The idea behind restricting your carb intake is to reach a state of ketosis in which your body, having used all its glucose stores, begins burning fat for energy. Urine and blood tests can confirm ketosis, but certain signs can also reveal the body's switch from glucose use to ketones for fuel, including the presence of acetone breath, a decrease in appetite and constipation. While low-carb diets help you lose weight, not much is known about the long-term effects of ketosis, so you should consult with your doctor before starting a low-carb diet.
Noticeable Signs of Ketosis
It takes about three to four days for your body to burn through your glucose and start using fat for energy. One of the first things you -- or more likely your friends -- may notice once you hit ketosis is your breath. Ketone production creates acetoacetate, beta-hydroxybutyric acid and acetone. Acetone is a toxic chemical you may know better as nail polish remover. It causes your breath to smell sweet or fruity, similar to nail polish.
Feeling less hungry may also be a sign you've reached ketosis. Its been theorized that ketosis affects appetite hormones, decreasing your desire to eat, according to a 2013 article published in the European Journal of Clinical Nutrition.
Although not a pleasant sign, constipation may also indicate ketosis. Without carbs, you're not getting enough fiber, which may make it more difficult to have a bowel movement.
Measurable Signs of Ketosis
Your breath, appetite and bowel function may indicate you're in ketosis, but you may want to confirm it with measurable tools. Your body excretes ketones through urine. Urine ketone testing strips, which you can find at your local pharmacy, are commonly used to test for ketosis. These strips may be able to tell you when you're in ketosis before any of the noticeable signs occur. Talk to your doctor about how to use these strips.
Although usually reserved for people with diabetes, a blood test may also be used to determine ketosis. However, as an invasive test that requires a doctor's order, it may not be necessary on your low-carb diet if you're showing other signs.
Low-Carb Diet and Weight Loss
Getting into ketosis and burning body fat certainly makes the low-carb diet appealing, especially when it also helps control appetite. However, your weight loss may be more about calories than ketosis. Although every low-carb diet is different, some of the most popular cut your caloric intake by as much as 500 calories a day, according to a 2001 article published in The American Journal of Cardiology. A 500-calorie deficit each day will theoretically result in a 1-pound weight loss over a week's time.
To lose weight, you need to create a negative calorie balance, which means you're consuming fewer calories than you're burning. Any diet -- whether low-carb or not -- that limits your calorie intake helps you lose weight. The key is to find one that suits your taste buds and that you can stick to for life.
Side Effects of Ketosis
While diets that help get you into ketosis have been shown to help with weight loss and to improve a number of health markers, such as lowering blood glucose levels, cholesterol and triglycerides, there are side effects. Common issues include dehydration and the formation of kidney stones. Drinking plenty of water -- at least 8 cups a day -- while following a low-carb diet may help prevent some of these side effects. Also, restricting your carb intake enough to get into ketosis means you need to eliminate nutrient-rich foods, including fruits, vegetables and whole grains, which may lead to nutritional deficiencies.
Drinking too much alcohol can also lead to ketosis. If you're experiencing symptoms of ketosis and not following a low-carb diet, see your doctor immediately.
Signs for Concern
Under most circumstances, ketosis on a low-carb diet causes mild acidosis, a condition in which your body's pH is slightly lower than normal, which is considered safe, according to a 2015 article published in Nutrition Journal. Some signs of ketosis may, however, indicate that you're in ketoacidosis, which is a life-threatening condition that causes your blood pH to fall below 7. Normal blood pH falls between 7.35 and 7.45. Ketoacidosis is common in people with type 1 diabetes, but a rare occurrence on a low-carb diet.
Signs of ketoacidosis include confusion, nausea, vomiting, dehydration, shortness of breath, rapid heartbeat, fatigue and increased urination and thirst. If you're experiencing any of these signs on your low-carb diet, call your doctor immediately or go to the nearest emergency room.
- European Journal of Clinical Nutrition: Beyond Weight Loss: A Review of the Therapeutic Uses of Very-Low-Carbohydrate (Ketogenic) Diets
- The American Journal of Cardiology: Metabolic Effects of High-Protein, Low-Carbohydrate Diets
- Diabetes.co.uk: Ketosis
- Experimental and Clinical Cardiology: Long-Term Effects of a Ketogenic Diet in Obese Patients
- University of California at San Francisco: Ketones
- British Journal of Nutrition: Very-Low-Carbohydrate Ketogenic Diet V. Low-Fat Diet for Long-Term Weight Loss: A Meta-Analysis of Randomised Controlled Trials
- Diabetes Forecast: How the Body Uses Carbohydrates, Proteins and Fats
- Agency for Toxic Substances and Disease Registry: Acetone
- New England Journal of Medicine: Comparison of Weight-Loss Diets With Different Compositions of Fat, Protein and Carbohydrates
- FamilyDoctor.org: What It Takes to Lose Weight