Low-Carbohydrate Diets

Stephen Barrett, M.D.

Many promoters of dietary schemes would have us believe that a special substance or combination of foods will automatically result in weight reduction. That's simply not true. To lose weight, you must eat less, or exercise more, or do both.

There are about 3,500 calories in a pound of body weight. To lose one pound a week, you must consume about 500 fewer calories per day than you metabolize. Most fad diets, if followed closely, will result in weight loss—as a result of caloric restriction. But they are usually too monotonous and are sometimes too dangerous for long-term use. Moreover, dieters who fail to adopt better exercise and eating habits will regain the lost weight—and possibly more. My advice to people who are considering a low-carbohydrate diet is not to try it on their own by reading a book but to seek supervision from a physician who can monitor what they do.

The most drastic way to reduce caloric intake is to stop eating completely. After a few days, body fats and proteins are metabolized to produce energy. The fats are broken down into fatty acids that can be used as fuel. In the absence of adequate carbohydrate, the fatty acids may be incompletely metabolized, yielding ketone bodies and thus ketosis. Prolonged fasting is unsafe, because it causes the body to begin to digest proteins from its muscles, heart, and other internal organs.

Low-carbohydrate diets also produce ketosis, but if properly designed, they enable the body's nutritional needs to be met by dietary protein, dietary fat, stored body fat, and stored glycogen, so that body muscles are spared [1]. As this "nutritional ketosis" begins, there is a diuretic (water loss) effect, leading the dieter to think that significant weight reduction is taking place. However, most of the early loss is water rather than fat; the lost water is regained quickly when if the dieter resumes eating carbohyrate (as would occur, for example, with a balanced diet). Appetite, often reduced during ketosis, also returns when a balanced diet is resumed. In the past, it was thought that patients restricted their caloric intake because the food restrictions made the low-carbohydrate diet monotonous. However, current theorists suggest that appetite reduction has a hormonal basis [2].

The most widely publicized low-carbohydrate diet has been the one advocated by the late Robert C. Atkins, M.D., of New York City. His 1972 book Dr. Atkins' Diet Revolution sold millions of copies within the first two years. His 1992 update, Dr. Atkins' New Diet Revolution, has sold even more. The current plan has four steps: a 2-week "induction" period, during which the goal is to reduce carbohydrate intake to under 20 grams per day, and three periods during which carbohydrate intake is progressively raised but kept below what Atkins called "your critical carbohydrate level" for losing or maintaining weight [3]. The dieter is permitted to eat unlimited amounts of noncarbohydrate foods "when hungry," but, as noted above, the diet tends to suppress appetite. The plan calls for checking one's urine for ketone bodies to ensure that the desired level of ketosis is reached. Atkins also recommended large amounts of nutritional supplements. Some physicians prolong the "induction" phase under monitoring.

Research Findings

The AMA Council on Foods and Nutrition [4], Consumer Reports [5], and many individual experts have warned that the unlimited intake of saturated fats under Atkins' food plan can increase the dieter's risk of heart disease. In 2000, experts at the University of Kentucky did a computer analysis of a week's worth of sample menus and reported that the diet contained 59% fat and provided fewer servings of grains, vegetables, and fruits than recommended by the U.S. Dietary Guidelines. Noting that the diet could produce short-term weight loss, they thought that long-term use would probably increase the risk of both cardiovascular disease and cancer [6]. However, clinical trials have not upheld this prediction.

Another study was done by researchers at the Bassett Research Institute in Cooperstown, New York, who followed 18 Atkins dieters for a month. During the 2-week induction period, the dieters consumed 1,419 calories a day, compared with 2,481 calories a day before starting the diet, and lost an average of about 8 pounds. In the next phase, dieters averaged 1,500 calories a day and lost an additional 3 pounds in two weeks. Dieters in both phases cut back on carbohydrates by more than 90%, but the actual amounts of fat and protein they ate changed little. Some patients felt tired, and some were nauseated on the plan. Most indicated that they were eager to go back to their regular diet [7].

Another study found that (a) 41 overweight people who followed the Atkins diet for six months lost an average of 10% of their initial body weight; (b) most lowered their blood cholesterol level by 5%; (c) some increased their cholesterol level; and (d) 20 subjects who continued the program had maintained their weight loss at the end of a year [8].

In yet another study, researchers who compile the National Weight Control Registry analyzed the diets of 2,681 members who had maintained at least a 30-pound weight loss for a year or more. Because the Atkins diet had been used for more than 30 years, the researchers reasoned that, if it worked, its followers would be well represented. However, they found that only 25 (1%) of these successful people had followed a diet with less than 24% of their daily calories in the form of carbohydrates. The mean duration of successful weight maintenance in this low-carbohydrate group was 19 months, whereas the mean duration of dieters who consumed more than 24% of their daily calories as carbohydrates was 36 months. Because so few Atkins dieters were found in the Registry, the researchers concluded that the Atkins diet may not create the favorable "metabolic advantage" claimed for it [9].

