What are ketones?

Ketones are chemicals your liver makes. You produce them when you don't have enough insulin in your body to turn sugar (or glucose) into energy. You need another source, so your body uses fat instead. Your liver turns this fat into ketones, a type of acid, and sends them into your bloodstream. Your muscles and other tissues can then use them for fuel. If you don't have diabetes, this process doesn’t become an issue. But if you do have diabetes, you can build up too many ketones in your blood -- and that can become life-threatening.

If you're on the keto diet, then ketones in urine are the goal. But if you have diabetes, they could be dangerous.

All the news about the ketogenic diet makes it seem like a good idea to achieve nutritional ketosis—when your body burns through all the carbs you’ve stored and begins breaking down fat for energy. And while the jury is out on how effective that diet is for weight loss, nutritional ketosis is typically not dangerous. However, for people living with diabetes, ketoacidosis can be life-threatening.

“When you eat a very low-carb diet, do a period of prolonged exercise, or go for a long period of time without eating, there is some increase in the level of ketones in the body, but it's not necessarily dangerous because the ketones are at a low to moderate level,” explains Rekha Kumar, MD, endocrinologist at New York-Presbyterian/Weill Cornell Medical Center. “But people with type 1 diabetes who don't make enough insulin can reach very high levels of ketones, which can cause the blood to have acid in it.”

Not everyone with diabetes needs to monitor their ketone levels, but knowing what ketones are and when you should check can help you manage your diabetes.

Ketones are a breakdown product of fat. Normally carbs—in the form of glucose—are the body's primary source of fuel, but when you don't have enough glucose, the body turns to fat for energy. As the body oxidizes fat, ketones are produced in the liver.

Although this can happen when someone doesn't eat enough carbs (as on the keto diet), it also happens when the body doesn't produce insulin, as with type 1 diabetes.

“If you don't have enough insulin in your blood, the body thinks it's in a state of starvation,” explains Nestoras Nicolas Mathioudakis, MD, clinical director of the division of endocrinology, diabetes, and metabolism at Johns Hopkins School of Medicine. “Sugar levels will rise in the blood, but without insulin, it can't be taken out of the blood and used as an energy source.”

So your body breaks down fat, causing acidic ketones to build up in the blood. That's why people on the keto diet test for ketones; it's a sign their bodies have begun breaking down fat for energy, and might ultimately trigger weight loss.

But for people with diabetes, going into a state of keteosis is dangerous. Left untreated, this can lead to diabetic ketoacidosis, which can be deadly.

Signs you should test for ketones

The symptoms of high ketone levels are a bit vague. “If you have type 1 diabetes and feel off, test for ketones,” says Dr. Kumar, medical director of the American Board of Obesity Medicine. If you experience any of the following, check your ketone levels:

  • Weakness or fatigue 
  • Nausea or vomiting 
  • Excessive thirst and/or dry mouth 
  • Frequent urination 
  • Confusion 
  • Fruity-smelling breath 
  • Difficulty breathing

Also test for ketones if your blood sugar is more than 240 mg/dl (or the level your doctor advises) for several hours. Illness, stress, and infection can cause your body to produce more ketones, so check in these situations as well.

How to test for ketones

Whether you're on the keto diet or need to monitor ketones as part of your diabetes management, strips sold over the counter in pharmacies are an easy way to test for ketones. You either collect a urine sample or pee on the strip. As you wait (the directions will tell you how long), the strip will change color. Then you compare the color of the strip to a chart on the box. Darker colors indicate higher levels of ketones.

You can also do a blood test for ketones, similarly to how a blood glucose monitor works.

What to do if your ketone levels are elevated

If your ketone levels are low and you feel OK, test again in a few hours, being sure to drink water to stay hydrated and avoid exercise, as activity can increase levels of ketones. 

If your ketone levels are moderate, call your doctor. He or she may be able to provide care over the phone. “You may just need to adjust your insulin dose,” Dr. Kumar says. 

However, if your ketone levels are high and/or you feel ill, tired, nauseous, in pain, and/or are vomiting, go to the emergency room. “You may need more aggressive treatment to stop ketone formation,” Dr. Mathioudakis says.