Obesity and Fatty Acid Flux Comparison Trials
Condition: Obesity
MeSH terms: Obesity
Study type: Observational

Summary: 
      This study will explore factors that affect obesity and obesity-related diseases in both
      Caucasians and African Americans. By looking at the rate at which the human body burns
      calories while at rest (resting energy expenditure, or REE) and at the rate at which fat
      travels through the blood (fatty acid flux), this study will examine the relationship between
      REE and fatty acid flux, both of which are determinants of obesity. Researchers will compare
      the test results of Caucasians and African Americans to determine if race has an effect on
      the relationship between REE and fatty acid flux.

      Volunteers must be between 18 and 49 years of age. Equal numbers of typical weight,
      overweight, and obese participants will be recruited. Candidates will be screened with a
      physical examination, electrocardiogram, and blood tests, and will be interviewed about diet
      and exercise habits, family and medical history, and employment.

      Participants will be placed on a two-week maintenance diet (prepared by a dietician to
      regulate and maintain calorie consumption) and must visit an outpatient clinic for weight
      measurement for 10 consecutive weekdays. During the two-week diet, participants will also
      undergo two 20-minute computerized scans to measure abdominal and body fat. At the end of the
      two weeks, participants will then be hospitalized for two days to allow researchers to
      conduct blood tests, oral glucose tests, and a physical examination to measure REE and fatty
      acid flux levels for comparison.
    

Detailed description: 
      Thirty percent of Americans are obese. Women are more severely affected than men.
      African-Americans are more severely affected than Caucasians.

      To understand the metabolic consequences of obesity, it is essential to know the rate at
      which free fatty acids (FFA) are released from adipose tissue. Circulating FFA contribute to
      the complications of obesity particularly diabetes and heart disease. As there are sex and
      race differences in the prevalence of all these conditions there may be sex and race
      differences in FFA flux. FFA flux represents the rate at which FFA circulate. FFA flux is the
      result of three processes going on at the same time, (1) the rate FFA are released from
      adipose tissue, (2) the rate circulating FFA are used for energy, and (3) the rate FFA leaves
      the circulation to re-enter adipose tissue. No data is available on whether sex and race
      differences in FFA flux exist. Further, when comparing subjects of different size, sex and
      race, it is unknown whether FFA flux should be corrected for lean body mass or resting energy
      expenditure.

      To determine if there are sex and race differences in FFA flux and to ensure adequate
      enrollment of both African American and Caucasians, this investigation is a collaborative
      effort between the National Institutes of Health (NIH) in Bethesda, Maryland and the Mayo
      Clinic in Olmsted County, Minnesota. The greater Washington, DC, metropolitan area, where NIH
      is located, has a large African-American community whereas over 90 percent of residents of
      Olmsted County are Caucasians. Therefore, sex differences in FFA flux in African Americans
      will be mainly studied at the National Institutes of Health. Sex differences in FFA flux in
      Caucasians will be mainly studied at the Mayo Clinic. But, to confirm the ability to combine
      data from two different sites, some Caucasians will be enrolled at NIH and some African
      Americans will be enrolled at the Mayo Clinic. The results of the two studies will be
      combined to determine if there are race differences in FFA flux.

      At NIH, 50 African-Americans (25M, 25W, age range 18-49 years) and 14 Caucasians (7M, 7W age
      range 18-49 years) will be enrolled. Equal numbers of normal weight, overweight and obese
      subjects will be recruited. As outpatients, participants will be placed on weight maintaining
      diets for two weeks and then admitted for a two-day hospital stay. On each in-hospital
      morning, resting energy expenditure will be measured and stable isotopes infused to measure
      FFA flux. Stable isotopes are naturally occurring forms of elements, which are safe and
      non-radioactive.

      From the study of African-Americans at NIH it will be possible to determine if (a) the rate
      of FFA release in African-Americans is more highly related to lean body mass or to resting
      energy expenditure, and (b) if there is a sex difference in this relationship. Then as
      described above, the results from the Mayo Clinic and NIH will be combined to determine if
      there are race differences in the FFA flux.
    

Keywords: Obesity; Resting Energy Expenditure; Metabolic Rate; Visceral Fat; Body Fat Distribution