- Click here for explanation of classification scheme.

To determine the lipid-lowering effects of dietary corn bran, fed in moderate supplemental doses to men with hypercholesterolemia, consuming a low-fat diet.

• Men
• Hyperscholesterolemia (cholesterol level above 5.2mmol per L)
• Never been prescribed medication for lowering serum lipid levels
• Sedentary (not involved in organized exercise program and did not exercise regularly).

Not described.

Recruitment

Subjects were recruited through a newspaper article in a local newspaper. 

• More than 75 telephone calls were screened
• 40 potential subjects were scheduled for interview by one of the two principal investigators
• Two educational sessions were held and 29 subjects were selected to participate in the study: During the educational sessions, potential subjects were briefed on the purpose of the project, given a tour of the research facility and provided with information on the methods to be used.

Design

The 98-day study was divided into one two-week pre-period and two six-week experimental periods stratified in a crossover design. 

• Two-week adjustment period, in which subjects consumed a low-fat diet
• Subjects were assigned to one of the two experimental treatments:
  • The low-fat controlled diet plus 20g corn bran supplement
  • The low-fat controlled diet plus 20g wheat bran. 

The median baseline serum cholesterol value for the subjects was 7.8mmol per L. Therefore, subjects were blocked accordingly (more than 7.8mmol per L and less than 7.8mmol per L) and were assigned to initial treatment periods so that half of each group was placed in each experimental treatment in a stratified design. 

Intervention

• Throughout the 14-week study, subjects were fed a completely controlled diet, which provided:
  • 30% of energy from fat
  • 10% of energy from polyunsaturated fatty acids
  • 12% of energy from monounsatured fatty acids
  • 8% of energy from saturated fatty acids.
• The diets were formulated based on calculated values and then analyzed to ensure constancy. All meals were prepared in the metabolic diet kitchen and a new menu was introduced every seven days. No differences (P<0.05) between dietary treatments were found for fat or protein. 
• When energy adjustments were needed for weight maintenance, diets were reformulated to ensure that percentages of energy from total fat, polyunsaturated fatty acids, monounsaturated fatty acids and saturated fatty acids remained constant
• Each day subjects consumed morning meals in the dining room of the kitchen. The noon and evening meals were prepared by laboratory technicians, but subjects were allowed to consume these meals at work or at home.
• Subjects kept daily records of all foods consumed during the controlled feeding portion of the study. Also, each subject was interviewed daily to determine adherence to the diet. This information was checked against questionnaires filled out each morning by the subjects to verify adherence to the controlled regimen.
• Corn and wheat bran supplements were added to the experimental diets in the form of baked products. No adverse side effects were experienced by subjects during the 12 weeks of bran supplementation. 
• Neutral detergent residue, acid detergent residue and cellulose-lignin contents were measured in food composites and fiber samples by means of the method of Robertson and Van Soest. Hemicellulose was calculated by the difference of neutral detergent residue minus acid detergent residue. Duplicates of all samples were collected and all analyses were performed on duplicated sub-samples.

Statistical Analysis

• SPSS X software (version 10, 1988, Statistical Package for the Social Sciences, Chicago, Illinois)
• Differences in serum lipid parameters in four study periods: Baseline, low fat, low fat+corn fiber and low fat+wheat fiber
• Two-way analysis of variance with repeated measures (P<0.05)
• Paired T-test was used to assess the differences between treatment periods for each subject
• Because no interaction (P<0.05) between fiber treatment and intake period was observed, the data were combined and values are presented as pooled means ±standard deviation.

Timing of Measurements

• Baseline measurements of serum lipids were calculated by averaging the values from blood drawn after two fasting periods, seven days apart before the onset of the 14-week study
• Starting and ending measurements of serum lipids:
  • First and last blood collections of the two-week pre-period 
  • Each of the six-week treatment periods
    • Fasting blood samples were drawn for lipid analysis on Day One of each of the 14 weeks of controlled feeding and on the morning after the last day of controlled feeding.

Dependent Variables

• Total cholesterol (TC): Analyzed according to the enzymatic method of Allain et al
• Low-density lipoprotein cholesterol (LDL-C): Calculated LDL-C = TC - (VLDL-C + HDL-C)
• High-density lipoprotein cholesterol (HDL-C): Analyzed according to the enzymatic method of Allain et al, after precipitation by dextran sulfate
• Very-low density lipoprotein cholesterol (VLDL-C): Calculated VLDL-C = triglyceride/5
• Triglyceride: Measured using the methods of Bucolo and David.

Independent Variables

Diets (low-fat controlled with corn bran and low-fat controlled with wheat bran): Measured by daily records of all foods consumed during the controlled feeding portion of the study, daily interviews, questionnaires filled-out each morning to verify adherence to controlled regimen).

Control Variables

• Weight
• Fat (saturated, monounsaturated, and polyunsaturated fatty acids) and protein content of diets.

Initial N

29 men.

Attrition (Final N)

• No attrition reported
• 29 men (although some statistical analyses contain sample sizes less than 29, as some subjects failed to provide a blood sample at each collection time).

Age

• Mean, 55.9 years
• Range, 38 to 70 years.

Ethnicity

Not reported.

Anthropometrics

• Weight was monitored throughout the course of the study and energy intake was modified to ensure minimal weight fluctuation
• Mean change in body weight per subject was 1.79±3.2 lbs over the course of the 14-week study (from the beginning of the two-week pre-period until the end of the second six-week treatment period
• Initial serum lipid values ranged from 5.4mmol to 9.0mmol per L (mean, 6.9±0.8mmol per L).

