A recent meta-analysis of randomized controlled trials found that higher whole-grain intake was associated with improvements in several cardiometabolic risk factors in adults, though many individual changes were small and clinically irrelevant. Dose-response analyses identified clinically relevant effects for some outcomes at specific intake levels.
Study
The researchers conducted a systematic review and meta-analysis of randomized controlled trials investigating the effects of whole-grain consumption on cardiometabolic risk factors. In particular, they aimed to assess the dose-response relationship between whole-grain consumption and cardiometabolic risk factors.
Eligible trials lasted at least two weeks and compared a diet containing whole grains with a low-whole-grain diet, usual or routine care, or a diet containing refined grains. Whole-grain interventions generally provided between about 12 and 213 g per day of whole grains, measured as dry weight.
The review included 101 publications representing 87 randomized trials. The primary outcomes were body weight, LDL cholesterol, fasting plasma glucose, and adverse events. Multiple secondary outcomes were also evaluated, including waist circumference, body fat, blood pressure, HbA1c, fasting insulin, and lipoprotein profiles. Health-related quality of life and inflammatory markers were also measured.
Findings
The dose-response analysis found that an increase of 48 g per day of whole grains, equivalent to about 90 g of fresh weight or three servings, was linearly associated with reductions in LDL cholesterol, body weight, fasting glucose, waist circumference, HOMA-IR, a measure of insulin resistance, triglycerides, total cholesterol, systolic blood pressure, C-reactive protein and interleukin-6.
Nonlinear analyses suggested that some outcomes showed their greatest reductions at moderate intake levels rather than in strictly progressive fashion.
For total cholesterol, LDL cholesterol and triglycerides, the largest estimated reductions were associated with an intake of about 80 g of whole grain per day. At this intake, the reductions were approximately 0.21, 0.16 and 0.08 mmol/L, respectively. The LDL cholesterol reduction exceeded its predefined threshold for clinical importance. The authors also interpreted the reduction in triglycerides as clinically relevant, while the total cholesterol estimate remained below its listed threshold.
HDL cholesterol initially decreased slightly with increasing whole-grain intake up to about 60 g per day and then increased at higher intakes. Relatively few data points were available at these higher intake levels.
The largest estimated increase was at approximately 220 g per day, corresponding to 0.19 mmol/L, exceeding the predefined minimally important difference. This high-intake estimate is less certain because few trials tested such doses.
The pattern for systolic blood pressure was also nonlinear. The greatest estimated reductions occurred at approximately 60 and 80 g per day, with reductions of 2.44 and 2.35 mmHg, respectively, exceeding the predefined minimally important difference.
C-reactive protein showed another nonlinear pattern, with the greatest reduction (0.58 mg/L) at around 60 g per day, but the estimated reduction decreased at higher intakes.
The effects on diastolic blood pressure, TNF-alpha (an inflammatory marker), and interleukin-6 remained clinically irrelevant across the dose range.
Conclusion
This meta-analysis of randomized trials found that increasing whole-grain consumption was associated with modest improvements in several cardiometabolic measures. The authors suggest that intakes of around 60 to 100 g/day dry weight may be associated with improvements in multiple cardiovascular risk factors and caution that “these targets should be interpreted as evidence-based benchmarks rather than universal prescriptions.”
The dose-response analyses suggested that some cardiometabolic effects may be greatest at moderate rather than continuously rising levels of whole-grain consumption.
Source:
https://www.news-medical.net/news/20260916/Scientists-tested-how-much-whole-grain-makes-a-difference-The-answer-was-not-simply-e2809cmoree2809d.aspx