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Diet modification is a critical aspect of any effective strategy for hypertension prevention and control (1). Most recently, an eating pattern tested in the Dietary Approaches to Stop Hypertension (DASH) trial has been recommended for blood pressure reduction (1). This eating pattern, termed the DASH combination diet, emphasizes fruits, vegetables, and low-fat dairy products and has been shown to reduce systolic and diastolic blood pressure substantially (24). Nutrients shown to be related to decreased blood pressure include potassium (5-7), calcium (8-10), magnesium (11-14), protein (15-16), and fiber (17). Those related to higher blood pressure include sodium (5); ratios of cations, such as sodium-to-potassium (5,7); fat (usually saturated fat) (18); and alcohol (7). Despite this wealth of information, little is known about the diets of special populations, particularly those at risk for hypertension. Furthermore, the influence of common demographic variables on the diets of these groups is not well understood.
The ability to generalize findings from randomized controlled trials is often questioned, because participants in these trials are usually highly selected (eg, they may have attained a higher educational level or be more conscious about their health than average) (19). It is, therefore, instructive to assess whether persons who volunteer to participate in diet intervention studies differ from the general population in dietary practices and common demographics. This report describes the dietary profiles of DASH participants before their entry into the study. We first compared the DASH participants' pre-enrollment food and nutrient intake profiles with data for the general US population to estimate the extent to which their eating patterns were typical of their age-sex peers. We then compared the usual dietary patterns of the African-American and white participants within the DASH study population. Because of common eligibility criteria and recruitment pathways, African-Americans and whites in randomized controlled trials may be more similar in some respects than they are in the general population, while other differences that reflect differences in the general population may still be observed (2022). We also examined usual dietary intake in relation to age, obesity, and socioeconomic status.
DASH was a multicenter, randomized, controlled feeding trial designed to compare the effects of 3 dietary patterns on blood pressure. Details of the study design, methods used to set nutrient targets, and a detailed diet description are reported elsewhere (4,23-25). Briefly, the 3 diets that were compared included a control diet representative of what many Americans eat; a fruits and vegetables diet similar to the control diet but with a higher content of fruits and vegetables; and a combination diet that emphasizes fruits, vegetables, and low-fat dairy products. It includes whole grains, poultry, fish, and nuts and is reduced in fats, red meat, sweets, and sugar-containing beverages (2-4).
DASH recruited 459 participants aged 22 years and older with higher-than-optimal blood pressure ([less than]160 mm Hg systolic and 80 to 95 mm Hg diastolic). Because hypertension and its complications occur more often among Americans of African descent than those of European descent, the study recruited more African-Americans (60%) than whites. One-third of the study sample (n=133) had hypertension (in DASH, hypertension was defined as blood pressure of 140 to 159 mm Hg systolic or 90 to 95 mm Hg diastolic). Other clinical exclusion criteria used in DASH are described elsewhere (23,24). Exclusion criteria relevant to diet included a body mass index greater than 35 (calculated as kg/[m.sup.2]), a special diet prescribed by a health professional, alcohol consumption exceeding 14 drinks per week, and reluctance to discontinue the use of magnesium or calcium antacids or vitamin and mineral supplements. Persons unable or unwilling to eat certain foods for religious or other reasons, or because of allergies or other forms of intolerance, were excluded from the study.
Study Protocol and Data Collection Procedures
Eligibility for DASH was determined during 3 screening visits, each separated by at least 1 week. Demographic data, including marital status and categories of education and income, were collected during screening. Participants then entered a 3-week run-in period during which they were provided the control diet. The run-in phase was followed by an 8-week intervention period during which participants were randomized to remain on the control diet, consume the fruits and vegetables diet, or consume the combination diet. The primary outcome variable was the change in diastolic blood pressure from the end of run-in until the end of intervention.
Usual Diet Assessment
Dietary data collection
A food frequency questionnaire (FFQ) originally developed at the National Cancer Institute (26) was used to collect information about the usual dietary intake of participants during the year preceding DASH enrollment. We altered the questionnaire by adding 6 food items reported to contribute significantly to the diet of African-Americans (27) (chicken/turkey potpie, ham hocks, grits, okra, Kool-Aid [Kraft Inc, White Plains, NJ] …