Obesity and Free Fatty Acid Flux

This study, conducted at the National Institutes of Health in Bethesda, Maryland, and at the Mayo Clinic in Rochester, Minnesota, will explore obesity among Caucasians and African-Americans by examining the relationship of resting energy expenditure (REE) to fatty acid flux. REE is the rate the body uses calories while at rest. Fatty acid flux is the rate that fat travels through the blood. If fat travels through a person’s blood without being used for energy, that person is more likely to become obese. Obesity and obesity-related diseases, such as diabetes and heart disease, are more common in African-Americans than Caucasians. The reason for this is not known, but it may be related to REE and fatty acid flux. Test results of Caucasians and African-Americans will be compared to determine if there are race differences in the fatty acid flux.

Official Title

Free Fatty Acid Flux in African Americans

Conditions

Study Type

Observational

Study Design

Natural History

Further Details

African-Americans will be enrolled at NIH, and both Caucasians and African-Americans will be studied at the Mayo Clinic. Candidates must be between 18 and 49 years of age. Equal numbers of normal weight, overweight, and obese individuals will be recruited. Candidates will be screened with a physical examination, electrocardiogram, and blood tests, and will be interviewed about diet, exercise, medical history, family, and employment. Participants will undergo the following procedures on an outpatient basis:-2-week weight maintenance diet and clinic visits on 10 consecutive weekdays: A dietitian will design a diet for each participant that is geared to maintaining the same weight throughout the study so that the rate the body uses calories remains constant. For 2 weeks (except weekends), study subjects come to the clinic in the morning to be weighed, eat breakfast, and receive carry out food for the rest of the day (and on Fridays, for the weekend). -Computed tomography (CT) and dual energy x-ray absorptiometry (DEXA) scans: On one dietary visit, subjects have a CT scan of the abdomen to see how much fat is deposited there and a DEXA scan to measure total body fat. For each scan, the subject lies on the back on a table for about 15 or 20 minutes. After the 2-week diet, subjects are hospitalized for 2 days for the following tests:-REE and measurement of fatty acid flux: These tests are done twice on consecutive days, because the measurements vary from day to day in the same person. Two readings give a more precise picture of the rate the body uses calories when at rest and the rate that fat travels through the blood. For each procedure, the subject eats dinner at 6:00 p.m., after which a small plastic tube is placed through a needle into an arm vein. The next morning, two stable isotopes (naturally occurring forms of chemical elements such as hydrogen or carbon that are slightly heavier than the more common forms of the same element) are infused into the vein. A second tube is placed in a vein in the other arm, and the hand of that arm is placed in a hand warmer (a clear plastic box with warm air). A blood sample is taken from the second tube every 10 minutes over a 1-hour period, for a total of five samples. For the last 30 minutes of the test, the participant breathes normally under a clear plastic hood, in order to measure REE. The tubes are then removed and the participant eats breakfast. -Oral glucose tolerance test (OGTT): On the second morning of the hospitalization when the REE measurement is completed, subjects have an OGTT. For this test, the subject drinks a sugary solution. Blood samples are taken every 30 minutes for 3 hours. When the test is finished, the subject eats breakfast, has his or her vital signs checked, and is discharged. 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% of residents of Olmsted County are Caucasians. Therefore, sex differences in FFA flux in African Americans will be studied at the National Institutes of Health. Sex differences in FFA flux Caucasians will be studied 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) 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.

Study Start

Eligibility & Criteria

Genders Eligible for Study: Both Criteria INCLUSION CRITERIA – Population:A total of 120 subjects, age range 18 to 49 will be recruited.- 64 African-Americans (32 men, 32 women)- 56 Caucasians (28 men, 28 women)Within each racial group equal numbers of normal weight, overweight and obese subjects will be recruited.African-Americans: Individuals will be considered to be African-American if they self-identify as African-American and were born in the United States. Further they must describe both parents as being African-American and born in the United States.Age: We will recruit subjects between the ages of 18 and 49 years.Weight: Enrollees must weigh less than 136 kg (300 lbs) and have a BMI less than 36 kg/m(2).Screening Blood Work: To enroll subjects must have normal hemoglobin levels, electrolyte panel and normal kidney, thyroid and liver function tests.Hysterectomy: Women who have had hysterectomies may participate as long as they are less than or equal to 49 years of age and have normal gonadotropin levels.Weight and Exercise Regimens: Subjects must report that they have been weight stable for at least 3 months and will not initiate a rigorous exercise regimen during participation in the study.EXCLUSION CRITERIA:Age: As above, subjects less than 18 years or greater than 49 years will not be enrolled.Weight: Subjects greater than 136 kg (300 lbs) or BMI greater than 36 kg/m(2) will not be enrolled.Medications: Subjects taking medications that are known to affect the parameters under investigation will be excluded. Some examples of such medications are: oral contraceptives, depoprovera, antihyperglycemic medications, antihypertensives, hypolipidemics, steroids or antiobesity agents.Medical conditions, specifically: Diabetes, Hypertension and Hyperlipidemia.Breastfeeding: Women who are breastfeeding or have an infant less than four months of age will be excluded.Pregnancy: Pregnant women will be excluded from participating.Minority Status other than African-American: After the sample size necessary to achieve clinically relevant data is calculated, the plan is to seek permission from the IRB to expand this study by the enrollment of other minorities.

Total Enrolment

50

Contact Details

[1] National Institute of Diabetes and Digestive and Kidney Diseases