One day they're in, the next day they're out again. But whether we're talking about Atkins or South Beach, low-carb diets are one fad that never seems to die.
If you haven't tried a low-carb diet, you may not know that many of these programs restrict all kinds of carbohydrates, and not just the obvious ones, such as bread, rice, and pasta. For example, Atkins, perhaps the best-known low-carb diet around, also excludes most grains, beans, fruits, potatoes, and starchy vegetables, while allowing lots of beef, pork, chicken, eggs, and butter.
Low-carb diets work because when you consume low levels of carbohydrate, your body has to resort to burning stored carbohydrates (glycogen) in order to fuel itself. Then your body starts to burn stored fat, resulting in a process called ketosis. Ketosis is what happens when the body burns fat without carbohydrate, resulting in the buildup in the bloodstream of a by-product called ketones. Ketones suppress appetite but may also cause you to feel tired or nauseated.
In theory, low-carb diets sound like a great way to lose weight. One study found a low-fat, low-carb, high-protein diet to be as effective for weight loss as a low-fat, high-carb, low-protein diet. Both diets also lowered blood cholesterol and insulin, but the patients on the low-carb diet reported less hunger and more satisfaction.
It is important to note, however, that the diet in this study differed from the popular Atkins, which is high in fat. But another study which compared an Atkins-style diet to a low-calorie, low-fat, high-carbohydrate diet found that subjects on the Atkins-style plan initially lost more weight and had a greater increase in HDL or "good" cholesterol than those on the high-carb plan. After one year, however, weight loss for both groups was similar, and subjects on both diets were equally likely to drop out.
But while being able to eat all the steak, butter, and eggs you want and still lose weight may sound like a great plan, there is a downside: A diet that's rich in meat and high in fat can take a toll on your health.
One recent study, published in the Journal of the American Medical Association, suggested that eating lots of red meat over a prolonged period is associated with a higher risk of colorectal cancer. Because of the increased strain so much meat puts on your kidneys, low-carb diets can also increase your risk of kidney stones and may deplete your calcium levels, putting you at risk for osteoporosis. You may also be at increased risk of developing gout.
And while the Atkins diet was shown to raise HDL levels in the short term, so far there is no research on how this diet - which is high in cholesterol-promoting saturated fat - affects heart health in the long term. As well, because this diet cuts out so many foods that provide vital nutrients - things like whole grains, fruits, and veggies - it's important to think about the long-term effect this could have on your ability to fight other diseases.