Back in the early 1970s researchers traveled into the jungle in Northern Brazil to visit a group of Indians. The Yanamomo tribe had lived in isolation for thousands of years and had only been contacted in the 1950s. What made them a subject of interest was their diet; their staple food was a kind of large cooking banana, supplemented occasionally with game, fish, wild vegetables and insects. This diet contained almost no salt. At the time, it was regarded as normal that blood pressure rose gradually with age. However, the BP of the Yanamomo Indians remained remarkably stable throughout life, ranging from 107/66 in teenagers to 100/63 in those >50. The investigators went on to perform 24h urine collections on a number of the Indians – this was difficult – in their own words “the collections were complicated by the rather difficult conditions under which the work was conducted as well as the free and unfettered nature of the Yanomamo psyche, which found it difficult to take seriously the concept of a 24 hr urine”. Despite this they managed to acquire complete collections on 26 male subjects and took a series of collections on themselves as western controls.
The results were remarkable.
- The mean 24 hr sodium excretion was 1mEq/24hrs in the Indians compared to 152 mEq/24hrs in the controls.
- Potassium excretion was 152 v 38 mEq/24hrs and Chloride was 14 v 102 mEq/24hrs.
- Urinary aldosterone excretion was 75 v 3 ug/24 hrs.
- The plasma renin activity was also significantly higher in the Indians.
The high potassium/low sodium diet that they were consuming resulted in appropriate hyperaldosteronism in the absence of hypertension. It is likely that this diet is similar to the one our ancestors in Africa were accustomed to. Perhaps the low level of aldosterone that we regard as normal in the west is actually an adaptation to the extremely high level of salt in the western diet – certainly, these Indians prove that we can survive comfortably on less than 1% of our usual salt consumption. It is interesting to note the extremely high urinary anion gap in the Indians – mean 130. What was the anion excreted with the potassium? In all likelihood this was bicarbonate. The potassium in bananas exists in the form of potassium citrate and this would need to be excreted along with the potassium to maintain normal acid-base balance. Unfortunately we do not have any record of the acid base status of the subjects so that is a subject for conjecture. Other studies of isolated tribes who were contacted in the last 70 years have shown a gradual rise in BP in the years after contact. This may be due to increasing quantities of salt in their diets as they are “civilized”.
Here is a previous post from Matt on dietary salt reduction.