Dietary Energy Restriction and Metabolic Aging in Humans

This study is a 3-phase investigation designed to test two caloric restriction (CR) regimens for participant compliance and variability in metabolic and physiologic effects. Initially, and through phase 1 (1 week pre-phase, and 6 weeks phase 1), participants will maintain normal habits at home.

Then for phase 2 (24 weeks), the 44 participants will be randomized to one of two diets (Diet HG or Diet LG), which they will consume at either 70% or 90% of baseline energy intake. The participants randomized to 90% CR (both diets) will form the control group. All food will be provided during this phase, and participants will be required to attend weekly group or individual meetings with the behavioral counselor and dietitian, and perform regular self-monitoring.

During phase 3 (24 weeks), participants will prepare their own food at home according to their CR regimen and will eat to maintain the CR specified for phase 2. They will continue to attend the weekly meetings and to perform self-monitoring.

Diet HG: a diet based on the USDA Food Guide Pyramid, but with additional emphasis on adequate fiber and low energy density foods, including use of whole grains rather than refined carbohydrates, limited liquid calories, high variety of low energy items such as fruits and vegetables and low variety of high-energy discretionary foods.

Diet LG: a modification of the HG diet in which low energy density is maintained even though the percent of energy from fat and protein is increased (by increased use of high-protein foods and foods with high water content) and use of different carbohydrate sources and physically intact food items (whole grains, raw fruits and vegetables) to further lower glycemic load through reducing the glycemic index (GI). High fiber intakes, low energy density, limited use of liquid calories, high variety of low energy items such as fruits and vegetables and low variety of high-energy discretionary foods will be the same as for the HG diet.

Inclusion criteria

• Healthy men and women (based on standard laboratory tests and a screening examination)
• 20-42 years of age
• BMI in the range 25-29.9 kg/m2
• Proportional representation of minorities in the Greater Boston Area (7 percent Black, 11 percent Hispanic, 82 percent non-Hispanic white)
• Able to accurately complete a food record
• Stage of change >1 for weight loss and changing dietary intake
• Must have an immediate adult family member who is supportive of weight loss

Exclusion criteria

• Known serious disorders that affect longevity, energy metabolism, body composition and immune responsiveness, including diabetes, cancer, heart disease, cachexia, eating disorders (anorexia and bulimia and any vomiting for means of weight control), depression, alcoholism, inflammatory disorders and AIDS, and individuals taking medicine that is anticipated to influence lifespan or energy metabolism
• Abnormal kidney function as assessed by serum creatinine, BUN and urinalysis, and abnormal liver function as assessed by SGPT, SGOT alkaline phosphatase, and bilirubin, abnormal normal thyroid function as assessed by serum T4 and TSH and fasting serum glucose levels <125 mg/dl
• Smoking, highly restrained eating, reported endurance training (participation in sports or training >12 hours per week), alcohol intake of 14 oz. per week or more, major medical and/or psychiatric disorders, plans to have a child within 3 years (1 year for Pilot study), past childbearing (for women) within the last 2 years, or breastfeeding within the past year
• Amputees
• Have required treatment for any psychiatric disorder
• Gained or lost >15 lb weight within the past year, or taking medications known or suspected to have an important influence on lifespan, energy metabolism, body composition or immune function
• Early death from cardiovascular diseases, cancer, or a diabetes-related illness (before the age of 45 years) in one or both of the parents
• Unable to remain in the program for at least 1 year, or unsuitable for home-based programs (including individuals reporting binge eating disorders or clinical depression, and women intending to become pregnant)