketosis while offering more flexibility and a wider variety of nutrients, such as those from low-carb veggies, than the carnivore diet. It also tends to feel more livable long term and can serve as a soft entry point into more structured ketogenic eating.

Best for: Those who want the simplicity of animal-based eating without fully eliminating plant foods, or keto dieters looking to reduce carb intake even further.

Effectiveness: HighSustainability: Moderate to High (more flexibility than a strict carnivore)

How to Achieve and Maintain Ketosis Safely

Dietary Approach

If you’re serious about starting a keto diet, it’s usually best to start by reducing your daily carbs to under 50 grams. This means:

• Prioritizing leafy greens, cruciferous vegetables, and avocados.

• Avoiding grains, sugars, most fruits, and starchy vegetables like potatoes and corn.

• Eat a moderate amount of protein, about 10-20% of your calories, as too much can be converted to glucose via gluconeogenesis, slowing your transition into ketosis.

• Increase healthy fats to make up 70–80% of your calories. Good sources include:

  • Extra virgin olive oil

  • Avocado oil

  • Coconut oil

  • Nuts and seeds (almonds, macadamias, flax, chia)

  • Fatty fish (salmon, sardines, mackerel)

Timeline

Keep in mind that adapting to ketosis is a process, not a sudden switch. Keep your expectations and your planning realistic, as this is the common timeline:

• Days 1–3: You may feel tired, irritable, or foggy, which is sometimes called “keto flu.”

• Days 4–7: Symptoms may persist, such as cramps, dizziness, or disrupted sleep.

• Weeks 2–4: Energy levels typically rebound, and mental clarity improves.

Luckily, these side effects are only temporary. It is worth paying extra attention to your hydration and electrolyte intake during this time, as plenty of fluids and essential electrolytes like sodium, potassium, and magnesium can help ease the transition.

Monitoring and Adjustment

Like any process, pursuing ketosis can take some time and may come with bumps in the road. Tracking ketone levels using breath or blood meters is one way to gain insight into your progress. It’s equally important to tune into how you feel, especially your energy, focus, and overall appetite. 

If you’re not seeing any results, check your carb intake, fat quality, and hydration levels. Remember: small tweaks make a big difference.

Who Should (and Shouldn’t) Try Ketosis for Weight Loss

Not every diet is suitable for everyone, including keto diets. While ketosis offers compelling benefits for many, your personal health history, goals, and lifestyle should ultimately guide your decision. So, let’s take a look at which groups may benefit from ketosis and who should approach it with caution or only with medical guidance.

Who May Benefit from Ketosis

• People with insulin resistance or prediabetes. Because ketosis naturally lowers insulin levels and can improve blood sugar regulation, it has proven particularly helpful for individuals whose bodies struggle to process carbohydrates efficiently. This means that people with insulin resistance or those on the verge of developing type 2 diabetes can benefit from a ketosis-inducing diet.

• Those struggling with carb cravings or binge cycles. If you experience intense carb cravings or binge cycles, ketosis can help with this by stabilizing blood sugar levels. It can also reduce powerful cravings as it suppresses hunger hormones, which can lead to more control and fewer energy crashes.

• Individuals with significant weight to lose. Ketosis enables the body to access stored fat for energy, and therefore, it may provide more visible results early on than other diets, especially for people with a higher starting weight. The appetite-suppressing effect also makes long-term calorie reduction more manageable without experiencing constant hunger.

Who Should Avoid Being in Ketosis

However, there are also groups of people who should either approach ketosis only with caution and guidance or avoid it altogether. Those groups include:

• Those with a history of eating disorders. Keto diets can be highly structured but also very restrictive. Those traits can trigger disordered eating behaviors or enhance already existing obsessive tendencies. If you’ve had past struggles with anorexia, bulimia, or binge eating disorder, it’s best to avoid ketosis unless supervised by a healthcare professional trained in both nutrition and mental health.

• People with certain medical conditions. Ketosis heightens demands on the liver, kidneys, and gallbladder. Therefore, if you have a history of gallstones, liver problems, or kidney disease, you should avoid keto diets. If you’re unsure, consult with your consult with a medical provider before making major dietary changes. 

• Pregnant or breastfeeding women. While low-carb eating can be safe in some cases, the strict nature of ketosis may limit vital nutrients needed during pregnancy and lactation. These life stages require balanced, nutrient-dense eating patterns to support both mother and baby; therefore, any major dietary changes should be carefully considered in consultation with a healthcare provider.

• Those on specific medication. Certain medications, especially those for blood pressure, blood sugar, or diuretics, can exacerbate the fluid shifts and electrolyte changes common in early ketosis. If you’re on prescription drugs, talk to your doctor before starting a ketogenic plan, as dosages may need adjusting.

Final Thoughts: Is Ketosis Right for You?

Ketosis can be a useful tool. It is a natural process that enables your body to shift into fat-burning mode. Decades of clinical research have demonstrated that it creates a metabolic environment that supports weight loss, appetite regulation, and insulin balance. These traits have likely led to the high popularity of keto diets.

However, like any lifestyle change, its effectiveness depends on sustainability. What works for one person might not suit another, and some people should not expose themselves to the restrictive nature of most keto diets.

The good news? With the right approach, ketosis can be more than a temporary phase: It can be a powerful tool for long-term health and balance.