High-protein, low-carb diets

Over the last 20 years, obesity has become a major health problem in the United States. More than 60 percent of adults are estimated to be either overweight or obese, and up to 80 percent of these adults report trying to lose or maintain their weight.

In response, many diets and other weight-reduction methods abound. One diet that's gained popularity is the high-protein, low-carbohydrate diet. Versions include Atkins, Carbohydrate Addicts, Protein Power, South Beach, Stillman, Sugar Busters and the Zone. In response to the low-carb trend, low-carb and carb-free foods are appearing on store shelves and restaurant menus -- despite the fact that the U.S. Food and Drug Administration (FDA) hasn't yet defined these terms.

High-protein, low-carb diets may initially result in rapid weight loss, but further research is needed to know if they're a safe or effective way to maintain weight loss.


Nutrition basics
The foods we eat supply our bodies with the energy and nutrients needed to function every day. A healthy diet includes carbohydrates, protein, fats, vitamins, minerals and water. Each has a different function and is needed in different amounts. Let's look at the role of each of these nutrients.
Carbohydrates
Simple and complex carbohydrates are our main sources of energy. In our bodies, carbohydrates are converted into glucose. Insulin, a hormone produced by the pancreas, plays an essential role in moving glucose into the cells to be converted into energy. Think of insulin as the key that opens our cells, allowing the glucose to enter. During digestion, glucose levels in the blood rise. This stimulates the pancreas to release insulin into the bloodstream.

Simple carbohydrates, known as sugars, are found in fruits and foods containing refined sugar, such as jam, jelly, syrup, candy, cakes, cookies, ice cream, pie and sweetened cereal. When eaten, simple carbohydrates are quickly converted into glucose to provide a rapid boost of energy. Complex carbohydrates, known as starches, are found in foods such as breads, cereals, pasta, rice, potatoes, fruits and vegetables. During digestion they're first changed into simple sugars and then into glucose. This longer digestion process provides a slower, steadier source of energy than the sugars. Excess carbohydrates that aren't needed in the cells are stored in the liver and muscles as glycogen, which can be converted into glucose if energy is needed quickly. If glycogen stores are full, excess carbohydrates become body fat.

The glycemic index (GI) is a newer system of classifying carbohydrates. This index measures how quickly and how much carbohydrates raise blood sugar after they're eaten. Foods with a high GI quickly produce a high blood sugar, such as sugar, honey, candy, soft drinks, potatoes, bananas, and highly processed grains and cereals. Foods with a low GI produce a slower, lower change in blood sugar. Included in this group are foods often high in fiber, such as most whole fruits, legumes, whole grains, and whole-grain breads and cereals. Researchers have linked diets containing lots of high GI foods with an increased risk of diabetes and heart disease. They've also found that diets containing low GI foods may help control diabetes.

Protein
Protein is a complex combination of simpler substances known as amino acids. Protein is found in all body cells and is a major component of muscles, bones, skin, hair and other organs. It's essential for normal growth, tissue repair and the production of hormones and enzymes that regulate body functions. During digestion, these complex compounds are slowly broken down into individual amino acids and carried by the blood to the body cells. Foods high in protein include meat, fish, poultry, egg whites, dairy products, nuts and beans. If we eat more protein than we need, the excess is stored as body fat, which can later be converted into energy. If carbohydrate and fat stores cannot provide enough energy, proteins can also be converted into energy.

Fats
Fats provide energy, help produce hormones and allow your body to absorb vitamins A, D, E and K. Unused fats are stored to help maintain body temperature and cushion and protect vital organs. Fats help satisfy your appetite and delay hunger because they're digested slowly. Dietary fats are classified as unsaturated, saturated or trans fats.

Unsaturated fats are found in olive, peanut and canola oils, and fatty fish such as salmon, sardines, herring and mackerel.
Saturated fats are found in animal products such as meat, seafood, egg yolks and dairy products, as well as coconut, palm and palm kernel oils.
Trans fats are described as "hydrogenated" or "partially hydrogenated" and are found in foods such as margarine and shortening, as well as products such as cookies, crackers, cake, donuts and commercial french fries.
Too much dietary fat, especially from saturated and trans fats, increases the risk of heart disease and possibly some types of cancer. Saturated and trans fats have been linked to higher blood cholesterol levels, a major risk factor for heart disease. Replacing saturated and trans fats with unsaturated fats can help lower this risk.


