Abstract
Background: Three daily portions of whole-grain foods could lower cardiovascular disease risk, but a comprehensive intervention trial was needed to confirm this recommendation. Objectives: We aimed to assess the effects of consumption of 3 daily portions of whole-grain foods (provided as only wheat or a mixture of wheat and oats) on markers of cardiovascular disease risk in relatively high-risk individuals. Design: This was a randomized controlled dietary trial in middle- aged healthy individuals. After a 4-wk run-in period with a refined diet, we randomly allocated volunteers to a control (refined diet), wheat, or wheat + oats group for 12 wk. The primary outcome was a reduction of cardiovascular disease risk factors by dietary inter- vention with whole grains, which included lipid and inflammatory marker concentrations, insulin sensitivity, and blood pressure. Results: We recruited a total of 233 volunteers; 24 volunteers with- drew, and 3 volunteers were excluded. Systolic blood pressure and pulse pressure were significantly reduced by 6 and 3 mm Hg, respec- tively, in the whole-grain foods groups compared with the control group. Systemic markers of cardiovascular disease risk remained un- changed apart from cholesterol concentrations, which decreased slightly but significantly in the refined group. Conclusions: Daily consumption of 3 portions of whole-grain foods can significantly reduce cardiovascular disease risk in middle-aged people mainly through blood pressure-lowering mechanisms. The observed decrease in systolic blood pressure could decrease the incidence of coronary artery disease and stroke by ≥15% and 25%, respectively. This trial was registered at clinicaltrials.gov as ISRCTN27657880. Am J Clin Nutr 2010;92:733-40.
Generated Summary
This study is a randomized controlled dietary trial that investigates the effects of increased consumption of whole-grain foods on blood pressure and other cardiovascular risk markers in healthy middle-aged individuals. The study included a 4-week run-in period with a refined diet, followed by a 12-week intervention where volunteers were randomly assigned to a control group (refined diet), a wheat group, or a wheat + oats group. The primary outcome was to assess the reduction of cardiovascular disease risk factors through dietary intervention with whole grains, including lipid and inflammatory marker concentrations, insulin sensitivity, and blood pressure. The study aimed to determine if the consumption of three daily portions of whole-grain foods (wheat or a mixture of wheat and oats) could lower cardiovascular disease risk in relatively high-risk individuals. The interventions were designed to be practical and realistic for free-living individuals, with no alteration of their usual lifestyle. The prescribed dietary changes aimed to compare a diet on the basis of refined cereal products with a diet where 3 servings of refined cereals foods were substituted with either 3 servings of whole-wheat foods or with 1 serving of whole wheat foods and 2 servings of oats.
Key Findings & Statistics
- Participants: 233 volunteers were recruited. 24 withdrew, and 3 were excluded. 206 participants completed the intervention.
- Baseline Characteristics (Table 1):
- Mean age of participants ranged from 51.6 to 52.1 years across the refined, wheat, and wheat + oats groups.
- BMI ranged from 27.0 to 28.0 kg/m² across the groups.
- Systolic blood pressure (SBP) at baseline was 131.2 ± 1.4 mm Hg in the refined group, 125.9 ± 1.4 mm Hg in the wheat group, and 131.7 ± 1.4 mm Hg in the wheat + oats group.
- Diastolic blood pressure (DBP) at baseline was 79.1 ± 0.8 mm Hg in the refined group, 75.7 ± 0.8 mm Hg in the wheat group, and 78.4 ± 0.8 mm Hg in the wheat + oats group.
- Effect of Intervention on Dietary Intake (Table 2):
- NSP (Non-starch polysaccharides) intake: Significantly lower in the refined group (11.3 g/d) compared to the wheat + oats (16.8 g/d) and wheat groups (18.5 g/d) (P < 0.001).
- Micronutrient Intakes (Table 3):
- Zinc and Magnesium: Significantly greater intakes in both WGF (whole-grain food) groups compared to the refined group.