The nutrition committee of the American Heart Association has issued a science advisory warning that high-protein diets have not been proven effective and pose health risks. The report covered the Atkins, Zone, Protein Power, Sugar Busters, and Stillman diets. The committee stated:

In 1999. Atkins set up a foundation to provide "funding for research and education on the role of controlled carbohydrate nutritional protocols in treating and preventing a wide range of medical conditions." [11] The availability of funds has generated responsible research.

In 2002, a 6-month study funded found that followers of the Atkins diet lost more weight than comparable people on a high-carbohydrate diet and improved their blood cholesterol and triglyceride levels [12]. However, the dropout rate was much higher in the low-carbohydrate group and the improved lipid levels did not necessarily mean that the diet would have a cardioprotective effect in the long run [13]. In response to publicity about the study, the American Heart Association cautioned:

In 2003, experts who evaluated reports indexed since 1966 in MEDLINE found that weight loss was associated with longer diet duration and calorie restriction but not with reduced carbohydrate content. The researchers concluded:

There is insufficient evidence to make recommendations for or against the use of low-carbohydrate diets, particularly among participants older than age 50 years, for use longer than 90 days, or for diets of 20 g/d or less of carbohydrates. Among the published studies, participant weight loss while using low-carbohydrate diets was principally associated with decreased caloric intake and increased diet duration but not with reduced carbohydrate content [15].

In July 2003, researchers at the University of Pennsylvania reported the results of a controlled study of 63 people who were randomly assigned to either the Atkins diet or a conventional diet. The low-carbohydrate (Atkins) group lost about 4% more weight for the first 6 months, but there was no significant difference between two groups at 1 year. The low-carbohydrate diet appeared to improve risk factors for heart disease, but the authors concluded that more research was needed on the safety and effectiveness of this regimen [16]. In June 2004, Philippe O. Szapary, M.D., an assistant professor who was part of the University of Pennsylvania team, told me:

Two one-year clinical trials that compared the Atkins diet with several other popular diets have found that each could achieve modest weight loss and improvement in cardiac risk factors for participants who were relatively compliant [18]. In the first study, the average loss ranged from 4.6 pounds for the Atkins dieters to 7.3 pounds for the Ornish dieters. In the second study, the average ranged from 10.3 pounds for the Atkins group to 4.8 pounds for the Ornish group [19]. A meta-analysis that included the first of these studies plus four others concluded:

Low-carbohydrate, non–energy-restricted diets appear to be at least as effective as low-fat, energy-restricted diets in inducing weight loss for up to 1 year. However, potential favorable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavorable changes in low-density lipoprotein cholesterol values when low-carbohydrate diets to induce weight loss are considered [20].

The importance of careful monitoring is illustrated by the case of Jody Gorran, a 53-year-old Florida business executive who sued Atkins Nutritionals, Inc. and Atkins's estate for negligent misrepresentation, product liability, and deceptive and unfair trade practices. The suit, filed in 2004, charges that Gorran's total and LDL-cholesterol levels shot up from very low to abnormally high within two months after he began following the Atkins diet, but he continued using it because passages in Atkins's book and Web site reassured him that it was safe to do so. About two years later, he developed angina and required angioplasty to unblock a coronary artery that had nearly closed. His suit sought damages plus a court order to force Atkins's books, Web sites, and product promotions to warn that low-carbohydrate diets can be hazardous to health and increase the blood level of LDL-cholesterol [21]. The court ruled that the diet consists of "ideas and advice" that are protected by the First Amendment [22].

In July 2008, the New England Journal of Medicine published the results of the first two-year study involving a low-carbohydrate diet. The study compared a low-carbohydrate diet, a 30%-fat diet recommended by the American Heart Association, and a 35%-fat "Mediterranean" diet that included portions of olive oil and nuts. Among the 272 participants who completed the study, the average weight loss was about 6.3 pounds for the low-fat group, 9.7 pounds for the Mediterranean-diet group, and 10.3 pounds for the low-carbohydrate group, and the low-fat group showed less improvement than the other groups in blood cholesterol levels [23]. Many news reports have represented this study as showing that Atkins was right and that the low-carbohydate diet scored better than the others. However, such conclusions are simplistic. The actual average dietary fat content of the three groups turned out to be 30% for the "low-fat" group, 33% for the Mediterranean diet group and 40% for the low-carbohydrate group. The amount of weight lost was small, differences among the groups were not large, and the study was done with close monitoring and may not reflect what happens when people diet on their own. The study merely adds to the evidence that a 40%-fat, low-carbohydrate diet can be an alternative to a 30%-fat diet, which I would consider to be moderate rather than low in fat. Although the low-carbohydrate diet was said to be based on the Atkins diet, using Atkins's books to construct one's diet would probably result in a diet that is 45% to 60% fat.

