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Blood pressure.

Article Excerpt
KEY POINTS

* Most population epidemiological studies have shown an inverse association between estimated protein intake and blood pressure. Total and plant proteins are consistently associated with lower blood pressure. Inverse associations of animal protein with blood pressure have also been shown.

* A reduction in blood pressure with protein, in comparison with carbohydrate, is a consistent finding in controlled trials. Animal (including lean red meat and milk proteins) and plant (primarily soy) proteins appear to be similar with respect to effects on blood pressure.

* It remains uncertain whether protein itself can lower blood pressure, or whether the benefits are due to partial replacement of some other factor in the diet, such as refined carbohydrate. Potential mechanisms remain speculative.

* The implications of the available research for 'healthy eating' advice remains uncertain: the long-term effect of a dietary approach to increase protein intake, which is widely applicable to the population, needs to be evaluated, as does the influence of refined carbohydrate on blood pressure.

INTRODUCTION

It was initially thought that a higher intake of animal protein specifically, and total protein intakes more generally, are detrimental for blood pressure. This idea derived from studies showing that vegetarian diets, which are lower in total protein and lack meat protein, can lower blood pressure. (1) However, several studies have investigated whether type of dietary protein (animal vs plant) could explain the lower blood pressure with vegetarian diets. (2-5) In addition, more recently, several studies have shown that non-vegetarian diets rich in vegetables, fruits and legumes can also lower blood pressure. (6) This paper takes the position that it is possible that higher protein intakes could actually benefit blood pressure.

The relationship between protein intake and blood pressure has been investigated in many population studies. (7-9) In cross-sectional and longitudinal epidemiological studies, the estimated protein intake has generally been inversely associated with blood pressure. Higher total and plant protein intake is consistently associated with lower blood pressure. Higher animal protein intake has also been associated with lower blood pressure in several epidemiological studies. This paper reviews research addressing the links between dietary components, notably protein and carbohydrate, with blood pressure.

TOTAL PROTEIN INTAKE

Most cross-sectional population studies have shown an inverse association between estimated protein intake and blood pressure. (7-12) For example, the INTERSALT study, which involved over 10000 men and women, reported an inverse relationship between urinary nitrogen and urea--as indicators of total protein intake--and blood pressure. Estimates from the present study indicate that an increase of 37 g/day of protein would lead to falls in population mean systolic and diastolic blood pressures of ~3 and ~2.5 mmHg, respectively. (10) The estimated fall in blood pressure in individuals with elevated blood pressure may be greater. An increase in protein intake of 37 g/day represents a modest shift in protein intake from 30% below the population mean to 30% above the mean. To date, there have been more than 25 reported cross-sectional studies, with approximately two-thirds reporting...