A to Z

A Comparative Weight Loss Study of the Atkins, Zone, Ornish, and USDA/LEARN Diets

Obesity is the single most significant nutrition-related health issue of the new millennium. Several "medical experts" have designed and promoted weight loss diets that dramatically differ from one another, and from the USDA Dietary Guidelines. These diets have gained surprisingly widespread and persistent popularity among Americans, despite a lack of scientific evidence supporting their claims. The objective of the A TO Z Study was to examine various health outcomes (e.g. benefits, risks, success) of FOUR popular weight loss strategies representing a spectrum of low to high carbohydrate intake, and compare them.

Study Design

Over 300 free-living pre-menopausal, overweight women were randomly assigned to follow either the Atkins (extremely low carbohydrate), Zone (low-carbohydrate, high protein), Ornish (very low fat), or USDA/Food LEARN (high carbohydrate/moderate-low fat) diet for 1 year.


At the completion of the study, the women assigned to follow the Atkins diet lost more weight (~10 pounds average weight lost in 1 year) and also experienced metabolic effects that were comparable with or more beneficial than the other participants.

To learn more about the details of the study, read: