Written by Marcia J. Egles, MD. In research with 233 middle-aged participants, it was found about a 4% benefit in cystic blood pressure in those with high fiber intake.
A recent clinical trial from Scotland (1) has added to the evidence that the consumption of whole grains may be beneficial in lowering elevated blood pressure. High blood pressure, or hypertension, carries risk for heart and kidney disease and stroke. The 16-week, randomized, controlled clinical trial showed that healthy middle-aged adults who replaced refined grains with whole grains in their diets showed improvements in their blood pressure.
The government-funded study sought firm evidence to justify national nutritional policies advocating an increase in dietary whole grains in order to combat cardiovascular disease. A prior analysis of 12 cohort studies (2) had concluded that three daily servings of whole grains may be cardioprotective, but to date no adequate clinical trials had been performed.
Two other studies have reported that an increase in dietary fiber of 10-15 grams per day for 8 weeks was associated with a one to three point fall in blood pressure (3,4). Population surveys in the United Kingdom have shown widespread consumption of refined grains (cereals and white bread), but relatively low intakes of whole grains. The most common whole grain eaten in the United Kingdom is wheat, followed by oats (1).
A total of 233 participants, generally healthy men and women aged 40-65, were recruited to a 16-week trial. Obese (body mass indices up to 35) and sedentary persons were included, but those with known heart disease, poorly controlled high blood pressure, severely elevated cholesterol, or diabetes were excluded. Those whose typical diets included large amounts of whole grain foods were also excluded.
For a four week period, all the participants ate a refined grain diet with refined cereals and white bread. They otherwise ate as usual without restriction, but had to keep food records for the duration of the study. After the four weeks, they were divided into three treatment groups:
- Group One: Continued with the refined food diet (Control Group)
- Group Two: Replaced three servings of the refined grains with three servings of whole wheat
- Group Three: Replaced three servings of refined grain with three servings of whole grain wheat and oats
The participants received assistance in keeping records and were instructed as needed how to exchange the refined grains with the whole grains. All of the refined grains and whole grain food products were provided to the participants as part of the study. The study could only be single-blinded, as opposed to double-blinded, since the participants knew what they were eating.
After six weeks, the wheat plus oats whole grain group had a five point decrease on average in their systolic blood pressures as compared to the control group. (In the blood pressure reading of 120/70, the 120 is the systolic blood pressure and the 70 is diastolic.
No reductions in diastolic blood pressure were observed. Other blood pressure lowering factors such as weight loss or salt intakes were unchanged. Other indicators of disease including blood levels of glucose, triglycerides, and c-reactive protein were unchanged. There was a slight (3%) and unexpected decrease in cholesterol in the control group. Because of vitamin-fortified refined grain products, B vitamins and vitamin D intakes were slightly higher in the control group at 12 weeks.
The researchers recommend that three daily servings of whole grains be included as part of the adult diet. They project that adherence to this recommendation could result in decreases in the incidences of coronary artery disease and stroke by as much as 15% and 25% respectively in the United Kingdom(1,4).
Source: Tighe, Paula, et al. “Effect of increased consumption of whole-grain foods on blood pressure and other cardiovascular risk markers in healthy middle-aged persons: a randomized controlled trial.” The American journal of clinical nutrition 92.4 (2010): 733-740.
© 2010 American Society for Nutrition
Posted August 25, 2010.
References:
- Paula Tighe et al, “Effect of increased consumption of whole-grain foods on blood pressure and other cardiovascular risk markers in healthy middle-aged persons: a randomized controlled trial”. Am J Clin Nutr doi: 10.3945/ajcn.2010. 29417.
- Anderson JW, Hanna TJ. Whole grain foods and heart disease risk. J AmColl Nutr2000;19:291s–9s.
- Whelton SP, Hyre AD, Pedersen B, et al. Effect of dietary fiber intake on blood pressure; a meta-analysis of randomised, controlled clinical trials.J Hypertens 2005;23:475–81.
- Streppel MT, Arends LR, van’t Veer P, Grobbee DE, Geleijnse JM. Dietary fiber and blood pressure: A meta-analysis of randomized placebo-controlled trials. Arch Intern Med 2005;165:150–6.
