Ketones at levels typically seen during low carbohydrate eating are a signal of fat burning
When carbohydrate intake goes low enough (typically 50 grams a day or less), the body’s physiology shifts from a predominantly glucose (sugar)-burning metabolism to more of a fat-burning metabolism. This is what you want to happen when you are trying to lose weight! Lowering carbohydrate intake allows your body to reduce the production of insulin. Or if you have diabetes and take insulin shots, lowering carbohydrate intake allows you to lower your insulin shot doses. This is important because insulin is a potent stimulator of fat storage (lipogenesis) and a potent inhibitor of fat burning (lipolysis). In other words, lowering carbohydrate intake leads to lower insulin levels, which leads to more fat burning.
Fatty Acids and Ketones In The Body
Ketoacidosis and Diabetes
Ketones have one unhealthy connotation, however. In patients with type 1 diabetes who become ill and do not receive enough insulin medication, ketones can build up to very high levels, causing life-threatening ketoacidosis. Fortunately, this is very unlikely to occur in people whose pancreas still makes insulin. In fact, in one my earliest research studies, I measured the acid and ketone levels in the blood of patients who were following a very low carbohydrate nutritional approach, and none of the blood samples were acidotic. Ketone levels were elevated, demonstrating that fat-burning was occurring, but the levels were not nearly as high as would be seen in diabetic ketoacidosis.
As I mentioned in the previous entry, people with diabetes should check with their doctor before they lower their carbohydrate intake substantially because certain diabetes medications can cause blood glucose to go too low—these medications will need to be reduced or stopped. Also, patients with diabetes who take medicines called SGLT2 inhibitors (canagliflozin, dapagliflozin, and empagliflozin) may be at risk for ketoacidosis even if their blood glucose is controlled, so I recommend stopping these types of medication before reducing carbohydrate intake substantially.
How can you know if you are burning fat?
As I have outlined, ketones are a marker of fat-burning during low-carbohydrate nutrition. As such, some low carbohydrate nutrition followers like to measure their ketone levels to ensure they are lowering carbohydrate intake adequately. This can be done by urine strips, breath testing, or even special finger stick strips similar to those used for measuring glucose levels in diabetes. While it is not critical to measure your ketones to be successful with a low-carbohydrate way of eating (weight loss is also a good marker!), it helps to understand the changes in your metabolism that are occurring. Metabolizing your fat into ketones can be one of several safe and effective ways to lose weight and improve your health.