Atkins' Diet - Discussion Paper

REBECCA K. KIRBY, M.D., M.S., R.D.,
Physician and Senior Research Scientist, Center for the Improvement of Human Functioning International, Inc.

Dieting seems to be a national pastime in the United States, yet our obesity statistics continue to climb. In the past two decades, the prevalence of obesity in this country has doubled. More than 60 percent of the adult population is overweight or obese.¹ Children are at increasing risk for overweight and obesity as well.

The dieting phenomenon has revitalized an interest in low-carbohydrate diet plans, embodied in the publication “Dr. Atkins’ New Diet Revolution.”² This book is an updated version of a diet plan that was originally published in 1972.³ Dr. Atkins asserted that obesity is due to an over-consumption of carbohydrates that leads to insulin resistance and hyperinsulinemia.

This resurgence of interest in low-carbohydrate dieting stems in part from the successful promotion of low-fat diets. Government surveys show that the percentage of total calories from fat in American diets has declined. However, Americans have compensated for that decline with an increase in total calories consumed. The increase in calories comes primarily from carbohydrates. Despite some increase in the consumption of whole grains, fruits, and vegetables, consumption of sugar and refined carbohydrates has increased disproportionately.⁴

The poor choices Americans make in food selection have been compounded by larger portion sizes and less exercise. The resultant increase in obesity has brought with it an increase in morbidity, evidenced by an increase in type 2 diabetes and metabolic syndrome.

An evidence-based report on the risks of obesity was compiled by the National Institutes of Health (NIH).⁵ This document, entitled “Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults,” provides physicians with a practical guide to the management of obesity in their patients.

As outlined in the NIH report, obesity is a multifactorial, chronic disease for which good dietary habits, social support, and exercise are keys to successful management. What continues to drive debate is the question of what constitutes good dietary habits. This uncertainty over the best way to manage the epidemic of obesity has rekindled the low-fat/low-carbohydrate diet controversy.

The diet plan outlined in “Dr. Atkins’ New Diet Revolution” calls for reducing carbohydrate intake to 20 g of dietary carbohydrate during a two-week induction phase. After the induction phase, carbohydrate consumption is incrementally increased by 5 g a week. During the third phase, carbohydrate consumption can be incrementally increased by 10 g a week, as long as weight loss continues. In the fourth phase, the goal weight is reached, and a critical carbohydrate level for maintaining that weight determines the amount of daily carbohydrate intake.

This diet program is designed to deplete glycogen stores and cause a shift into ketosis, so ketone bodies are used for fuel in place of glucose. Dieters are advised to eat three meals a day, drink eight glasses of water, take supplements, and exercise. Lipolysis testing strips are used to monitor fat-burning metabolism.

The premise of the ketogenic diet is to lower endogenous insulin levels and promote the use of body fat as fuel. During partial fasting with carbohydrate restriction, insulin declines, and glucagon increases. This shift in the insulin-to-glucagon ratio results in mobilization of free fatty acids from adipose tissue, increased mobilization of amino acids from muscle, and increased fatty acid oxidation by the liver.⁶

The brain requires about 100 to 150 g of glucose daily. To support this demand, blood glucose levels are sustained during continued carbohydrate restriction by depletion of glycogen stores from the muscle and the liver. As glycogen is released, there is a release of glycogen-bound water, accounting for a rapid fall in body weight.

In response to glycogen depletion, ketone bodies, generated by fatty acid oxidation, become a substitute for glucose. As ketone concentrations increase, they replace glucose as the primary brain fuel, although some glucose can be generated from amino acids. With continuation of a low carbohydrate intake, fat and protein from the diet plus body fat and protein stores are broken down to supply glucose and ketone bodies for fuel.

Is there a better outcome in terms of weight loss, body composition, improvement in lipid profile, and glycemic control with low-carbohydrate diets for weight loss?

There is a growing body of research on the obesity epidemic and the ensuing dieting epidemic that looks at the issues of efficacy and safety of low-carbohydrate dietary regimens. Studies reported in JAMA,⁷ The New England Journal of Medicine,⁸ Current Atherosclerosis Reports,⁹ Obesity Research,¹⁰ and Nutrition Reviews¹¹ have examined and reviewed the research.

