People with diabetes, particularly those with Type 1 diabetes, have been at least vaguely aware of the word ketones for a long time. With the recent resurgence of popular interest in low-carbohydrate diets, however, just about everyone seems to be talking about ketones these days. But does anyone really know what a ketone is? Are they a danger to your health (as in diabetic ketoacidosis), or a sign that you have lowered your carbohydrate intake enough to cause weight loss (as some people who follow low-carbohydrate diets believe)?
What are ketones?
Ketones are end-products of fat metabolism in the body. That is, they are formed when fat is burned for energy by the muscles. Chemically, they are acids known as ketone bodies, and there are three types: beta-hydroxybutyric acid, aceto-acetic acid, and acetone. But you don’t have to be a chemist to understand what role they play in the body.
To get to know ketones, it’s helpful to understand how your body burns fuel. A simple analogy is that of an automobile. For a car engine to run, the engine must burn fuel (gasoline), and when the fuel is burned, exhaust (carbon monoxide) is created. The carbon monoxide is the end-product of gasoline combustion.
Your body also has an engine that must burn fuel to operate. The engine is muscle, and the fuel is fat, carbohydrate (glucose), and, in certain conditions, protein. When fat is burned, the “exhaust” is ketones, and when glucose is burned, the “exhaust” is lactic acid.
Fat is more desirable as a fuel than glucose because there are more calories in a gram of fat (9 calories per gram) than there are in a gram of glucose (4 calories per gram), so you get more energy per gram of fat burned. In a sense, you could call fat a high-test fuel. But there is one catch to burning fat: To burn it efficiently, with little “exhaust,” you have to burn glucose at the same time. If you don’t have glucose available for fuel (because you are on a low-carbohydrate diet, for example), you will form ketones when your muscles burn fat.
For most people, the ketones that form as a normal product of fat burning and weight loss are nothing to be concerned about because they are simply burned for energy by the body, and any excess are passed out of the body in the urine. In fact, while the brain normally uses glucose for energy, during exercise — and particularly during long-distance events like marathons, when glucose reserves may drop very low — the brain can use ketones for energy. Your liver makes extra ketones when glucose reserves are low so that your brain has enough energy.
For people with Type 1 diabetes, however, having measurable amounts of ketones in the urine (or blood) is cause for concern. Ketones in a person with Type 1 diabetes may be a sign that his diabetes is out of control, he is ill or has an infection, or he is under extreme stress. Because above-normal levels of ketones in the blood can lead to diabetic ketoacidosis, a life-threatening condition, people with Type 1 diabetes who have measurable ketones in their blood or urine should speak with their diabetes educator or doctor promptly.
Low-carbohydrate diets are sometimes called “ketotic” diets because they cause the body to burn mostly fat for energy (since the intake of carbohydrate is so low), which in turn causes the formation of ketones. Some people who follow low-carbohydrate diets periodically test their urine for ketones to see if fat-burning is indeed taking place. However, people who are losing weight on any diet might have a trace of ketones in their urine since a person who is losing weight is almost certainly burning and losing fat.
With all the talk of ketones, some people have gotten the mistaken impression that ketones are a sort of magic bullet that melts fat from the body, no matter how much a person eats. That’s simply not the case. Ketones are only by-products of the metabolism of fat and are markers that show that you are burning fat. They have no active role in burning fat or weight loss. In fact, ketone levels in people who are on low-carbohydrate diets are just barely above baseline, indicating they have no role in producing weight loss. The reason people lose weight on low-carbohydrate diets is not because of ketones; it’s because they have cut out a large food group from what they eat, and as a result, they end up eating fewer calories.
Another unproven belief about both ketones and low-carbohydrate diets is that they suppress appetite, and that’s why people lose weight. Some scientists believe that the excess fat a person eats while on a low-carbohydrate diet has a satiating effect, causing people to eat less. Other experts believe that an elevated level of ketones causes a decrease in appetite, while still others believe that a high protein intake suppresses appetite. There are some studies in rats to suggest that elevated levels of protein during low-carbohydrate diets can cause a decrease in appetite, but so far, research on the effect of ketones and fat on appetite is inconclusive.
