Cereal compliance was determined by participant self-report in a daily cereal calendar. In addition, dietary intake was reviewed both at baseline and at the end of the 6-week intervention, using 3-day food records. Side effect data were gathered from participants at baseline and the end of the intervention. Side effects were assessed via a questionnaire consisting of 21 items relating to potential side effects from increased fiber intake (eg, loose stools, flatulence) or hypertension (eg, headaches, dizziness). Participants reported the frequency at which they experienced these side effects on a scale ranging from “never” to “very frequently” (event occurring once or more per day). Each response was assigned a numerical value. Prestudy and post study averages were used in analyses.
Blood Pressure, Plasma Lipid Concentrations, Glucose Metabolism, and Insulin Sensitivity
Blood pressure was measured weekly for each participant for the duration of the study. Each participant reported to the Hypertension and Cholesterol Research Clinic located at the University of Minnesota Medical School at approximately the same time for each blood pressure reading. All readings were obtained in the morning after participants had rested quietly, seated, for at least 5 minutes in an examination room. An examiner who was blinded to the treatment groups took readings on the right arm using a mercury column sphygmomanometer (Korotkoff phase V for DBP). Standard cuff size was used unless upper arm circumference exceeded 31 cm, in which case the examiner used a large cuff with 15 x 35-cm bladders. Measurements were repeated 4 times in 2-minute intervals. The mean of the last 3 readings was calculated and used in analyses.
To determine plasma lipid concentrations (total, high-density lipoprotein [HDL], and low-density lipoprotein [LDL] cholesterol and triglycerides), pretreatment and posttreatment blood samples were drawn. A 75-g, 3-hour oral glucose-tolerance test (OGTT) was administered before and after treatment to assess participants’ glucose tolerance and insulin response. Whole blood sampling occurred at -30, 0, 30, 60, 90, 120, 150, and 180 minutes. A measure of insulin sensitivity was assessed within 48 hours after the OGTT by means of the modified frequently sampled intravenous glucose tolerance test (FSIGT).28 The glucose and insulin data derived from this test were used to calculate the insulin sensitivity index (SI) employing the minimal-model method developed by Bergman.29
Statistical methods
Reported results are expressed in terms of means ± SD or means SE. Student’s t test for independent samples was used to compare the 2 treatment groups at baseline and to compare mean change scores between the 2 groups. Additionally, area-under-the-curve analyses were performed to compare OGTT insulin curves. All analyses were performed on data from an intent-to-treat population, which included all randomized participants. Statistical tests were 2 sided, performed at the 5% level of significance, and conducted with Statistical Analysis System software (SAS Institute, Cary, N.C.).
Results
No statistically significant differences in baseline characteristics occurred between the groups, although this comparison is limited by the small sample size Table 2. LDL cholesterol and total cholesterol levels and blood pressure were somewhat higher in the treatment group. The blood pressure measurements in the treatment group resulted in an average SBP of 143 ± 3.7 mm Hg before intervention and 135 ± 2.6 mm Hg after intervention (an average of the last 2 study visits, P < .01) Table 3. No significant change in SBP was observed in the control group. A significant difference between the treatment and control groups was observed for the change in SBP (P < .02). DBP dropped from 93 ± 1.9 mm Hg to 87 ± 2.2 mm Hg after the oat fiber intervention (P = .02), with no significant change in the control group (P = .94). A borderline significant trend was noted for the change scores of DBP between groups (P = .055).
Changes in fasting insulin, insulin sensitivity (SI), and insulin curves derived from the oral glucose tolerance tests were assessed. Fasting insulin values Table 3 were taken from the OGTT (preglucose infusion values). Neither the control group (P = 1.00) nor the treatment group (P = .753) showed a significant change in fasting insulin levels. The Bergman minimal model method was used to estimate insulin sensitivity and showed no significant change in either group. Area-under-the-curve analysis of the insulin data derived from the OGTTs before and after treatment with oat cereal (Figure 1 and Figure 2) suggested a trend toward significance in terms of less insulin required to clear a glucose load (top of graphs, P = .093), with no significant changes in the control group (bottom).