Eat More Protein and Lower Your BP

Summarized by Robert W. Griffith, MD
January 30, 2006

Introduction

Many, if not most, US adults have high blood pressure (hypertension, i.e. blood pressure over 140/80 mmHg) or a condition known as prehypertension (blood pressure between 120-140 systolic or 70-80 diastolic mmHg). As both conditions normally progress to cardiovascular disease (coronary arterial disease, heart attack, heart failure, stroke, and so on) it's important that lifestyle changes are adapted to combat them. The DASH diet (Dietary Approaches to Stop Hypertension) has proved a successful tactic for many. While it's been shown that a high total intake of dietary protein is associated with lower blood pressure, the different roles of vegetable and animal proteins are not clear. However, a step forward has just been taken by a report in the Archives of Internal Medicine; it's an international study of the dietary intake of vegetable protein in relation to the development of hypertension. We summarize it here.

What was done

Randomly selected population samples from Japan, China, UK, and USA provided data from 4,680 middle-aged men and women. Blood pressure was measured at four visits over 3 to 6 week intervals. At each visit the participant completed a detailed food diary covering the previous 24 hours, along with information on any food supplements, alcohol, medications, and physical activity.Two 24-hour urine specimens were collected at the first and third visit, and analyzed at a central laboratory. The dietary information was analyzed for animal and vegetable (non-animal) protein expressed as a percentage of total energy (calorie) intake.

What the study showed

The average age of the participants was 49. Average systolic blood pressures ranged from 117 mmHg in Japanese to 121 mmHg in Chinese. Diastolic pressures ranged from 73 mmHg (Japan, China, USA) to 77 mmHg (UK).Average body mass index (BMI) levels, calorie, and animal protein intake were lowest in China, and highest in USA; vegetable protein intake, however, was lowest in the USA (5.2% of calories) and highest in China (10.0% of calories). In each of the 4 countries, the higher the vegetable protein intake, the lower the animal protein intake.

• After adjustments were made for factors that might influence the outcome (including age, gender, history of cardiovascular disease or diabetes, physical activity, and alcohol intake) it was found that those subjects with an average vegetable protein intake of 9% or greater per kilocalories consumed had a blood pressure 2.14 mmHg lower than those eating less vegetable protein. Similarly, their diastolic pressures were on average 1.35 mmHg lower.
• After additional adjustment for height and weight the reductions for high vegetable protein intake were still significant - 1.11 mmHg lower systolic and 0.71 mmHg lower diastolic pressure, on average.
• There were no significant associations between total protein intake or animal protein intake and blood pressure.The aminoacid content of the diets showed significant differences between the vegetable protein-predominant and the animal protein-predominant eaters. The authors of the study believe this is responsible for the differences in blood pressure detected.

What this study means

This was a cross-sectional, or observational study, which gives it less credence than a prospective, or longitudinal study. It cannot demonstrate cause-and-effect, whereas a well-designed prospective study might be able to do so. Nevertheless, the results represent an important step in our understanding of the role of diet in cardiovascular disease.

While earlier studies of this nature have shown a correlation between high total protein intake and lower blood pressure levels, this study has refined the finding, placing the benefit clearly on the shoulders of vegetable protein, rather than animal protein. This fits in well with other nutritional studies that show the benefits of a high vegetable, fruit, and grain diet on cardiovascular outcomes such as coronary heart disease, heart attack, stroke, and heart failure. (Elevated blood pressure can be regarded as an early stage of gradually progressive cardiovascular disease.)

The average reductions in blood pressure demonstrated in the study may seem small; they are, however, only slightly smaller than some of the average reductions achieved by other approaches to lowering blood pressure in people without hypertension - e.g. adapting the DASH diet, embarking on a physical activity program, or losing weight.

As we've said many times before, the conclusion is that you should eat more vegetables, fruit, and grains, and cut back on the red meat.

Source

• Association between protein intake and blood pressure. P. Elliott, J. Stamler, AR. Dyer,  et al., Arch Intern Med, 2006, vol. 166, pp. 79--87

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