Low-carb diet: Can it help you lose weight?

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 varies in the type and amount of carbs you can eat.

You or your healthcare team may choose a low-carb diet to help you lose weight. Some low-carb diets may have benefits beyond weight loss, such as lowering your risk of type 2 diabetes or metabolic syndrome.

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

• Want a diet that limits carbs to help you lose weight.
• Want to change your eating habits.
• Want to better manage your blood sugar.
• Want to lower your risk of metabolic syndrome, heart disease or type 2 diabetes.

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

A low-carb diet limits the amount of carbohydrates you eat.

Carbs include three types:

• Sugars, also called simple carbs, such as table sugar.
• Starches, also called complex carbs, such as brown rice.
• Fiber, the parts of foods that are harder for the body to digest, such as apple skins, beans and whole-grain bread.

The body uses carbs as its main energy source. As the body digests food and beverages, it breaks down complex carbs, such as whole grains or white flour, into simple sugars, also called carbs. In general, you digest complex carbs more slowly. Glucose is a type of simple sugar released into the blood as you digest food.

Common sources of healthy carbohydrates include:

• Vegetables, such as Brussels sprouts or cucumbers.
• Whole grains, such as whole-wheat bread, brown rice, oats and quinoa.
• Fruits, such as apples or oranges.
• Legumes, such as black beans, lentils and chickpeas.

Complex carbohydrates are further divided into refined grains, such as white flour, and whole grains, such as whole-wheat flour. Whole grains are healthier than refined grains and simple carbohydrates because they:

• Have more fiber.
• Have more vitamins and other nutrients.
• Have beneficial health effects on blood pressure and blood glucose, as well as cancer, heart disease and other conditions.

Refined grains, such as white flour, often are added to processed foods. Milling and grinding grains such as wheat processes or refines them. This takes out fiber and nutrients. It makes the grains stay fresh longer, but it makes them less healthy for you. Examples of food made with refined grains are white bread and pasta.

In the body, the pancreas releases the hormone insulin, which helps glucose enter the body's cells, like a key unlocks a door. The cells can use glucose for energy only after insulin helps the cells absorb it. The body stores extra glucose in the liver and in muscles. The body also can store extra glucose as body fat.

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

Most low-carb diets focus on proteins, as well as some healthy fats and nonstarchy vegetables. Examples of vegetables low in carbohydrates are lettuce, cucumbers and broccoli.

A low-carb diet generally limits:

• Refined and whole grains such as white bread and whole-grain products.
• Fruits high in carbs, processed fruit products with added sugar, and fruit juice.
• Starchy vegetables such as potatoes and corn.
• Alcoholic drinks that have carbs.

Low-carb diets vary in how many carbs you can eat each day. One gram of carbohydrate has about 4 calories. On average, a low-carb diet allows 60 to 130 grams of carbohydrates a day. So, if you eat 130 grams of carbs, that's 520 calories.

Some very low-carb diets suggest eating less than 60 grams of carbohydrates or 240 calories from carbs each day. Some low-carb diets allow fewer 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 adults ages 19 to 59 eat 130 grams of carbs a day. This is 520 calories from carbs each day. These guidelines also suggest you eat more whole grains and limit foods or drinks with added sugar, sodium and saturated fat.

Most people can lose weight if they limit calories and boost their physical activity. You lose weight when the calories you eat or drink is less than what you need for daily activities and exercise. To lose 1 to 1.5 pounds (0.5 to 0.7 kilograms) a week, you generally 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 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 or can't be kept up.

Cutting calories and carbs may not be the only reason low-carb diets can lead to weight loss. Some studies show that people may lose weight because the extra protein and fat helps them feel full longer. Feeling full longer helps you eat less over time.

Low-carb diets that focus on healthy sources of carbs, such as whole grains and fiber-rich foods; healthy sources of fat and protein; and limiting added sugars may help lower the risk of:

• Type 2 diabetes.
• Heart disease.
• Metabolic syndrome.
• Stroke.
• Cancers of the digestive system, such as colon or rectal cancer.
• High cholesterol.
• High blood sugar.

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

• Constipation.
• Headache.
• Muscle cramps.

Severe limits to carbs can cause your body to break down fat into ketones for energy, leading to ketosis. Ketosis can cause side effects such as bad breath, headache, tiredness, weakness and flu-like symptoms.

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

There are some concerns that eating more fat and protein from animal sources when following a low-carb diet may raise your risk of heart disease or some cancers. But more research is needed to see if it raises your risk of these conditions.

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 increase your cholesterol and your risk of heart disease. Consider more plant-based nutrients instead.