A low-carb diet limits carbohydrates, often called carbs — such as those found in grains, starchy vegetables and fruit. A low-carb diet focuses on foods high in protein and fat. Many types of low-carb diets exist. Each diet has varying limits on the type and amount of carbs you can eat.

A low-carb diet is generally used for weight loss. Some low-carb diets may have health benefits beyond weight loss, such as lowering your risk of type 2 diabetes and metabolic syndrome.

Why you might follow a low-carb diet

You might choose to follow a low-carb diet because you:

• Want a diet that limits some carbs to help you lose weight.
• Want to change your overall eating habits.
• Enjoy the type and amount of food used in low-carb diets.

Check with your health care provider before starting any weight-loss diet, especially if you have any health conditions, such as diabetes or heart disease.

A low-carb diet limits the amount of carbohydrates you eat. Carbs are grouped as:

• Simple natural, such as lactose in milk and fructose in fruit.
• Simple refined, such as table sugar.
• Complex natural, such as whole grains or beans.
• Complex refined, such as white flour.

Common sources of natural carbohydrates include:

• Grains.
• Fruits.
• Vegetables.
• Milk.
• Nuts.
• Seeds.
• Legumes, such as beans, lentils and peas.

In general, you digest complex carbs more slowly. Complex carbs also have less effect on blood sugar than refined carbs do. They also offer fiber.

Refined carbs such as sugar or white flour are often added to processed foods. Examples of foods with refined carbs are white breads and pasta, cookies, cake, candy, and sugar-sweetened sodas and drinks.

The body uses carbs as its main energy source. During digestion, complex carbs are broken down into simple sugars, also called glucose, and released into your blood. This is called blood glucose.

Insulin is released to help glucose enter the body's cells, where it can be used for energy. Extra glucose is stored in the liver and in muscles. Some is changed to body fat.

A low-carb diet is meant to cause the body to burn stored fat for energy, which leads to weight loss.

Typical foods for a low-carb diet

In broad terms, a low-carb diet focuses on proteins and some nonstarchy vegetables. A low-carb diet generally limits grains, legumes, fruits, breads, sweets, pastas and starchy vegetables, and sometimes nuts and seeds. But some low-carb diet plans allow small amounts of fruits, vegetables and whole grains.

A daily limit of 0.7 to 2 ounces (20 to 57 grams) of carbohydrates is typical with a low-carb diet. These amounts of carbohydrates provide 80 to 240 calories. Some low-carb diets greatly limit carbs during the early phase of the diet. Then those diets allow more carbs over time.

In contrast, the Dietary Guidelines for Americans recommend that carbohydrates make up 45% to 65% of your total daily calorie intake. So if you eat or drink 2,000 calories a day, carbs would account for between 900 and 1,300 calories a day.

Weight loss

Most people can lose weight if they limit calories and boost their physical activity. To lose 1 to 1.5 pounds (0.5 to 0.7 kilograms) a week, you need to eat 500 to 750 fewer calories each day.

Low-carb diets, especially very low-carb diets, may lead to greater short-term weight loss than do low-fat diets. But most studies have found that at 12 or 24 months, the benefits of a low-carb diet aren't very large.

Cutting calories and carbs may not be the only reason for the weight loss with low-carb diets. Some studies show that you may shed some weight because the extra protein and fat helps you feel full longer. Feeling full longer helps you eat less.

Other benefits

Low-carb diets that focus on healthy sources of carbs, fat and protein may help lower the risk of type 2 diabetes and heart disease. In fact, almost any diet that helps you shed excess weight may improve blood sugar and cholesterol levels, at least in the short term.

A sudden and large drop in carbs can cause short term side effects, such as:

• Constipation.
• Headache.
• Muscle cramps.

Severe carb limits can cause your body to break down fat into ketones for energy. This is called ketosis. Ketosis can cause side effects such as bad breath, headache, fatigue and weakness.

It's not clear what kind of possible long-term health risks a low-carb diet may pose. If you limit carbs in the long term, it may cause you to have too little of some vitamins or minerals and to have digestive issues.

Some health experts think that if you eat large amounts of fat and protein from animal sources, your risk of heart disease or certain cancers may go up.

If you opt to follow a low-carb diet, think about the fats and proteins you choose. Limit foods with saturated and trans fats, such as meat and high-fat dairy products. These foods may make your risk for heart disease go up.