DIETFITS study (diet intervention examining the factors interacting with treatment success) - Study design and methods.

Numerous studies have attempted to identify successful dietary strategies for weight loss, and many have focused on Low-Fat vs. Low-Carbohydrate comparisons. Despite relatively small between-group differences in weight loss found in most previous studies, researchers have consistently observed relatively large between-subject differences in weight loss within any given diet group (e.g., ~25kg weight loss to ~5kg weight gain). The primary objective of this study was to identify predisposing individual factors at baseline that help explain differential weight loss achieved by individuals assigned to the same diet, particularly a pre-determined multi-locus genotype pattern and insulin resistance status. Secondary objectives included discovery strategies for further identifying potential genetic risk scores. Exploratory objectives included investigation of an extensive set of physiological, psychosocial, dietary, and behavioral variables as moderating and/or mediating variables and/or secondary outcomes. The target population was generally healthy, free-living adults with BMI 28-40kg/m2 (n=600). The intervention consisted of a 12-month protocol of 22 one-hour evening instructional sessions led by registered dietitians, with ~15-20 participants/class. Key objectives of dietary instruction included focusing on maximizing the dietary quality of both Low-Fat and Low-Carbohydrate diets (i.e., Healthy Low-Fat vs. Healthy Low-Carbohydrate), and maximally differentiating the two diets from one another. Rather than seeking to determine if one dietary approach was better than the other for the general population, this study sought to examine whether greater overall weight loss success could be achieved by matching different people to different diets. Here we present the design and methods of the study.

Weight loss on low-fat vs. low-carbohydrate diets by insulin resistance status among overweight adults and adults with obesity: A randomized pilot trial.

OBJECTIVE: To test for differential weight loss response to low-fat (LF) vs. low-carbohydrate (LC) diets by insulin resistance status with emphasis on overall quality of both diets. METHODS: Sixty-one adults, BMI 28-40 kg/m(2) , were randomized in a 2 × 2 design to LF or LC by insulin resistance status in this pilot study. Primary outcome was 6-month weight change. Participants were characterized as more insulin resistant (IR) or more insulin sensitive (IS) by median split of baseline insulin-area-under-the-curve from an oral glucose tolerance test. Intervention consisted of 14 one-hour class-based educational sessions. RESULTS: Baseline % carbohydrate:% fat:% protein was 44:38:18. At 6 months, the LF group reported 57:21:22 and the LC group reported 22:53:25 (IR and IS combined). Six-month weight loss (kg) was 7.4 ± 6.0 (LF-IR), 10.4 ± 7.8 (LF-IS), 9.6 ± 6.6 (LC-IR), and 8.6 ± 5.6 (LC-IS). No significant main effects were detected for weight loss by diet group or IR status; there was no significant diet × IR interaction. Significant differences in several secondary outcomes were observed. CONCLUSIONS: Substantial weight loss was achieved overall, but a significant diet × IR status interaction was not observed. Opportunity to detect differential response may have been limited by the focus on high diet quality for both diet groups and sample size.

Effects of Tai Chi and Western exercise on physical and cognitive functioning in healthy community-dwelling older adults.

OBJECTIVE: To compare the effects of Tai Chi (TC, n = 37) and Western exercise (WE, n = 39) with an attention-control group (C, n = 56) on physical and cognitive functioning in healthy adults age 69 +/- 5.8 yr, in a 2-phase randomized trial. METHODS: TC and WE involved combined class and home-based protocols. Physical functioning included balance, strength, flexibility, and cardiorespiratory endurance. Cognitive functioning included semantic fluency and digit-span tests. Data were analyzed using intention-to-treat analysis. RESULTS: At 6 mo, WE had greater improvements in upper body flexibility (F = 4.67, p = .01) than TC and C. TC had greater improvements in balance (F = 3.36, p = .04) and a cognitive-function measure (F = 7.75, p < .001) than WE and C. The differential cognitive-function improvements observed in TC were maintained through 12 mo. CONCLUSION: The TC and WE interventions resulted in differential improvements in physical functioning among generally healthy older adults. TC led to improvement in an indicator of cognitive functioning that was maintained through 12 mo.

Micronutrient quality of weight-loss diets that focus on macronutrients: results from the A TO Z study.

BACKGROUND: Information on the micronutrient quality of alternative weight-loss diets is limited, despite the significant public health relevance. OBJECTIVE: Micronutrient intake was compared between overweight or obese women randomly assigned to 4 popular diets that varied primarily in macronutrient distribution. DESIGN: Dietary data were collected from women in the Atkins (n = 73), Zone (n = 73), LEARN (Lifestyle, Exercise, Attitudes, Relationships, Nutrition) (n = 73), and Ornish (n = 72) diet groups by using 3-d, unannounced 24-h recalls at baseline and after 8 wk of instruction. Nutrient intakes were compared between groups at 8 wk and within groups for 8-wk changes in risk of micronutrient inadequacy. RESULTS: At 8 wk, significant differences were observed between groups for all macronutrients and for many micronutrients (P < 0.0001). Energy intake decreased from baseline in all 4 groups but was similar between groups. At 8 wk, a significant proportion of individuals shifted to intakes associated with risk of inadequacy (P < 0.05) in the Atkins group for thiamine, folic acid, vitamin C, iron, and magnesium; in the LEARN group for vitamin E, thiamine, and magnesium; and in the Ornish group for vitamins E and B-12 and zinc. In contrast, for the Zone group, the risk of inadequacy significantly decreased for vitamins A, E, K, and C (P < 0.05), and no significant increases in risk of inadequacy were observed for other micronutrients. CONCLUSIONS: Weight-loss diets that focus on macronutrient composition should attend to the overall quality of the diet, including the adequacy of micronutrient intakes. Concerning calorie-restricted diets, there may be a micronutrient advantage to diets providing moderately low carbohydrate amounts and that contain nutrient-dense foods.