- Vitamin B-6 and Vitamin D: Daily intakes were significantly lower in both WGF groups.
- Riboflavin: Significantly lower in the wheat + oats group than the refined group.
- Folate: Significantly higher in the refined group than in the wheat + oats group.
- Blood Pressure (BP):
- Systolic BP: Significantly reduced in both WGF groups compared to the refined group (P = 0.01).
- Pulse Pressure (PP): Significantly lower in both WGF groups compared to the refined group (Figure 3).
- Plasma Lipids (Table 4):
- Triglyceride concentrations: Significantly higher at baseline in the refined group than in the wheat + oats group.
- No significant effects on triglyceride, HDL, and apolipoprotein A₁ concentrations due to the treatments.
- Serum Lipid Response (Table 4):
- Total Cholesterol: Decreased in the refined group after 12 wk (5.75 ± 0.11) compared to baseline (5.94 ± 0.14).
- LDL Cholesterol: Decreased in the refined group after 12 wk (3.50 ± 0.11) compared to baseline (3.66 ± 0.12).
- Insulin, Glucose, and Sensitivity (Table 5):
- Insulin, glucose, and markers of insulin sensitivity (HOMA-IR, QUICKI) did not change significantly.
- No significant change in hsCRP (high-sensitivity C-reactive protein) and IL-6.
- Effect on BP: The decrease in SBP in the wheat + oats group (5 mm Hg) was significantly greater than the decrease in the refined group (1.3 mm Hg). The decrease in SBP in both WGF groups was significantly greater than the decrease in the refined group (P = 0.01; Figure 2A).
- Impact on PP: The pulse pressure (PP) was significantly lower in both WGF groups than in the refined group (Figure 3), an effect already apparent in the wheat + oats group (P = 0.03) at 6 wk.
Other Important Findings
- The daily consumption of 3 portions of WGFs significantly decreased systolic blood pressure (SBP) and pulse pressure (PP) in middle-aged, healthy, overweight men and women.
- The observed decrease in SBP (5-6 mm Hg) could decrease the incidence of coronary artery disease and stroke by ≥15% and 25%, respectively.
- The decrease in SBP and PP was not related to changes in heart rates or weight loss.
- Total cholesterol and LDL-cholesterol concentrations decreased slightly but significantly in the refined group after 12 wk of intervention.
- The study found no significant changes in glucose and insulin concentrations or markers of insulin resistance.
- The treatments did not significantly affect markers of inflammation, specifically hsCRP and IL-6.
Limitations Noted in the Document
- The study acknowledges that BP in the baseline measurements was significantly different between the groups, which could introduce a source of error or bias.
- The study did not include severely hypercholesterolemic volunteers, which may limit the generalizability of the findings to this specific population.
- The lack of detailed measurement of sodium and potassium intake is a limitation, as these factors could potentially influence BP.
- The study’s findings may not be directly comparable to studies using supplemental fiber or specifically formulated foods.
- The study’s duration was 12 weeks, which may not be sufficient to observe long-term effects.
Conclusion
This study provides evidence that the consumption of three daily portions of whole-grain foods can significantly reduce cardiovascular disease risk in middle-aged people, primarily through blood pressure-lowering mechanisms. The decrease in systolic blood pressure observed in the whole-grain groups was substantial enough to potentially reduce the incidence of coronary artery disease and stroke. The findings support current dietary recommendations to increase whole grain intake to combat cardiovascular disease. The study’s findings have implications for public health and provide a sound scientific basis for advising the daily consumption of 3 servings of WGFs to combat CVD. The study also underscores the importance of whole grains in a dietary pattern that could be useful for public health recommendations. Despite these benefits, the study’s results did not show significant changes in lipid concentrations and did not support the previously held belief that whole grains improve insulin sensitivity, likely due to the characteristics of the participant group. The lack of a beneficial effect on blood lipid concentrations may be because the study did not include severely hypercholesterolemic volunteers. It should also be noted that the study did not include detailed measurement of sodium and potassium intake, which could have influenced the results.