The Bottom Line

Atkins advocated his diet for more than 30 years and stated that more than 60,000 patients treated at his center had used his diet as their primary protocol. However, he never published any study in which people who used his program were monitored over a period of several years. It would not have been difficult for him to compile simple data, but I have seen no evidence that did so. Recent studies of up to two years have found that low-carbohydrate diets can produce modest weight loss and reduction in cardiac risk factors, which means that they are safer than previously thought. However, it has not yet been determined whether such diets are safe for long-term use or can reduce the incidence of coronary heart disease.

The popularity of low-carbohydrate diets has encouraged food companies to market low-carbohydrate foods for people who want to "watch their carbs." Most of these foods are much higher in fat than the foods they are designed to replace. I believe that "low-carb" advertising is encouraging both dieters and nondieters to eat high-fat foods, which is exactly the opposite of what medical and nutrition authorities have been urging for decades. Following a low-carbohydrate diet under medical supervision may make sense for some people, but a population-wide increase in fat consumption would not. My advice to people who are considering a low-carbohydrate diet is not to try it on their own by reading a book, but to seek supervision from a physician who can monitor what they do.

For Additional Information


  1. Westman E and others. Low-carbohydrate nutrition and metabolism. American Journal of Clinical Nutrition 86:276-284, 2007.
  2. Boden G and others. Effect of a low-carbohydrate diet on appetite, blood glucose levels, and insulin resistance in obese patients with type 2 diabetes. Annals of Internal Medicine 142:403-411, 2005.
  3. Four steps to a healthy new lifestyle. Atkins Center Web site, accessed April 2001 through February 2005.
  4. White PL. A critique of low-carbohydrate ketogenic weight reduction regimens: A review of Dr. Atkins' diet revolution. JAMA 224:1415-1419, 1973.
  5. Top-selling diets: Lots of gimmicks, little solid advice. Consumer Reports 63:60-61, 1998.
  6. 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.
  7. Miller BV and others. Effects of a low carbohydrate, high protein diet on renal function. Obesity Research 8(supplement 1):82S, 2000.
  8. Hellmich N. Success of Atkins diet is in the calories. USA Today, Nov 8, 2000.
  9. Wyatt HR and others. Long term weight loss and very low carbohydrate diets in the National Weight Control Registry. Obesity Research 8(suppl 1):87S., 2000.
  10. St. Joer TS and others. Dietary protein and weight reduction. Circulation 104:1869-1974, 2001.
  11. Robert C. Atkins, M.D., world-famous nutrition expert and best-selling author dies at 72. Atkins Center news release, April 17, 2003.
  12. Westman EC and others. Effect of 6-month adherence to a very low carbohydrate diet program. American Journal Medicine 113:30-36, 2002.
  13. Fumento M. Hold the lard: The Atkins diet still doesn't work.
  14. American Heart Association statement on high-protein, low-carbohydrate diet study presented at scientific sessions. American Heart Association press release, Nov 19, 2002.
  15. Bravata DM and others. Efficacy and safety of low-carbohydrate diets: A systematic review. JAMA 289:1837-1850, 2003.
  16. Foster GD and others. A multicenter, randomized, controlled trial of a low-carbohydrate diet for obesity. New England Journal of Medicine 348:2082-2090, 2003.
  17. Szapary P. Telephone interview by Dr. Stephen Barrett, June 24, 2004.
  18. Dansinger ML and others. Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial. JAMA 593:43-53, 2005
  19. Gardner CD and others. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women. The A TO Z Weight Loss Study: A randomized trial. JAMA 297:969-977, 2007.
  20. Nordmann AJ and others. Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors. A meta-analysis of randomized controlled trials. Archives of Internal Medicine 166:285-293, 2006.
  21. Complaint. Jody Gorran v. Atkins Nutritionals Inc. Palm Beach (Florida) County Court, filed May 26, 2004.
  22. Opinion. Jody Gorran v. Atkins Nutritionals Inc. U.S. District Court for the Southern District of New York. Case No. 05 Civ. 10679 (DC). Filed Dec 11, 2006.
  23. Shai and others. Weight loss with a low-carbohydrate, Mediterranean, or low-fat diet. New England Journal of Medicine 359:229-241, 2008.

This article was revised on August 20, 2008.

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