Black soy peptides have been shown to possess properties that may decrease blood pressure. To examine the effects of black soy peptides supplementation on blood pressure and oxidative stress in subjects with pre-hypertension or stage I hypertension.

Trial participants included men and women aged 30 to 65 years who had an average systolic blood pressure (SBP) between 130 to 159 mmHg, average diastolic blood pressure (DBP) between 80 to 99 mmHg, or both, based on an average of six measurements during two screening visits. Participants were supplied with 84 pouches of placebo (casein) or black soy peptide (3 pouches/day) at 0-week and at 4-week visits. Test group subjects received pouches containing black soy peptides (4.5 g/day total soy peptides for 8 weeks). The control group received pouches containing casein that had a similar appearance to the black soy peptide tablet. During the intervention, we instructed study participants to continue their current food intake patterns and lifestyles so that total energy intake and energy expenditure would be constant during the course of trial. Participants brought back unconsumed pouches at their 4- and 8-week follow-up visits. The dietitian counted the number of returned pouches, and we used this to assess the participants' adherence to their assigned intervention.

Inclusion Criteria:

• Average systolic blood pressure (SBP) between 130 to 159 mmHg
• Average diastolic blood pressure (DBP) between 80 to 99 mmHg, or both, based on an average of six measurements during two screening visits

Exclusion Criteria:

• Previous diagnosed clinical hypertension
• Self-reported use of anti-hypertensive medication
• Abnormal liver or renal function
• History of cardiovascular disease, cancer, thyroid or pituitary disease, or any other serious life-threatening illness that required regular medical treatment