Low-carb (high-protein) diets
Popular "fad" diets have been around for decades and are appealing because they often result in rapid, seemingly effortless weight loss, at least initially, owing to loss of body water. Recently, there has been an enormous resurgence in the popularity of low-carbohydrate (high-protein) diets. Such diets promote the same basic idea that was put forth in the 1960s: Eat high-protein foods (such as meat and eggs), and restrict carbohydrate-rich foods (such as potatoes, pasta, fruits, and certain vegetables).
Once relegated to the realm of quackery, these diets are being advocated because carbohydrates are thought to promote weight gain by increasing the body's production of insulin, which speeds up the conversion of food to body fat. Proponents of low-carbohydrate diets also claim that carbohydrates are less filling than other foods, causing people to consume more calories in an effort to satisfy their hunger. Furthermore, in some people, a low-fat, high-carbohydrate diet has been shown to raise triglyceride levels and lower HDL cholesterol levels--two components of metabolic syndrome, which can lead to heart disease and type 2 diabetes.
High-protein diets are being taken seriously by some researchers who recognize that people can lose weight on them. In two recent studies, overweight and obese people who were placed on a diet very low in carbohydrates lost more weight over a six-month period than subjects who followed a low-fat, reduced-calorie diet. However, in both studies, there was no significant difference between the two groups in the amount of weight lost after a year of following the diets. These findings indicate that a low-carbohydrate diet produces more weight loss initially but that dieters following a low-fat diet continue to lose weight over time. More research is needed to determine whether dieters following a low-carbohydrate diet can maintain weight loss or continue to lose weight over a longer period of time.
Furthermore, the long-term effects of a low-carbohydrate diet, which is typically heavy on meat and saturated fat, on coronary heart disease are currently unknown. In the aforementioned studies, subjects following the low-carbohydrate diet experienced a reduction in triglyceride levels and an increase in HDL levels; however, these lipid changes are typical following weight loss. Future studies need to evaluate lipid changes on a long-term basis.
Moreover, the long-term effects of a diet devoid of antioxidants and phytochemicals from fruits, vegetables, and whole grains, which are very restricted on a low-carbohydrate meal plan, are unknown.
Also, several specific health concerns are associated with a diet that places such a heavy emphasis on the consumption of protein and the restriction of carbohydrate. Consuming too much protein places extra stress on the liver and kidneys because they have to metabolize and excrete more than normal amounts of waste products. Kidney stones can be caused or aggravated by the high uric acid levels created by high-protein foods. And for those who have diabetes or kidney disease, high-protein diets may speed the progression of kidney disease, even if the diet is followed for a short time. Furthermore, some studies suggest that eating too much protein causes excessive calcium loss, which can contribute to osteoporosis.
Restricting carbohydrate intake is unhealthy as well. Drastically reducing carbohydrate consumption increases the metabolism of fatty acids and causes ketosis. This condition results when excessive amounts of acidic substances known as ketone bodies are released into the bloodstream. Ketosis can be dangerous for people with known or unrecognized heart disease, diabetes, or kidney problems. In addition, restricting carbohydrates can lead to vitamin and mineral deficiencies. Healthful, carbohydrate-rich foods, such as whole grains, fruits, and vegetables, provide essential nutrients as well as fiber and phytochemicals that work together to help prevent disease and promote good health. In fact, one of the basic underlying problems with most high-protein diets is their failure to promote a balanced diet and to teach long-term healthful eating habits.
High-protein, low-carbohydrate diets are best used selectively on a short-term basis, if at all, and under medical supervision. The many limitations and risks associated with high-protein diets raise important questions about their long-term safety and effectiveness. In fact, a 2003 advisory by the American College of Preventive Medicine states that there is currently little evidence to support the safety and effectiveness of popular diets that promote unlimited consumption of protein or fat.