High-protein, low-carb diet basics
High-protein, low-carb diets are based on the theory that carbohydrates stimulate the production of insulin, which increases appetite and promotes weight gain. When carbohydrates are eliminated or limited in favor of more protein, a slower, steadier supply of energy is thought to lead to appetite control and weight loss. "Bad carbs," or those with a high glycemic index, are typically limited in these diets. Carbs with a low GI, or "good carbs," may be allowed. Some high-protein, low-carb diets limit fats or focus on unsaturated fats. Others are more liberal with fat intake.
If you're not eating carbs, your body will use stored carbohydrates (glycogen) and then stored fat to meet your energy needs. More weight is typically lost early in a high-protein, low-carb diet because large amounts of water are excreted in the urine when glycogen is converted to energy. When the fat stores are used, a byproduct known as ketones is produced and circulates in the bloodstream. This condition, known as ketosis, has been shown to decrease appetite.


Benefits
High-protein, low-carb diets help decrease your appetite. Most are low in calories, which helps assure potentially rapid weight loss. After one year, however, weight loss appears to be about the same as low-fat, moderate-protein, high-carb diets. High-protein, low-carb diets may help improve blood cholesterol and triglyceride levels, major contributors to heart disease. One recent short-term study noted improvement even when the diet was high in fat. However, more research is needed.

Disadvantages/risks
Thus far, no short-term medical risks of high-protein, low-carb diets have been identified. A lack of dietary fiber can cause constipation, however, and you may need to add high-fiber foods or take supplements because the diet may not provide all the vitamins and minerals necessary for good health. Some dieters report boredom with the limited food choices.
Long-term risks of high protein, low-carb diets have not yet been studied. It may be years before researchers can adequately evaluate the effect on health conditions such as kidney disease, heart disease, cancer and osteoporosis.

When ketosis occurs, it can cause fatigue, bad breath and nausea. Some authorities question the possible long-term effects of ketosis on the kidneys, since ketones are filtered out of blood by the kidneys. Some evidence has suggested that high-protein diets may contribute to decreased kidney function in later years.

Some researchers are concerned that high-protein, low-carb diets that contain large amounts of fat -- especially saturated and trans fats -- may increase the risk of heart disease and colon cancer. Even though recent short-term studies have shown actual improvement in blood cholesterol and triglyceride levels, the long-term effects are unknown.

Diets that contain large amounts of protein may also increase the risk of osteoporosis, a condition characterized by decreased bone density and an increased risk of fractures. The digestion of protein requires calcium, a mineral that's essential in maintaining bone density. If you eat large amounts of protein but not enough calcium, the mineral is taken from your bones. This is an especially important consideration for postmenopausal women and others who already have an increased risk of osteoporosis. Although following a high-protein, low-carb diet for a short time may not weaken your bones, the long-term effects are unknown.


When a high-protein, low-carb diet may not be appropriate
High-protein, low-carb diets are not recommended for children, pregnant women or people who have kidney or liver disease.

Pregnancy-specific information
Dieting and weight loss are not recommended during pregnancy. Good nutrition supplies your baby with the proper nutrients and calories needed for normal growth and development. Recent studies suggest that a mother's high-protein diet may cause a baby to be smaller than normal at birth, as well as increase the baby's risk of high blood pressure later in life. If you're pregnant, discuss your nutritional needs with your doctor.

Senior-specific information
Again, the long-term effects of high-protein, low-carb diets on health conditions common in older adults -- such as kidney disease, heart disease, cancer and osteoporosis -- are unknown. If you're considering a high-protein, low-carb diet, discuss the risks and benefits with your doctor.

Considerations
When choosing a diet or weight-loss program, it's important to consider the risks and benefits with your doctor. Remember that most authorities still recommend regular physical activity and a healthful diet that includes a balance of foods. The U.S. Department of Agriculture food guide pyramid is a good place to start. Make sure to eat plenty of fruits and vegetables, whole-wheat grains and lean meats, such as chicken and fish.
Be cautious about diets that claim to help you lose large amounts of weight in a short time. For healthy weight loss and better success keeping the weight off in the long run, most authorities recommend losing no more than an average of 2 pounds per week. For each pound you want to lose, you must burn 3,500 more calories than you consume. If you're able to reduce your caloric intake by 500 calories a day, burn the same amount of calories through increased physical activity or reach the 500-calorie point through a combination of both, you'll lose about 1 pound per week -- a rate considered safe for most people.