Essentials for Eaters and Dieters

Evaluation of Popular Diets


atkins logo

Induction - This stage is followed for two weeks in which carbohydrates are severely reduced to 20 grams per day. The dieter is allowed to eat liberal amounts of protein, fat, and dairy and must eliminate all fruits, bread, pasta, grains, beans, nuts and seeds. The 20 grams of carbohydrates must come from salad greens and other vegetables. This is approximately 2 cups of loosely packed salad plus one cup of another vegetable.

Ongoing Weight loss - In this stage you will consume more carbohydrates but only so many in that you do not slow weight loss. The amount of carbohydrates you can have per day is determined by experimentation and is referred to as your critical carbohydrate level or CCLL.

Pre-Maintenance - This stage begins when the dieter has no more than ten pounds left to lose. Carbohydrates are increased until weight loss is deliberately slowed thereby establishing a new CCLL. You are allowed intake of whole grains, fruits and vegetables as long as you do not consume more grams of carbohydrates than your CCLL.

Lifetime Maintenance - This stage begins when all desired weight is lost. The dieter must continue to consume no more than the critical carbohydrate level determined in pre-maintenance. As an example, if you exercise, the maximum grams per day are around 90 grams.

Analysis - The basic concept behind this diet is that simply restricting carbohydrate equals weight loss. This is not the case. Weight loss comes from a decrease in calories. If you restrict carbohydrates but overeat fat and protein, you won’t lose weight. A likely reason this diet gained popularity is that it partially fits the formulation of a weight loss diet, that is, reducing carbohydrate intake while preserving protein consumption (see Where to Cut Calories). As a weight maintenance diet, the Atkins diet falls outside of healthy diets because it limits fruits and vegetables and doesn’t control saturated fat intake. Another problem of this diet is the exclusion of many food groups from diet, making it difficult to adhere to for long.

South Beach

South Beach Logo

First Phase - The first stage for “fast” weight loss is followed for two weeks in which the dieter eliminates virtually all carbohydrates including fruit. The dieter can eat normal-size helpings of meat, chicken, turkey, fish, and shellfish. The dieter can also have plenty of vegetables, eggs, cheese, and nuts.

Second Phase - In this stage of continuing weight loss of 1-2 pounds per week, one can selectively re-introduce a “favorite carb” back into the diet be it potatoes, chocolate, pasta, rice or fruit. However, you can only eat carbohydrates in very limited amounts.

Third Phase - This stage of weight maintenance involves eating normal foods and normal portion sizes as long as they are low in saturated fat.

Analysis - This diet, like the Atkins diet, also assumes that excluding certain groups of foods is sufficient to maintain prolonged negative energy balance. Phase one in the South Beach diet is basically the same as the Atkins diet except it is recommended only for 2 weeks. The author claims that 8-13 pounds of weight loss is typical during this period.  However, most of the lost weight is likely a temporary loss of glycogen and water because of severe restriction of carbohydrates, and will come back later (see How fast can we lose weight?). Remember, only fat loss counts.

Phase two of the South Beach diet is quite similar in food composition to our recommended weight loss diet.

Although phase three of the South Beach is not well defined, most recommendations are within a healthy weight-maintenance diet. Though more liberal than Atkins in its allotment of fruits and vegetables, South Beach advises consumers to eat only whole grain carbohydrates and to eliminate “processed grains” such as white flour and white rice because they are “bad carbs”. This exclusion of a food group is not necessary for healthy eating or weight loss. Balanced consumption of various food groups, in particular, adequate incorporation of fruit, vegetable and protein, is more important for healthy weight maintenance (see Selecting Carbohydrates – Are Some Carbs bad?)


The Ornish Diet does not have specific phases like some of the other popular diets. Instead, it focuses on weight loss through the restriction of dietary fat to 10% of total calories. The diet promotes eating foods that are low in fat but still high in nutrients and fiber. The diet focuses on a vegetarian diet full of vegetables, fruits and grains because animal products tend to have a higher cholesterol and fat content, especially saturated fat. It also recommends substituting simple carbohydrates, such as white rice, pasta and bread, for their whole grain counterparts.

  • Foods discouraged: beef, pork, full-fat dairy products, egg yolks, nuts, and seeds
  • Foods acceptable (in moderation): lean chicken, fish, and low-fat dairy products
  • Foods encouraged: whole grain carbohydrates (bread, pasta, rice), nonfat dairy products, fruits, vegetables, beans

By reducing the amount of animal products and simple carbohydrates, you will be lowering the amount of fat and calories in your diet, which will lead to weight loss. In addition, eating an increased amount of plant products and whole grain carbohydrates increases the amount of fiber in your diet. Eating high fiber foods will fill you up faster and keep you satiated longer, which will help prevent overeating.

Analysis - The Ornish diet has even been shown to reverse some forms of heart disease. However, it is a strict diet. Many people may find it hard to maintain since it advises consumers to select meals from a very narrow range of foods. 

Another concern with long-term use of this diet is the risk of protein deficiency. The restriction of animal products may make it difficult to meet the recommended daily amount for protein, so it is important to consume an adequate amount of lean meats, beans and nonfat dairy while on the diet.


Both the Atkins diet and South Beach diet emphasize multiple stages in their programs. However, for healthy eating, there are only two essential stages: a weight loss diet and a weight maintenance diet.  For long-term success, it is important for dieters to understand the principles of these two stages instead of just following what popular diets tell us to do.

Atkins, South Beach and Ornish diets became popular because they actually result in weight loss for some. The Ornish diet has even been shown to reverse some forms of atherosclerosis. These diets appear to result in weight loss without consciously reducing total food intake because they exclude many items from your food list.  Low variety leads to reduced intake overall and people lose weight.

However, this exclusion approach will not work for some, if they increase consumption of the food groups they are permitted to eat. Also, this exclusion approach could backfire to keep weight off for long term.  People tend to drop out when they grow tired of the same foods over and over.  Or, when people “reintroduce” banned food items after weight loss, their weight may easily bounce back.  This is why we recommend consumers establish a weight maintenance diet that is least restrictive, enjoyable and easy to adhere to before attempting weight loss.

Essentials for Eaters and Dieters | Version 2.0
Copyright ©2005, 2006 University of Illinois Board of Trustees