The jury is still out on the long-term safety and effectiveness of diets that are low in carbohydrates for the general population, although some nephrologists link a growing incidence of kidney stones to high-protein diets. (Low-carbohydrate diets tend to be high in protein.) Most diabetes experts, however, agree that a low-carbohydrate, high-protein diet is not worth the risk for people with diabetes because they have a high risk of developing kidney disease, and a high protein intake can be stressful on the kidneys in those with kidney disease.
Diabetes is the leading cause of kidney failure in the United States, accounting for approximately 43% of all Americans who start treatment for kidney failure each year. Between 10% and 21% of all people with diabetes will get some type of kidney disease. You may find it easier to control your blood glucose if you severely restrict your carbohydrate intake, but keep in mind that even in people without kidney disease, no one knows the effects of a high-protein diet on the kidneys over the long term. If you’re considering a low-carbohydrate, high-protein diet for weight loss or blood glucose control, check with your doctor or diabetes educator first.
Exercise and ketones
During exercise, both fat and glucose are burned for fuel by the muscles. If your glucose stores are low, fat will be your body’s primary fuel. If you exercise and burn lots of fat without glucose, you will make ketones. People who are very lean and efficient at burning fat, people who are losing weight, and people who do lots of endurance exercise (like training for a marathon) use up their stores of glucose rather quickly, and when they do, they frequently develop ketones in the blood. The type of ketone they develop is acetone, and it’s not unusual for their breath to smell fruity or like alcohol as the acetone leaves the body through their breath.
For people with diabetes, exercise typically lowers blood glucose. But sometimes exercise can raise blood glucose. This can happen when you are low on insulin. As you exercise, your liver converts stored glycogen into glucose to use for energy and pumps it into your bloodstream. If there’s little insulin available, your muscles can’t use the glucose and your blood glucose level will rise. If you have even a trace of ketones when you begin your exercise and your blood glucose rises as you exercise, the amount of ketones in your blood may rise as well, particularly if you have Type 1 diabetes. Although diabetic ketoacidosis as a result of exercise is very rare, it is possible, so precautions need to be taken. The American Diabetes Association guidelines for exercise, blood glucose, and ketones are as follows:
- Avoid exercise if blood glucose levels are greater than 250 mg/dl and ketones are present.
- Use caution if blood glucose levels are greater than 300 mg/dl and ketones are not present.
If your blood glucose level is higher than 250 mg/dl, you do not have ketones in your blood or urine, and you want to exercise, I recommend starting your workout then stopping after 15 minutes to see if your blood glucose level is rising or dropping. If it’s dropping, it’s OK to continue exercising. If it’s rising, you should stop exercising and follow your doctor’s recommendations for treating high blood glucose.
As stated earlier, for most people, ketones are nothing to worry about. But when you have diabetes, particularly Type 1 diabetes, it may be a signal that your diabetes is out of control. Your body may make ketones when you are sick, have an infection, are injured, or are experiencing high levels of stress. They can appear in your urine (ketonuria) and in your blood (ketonemia).
The problem with high levels of ketones is that they are relatively strong acids, and because of their acidity, their presence in the blood can reduce the ability of oxygen to bind to hemoglobin, the molecule that transports oxygen to cells that need it. That means muscles and other organs might not function as well as they should. In addition, high levels of ketones for people with Type 1 diabetes can lead to dehydration and diabetic ketoacidosis (sometimes called DKA). Diabetic ketoacidosis is rarely seen in people with Type 2 diabetes because their pancreases usually still produce some insulin, which means that the body is able to burn some glucose.
Testing for ketones
People with Type 1 diabetes have most likely been asked by a doctor or diabetes educator to test their urine for ketones at one time or another. The development of the Precision Xtra meter has also made it possible to check blood levels of ketones at home. Two other home analyzers, the CardioChek and the CardioChek/PA (which also measure blood cholesterol levels), can also measure blood ketone levels. It’s a good idea to review ketone testing guidelines with your doctor or diabetes educator, but here are some general guidelines for who should test and when:
- People with Type 1 diabetes whose blood glucose level is over 250 mg/dl for two readings in a row or who are sick should always test for ketones.