The review published in JAMA is a meta-analysis examining diets with 60 g of dietary carbohydrate or less.⁷ The analysis found greater weight loss in the short run with the lower carbohydrate diets. However, because of the large diversity of diet protocols examined in the meta-analysis, no other benefit of low-carbohydrate diets was clearly defined. Significant weight loss was associated with calorie restriction and longer duration of diets. More weight loss occurred in the more obese subjects. The authors concluded that because of a lack of studies with adequate follow-up it was not possible to make recommendations on the long-term safety and efficacy of low-carbohydrate diets.

A one-year study of obese subjects compared a low-carbohydrate diet using the Atkins’ plan with a conventional low-fat diet.⁸ Although there was a significantly greater weight loss at the end of three months and six months with the Atkins’ protocol, a similar weight loss was documented at the end of one year for subjects in both groups. Lipids and insulin sensitivity were the same after one year, except for a significant improvement in the triglyceride and high-density lipoprotein cholesterol levels in the Atkins’ group. The low-fat diet group had a higher attrition rate, although the difference was not statistically significant.

The same issue of The New England Journal of Medicine included results of a six-month study that also showed improved weight loss at six months on a low-carbohydrate diet.¹² Morbidly obese and diabetic or insulin-resistant subjects were counseled to follow a low-carbohydrate diet or a low-fat diet. It is important to note that the composition of the diets changed by the end of the study. At six months, the subjects in the low-carbohydrate group had begun consuming a more moderate low-carbohydrate diet, with approximately 37 percent of their calories from carbohydrates. The subjects following the low-fat diet increased their fat consumption to ³³ percent of calories, a percentage that is similar to that in the average American diet. The dieters consuming the moderately low carbohydrate diet showed a significantly greater weight loss and improved triglyceride levels. The diabetic subjects had improved glucose levels, although the A1C was not significantly different. Insulin sensitivity improved only in those without diabetes.

Subjects in another study were placed on 1,000-calorie diets and monitored in a hospital setting for six weeks.¹³ One group received a diet with 45 percent of calories from carbohydrates, and the other group received a diet with 15 percent of calories from carbohydrates and 60 g of fat. There was no difference in weight loss or body composition between very-low and moderate carbohydrate intake. A more significant drop in glucose, cholesterol, and high-density lipoprotein (HDL) cholesterol levels occurred in the 15 percent carbohydrate group. A significant decrease in triglyceride and insulin levels also was observed in the 15 percent carbohydrate group but not in the 45 percent carbohydrate group.

However, another study comparing a low-carbohydrate diet with a diet including 30 percent of calories from fat and 55 percent from carbohydrates found that both diet groups improved their lipid profiles, blood pressures, fasting glucose, and insulin levels.¹⁴ Although both groups restricted their calories by the same amount, the low-carbohydrate group lost more weight, more fat mass, and more lean body mass.

A diet that is low in carbohydrates and not limited in protein intake may be in the higher end of the acceptable macronutrient distribution range of 10 to 35 percent of calories from protein. A recent review of the efficacy of high-protein diets showed that total weight loss and loss of body fat did not differ between high-protein diets and control diets.¹¹

Conversely, another study reported that in comparing a diet including 30 percent of calories from protein with a diet including 16 percent of calories from protein, there was a greater loss of fat to lean body mass in the high-protein group.¹⁵ The high-protein group also showed improvement in postprandial insulin response and lower triglyceride levels.

In subjects with type 2 diabetes, a high-protein diet was found to improve glycemic control in addition to lowering triglyceride levels.¹⁶ Other investigators also have found a drop in triglyceride levels and less loss of lean body mass in subjects on high-protein diets. However, the authors stated that the improvement in insulin resistance found with high-protein diets may be attributable to calorie restriction and weight loss.¹⁷

The popularity of low-carbohydrate diets has introduced questions of safety for long-term weight management. The issues regarding safety center around the high protein and fat intake, and restricted nutrient composition, plus the metabolic state of ketosis and the initial diuresis that occurs with a very-low-carbohydrate diet. A death has been reported in a teenager on a very-low-carbohydrate diet; the death was attributed to a low potassium level resulting from poor dietary intake.¹⁸

A high protein intake increases the output of urea, acidifies the urine, and can cause dehydration. Since low-protein diets historically have been used to delay the progression of renal disease, the effect of high-protein diets on renal function has been questioned. However, in persons with normal renal function, no adverse effects of a high-protein diet have been definitely established.^10,11

The evidence on the impact of a long-term high-protein diet on bone mass is inconclusive. High-protein diets increase urinary calcium excretion. Dietary studies on increased fracture risk have shown both positive and negative correlation with protein intake.^10,11 However, no effect on bone turnover markers or urine calcium was observed in subjects on a high-protein diet with moderate carbohydrate intake,¹⁷ and no change in bone mass was found after six months on a low-carbohydrate diet.¹⁴ Undernutrition and low dietary protein intake can increase rates of bone loss.¹⁹ The impact of either long-term high-protein or low-protein diets on skeletal homeostasis is unclear.

