This is a 6 month long study to evaluate the inclusion or exclusion of beef within a weight loss program.

This study will compare two protein sources: proteins to include beef as the sole source of red meat compared to proteins excluding red meat within the context of an effective higher-protein weight loss and maintenance program derived from the Colorado Diet.

All subjects will participate in a group-based program consisting of 16 weekly classes in 3-phases designed to produce weight loss and teach participants how to achieve a lifestyle to keep weight off permanently. All groups will be closed (same subjects, same leader) and will consist of 20 participants. Participants in both groups will receive instruction in cooking, recipes, and shopping instruction (using our grocery laboratory). This training will include strategies, tips and preparation techniques for preparing high protein meals according to their assigned groups. All subjects are given exercise plans and all subjects will receive memberships to the Anschutz Health and Wellness Center fitness center for the duration of the study.

After completion of the 16-week program, subjects will be asked to follow the program on their own for an additional 2 months.

This is a randomized study involving 120 study subjects (60 per arm). The investigators will compare the efficacy of inducing weight loss of two treatment arms derived from the Colorado Diet. Subjects will be randomly assigned to one of two study arms and instructed to follow the higher-protein diet by participating in weekly group classes for the first four months of the study. There will be 6 classes of 20 subjects each (three classes for each treatment group). Subjects will be followed in the study for 6 months. Subjects will be randomized into one of two treatment groups as follows:

• Group 1(SOS+B): Subjects will participate in a State of Slim group class, receive a State of Slim book (describing the Colorado Diet), and will receive stipends to be used to help purchase protein food items allowed in the Colorado Diet as modified. The Colorado diet is a high protein (estimated 120-160g/day), low carb and low fat diet. Subjects will be directed and instructed to include beef as their sole source of red meat as a protein source during the study. Subjects will follow the diet protein guidelines, but will be directed and instructed to consume 4 or more servings of beef per week and instructed not to consume any other red meats. Other red meats to be avoided include pork, veal, lamb, buffalo and venison. Subjects will be advised to use the monetary stipends to purchase items from the lists of acceptable foods from the SOS book (to include beef products). Processed beef items will be allowed as identified by a list provided to the subjects.
• Group 2 (SOS): Subjects will participate in a State of Slim class, receive the State of Slim book (describing the Colorado Diet), and will receive stipends to be used to help purchase protein food items allowed in the Colorado diet as modified. Subjects will be directed and instructed to exclude beef and instructed not to consume any other red meats. Other red meats to be avoided include pork, veal, lamb, buffalo, and venison.

Inclusion Criteria:

1. Males and females between 18 - 50 years old
2. BMI of 27 or greater
3. Weight stable (have not lost or gained more than 10 pounds in the last 3 months)
4. Generally healthy
5. Able to exercise 70 minutes per day at moderate intensity
6. Willing and able to participate in a weekly group class for the first 16 weeks of the study and willing to participate in 4 study visits over the 6 month study period

Exclusion Criteria:

1. Pregnant or trying to become pregnant.

2. Diagnosis of type 1 or type 2 diabetes

3. Individuals following a vegetarian/vegan only diet

4. Food allergies (to red meats or other common protein sources)

5. Taking medications that could cause weight loss or weight gain (such as steroids, tricyclic antidepressants, chemotherapy, antipsychotics, prescribed or over the counter weight loss agents). Oral contraceptives can be used as long as subject agrees to not change use of these during the study. Vitamins and minerals which do not have a weight effect are allowed as long as use is continued without change during the study.

6. Current Eating disorder (anorexia or bulimia)

7. Current alcohol or drug abuse or dependence (Subjects who have quit smoking in the last 6 months will be excluded. Smokers whose smoking habits have been stable for the last 6 months and which remain stable during the study can be included).

8. Any medical condition for which following a high protein diet and/or 70 minutes of exercise daily would be inadvisable

9. LDL cholesterol levels above 160 mg/dl or triglycerides above 400 mg/dl.

10. Untreated or unstable hypothyroidism. Thyroid medications must be stable for at least 3 months.

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