Research Review by Guest Contributor Denis Collier ©
RD, MSc, PFLC Registered Dietitian - Exercise Physiologist - Conditioning Specialist


Sept. 2005


Nutrition Review of Low Carbohydrate Dieting



There is perhaps no hotter topic in the world of nutrition than that of low-carbohydrate dieting for weight loss. In the last several decades, the growing obesity problem in North America has spawned a myriad of diet books, pills and programs. Few have received as much main stream popularity as the low carb diet craze that came into prominence in the late 1990`s.

Advocates of this approach would have you believe they have at long last uncovered the weight loss secret that has eluded us for generations. But from a scientific point of view, what does the research say about the effectiveness of this dietary strategy? Such is the focus of this brief review.


Obesity is the most common metabolic condition in industrialized nations. It has been reported that 30.5% of Canadians between the ages of 20 and 64 have a body mass index greater than 271 (a BMI greater than 25 qualifies as overweight, while greater than 30 qualifies as obese). The prevalence of overweight in the U.S. was 65% in 1999-2000, while 30.5% of the population qualified as obese(2).


Obesity is known to reduce the quality of life, increase morbidity and lead to premature death(1)(2). Cardiovascular disease, cancer and diabetes accounted for 65% of all deaths in the United States in the year 2000 and excess body weight is a known contributor to all these disease processes(2). In their 1999 review, Birmingham et al. found that more than 20% of all cases of endometrial cancer, gall bladder disease, hypertension, pulmonary embolism and type 2 diabetes in Canada were attributable to obesity.

Other comorbidities that have been linked to obesity include postmenopausal breast cancer, colorectal cancer, coronary artery disease, hyperlipidemia, stroke(1) and hypertension(2). In addition, obese individuals are affected by various psychological and social restrictions(1).

The estimated total direct cost of obesity to the health care system in Canada in 1997 was $1.8 billion dollars(1). The authors of the investigation also suggested that this is likely a conservative estimate. In the U.S. the estimated direct and indirect annual costs from obesity are approximately $117 billion(2).

It is anticipated that the prevention and treatment of obesity, as a main underlying cause of cardiovascular disease, cancer and diabetes, will lead to significant reductions in disability, premature mortality and health care costs in North America(1)(2).


Dieting Before the Low Carb Craze:

In 1997, the American Dietetic Association released a position statement on weight management. They stated that successful weight management to improve overall health for adults requires a lifelong commitment to healthful lifestyle behaviours emphasizing sustainable and enjoyable eating practices and daily physical activity(3).

Prior to 1997, these had been the basic recommendations of most major diet plans. "Weight Watchers" had been in existence for years, operating on the basic premise of restricting portion sizes and Calories via a specific point system.

The first major shift from this conventional thinking toward a low carbohydrate approach could be traced to the appearance of "The Zone Diet" in 1995. Although this diet does not specifically preach carbohydrate avoidance to the same degree as later diets, it does include a carbohydrate recommendation lower than common previous recommendations. The premise of "The Zone Diet" is to consume the proper macronutrient ratio (specifically, 40:30:30% of carbohydrate, protein and fat, respectively) at every meal.

Low-Carb Dieting:

The stage for the low carb boom was set with the debut of "The Atkins Diet" in 1998. As the diet increased in popularity, and more and more people heralded its weight loss effects, a need for scientific inquiry was born. One of the first large reviews of low carb studies appeared in the Journal of the American Medical Association in 2003. The conclusion was that there was insufficient evidence to make recommendations for or against the use of low carbohydrate diets, particularly among individuals more than 50 years old, for use longer than 90 days or for diets of 20 grams of carbohydrates or less per day.

The reviewers issued no denial that some studies did find that participants lost weight on low-carbohydrate diets, but qualified this weight loss by saying that it was principally associated with decreased caloric intake and increased diet duration, not necessarily with reduced carbohydrate content(4).

A year later another review appeared in the American Journal of Clinical Nutrition. These reviewers identified 9 studies of free-living adults in which weight losses in subjects consuming diets high in protein and/or low in carbohydrate were compared with those in subjects consuming diets high in carbohydrate and/or low in fat.

On average, consumption of the high protein and/or low carbohydrate diets resulted in 12 week and 24 week weight losses that were 2.5 ± 1.8 and 4.0 ± 0.4 kilograms greater, respectively, than those that resulted from consumption of the high carbohydrate and/or low fat control diet(5). However, the studies reviewed were not without their problems. Four of the nine studies had an ad libitum energy intake for at least one group.

Also, the studies were generally of a very short duration. Two of the studies that did have a fixed energy intake were of only four and three weeks, respectively. Only six of the studies were greater than 12 weeks.

Most recently, a study by Dansinger et al. was published in the Journal of the American Medical Association comparing several popular dietary regimes. A one year randomized trial of the Atkins, Zone, Weight Watchers and Ornish diet plans aimed to determine their realistic clinical effectiveness and sustainability for weight loss and cardiac risk factor reduction. Subjects were divided into one of four groups (40 per group); one for each of the diet plans being investigated.