Limited nutrient composition will result if carbohydrates are restricted to fewer than 60 g a day. Less than optimal nutrient intake will result when any food group is eliminated. An optimal Atkins’ 20-gram carbohydrate menu that includes a variety of vegetables will still place a number of vitamins and minerals below 100 percent of Daily Value. In addition, a low-carbohydrate diet, which limits the intake of fruit and vegetables, legumes, and whole grains, is lacking in dietary fiber. Constipation is a common side effect of a very-low-carbohydrate diet. Nutrient deficiencies in the diet are only partially remedied by supplements. There are hundreds of phytonutrients in whole foods and other factors yet to be identified that are important for maximum health.

Weight loss can be achieved by a number of highly divergent strategies. The longer the duration, the more successful the diet. Over the long term, different weight loss programs have shown similar success.²⁰ Whatever the diet strategy, obese and overweight patients are likely to have a comorbid condition and should be followed closely in the family physician’s office.

Restrictive diets that exclude a food or a group of foods will invariably restrict not only calories but also nutrients. Although low-carbohydrate diets can be successful, a major problem with them is that many persons attempting to follow a low-carbohydrate regimen do not eat a variety of fruits and vegetables or even include the allowable carbohydrate intake in their diet but instead concentrate on eating meats and fats. This diet approach results in low fiber content, poor nutritional balance, and, possibly, electrolyte disturbance. A moderate carbohydrate intake with more diversity in food selection will provide not only a broader nutrient intake but also less boredom.

It is important to note, however, that Atkins and other low-carbohydrate plans that eliminate sugar and refined carbohydrates from the diet can help establish a more healthful restructuring of dietary patterns in this respect. Total sugar intake is highly predictive of body mass index.²¹ Steering patients toward the consumption of whole grains, beans, nuts, fruits, and vegetables will help them replace the empty calories of sugar and the limited food value of refined starches and sugary foods. Whole foods that are grown and eaten without major changes in nutrient content and that are not highly refined will, in general, have low glycemic loads. Diets with low glycemic loads promote stabilization of blood sugar levels, normalization of triglyceride levels, higher satiety, and lower food consumption.²² A low dietary glycemic load also has been shown to reduce the risk of cardiovascular disease²³ and the risk of developing type 2 diabetes.²⁴

Weight loss improves lipid profiles, glycemic control, and blood pressure. These three goals can be achieved with an objective of decreasing body weight by just 10 percent.⁵ However, what is important in weight management is long-term, successful maintenance of the lower weight. Whether the Atkins’ diet proffers a superior benefit in achieving these goals is inconclusive. Whether in the long run there are major drawbacks to this diet plan cannot be stated conclusively either. Normal kidney function does not seem to preclude a high-protein diet, but the long-term effects on bone status are unclear. While a diet high in saturated fat is associated with increased cardiovascular risks, it is important to consider the type of dietary fat. As with dietary carbohydrates, the quality of dietary fat may be more important than the quantity when evaluating cardiovascular risk factors.²⁵ Even the Atkins’ organization has started discussing limitations on saturated fat.

We need to be careful not to throw the baby out with the bath water, whether it’s low-fat yesterday, low-carb today, or something else tomorrow. With highly restrictive diets, there always will be limitations, and in any long-term eating plan, it is important that a variety of basic whole foods with their associated nutrients be included. Because of our diverse health requirements and inherent biochemical individuality,²⁶ some people will do better on low-fat diets and some people will do better on low-carb diets. Diets are not a one-size-fits-all proposition and should be tailored to the individual person. Most importantly, however, a lifestyle of healthful eating should be encouraged. Maybe we just need to get back to a balance of wholesome foods, moderation in quantity, and a commitment to being more active.

(Published: 2005)