Fact or Fiction: The Truth About Special Diets

Speaker: Linda M. Delahanty, MS, RN, LDN

People spend more than $60 billion on weight loss products and books each year in the United States. They are searching for an easy way to shed pounds, although it is much more important to have a balanced diet and for the long-term instead of relying on a short-term plan, according to Linda M. Delahanty, MS, RN, LDN, chief dietitian at the Massachusetts General Hospital Diabetes Center.

Most authors understand they have to present a “magic formula” to capture the public’s attention. These promises often include fast, easy weight loss without exercise and eating food that tastes great.

“They have to have the formula to sell the book,” said Delahanty, who presented at the 2013 Cardiometabolic Risk Summit.

The problem, however, is that many of the ideas presented in these books are not based on research and scientific studies. Examples of popular diet fads include the Dr. Atkins’ New Diet Revolution1 and the South Beach Diet.2

The Atkins Fallacy

The Atkins diet promises a plan for individuals to lose weight without counting calories and to keep the pounds off permanently, while also benefitting from increased energy and a healthier body.1 The recommended food is varied, which contributes to reductions in cholesterol, triglycerides, blood sugar levels, and heart disease risk.

“What more could a patient want?” asked Delahanty.

The Atkins diet claims that carbohydrates cause high insulin levels and leads to insulin resistance, weight gain, and obesity. Delahanty points out that research finds that insulin resistance is caused by weight gain. Atkins tells people that a low carbohydrate diet is the most important factor in weight loss, but Delahanty once again points to evidence that suggests a low calorie diet is the most effective way to lose weight. 

When people are deprived of carbohydrates and are hungry, they may begin to binge on carbohydrates. More so, the Atkins diet is not necessarily healthy—it is high in saturated fat and restricts milk, whole grains, legumes, fruits, and vegetables. Finally, the Atkins diet recommends adding supplements from Atkins Nutritionals, Inc. to the diet, but multivitamins have not been approved for weight loss.

Deflating South Beach

The South Beach Diet claims that people can eat delicious food, relying on the right carbohydrates and right fats, to lose 8 to 13 pounds in 2 weeks.2 Author Arthur Agatston, MD, believes that weight problems occur because of the inability to properly process sugars and carbohydrates coupled with a reliance on a high carbohydrate, low fat diet. Delahanty points out that the main reasons for weight problems and obesity are 3-fold: larger food portions, excess calories, and less exercise. Today, most Americans eat 100 to 300 calories per day over what is needed.

Although the South Beach diet is healthier than the Atkins diet and considers scientific evidence on fats and heart disease, Delahanty said it is too high in protein. Initial weight loss is due to dehydration and loss of muscle and fat tissue. She also pointed out that the South Beach Diet restricts intake of a lot of food, even healthy options.

“Anytime I see forbidden fruits (in a diet), that bothers me,” Delahanty said. 

Limitations of the Glycemic Index

The Atkins and South Beach diets rely on the glycemic index to choose foods to include and eliminate for their plans. The glycemic index is the degree to which a 50 gm carbohydrate portion of food raises blood glucose over 2 hours compared with a 50 gm carbohydrate portion of table sugar or white bread.3 Blood glucose response of sugar is assigned 100 and other foods are compared with that standard. 

Highly processed foods such as corn flakes, white bread, jelly beans, and pretzels have a glycemic index >70, while high fiber foods such as legumes, fish, oatmeal, bran cereals, and nuts have a glycemic index <55.

Delahanty points out some of the limitations of the glycemic index—it varies based on the blood sugar level before a meal, how the food is processed or prepared, the amount of food eaten, activity level, the time of day, and if a person is taking diabetic medications. A healthy diet should include lean meats, fish, poultry, low-fat or fat-free dairy products, legumes, nuts, whole grains, fruits, and vegetables.

Diets that are low in carbohydrates limit foods people can eat, which can lead to feelings of deprivation and food cravings. If deciding what to eat based solely on carbohydrates, Delahanty fears individuals will not consume nutritious foods, such as carrots, corn, beets, white potatoes, bananas, pineapple, and watermelon.

The Data

In a study,4 160 people were randomly assigned to follow 1 of the following diets for 4 months: Weight Watchers (low fat), Atkins (low carbohydrates), Zone (moderate carbohydrates and high protein), and Ornish (very low fat and high carbohydrates). After 2 months, each group lost weight and had a lower cholesterol, but 22% had not adhered to the diet. People who closely followed the diet plans lost the most weight. After 1 year, 35% of people had quit the Weight Watchers and Zone diets, while 50% had quit the Atkins and Ornish diets. 

According to Delahanty, people stop the diets because of limited food choices, numerous food restrictions, and lack of decision-making on what they can eat. Instead, the best weight loss plan focuses on a balance of carbohydrate, protein, and fat, relies on scientific evidence, does not forbid foods, and recommends monitoring food intake as well as physical activity.  ■


1.Atkins RC. Dr. Atkins’ New Diet Revolution. New York, NY: M Evans & Co; 2002.

2.Agatston A. The South Beach Diet. New York, NY: St. Martin’s Press; 2005.

3.American Diabetes Association Guide to Medical Nutrition Therapy for Diabetes. American Diabetes Association. Alexandra, VA; 2012.

4.Dansinger ML, Gleason JA, Griffith JL, et al. Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial. JAMA. 2005;293(1):43-53.