"Ketosis" is a word you'll probably see when you're looking for information on diabetes or weight loss. Is it a good thing or a bad thing? That depends.
Ketosis is a normal metabolic process, something your body does to keep working. When it doesn't have enough carbohydrates from food for your cells to burn for energy, it burns fat instead. As part of this process, it makes ketones.
If you're healthy and eating a balanced diet, your body controls how much fat it burns, and you don't normally make or use ketones. But when you cut way back on your calories or carbs, your body will switch to ketosis for energy. It can also happen after exercising for a long time and during pregnancy. For people with uncontrolled diabetes, ketosis is a sign of not using enough insulin.
Ketosis can become dangerous when ketones build up. High levels lead to dehydration and change the chemical balance of your blood.
Ketosis is a popular weight loss strategy. Low-carb eating plans include the first part of the Atkins diet and the Paleo diet, which stress proteins for fueling your body. In addition to helping your burn body fat, ketosis can make you feel less hungry. It also helps you maintain muscles.
For healthy people who don't have diabetes and aren't pregnant, ketosis usually kicks in after 3 or 4 days of eating less than 50 grams of carbohydrates per day. That's about 3 slices of bread, a cup of low-fat fruit yogurt, or two small bananas. You can start ketosis by fasting, too.