Intervention diets
After all baseline measurements were assessed, participants met with their randomized group. All participants received a handout that provided details on their assigned diet, including food groups that can be included and ones that should be avoided, and details on low-fat cooking instructions and the glycemic index [14]. Two registered dietitians with graduate degrees and expertise in all the study diets led the classes. These research dietitians provided participants with the orientation presentation that detailed menu planning and reviewed recipes given to each group. All groups were provided with several foods to sample during the first class. Self-monitoring dietary or energy intake was not required by any of the groups and was not discussed at group meetings. Partic- ipants were free to eat whenever they wanted and at a frequency of their own choosing as long as it adhered to their diet assignment. All participants were encouraged to limit fast foods and processed foods in favor of more minimally processed foods to meet low-fat and low-glycemic index dietary recommenda- tions. Participants could dine out and were instructed on how to make healthy choices at restaurants.
Table 1 provides an overview of the five intervention diets used in the New DIETs study as well as sample dinner menus. Because both low-glycemic index [15] and low-fat diets [10] are associated with weight loss, all participants were instructed to follow diets that favored low-glycemic index and low-fat foods. Participants were told they could include limited amounts of nuts and nut butters, avocados, seeds, and olives in their diets but were encouraged to focus on lower fat food options. There was no recommended restriction on energy intake for any of the five groups. All groups attended weekly 1-h meetings for 8 wk, with the exception of the omni group. The omni group allowed for the examination of consuming a usual diet (as all participants were following an omnivorous diet at baseline), while at the same time controlling for the selec- tion made by all participants to participate in a weight loss study.