Location

Metabolic diet kitchen of the Department of Home Economics and the Nutrition Research Laboratory of the Department of Agriculture at Illinois State University, Normal.

Mean daily intake of energy and selected nutrients of the low-fat controlled diets supplemented with bran^a 

Energy and Nutrients	Low-Fat Controlled Diet with Corn Bran	Low-Fat Controlled with Wheat Bran
Energy (kcal)	2,081±65	2,150±176
Cholesterol (mg)	315±27	329±19
Fiber (g)b	14.4±0.9	15.1±0.4
Carbohydrate (percentage kcal)	9.6±0.2	57.7±1.7
Protein (percentage kcal)	13.9±1.5	12.7±1.8
Total Fat (percentage kcal)	29.4±2.2	31.0±2.3
Saturated Fat (percentage kcal)	8.0±0.3	8.3±0.6
Monounsaturated Fat (percentage kcal)	11.8±0.4	12.0±0.2
Polyunsaturated Fat (percentage kcal)	9.6±0.3	9.6±1.1

 

a Mean ±standard deviation; N=3. Data reflect calculated values from Pennington JA. Bowes and Church’s Food Values of Portions Commonly Used. 15th edition. Philadelphia, PA: JB Lippincott Co; 1987.

^b Does not include the 20g supplemental fiber.

 

Other Findings

An analysis of diet history obtained from subjects before initiation of the study found that daily energy provided by total fat intake was 32.0±4.6%. Subject adherence to the dietary protocol was considered to be excellent, according to daily interviews, surveys and food records. The addition of both corn and wheat bran to the diets was well tolerated by all subjects: No adverse effects were noted. Mean change in body weight per subject was 1.79±3.2 lbs over the course of the 14-week study. Fat content of the diets as a percentage of energy remained constant. 

The two experimental diets (low-fat controlled diet plus corn bran or low-fat controlled diet plus wheat bran) were formulated to contain equal amounts of fat, protein and bran. Chemical analysis showed no differences (P>0.05) in fat, protein or acid detergent residue. The experimental diet containing corn bran was found to contain a greater (P<0.05) amount of neutral detergent residue than the diet containing wheat bran. Analysis of the fiber sources revealed significant (P<0.05) differences in fractionates. The corn bran contained less protein, more neutral detergent residue and greater amounts of hemicellulose than the wheat bran. When expressed as a percentage of acid detergent residue, both fiber sources contained similar amounts of the cellulose-lignin fractionate (94.2% and 95.4% for corn bran and wheat bran, respectively). 

Mean (±standard deviation) serum lipid parameters (mmol/L), as affected by low-fat, low-fat plus corn bran and low-fat plus wheat bran diets

Parameter and Diet		Baseline or Beginning Period	End of Period	Percentage Changeb	P-Value
Cholesterol	Low-fat (N=29)c	6.97±0.86d	6.06±0.65d	-13.1	0.001
	Low-fat plus corn bran (N=29)e	6.03±0.83d	5.72±0.86d	-5.2	0.005
	Low-fat plus wheat bran (N=26)e	6.11±0.68	5.95±0.99	-2.6	0.38
Triglyceride	Low-fat (N=29)	3.04±2.03d	2.18±0.94d	-28.3	0.02
	Low-fat plus corn bran (N=29)	2.24±1.12d	1.94±0.87d	-13.1	0.05
	Low-fat plus wheat bran (N=26)	2.73±2.36	2.17±0.87	-20.7	0.11
Very Low-Density Lipoprotein Cholesterol	Low-fat (N=29)	1.38±0.94d	0.99±0.42d	-28.3	0.02
	Low-fat plus corn bran (N=29)	1.01±1.09d	0.88±0.39d	-13.8	0.05
	Low-fat plus wheat bran (N=26)	1.25±1.09	0.99±0.73	-20.8	0.11
High-Density Lipoprotein Cholesterol	Low-fat (N=29)	0.96±0.26	0.94±0.21d	-2.7	0.21
	Low-fat plus corn bran (N=29)	0.94±0.23	0.88±0.18d	-5.6	0.09
	Low-fat plus wheat bran (N=26)	0.91±0.21	0.91±0.23	0.0	0.38
Low-Density Lipoprotein Cholesterol	Low-fat (N=29)	4.60±1.14d	4.13±0.68d	-10.2	0.001
	Low-fat plus corn bran (N=29)	4.08±0.83	3.93±0.86	-3.8	0.09
	Low-fat plus wheat bran (N=26)	3.93±1.01	4.06±0.91	-3.3	0.30

^b Percentage change was calculated by dividing the end of period mean by the appropriate baseline mean or beginning of period mean and subtracting the resulting value from 100.
^c Duration of pre-period was two weeks
^d Means within a row differ significantly according to significance level listed.
^e Duration of experimental periods was six weeks.

• The results of this study support other studies demonstrating that restriction of dietary fat to 30% of energy intake reduces levels of selected serum lipids
• Our study also suggests that supplementing a low-fat diet with corn bran is effective in further reducing serum lipid concentrations for men with hypercholesterolemia
• Although there are a few foods that naturally contain some corn fiber, such as corn bread (1.24g per serving), cornmeal (3.59g per serving) and whole-kernel corn (3.03g per serving), it is unrealistic to expect that consumers could ingest 20g of corn bran per day from existing foods. Corn bran itself can be found in some specialty food stores, but it would be more coarsely-ground than the experimental bran used in this study (Nutra/Balance Products in Indianapolis, Ind, has developed products such as cookies that contain this fine-grind corn bran, which indicates a potential market for corn bran products).