On the low carb, high fat keto diet, your body enters ketosis, a state in which you burn fat as your main source of fuel rather than carbs.

For many people, being in ketosis can help improve blood sugar levels, reduce appetite, and help maintain muscle mass — all of which may contribute to weight loss (1).

However, you may wonder whether there’s a target ketone level at which you can lose the most weight.

This article reviews the ideal ketone levels for weight loss and how to achieve and measure them.

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After starting the keto diet, it takes your body a few days to burn through its carbs, which are stored as glycogen in your liver and muscles. Once these carb stores are gone, you’ll switch to producing ketones from either dietary fat or stored body fat to burn as energy (2).

At that point, you may have detectable levels of ketones in your blood. Blood ketone levels while on the keto diet typically range from 0.5 – 3.0 millimoles per liter (mmol/L) (1).

These levels are the optimal range for nutritional ketosis — the state in which your body can use stored fat for energy most effectively, helping boost weight and fat loss (1).

Note that there’s a condition called diabetic ketoacidosis. It only occurs in people with diabetes and is characterized by extremely high levels of blood ketones alongside extremely high blood sugar levels (1).

However, the blood ketone levels seen in ketoacidosis are typically 10–15 times higher than those of nutritional ketosis. Also, ketoacidosis is often accompanied by severe symptoms, whereas nutritional ketosis is safe for most people (1).

Summary

Optimal blood ketone ranges for nutritional ketosis are 0.5 – 3 millimoles per liter (mmol/L). Nutritional ketosis is safe for most people and should not be confused with ketoacidosis, a severe complication of diabetes.

To achieve optimal ketone levels, you must restrict your carb intake. Most people on the keto diet restrict their carb intake to less than 50 grams of total carbs — or 25 grams of net carbs — per day (1).

Net carbs refer to the total number of carbs minus the amount of fiber.

Your body will not start to produce ketones on its own until it burns through your glycogen stores, which it will not do unless you cut off its supply of dietary carbs (2).

Once you shift into ketosis, your body can produce ketones for energy from either dietary fat or stored body fat (2).

You can also purchase ketone supplements, known as exogenous ketones, which will raise your ketone levels even if you’re still eating high amounts of carbs. These supplements have shown some benefits for athletes, but it’s unclear whether they aid weight loss (3, 4).

They may help reduce appetite, which can promote weight loss, but one goal of entering ketosis for weight loss is to burn your stored body fat rather than supplemental ketones. More research is needed to explore whether ketone supplements help or hinder weight loss (5).

Summary

To enter nutritional ketosis, you must drastically restrict your carb intake. Although you can raise your ketone level by using ketone supplements while still eating high amounts of carbs, this may not be helpful for weight loss.

The most reliable way to measure your ketone levels is to use a blood ketone meter.

These devices work similarly to blood sugar meters, as you use a lancet and a blood testing strip to collect a small blood sample from your fingertip, which the device then reads.

Although your body produces three types of ketones, most blood ketone meters check for beta-hydroxybutyrate, which is the most prevalent type (6).

There’s some disagreement among researchers about the best time of day to test ketone levels. You should pick a time and consistently test at that time to get the most accurate readings.

When you last ate appears to be a major contributing factor to your ketone levels, so you may want to do your ketone testing 3 hours after eating a meal (7).

Urine and breath testing

You can also check to see whether you’re in ketosis by using urine test strips or a breath test. These methods are less accurate but easier than using a blood ketone meter.

Urine tests, which are test strips that you dip in your urine, change color based on the presence of the ketone acetoacetate. The darkness of the strip is an indicator of the extent to which you’re in ketosis. The results may be inaccurate if you’re dehydrated (8).

Urine strips are inexpensive but also the least accurate testing method (8).

On the other hand, breath tests measure the amount of the ketone acetone in your breath in parts per million (ppm).

Reliable breath testing devices are fairly expensive and slightly less accurate than blood testing, but they’re painless and do not require the purchase of extra supplies like lancets or strips (9).

Breath acetone levels ranging from 2–40 ppm, and even higher in some instances, may indicate nutritional ketosis (10).

How often to test

Although you can test daily if you want to, it’s unnecessary. Plus, the cost of test strips can add up quickly. In fact, you do not have to test your ketone levels at all to be successful on keto.

However, you may want to check your ketone levels daily for a few days after starting keto to ensure that you reach nutritional ketosis, and then once a week or so while on the diet to ensure that you’re remaining in ketosis.

For some people, checking their ketone levels may provide a source of encouragement or motivation to stick with the diet.

Alternatively, some people may test more frequently if they want to see how their body responds to certain foods or a change in their carb intake.

If you want to test often, urine testing strips are by far the least expensive way to do so, although they’re also the least accurate.

Summary

The best way to measure your ketone level is with a blood ketone meter. You may want to check your levels 3 hours after a meal for the most accurate reading. That said, there’s no need to check your levels at all to be successful on keto.

Many people have found weight loss success using the keto diet.

Nutritional ketosis is defined as blood ketone levels of 0.5 – 3 mmol/L, which also represents the optimal ketone range for weight loss.

To achieve these levels, you need to significantly restrict your carb intake.

Using a blood ketone meter is the best way to check your ketone levels, but checking these levels is not necessary to lose weight on keto.