|Partnership for Esssential Nutrition
Low-Carbohydrate Diets: Do They Work and Are They Healthy?
The Partnership for Essential Nutrition is a broad-based group of non-profit consumer, nutrition and public health organizations formed in 2004 to promote programs, policies and research that will advance public understanding about the essentials of a nutritionally balanced diet for weight loss and beyond...
Members of the Partnership for Essential Nutrition are:
* Alliance for Aging Research
* American Association of Diabetes Educators
* American Institute for Cancer Research
* American Obesity Association
* National Consumers League
* National Women's Health Resource Center
* Pennington Biomedical Research Center
* Shape Up America!
* Society for Women's Health Research
* University of California at Davis Department of Nutrition
* Yale-Griffin Prevention Research Center
The United States is in the midst of a skyrocketing obesity epidemic. Today, more than 60 percent of American adults are overweight or obese, according to the Centers for Disease Control and Prevention (CDC),1 and many are investing in diet books, such as those promising rapid weight loss in a matter of weeks by greatly restricting the intake of carbohydrates while eating unlimited amounts of meat and fat.
But despite the popularity of these diet books, numerous studies have shown that low-carbohydrate diets are unlikely to produce long-term weight loss and may lead to severe health problems. Most doctors and nutritionists agree that these diets greatly restrict the consumption of essential nutrients, vitamins and fiber found in plants and whole grains -- all of which help prevent disease and promote improved health. For this reason, the short-run side effects of low-carbohydrate diets include severe constipation, gastrointestinal problems, difficulty in concentrating, loss of energy and a host of other problems.
Of far greater concern, however, is what can happen if people stay on these diets for long periods. According to scientists, losing weight on these types of diets can lead to such serious health problems as kidney stress, liver disorders and gout. These diets also increase the risk for coronary heart disease, diabetes, stroke and several types of cancer. Moreover, a number of new studies have been published that evaluate the short and long-term success of these diets for weight loss, finding that extreme low-carbohydrate diets stress the body and are likely to result in weight "snap back" -- the rapid weight regain that occurs when carbohydrates are reintroduced to a carbohydrate- restricted diet.
The Effectiveness of Low-Carb Diets
The most widely used low-carbohydrate diet is the one advocated by the late Dr. Robert C. Atkins, which was introduced in 1972 and changed in 1992. At the same time, severely restricting the intake of carbohydrates is the basis for a number of diet plans, including the High Protein Diet, Hollywood Diet, and South Beach Diet. In all cases, the premise is the same: a diet very low in carbohydrates leads to a reduction in the body's insulin production, promoting the use of fat and protein (muscle) stores as the body's main energy source.
According to the theory espoused by these diet plans, low-carb diets force the body to use fat as its main energy source, resulting in "ketosis," a process that is jump-started by eliminating carbohydrates, and specifically glucose, which is what the brain needs for normal functioning. When faced with no dietary carbohydrates, the brain first causes the body to metabolize the stores of carbohydrates in the liver and in the muscles and then to metabolize protein in the muscles, which can be converted to carbohydrates. With continued carbohydrate deprivation, the body converts to using fat and the brain is forced to use the metabolic breakdown products of fat, called "ketones," as the source of energy. In the process of making this stressful metabolic shift, people are said to be in a state of "ketosis" - characterized by a smelly breath (an acetone smell like nail varnish) and side effects such as nausea, fatigue, dizziness, and headaches.
Ketosis also produces metabolic dehydration, a type of dehydration that has nothing to do with what one eats or drinks. Metabolic dehydration occurs when the body uses its own stores of carbohydrates and protein, both of which are stored with water. In fact, a classic study reported in the Journal of Clinical Investigation2 found that although people tended to lose weight more quickly on low-carbohydrate diets, the additional weight loss was not fat loss but water loss due to metabolic dehydration. This form of weight loss is extremely stressful on the body and forces the brain to alter its metabolism.
Moreover, the prime reason that low-carbohydrate diets work at all is that people on these plans consume fewer calories than the body needs, which is the same principle used by every other diet. According to a scientific review published in the Journal of the American Medical Association,3 weight loss on low-carbohydrate diets is principally associated with decreased caloric intake. Even though low-carbohydrate diets promise that people can eat large amounts of meat, cheese, butter and other high-fat foods, in reality, the monotony of the diets is a major factor in why people lose weight because they end up being bored and eating less.
Although low-carbohydrate diets clearly produce weight loss, the real question is for how long? To answer this question, a number of studies have begun to examine the long-term results of low-carbohydrate diets compared to the widely recommended diet plans that are lower in saturated fats and high in fruits, vegetables and high-fiber containing carbohydrates. What researchers have found is that temporary additional weight loss on low-carbohydrate diets is entirely explained by metabolic dehydration and that there is no sustained difference after a year.
Some of the key findings are as follows:
* A review of studies on low-carbohydrate diets published in the May 2004 issue of the American Journal of Clinical Nutrition4 found no advantage to these diets compared to equal calorie diets that include carbohydrates. Conducted by researchers at the University of Wisconsin at Madison, this review concluded that calories, not the composition of the diet, was responsible for weight loss and there are no differences in satiety (the feeling of fullness) between the two dietary approaches.
* A classic study published in the Journal of Clinical Investigation5 found that any short-term differences in weight loss between those on either a low-carbohydrate or a balanced diet of equal calories is entirely due to water loss, which cannot be sustained over time. This study demonstrated that fat loss is entirely driven by a reduction in calories and was the first to describe "weight snap back"-- the rapid regain that occurs on low-carb diets when carbohydrates are reintroduced.
