Why was this study done?

Determining the optimal number of calories to consume for weight loss and maintenance is of utmost concern. This study was designed to test differing caloric diets to find one that was optimal for weight loss.

What did the study find?

This study found that a diet that consists of 630 calories a day on the weekdays, followed by a 1200 calorie diet on the weekends is an effective tool for weight loss. While this study determined that 630 calories was sufficient, current thinking (this study was done in 1983) suggests that 630 calories a day may be too low and personalized caloric recommendations (that include activity levels) may be more realistic and sustainable for weight loss.

630 Kcal Formula Diet Versus 1,200 Kcal Balanced Deficit Diet: Comparison of Weight Loss and Safety
Authors: Minear AL, Blankenbaker GM, Sacks PV. J Am Diet Assoc, 1983. 83.
PDF Abstract: J Am Diet Assoc, 1983.