Background:

- Sticking to a diet plan can be difficult, but is important for many different health reasons. Some people seem to have a harder time following and sticking to a diet plan than others. It is not clear whether people of different weights (lean or obese) might have differences in the way they adhere to diet plans. Researchers want to study three different groups of people based on their body mass index (BMI), which measures people based on their weight and height. The study will place the participants on a 6-week diet and see how well they follow the diet. The information from this study may help develop better weight-loss plans and healthy diet ideas.

Objectives:

• To understand what factors affect adherence to a diet plan.
• To collect information for future studies that may improve people's ability to stick to diets.

Eligibility:

- Individuals at least 18 years of age who are lean (BMI between 18.5 and 25) or obese (BMI greater than 30).

Design:

• Participants will be screened with a physical exam and medical history. Blood and urine samples will be collected. They will have a full-body scan to measure fat and muscle. They will also answer questions on eating behaviors, mood, and desire to change eating patterns.
• Participants will be separated into three groups. Each group will have a different diet. The lean group will have a heart-healthy diet designed to maintain the same weight. One of the obese groups will also have a heart-healthy diet designed to maintain the same weight. The other obese group will have a heart-healthy weight loss diet. In all groups, all food will be provided by the study doctors. Participants should not eat any food other than that provided for the study.
• Everyone will start with a 1-week food testing period to find the right number of calories for each group. After this first week, participants will attend one diet counseling session per week and will be contacted randomly once a week to check on the foods they have had in the past 24 hours. Participants will complete daily food diaries on paper as well as daily food records using a smart phone.
• Participants will come to the clinic twice a week to pick up the diet food. On one of those days, they will also have their counseling session.
• The study will last for 6 weeks. At the final study visit, participants will repeat the tests from the screening study.

Adherence, or "sticking to your diet" is important for successful initial weight loss and keeping off the weight over the long term (1). While early behavioral and dietary adherence have been associated with greater weight loss, sticking to a diet plan is difficult. It is not clear if adherence to any diet plan (even one which does not produce weight loss) is hard or whether people who are overweight have more difficulty with adhering to diet plans compared to people who are relatively lean.

The main aim of this study is to evaluate dietary adherence in 3 groups of individuals participating in a 6-week heart-healthy dietary intervention program. Two groups [1 (BMI < 25 kg/m(2)) and 2. Obese (BMI greater than or equal to 30 kg/m(2))] will receive a heart-healthy diet designed to maintain their weight, and the third group [3. Obese] will be given a heart-healthy diet that is 35% less than their daily calorie needs to lose weight. Participants will attend one counseling session per week and will be contacted randomly 1x/week by study staff for completion of a 24-hour dietary recall. They will complete daily food diaries and daily records using smart-phones. Prior to starting the assigned heart-healthy dietary intervention, participants will complete questionnaires that include questions about how motivated they are to follow a diet, lose weight, and change eating patterns. These findings may help us understand what factors affect adherence, and help us design weight loss studies that improve people's ability to stick to diet interventions.

-INCLUSION CRITERIA:

1. BMI

   • BMI greater than or equal to 30 kg/m(2) for the obese WMEN and UF groups but body weight less than 350 pounds to accommodate the DXA scanner
   • BMI less than or equal to 25 kg/m(2) (and BMI greater than or equal to 18.5 kg/m(2)) for the lean WMEN group

2. Age greater than or equal to 18 years. Minors under the age of 18 will be excluded because growth and pubertal issues are significant parameters that could affect our outcomes and also because the time requirements of the study are such that they would interfere with school schedules. Participants must be healthy, as determined by medical history, physical examination, and laboratory tests.

3. Weight stable (plus or minus 2 percent) for last 3 months

EXCLUSION CRITERIA:

Candidates will be screened by phone to exclude those with BMI greater than or equal to 26 kg/m(2) and BMI less than or equal to 29 kg/m(2), significant health problems, including cancer, hypertension, diabetes, current and past 3-month use of certain prescribed medications, especially those that could affect body weight, such as antidepressants and stimulants as well as smoking, or excess alcohol (greater than 3 drinks/d). Women must not be pregnant or lactating, and be at least 1 year postpartum. Candidates with a history of psychotic disorder or hospitalization for psychiatric illness within the past 1 year will not be eligible. They will need to be weight stable for the past 3 months (plus or minus 2 percent) and cannot be in treatment for obesity or currently receiving psychotherapy. Individuals who meet criteria according to the phone screen will be invited to come to the unit for a screening visit and their screening sheets are placed in a locked filing cabinet. Forms from potential volunteers who are ineligible are shredded.

6 weeks