Sodium restriction is recommended as a treatment for cardiovascular disease. This is based largely on the belief that high sodium diets cause water retention in the extracellular space, and this water retention increases blood volume and with it blood pressure. Animal studies looking at sodium intakes are interesting, but it should never be forgotten that different mammals have differing requirements for minerals and as such not all research is relevant to humans. However, as with humans, rats conserve sodium when pregnant, and this can lead to oedema and swelling. This sequestration of sodium is caused by a decreased excretion and an increased appetite for the mineral, and is necessary to allow haemodilution during pregnancy and to allow some storage of the mineral for late in gestation when the requirement for the mineral increases. Because of the oedema that accompanies the sodium retention, low sodium diets are often recommended during pregnancy for humans. However, it is unclear if these diets are actually beneficial.
The effects of dietary sodium restriction has been studied in rats during pregnancy. For example, in one study, pregnant rats were fed a diet containing various concentrations of sodium1 (0.173, 0.067, 0.040 or 0.022 % of food intake), while all other nutrients were maintained at optimal levels to maintain the health of the rats. Rats fed the two lowest sodium diets consumed less feed, gained less weight, displayed altered fluid patterns, had the smallest litters, had fewer live births and had more stillbirths compared to rats fed higher sodium intakes. The number of pups surviving lactation were also fewer in the rats fed the two lowest sodium intakes, and in fact no offspring survived lactation at the lowest sodium intake at all. At 21 days the offspring of the rats were sacrificed and a detailed analysis of their neural development made. The rat pups in the 0.040 % sodium group had lower brain weights, lower brain cholesterol and lower brain RNA compared to rat pups in the other sodium groups.
These results suggest that in rats, low sodium diets during pregnancy are detrimental to the health of the offspring and the mothers. Although vilified in the media and mainstream medical establishment, sodium is an essential element and required in gram amounts for human health. It is known that the requirement for sodium increases during pregnancy for valid physiological reasons and so sodium restriction diets may have detrimental effects on human health during this time. One of the problems with the Western diet is that it contains too much sodium and too little potassium. Vegetables and fruits contain more potassium than sodium, and so high quality diets always provide more potassium than sodium, and this balance is required to maintain health. It is the absence of potassium in the presence of high sodium intakes that can lead to health consequences. There is no need to restrict sodium in high quality diets because the sodium and potassium balance is provided at the right levels by the plant foods inherent to such diets.
Dr Robert Barrington’s Nutritional Recommendation: If you are having to limit sodium intake because intake it too high, this suggests that you diet is of low quality. Diets high in plant foods provide a naturally correct ratio of potassium to sodium. Evidence suggests that high intakes of sodium when in balance with other minerals are not problematic. Care should be taken when restricting sodium intake during pregnancy as the health consequences may be detrimental.