Participants completed a 3-day food record at baseline and at the end of the 12 weeks of intervention. Food records were examined for thoroughness by a licensed nutritionist and used to determine dietary changes. Nutrient intakes were calculated using the Nutrient Data System software (version 2.92) managed by the Nutrition Coordinating Center at the University of Minnesota School of Public Health.17
Statistics
The sample size calculation was based on a level of significance set at 0.05 and power at 80% to detect a 15% difference in medication reduction. Differences in medication reduction were determined by using the chi-square test of proportions. For continuous variables, Student’s paired and unpaired t tests were performed to determine differences within and between groups. In terms of medication reduction, logistic regression was used to adjust for potential confounders such as body weight and sodium intake. Multiple regression was employed to adjust blood lipid and glucose levels and BP findings for confounding. Because adjustment did not change the interpretation of the data, unadjusted findings are reported. The analyses of the data from this intent-to-treat population, which were determined to include all randomized patients, were conducted using the Statistical Analysis System (SAS Institute, Cary, N.C.). Results are reported as means ± SD unless noted otherwise. All P values are double sided.
Results
All the original 88 participants enrolled, all completed the 12-week trial, and all participated in the 6-week follow-up phase. Instructions to consume all dispensed cereals every day were followed well. Compliance was high for both groups (94.5% for the oat group and 92.7% for the control group) based on the amount of consumed cereal by weight. Randomization was largely effective; there were no apparent differences in baseline characteristics between each of the treatment groups (Table 2). Participants were primarily white (97%), with a mean age of 48 years (range 33 to 67 years).
BP and BP medication changes are summarized in Table 3. Among subjects in the oats group, 73% experienced a BP medication reduction during the intervention and had maintained that by the end of the study, as compared with only 42% in the control group (P < .05). Moreover, those in the oats group who did not experience a medication reduction had a 7-mm Hg decrease in SBP and a 4-mm Hg reduction in DBP. There was a small, nonsignificant change in SBP and DBP among those who did not experience a medication reduction in the control group. Medication reduction did not differ across classes of antihypertensive medication or our stratification variables of baseline soluble fiber intake or BP. Additionally, during the 6-week follow-up phase, 6 of the 18 (33%) individuals in the control group versus 22 of the 33 (67%) in the treatment group resumed taking medication.
Average BP in the oats group was lowered from 140/88 mm Hg at baseline to 134/85 mm Hg by the end of the first 4 weeks. Only the change in systolic BP was statistically significant (P < .05). Over the same 4-week period, the control group experienced a mean change of BP from 138/86 mm Hg to 136/85 mm Hg, which was not significant.
Baseline and postintervention lipid and glucose levels appear in Table 4. There were no significant modifications in any of the lipid parameters for the individuals in the control group, although there was a downward trend in all lipid measures. In the oats treatment group, mean total cholesterol (TC) concentration decreased by 31.7 mg/dL (15% drop). A similar decrease of 22.3 mg/dL (16% drop) was seen in the oats group’s average LDL-C levels. Blood glucose levels in the oats group also improved significantly (P < .01). The mean differences between post study and prestudy values (± SE) between the 2 groups, calculated for the average changes in TC, LDL-C, and glucose experienced by each of the groups, were -24.2 mg/dL (± 6.1), -16.2 mg/dL (± 4.4), and -15.03 mg/dL (± 4.3), respectively.
The frequency of dietary fiber-related and hypertension-related side effects decreased by 22% in the treatment group (Table 4). This finding was not observed in the control group. No weight changes were observed in either group, indicating that participants adjusted their diet to compensate for the addition of the cereals by substituting cereal for their standard breakfast and consuming them in place of afternoon snacks as determined by the food record inspection. Total daily energy intake (kcal/day) remained virtually unchanged when postintervention food intake was compared with intake at baseline. Participants in both groups did experience significant decreases in total fat and saturated fat intake along with significant increases in fiber (both soluble and insoluble), potassium, and calcium. The increase in total fiber intake was greater in the treatment group (P < .01) than in the control group (P < .05). In addition, the treatment group experienced a significant increase in magnesium not observed in the control group.