The mainstream viewpoint is that high sodium diets cause high blood pressure. The solution to this problem we are told is to restrict dietary sodium in order to lower blood pressure. As with all good lies, this particular turd is sprinkled with a half truths that on the surface makes it appear to be factually correct. However, the nutritional literature does not support the contention that high sodium diets cause blood pressure rises. Theory suggests that the reason that sodium is able to cause an increase in blood pressure is because it causes an increase in extracellular fluid volume. In particular sodium is said to increase both the blood fluid volume and the resistance to its flow by increasing the fluid in the vascular tissue. If this theory were true rises in blood pressure would occur quickly with increasing sodium intakes. However, feeding animals high intakes of sodium only causes rises in blood pressure some time after extracellular fluid volume has been affected. This suggests that the theory is flawed and that other factors modify the effects of sodium.
In particular two factors (possibly more) must be present for a high sodium diet to cause rises in blood pressure. First, the individual must be sensitive to the effects of sodium. Secondly, for high intakes of sodium to cause rises in blood pressure there must be a concomitant low intake of potassium (and possibly calcium and magnesium). In other words it is a macromineral imbalance that causes the increase in blood pressure and this is only a phenomenon that occurs in certain individuals. These factors explain the poor results seen in studies that try to lower blood pressure with low sodium diets. Vegetarians tend to have lower blood pressures that omnivorous individuals and this may be due to their high intakes of plant foods that provide favourable macromineral ratios, including a high potassium to sodium ratio. For example one study1 investigated the blood pressure of a group of vegetarians in comparison to a group of non-vegetarian controls to assess prevalence of high blood pressure.
The results of the study showed that vegetarians tended to have lower blood pressure than the meat eating controls (126 versus 147 systolic and 77 versus 88 diastolic, respectively). This trend was relevant at all ages of life in the subjects. Pair matching the subjects for their body weight also maintained the trend that vegetarians had lower blood pressure than their meat eating counterparts. The authors also controlled for factors such as family history of blood pressure, coffee and alcohol consumption, but these factors did not alter the trend. However, when the authors analysed the sodium and potassium ratio of the diets of the subjects (by urine analysis) they found that the sodium excretion of all subjects was similar, but the vegetarians had a significantly higher excretion of potassium. This suggests that they had higher intakes of potassium. The authors concluded that it was possible that the low potassium intakes of the meat eating subjects was the cause of their high blood pressure.
Dr Robert Barrington’s Nutritional Recommendation: Plant foods naturally contain high ratios of potassium to sodium. Eating a plant based diet therefore provides more potassium in the diet than sodium. This is likely the situation that is best for human health. The typical Western diet however contains more sodium than potassium, and this high sodium to potassium ratio may be a primary driver of high blood pressure in humans. It is interesting that being overweight is associated with high blood pressure, but overweight vegetarians have lower blood pressure than overweight meat eaters of the same weight. This association between body weight and blood pressure may simply signify that sodium is a marker for a poor diet, the latter of which causes the weight gain.
RdB
