The TREND Study: Tapered Reduction in Energy Intake as a Novel Approach to Dieting

Diets are the mainstay of many obesity treatment programs, yet they fail for a variety of reasons. Patients find it difficult to comply with caloric restriction during active weight loss, and to adhere to long-term changes that promote weight loss maintenance. Underlying these difficulties are a number of physiologic changes enacted by the body in response to energy restriction. These changes promote increased hunger, decreased satiety and slowed metabolic rate, making diet compliance and sustained weight loss very difficult. From the body's perspective, a rapid and substantial drop in caloric intake may represent a metabolic emergency, and it responds accordingly, in an attempt to maintain body weight.

Weight loss results only from achieving and maintaining a large energy deficit, but it is not known whether the initiation phase of diets would be more likely to promote success if it were done gradually, in the form of a caloric taper. We hypothesize that, by slowly introducing a prescribed caloric restriction over a period of 1-2 months (rather than using an immediate drop in calories), the body's homeostatic response to energy restriction might be blunted or circumvented, resulting in lower levels of hunger, improved satiety, and better preservation of metabolic rate during diet initiation - all factors that would promote adherence and successful weight loss.

To test this hypothesis, the investigators will conduct a pilot randomized feeding trial comparing two types of low-calorie diets with similar macronutrient composition. Although both diets will ultimately rely on similar caloric deficits to produce weight loss, they will differ at the point of diet initiation. The following will be compared: (1) a traditional diet, where the entire energy deficit is initiated immediately; and (2) a "caloric taper" diet, during which participants will be gradually reduced from baseline levels of energy consumption to the lower calorie level required for weight loss, over a 6-week period.

After a 2-week run-in to establish equilibrium weight among 40 eligible persons, 30 obese adults will be randomized to the 2 study arms and follow them for 52 weeks. We will compare the two groups with respect to the following outcomes, measured in terms of change from baseline (week 0) levels:

1. Circulating levels of the orexogenic hormone, Ghrelin, at weeks 1, 6, 12, 24, and 52;
2. Circulating levels of the "satiety" hormones, Leptin and Glucagon-like Peptide (GLP-1) at weeks 1, 6, 12, 24, and 52;
3. Body composition, as assessed with dual energy x-ray absorptiometry, at 24 and 52 weeks;
4. Resting metabolic rate as assessed by indirect calorimetry at 24 and 52 weeks;
5. Change in body weight (kg) and body mass index (kg/m2) at weeks 6,12, 24 and 52;
6. Self-reported hunger (using VAS) and compliance with program at weeks 1, 6, 12, 24 and 52.
7. Change in weight-related quality of life, using the IWQOL-LITE at weeks 12, 24, and 52.