* An analysis of the diets of 2,681 people who are listed in the National Weight Control Registry found that fewer than 1 percent who had maintained at least a 30-pound weight loss for a year or more followed a diet with less than 24 percent of the daily calories from carbohydrates.6 Because so few dieters following the Atkins plan were found in the registry, the researchers concluded that very low-carbohydrate diets do not offer a weight loss advantage over the long term (because only dieters with long term weight loss are admitted into the Registry in the first place).
While these studies suggest that the weight loss benefits of low-carbohydrate diets are short-lived at best, an increasing body of research also suggests that what people eat when they go on very low-carbohydrate diets -- proteins and increased amounts of saturated fat -- may put their health at risk. For example, researchers at the University of Kentucky analyzed a week's worth of menus of people following the Atkins Diet and reported that the diet contained 59 percent fat and provided significantly fewer servings of grains, vegetables and fruit than recommended by the U.S. Dietary Guidelines.7 Moreover, a study recently reported in the American Journal of Kidney Disease8 found that very low-carbohydrate diets deliver a marked acid load to the kidneys that increases the risk for kidney stone formation and the potential for bone loss contributing to osteoporosis. [See also Jane Brody's analysis of a 2004 National Academy of Sciences Institute of Medicine report in her article - Preserving a Delicate Balance of Potassium -- June 22, 2004 New York Times, Page D7, for more information about low carb diets and the risks of kidney overload and increased bone loss.]
The Views of Leading Medical/Health Groups
While the public health community is unanimous about the need to reduce obesity in those who are overweight, health officials also stress the importance of losing weight in a healthy manner that doesn't lead to weight snap back or put added stress on the body's vital organs. For this reason, a number of leading nutrition and medical societies have issued advisories warning that low-carbohydrate diets are unproven and may pose serious health risks.
One of the first to issue a warning against low-carbohydrate diets was the American Heart Association, which in 2001 issued a report about the health consequences of high protein diets.9 According to the AHA, restricting carbohydrate levels while consuming large amounts of protein-rich foods that are high in fat can increase the risk of heart disease, high cholesterol, diabetes, stroke and certain kinds of cancer. In taking this action, AHA reviewed the protein and fat levels of many of the most popular low-carb diets, finding that most of these plans greatly exceed the AHA's dietary guidelines of 15 to 20 percent protein and only 10 percent saturated fats a day. For example, the Atkins Diet allows 68 percent of the overall diet to come from fat with 26 percent of from saturated fat.
Also recognizing the potential health consequences of low-carbohydrate diets is the American Kidney Fund,10 which in 2002 warned that high-protein diets have the potential to cause scarring in the kidneys, which have to process more wastes from excess protein. Based on new research conducted on endurance runners whose kidneys were studied after being on a high-protein diet, AKF stated: "We have long suspected that high-protein weight loss diets could have a negative effect on the kidneys and now we have research to support our suspicions. Dehydration forces the kidneys to work harder to clean toxins from the blood."
Low-carbohydrate diets are also a major concern of the American Cancer Society and the American Institute for Cancer Research, which have issued statements advising against the use of low-carb diets. According to the 1997 report of AICR and the World Cancer Research Fund entitled Food, Nutrition and the Prevention of Cancer: a global perspective, diets high in saturated fat increase the risk of prostate and colon cancer. In addition, high-protein diets tend to be low in protective dietary fiber, which has been linked to a lower risk of lung, oral, esophageal, stomach and colon cancer.
Although carbohydrate levels need to be managed by people with diabetes, the American Diabetes Association has also cautioned against the use of low-carb diets.11 In its statement, the ADA said: "Studies in healthy subjects and those at risk for type 2 diabetes support the importance of including food containing carbohydrate from whole grains, fruits, vegetables and low-fat milk in the diet." This same position has been adopted by such organizations as the American College of Preventive Medicine and the American Dietetic Association.
The Bottom Line
Despite all the hype, research confirms that low-carb diets do not perform better in the long term than diets that incorporate essential carbohydrates. Moreover, leading nutrition and medical groups caution against the use of low-carb diets because of the increased risk for such serious health problems as kidney and liver disorders, gout, coronary heart disease, diabetes, stroke and several types of cancer. In sum, experts state that although weight loss is an important goal, choosing a healthy way to lose the weight and keep it off is what really counts.
1 Mokdad et al. The continuing epidemic of obesity in the United States. JAMA 2000; 284: 1650-51.
2 Composition of Weight Loss During Short-Term Weight Reduction. Journal of Clinical Investigation. Vol. 55. September 1976. Pgs 722-730.
3 Efficacy and safety of low-carbohydrate diets. JAMA 289 (14) 2003
4 American Journal of Clinical Nutrition, Vol 79, No. 5: 899S-906S, May 2004
5 Composition of Weight Loss During Short-Term Weight Reduction. Journal of Clinical Investigation. Vol. 55. September 1976. Pgs 722-730.
6 Wyatt HR and others. Long term weith loss and ver low-carbohydrate diets in the National Weight Control Registry. Obesity Research 8 (suppl 1): 87S., 2000
7 Anderson JW and others. Health advantages and disadvantages of weight-reducing diets: a computer analysis and critical review. Journal of the American College of Nutrition 19:578-590, 2000.2
8 Effect of low-carbohydrate high-protein diets on acid-base balance, stone-forming propensity, and calcium metabolism. Am J Kidney Dis 2002
9 Dietary Protein and Weight Reduction: A statement for Healthcare Professionals from the Nutrition Committee of the Council on Nutrition, Physical Activity, and Metabolism of the American Heart Association, 2001;104: 1869-1874
10 The American Kidney Fund: American Kidney Fund Warns About Impact of High-Protein Diets on Kidney Health: 25 April 2002
11 Evidence-Based Nutrition Principles and Recommendations for the Treatment and Prevention of Diabetes and Related Complications. Diabetes Care 25: 148-198, 2002