Your body easily converts carbohydrates into glucose -- your body's preferred source of energy. A low-carb diet limits the amount of glucose you'll make and forces your body to look for an alternative fuel source -- most commonly stored fat. Ketones are a chemical by-product of your body converting fat into energy. Most often ketones are eliminated in your urine, but your body also rids itself of extra ketones in your sweat and breath -- which is why low-carb diets can cause bad breath -- ketones don't smell good.
Low-Carb Diets
Dr. Robert Atkins was one of the first people to suggest a restricted-carb diet for weight loss. The Atkins diet is still one of the most popular low-carb diets and promises to "turn your body into a fat burning machine," according to the Atkins website. Low-carb diets are based on the theory that limiting foods that immediately turn to glucose will force your body to use stored fat for energy. Eating fewer carbs means your body will produce less insulin, which could lead to stabilizing blood sugar levels and reducing food cravings. The Zone, South Beach, Sugar Busters and Nutrisystem diets all limit carbs to some extent and emphasize choosing carbs that have little impact on blood sugar, such as vegetables, fruits, legumes, nuts and some whole grains.
Ketones
When your body converts stored fat into usable energy, an acidic by-product is released -- ketones. Your body is equipped to process ketones. Your body burns stored fat overnight, between meals, when fasting or, historically, in times of famine. Fat is stored precisely for this reason -- to be used as energy to keep your heart and brain functioning in the absence of food. Although normally you would be in and out of a ketogenic state, a low-carb diet may keep you in a constant state of ketosis.
Ketones, Diabetes and Kidney Function
Low-carb diets are often criticized for keeping people in a constant state of ketosis. There is some debate about the long-term health effects of a ketogenic diet. Your kidneys have to work harder to process the larger amounts of protein and ketones associated with low-carb dieting. This can be especially problematic for people with compromised kidney function and diabetics. Diabetics may not be able to eliminate ketones quickly enough, causing a buildup of ketones in the bloodstream. Ketoacidosis is a life-threatening diabetic coma that can result from too many ketones in the blood. Ketoacidosis can only occur with low insulin levels and high levels of both glucose and ketones. It's very unlikely to occur in non-diabetics, but if you have diabetes, consult your doctor before beginning a restricted-carb diet.
Do Low-Carb Diets Work?
In the short-term, a low-carb diet can help you lose weight. The reasons why low-carb diets work are debatable. Some people claim that a limited number of food choices leads to boredom and eating less. Others postulate that because your body burns more calories to consume protein, many of the calories consumed on a high-protein diet are used for digestion. MayoClinic.com suggests that a diet high in fat and protein may help you feel full longer, leading to eating fewer calories or that low-carb diets have a diuretic effect and much of your initial weight loss is simply water weight.
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