Diets that work best: Atkins, Ornish, Weight Watchers, or Zone Diet

It seems as though there is a new dieting "star" every few years. Most recently, the Atkins and South Beach diets have been the attention-getters. There is always a search on for the perfect diet, but losing weight is not an easy task, as anyone who has ever tried to diet can tell you. It's easier to blame your failed attempt at weight loss on the diet, and then move on to another diet. Why do you think there are well over 1,000 books about dieting lining the shelves in bookstores?


Experts in nutrition are critical of "fad" diets. Not many of them can be backed with scientific evidence, and many of them don't follow what should be considered "balanced" eating at all. But since so many individuals are obese, health professionals are becoming more interested in the potential of popular diets as a means to help their patients lose weight.


In January 2005, the Journal of the American Medical Association released results of a study of the effectiveness and sustainability of four popular diets: Atkins, Ornish, Weight Watchers, and Zone. After following individuals on each diet for a year, researchers discovered that while all four diets led to modest weight loss and improvements in several cardiovascular risk factors for the individuals, about 42 percent of the participants in the study had dropped out by the time the study had ended.


About the Study


The study included 160 individuals, age 22 to 72. Each individual was overweight, with a body mass index (BMI, a measure of weight in relation to height) between 27 and 42. (A "healthy" BMI is less than 25.) Each participant also had at least one cardiovascular disease risk factor, such as high cholesterol levels, high blood sugar levels, or high blood pressure.


Researchers randomly assigned participants to one of the four diets (Table 1). For the first two months, participants attended classes led by a dietitian and physician to receive counseling and positive reinforcement, and to address issues keeping the individuals from adhering to the diet.


Table 1. Diet Specifics




Diet Type



Carbohydrate restriction

Less than 20 grams (g) of carbohydrate daily, with a gradual increase toward 50 g



Macronutrient balance

40% of calories from carbohydrates, 30% from fat, and 30% from protein


Weight Watchers

Calorie restriction; portion control

Keep total daily "points" (each point is roughly 50 calories) in a range determined by current weight, for most this was between 24 and 30 points per day



Fat restriction

A vegetarian diet containing only 10% of calories from fat



To see how well the participants were following their diets, researchers analyzed food records and called the participants monthly, asking them to rate their adherence level on a scale of one to 10.


The researchers assessed body weight, waist size, and other cardiovascular risk factors at the beginning of the diet, and then again at two, six and 12 months. Participants were also asked about their exercise levels and medications at these times.


The Findings


At the end of a year, participants in all four diets experienced modest, but statistically significant weight loss (Table 2).  Since 42% of the participants dropped out before the end of the study, researchers used their baseline measurements to calculate their final 12-month outcomes. When those individuals were excluded from the final calculation, average weight losses became slightly greater. All four diets also led to modest, but statistically significant improvements in cardiovascular risk factors.


Table 2. Group outcomes at 12 months








Average weight loss (pounds)






Average calorie reduction






Participants completing 12 months

21 (53%)

26 (65%)

26 (65%)

20 (50%)



While there is no significant difference between any of the four diets, and while all led to similar benefits, the dropout rates suggest that participants found the two less extreme diets (Zone and Weight Watchers) easier to follow.


How Does This Affect You?


Finding from this study reveal that any of the four diets can lead to weight loss and a reduction in cardiovascular disease risks, but the key is sticking with the diets long enough to reap the benefits.


Study results show that it's not necessarily about which diet is best, but rather which diet is best for you. If any of the popular diets fit your temperament and lifestyle, you will probably find success - as long as you stick with it. If the participants in the above-mentioned study had been allowed to choose their own diet plan, researchers may have seen higher adherence rates. The Adkins diet, for example, would not be a good choice for an individual who loves to eat bread.


If you're thinking about trying one of the latest popular diets, it may help to talk to a nutritionist or dietitian before you begin. He or she can help you decide whether the diet is a good match for you, and suggest modifications which may help make the diet healthier and easier to follow.


It's also a good idea to get the support of others before you set out to lose weight. Research shows that people who receive regular support through group counseling, individual consultation, or online networks are more likely to be successful at weight loss in the long run.


The measure of a successful diet is not in how much weight you can lose or whether you can stick to the plan for a year. A good diet will help you establish lifelong eating and exercising behaviors that will help you achieve and maintain a healthy weight.




American Dietetic Association


American Obesity Association


Health-e-Weight for Women
Brigham and Women’s Hospital