- Pregnant women with diabetes are usually advised to check their urine for ketones every morning before eating and additionally if their blood glucose level is above 200 mg/dl or if they are ill.
- Most adults with Type 2 diabetes don’t need to worry about ketones, but check with your doctor or diabetes educator for specific instructions.
- Most of the time, children with Type 2 diabetes don’t need to check for ketones, but ask your doctor, especially if your child experiences unexplained weight loss or his blood glucose level consistently remains over 200 mg/dl.
Ketones are usually tested with urine test strips, which change color based on the presence and concentration of ketones in the urine. The results are usually expressed as “negative,” “trace,” “small,” “moderate,” or “large.” If the test result is positive, you should call your doctor or diabetes educator. You may need to take extra insulin, and your health-care provider will instruct you on how much. You should also drink lots of water or other calorie-free beverages to flush out excess ketones, continue to check your blood glucose level every three hours, and continue to test for ketones if your blood glucose level is over 250 mg/dl.
If you are losing weight, you may have a small amount of ketones in your urine. This is OK for people with Type 2 diabetes, as long as their blood glucose level is in a normal range, but people with Type 1 diabetes should check with their doctor. The mild ketosis (the presence of small amounts of ketones in the body) that occurs in people on low-carbohydrate diets should not be confused with the life-threatening levels of ketosis that someone who has Type 1 diabetes can develop. Diabetic ketoacidosis is a serious medical emergency that requires immediate medical attention.
The Precision Xtra blood glucose meter can measure ketones in your blood with special strips that take a fingerstick blood sample, just like the procedure for blood glucose monitoring. (Click here for information about both urine and blood ketone strips.) The device has been carefully tested in studies and is very accurate. Blood testing for ketones is superior to urine testing because it measures beta-hydroxybutyric acid, the primary ketone that’s formed in diabetic ketoacidosis, while urine testing measures acetoacetic acid. Urine testing can lead to a false negative result (which means it might show negative ketones when in fact you do have ketones), and there is a time delay to diagnosis of ketosis with urine testing since it takes some time for ketones to get from the blood to the urine. Another possible advantage to blood ketone testing is convenience. In a recent study of teenagers with Type 1 diabetes, teens preferred and were more likely to test their blood for ketones than they were to test their urine.
Here’s what the results mean when testing blood for ketones:
- Greater than 3.0 millimoles per liter (mmol/liter) is a serious metabolic condition and emergency medical care is necessary.
- 1.6–3.0 mmol/liter is a high level of ketones and means you are at risk for diabetic ketoacidosis. Your doctor or diabetes educator should be contacted immediately.
- 0.6–1.5 mmol/liter is a moderate level of ketones and probably indicates fat metabolism and weight loss, but not a deficiency of insulin. You should speak with your doctor or diabetes educator about what to do when ketones are in this range.
- Below 0.6 mmol/liter is a normal blood level of ketones.
While low-carbohydrate diets are usually discussed as tools for weight loss, that is not their only role. So-called ketogenic diets (diets that intentionally cause ketosis) have been used to treat epileptic seizures in children since the 1920’s. The diets, which do not work in adults, are high in fat, low in protein, and virtually carbohydrate-free. The precise mechanism of how ketones work to prevent epilepsy is unknown, but for some children with difficult cases of epilepsy that do not fully respond to medication, the ketogenic diet is another treatment option. There are several centers in the United States that provide the diet. You can find out more at the following Web site:
Ketogenic diets are also being tested for treatment of Parkinson disease. Some evidence suggests that ketones in the brain may help resolve some of the symptoms that people with Parkinson disease experience. Like epilepsy, the mechanism of action has not been discovered, and much more work needs to be done in this area.
Another piece of the puzzle
Understanding how your body works — and why it sometimes breaks down — puts you in the driver’s seat when it comes to your health and diabetes care. Knowing about ketones is vital mainly for people with Type 1 diabetes, but it doesn’t hurt for anyone to know what these substances are and what they can and can’t do for you.