Each group received dietary advice in small classes. Only the dietary component of each plan was monitored, not other things each plan might recommend; for example, each group was given same advice about exercise. All four diets resulted in modest statistically significant weight loss at one year, with no statistically significant difference between the diets. In each group, approximately 25% of the participants sustained a one year weight loss of more than 5% of initial body weight and approximately 10% lost more than 10% of initial body weight.

The investigators concluded that all the diets studied can reduce weight and several cardiac risk factors under realistic clinical conditions, but only for the minority of individuals who can sustain a high dietary adherence level. None of the diets produced satisfactory adherence rates; more people discontinued the Ornish and Atkins diets (20)(19), but this was not significantly more than the other two diets (who each had 14 people drop out(6).

The findings of this study were contrary to those of at least four other studies published since 2003 that found a low carbohydrate to be superior to standard diets for producing weight loss(6).


It is indisputable that several recent studies have found that low carbohydrate diets can produce weight loss. Some studies even purport that they can do so better than conventional diets. So should dietitians begin recommending a low carb diet plan for every over-weight client?

Not necessarily. The following are some issues that compromise the validity of these studies:
  1. High drop-out rate - Subjects found it difficult to adhere to the low carb diets prescribed in these studies(7). In the Dansinger study, a strong association was observed between self-reported dietary adherence and weight loss that was almost identical for each diet; in other words, the most important factor in losing weight was not which diet you were on, but how well you stuck to it. Practical techniques to increase dietary adherence rates are urgently needed(6).
  2. Failure to address the quality of weight loss - There is the possibility of significant losses of water weight on a low carb diet as water is lost with diminishing glycogen levels. Future studies should include a measure of body composition to provide more information about the quality of weight loss(5).
Short duration - Short term weight loss is not important. Trials are needed that span 5-10 years so that information can be gathered on long-term weight loss(7). The American Cancer Society, The American Diabetes Association and the American Heart Association recently collaborated on a scientific statement which reviewed strategies for the prevention and early detection of their respective diseases. They stated that although much remains to be learned about the role of specific nutrients or combination of nutrients in decreasing the risk of chronic disease, dietary patterns that emphasize whole-grain foods, legumes, vegetables and fruits and that limit red meat, full-fat dairy products and foods and beverages high in added sugars are associated with decreased risk for a variety of chronic diseases.

It is also critically important that individuals limit their overall caloric intake and become physically active to maintain a healthy body weight(2). Although much has happened in seven years, these recommendations are essentially the same as the position statement issued by the American Dietetic Association in 1997(3).

  • There is ample evidence that low carbohydrate dietary regimes can produce weight loss in the short term. However, there is no compelling evidence that low carb diets produce sustained, meaningful weight loss better than any other conventional (or non-conventional) diet.
  • A healthy weight loss plan must include behaviour modification toward healthier habits, especially increased physical activity and improved nutrition. Generally, the latter means determining a specific Caloric requirement then maximizing the nutrient density of the diet (i.e. consuming ample quantities of fibre, vitamins and minerals) within this Caloric framework. In summary, despite the latest trends emphasizing certain macronutrients over others, the research indicates that a Calorie is still a Calorie(5). These considerations are likely much more relevant than the macronutrient composition of the diet(7).
  • Finally, and perhaps most importantly, any weight loss plan must be one that the individual can live with. This is where every fad diet falls short. In order to maximize sales and meet the demands of the masses, such diets must adopt a "one size fits all" approach. Preferably, the right diet should be matched to the right person(7). The best way to achieve this end is by analysing the specific needs, wants, likes and dislikes of each individual, and collaborating with them to produce a plan that is both effective and sustainable.


  1. Reference List: Birmingham, C.L. et al. (1999). The cost of obesity in Canada. CMAJ, 160, 483-88
  2. Eyre H et al. (2004). Preventing cancer, cardiovascular disease, and diabetes: a common agenda for the American Cancer Society, The Ameican Diabetes Association and the American Heart Association. Circulation, 109, 3244-3255
  3. American Dietetics Association. (1997). Position of the American dietetics association: weight management. Journal of the American Dietetics Association, 97, 71
  4. Bravata, D.M. et al. (2003) Efficacy and safety of low carbohydrate diets: a systematic review. JAMA, 289(14), 1767-8, 1773.
  5. Buchholz, A.C. & Schoeller, D.A. (2004). Is a calorie a calorie? American Journal of Clinical Nutrition, 79(suppl), 899S-906S
  6. Dansinger, M.L. et al. (2005). Comparison of the atkins, ornish, weight watchers and zone diets for weight loss and heart disease risk reduction. JAMA, 293, 43-53
  7. Eckel, R.H. (2005). The dietary approach to obesity: is it the diet or the disorder? JAMA, 293, 96-98