- Click here for explanation of classification scheme.

• To examine if oats consumption lowers blood total cholesterol level
• To evaluate the effect of potential modifiers and confounders (age, gender, oats dose, initial blood cholesterol level) in the association between oats consumption and blood total cholesterol level.

Below are inclusion criteria for studies to be considered in this review:

• Identified from Medline search until March 1991, inquiries to list of all known investigators in the lipid-oats association (list provided by Quaker Oats), lists of unpublished trials
• Trials had to be controlled and randomized
• There must be at least four weeks between dietary intervention and blood lipid assessment
• Control group has to be very low or no soluble fiber
• Dietary intake must be formally assessed
• Weight changes must be evaluated
• Primary study investigators must agree to release raw data
• Must measure oats intake and total cholesterol concentration
• Must investigate individual effect of oats apart from other intervention.

 

None except not meeting inclusion criteria.

Recruitment

Studies were identified from Medline search until March 1991. Unpublished trials were identified by inquiring investigators known to be familiar in the lipid-oats association, according to a list of investigators provided by Quaker Oats. Then, investigators of these studies were contacted to obtain raw data.

Design

Meta-analysis and pooled analysis.

Statistical Analysis

Meta-regression using random-effects model, test of heterogeneity.

 

Timing of Measurements

Medline search was done until March 1991.

 Dependent Variables

• Change in total cholesterol level
• Keys score: Calculated using changes in saturated fatty acids, polyunsaturated fatty acids, dietary cholesterol and energy intake.

Independent Variables

Soluble fiber intake (g). 

Control Variables:

• Age (less than 50 years vs. 50 years or older)
• Gender
• Preliminary cholesterol level, which is the mean total cholesterol level before intervention.

For summary effect size calculation, N=12 studies were included, providing 22 treatment-control comparisons:

• Eight trials were parallel
• Three were two-by-two crossover design of oat bran and wheat bran
• One was three-by-three design using oat bran, rice bran and wheat bran
• Two trials measured apo A-I and apo B in addition to total cholesterol and LDL.

Characteristics of Studies

• Subject age range: 20 to 73 years
• Duration of studies: 18 days to 12 weeks
• Sample size range: 10 to 137 subjects
• Dietary assessment used: Majority of trials used three- or four-day food record.

 

 

Summary Effect Estimates of Oats Consumption on Total Cholesterol, Per Different Groups of Studies

Inclusion Criteria	Number of Primary Data Sets	X-square	P-value, Testing that Within-effect Size Variance is Equal to Between-effect Size Variance	Summary Effect Size (mmol per L)	95% CI (mmol per L)
A priori criteria	19	26.5	0.1	-0.15	-0.22 to -0.09
Broadened criteria	22	25.8	0.2	-0.13	-0.19 to -0.07
A priori criteria, but exclude multiple use of treatment groups	17	21.3	15	-0.16	-0.22 to -0.09
Broadened criteria, but exclude multiple use of treatment groups	19	22.7	0.2	-0.14	-0.20 to -0.09
A priori criteria, with only trials where wheat bran was the control	12	16.3	0.2	-0.22	-0.35 to -0.1
A priori criteria, with only trials where control groups had no comparison product	7	8.5	0.2	-0.11	-0.18 to -0.04

Effect Size for Change in Total Cholesterol Level by Dose and Initial Cholesterol Level

Intervention Dose	Effect Size When Initial Cholesterol Level Less than 5.9mmol per L	Effect Size When Initial Cholesterol Level of 5.9mmol or more per L
Less than 3.0g of soluble fiber from oats	-0.09±0.10 (N=6)	-0.27±0.04 (N=4)
3.0g or more of soluble fiber from oats	-0.13±0.12 (N=3)	-0.41±0.21 (N=6)

• Beneficial effects are more profound in population with higher baseline cholesterol level
• According to Keys score or 0.63 (P=0.001), replacing dietary fats and cholesterol with carbohydrates did not explain the reduction in blood cholesterol
• Gender, age and gender-age interaction term did not predict the change in effect size.

• About 3g per day of soluble fiber intake from oat products can decrease total cholesterol level 0.13 to 0.16mmol per L
• Effect of oats intake is greater among those with high initial blood cholesterol levels.

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• It is not clear to me how the "more rigorous" and "broadened" inclusion criteria differ
• According to the authors, analysis were conducted using one treatment-control comparison as unit of analysis. Therefore, some studies contributed more than once. There is no evidence showing whether this correlation may or may not have impacted the results.
• There was no quality grading for primary studies.
• Search strategy and search terms were not described. Only one electronic database was searched. List of potential investigators was provided by industry and profit organizations and may be potentially biased.