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.