A great many studies have shown the value of high potassium foods to reduce blood pressure, cardiovascular disease, and strokes. There are multiple theories about what part of high potassium foods provides these benefits. Theories include polyphenols, fiber, antioxidants, and lack of animal protein. These all have some evidence of benefit, but the strongest evidence is for a high potassium sodium ratio. One attempt to show that the health improvements are due to potassium in the diet is to have people continue their normal diet. Then make the only change in diet be the addition of potassium in the form of potassium salt to the diet. There have been several short-term studies of the effect of adding a potassium salt. A study published this year (1) showed that a short-term substitution of potassium salt lowered blood pressure. It used a stronger potassium salt than was used in the study discussed in the last post.
The Potassium Salt Study
The post that was discussed last week used a combination salt that had a one-to-one ratio of potassium to sodium. The study this week used a stronger potassium salt substitute which had a ratio of almost 3 to 1 of potassium to sodium.
The researchers studied patients with uncontrolled blood pressure. They showed a considerable reduction in systolic blood pressure in the patients. The mean systolic blood pressure in the experimental group fell from 143 to 127. Their mean diastolic blood pressure fell from 90 to 76.
However because of the design of the study the researchers were able to determine potential problems with the study that are missed in less well designed studies. The main two were (1) noncompliance with only using the salt provided, and (2) the bitter taste of the potassium salt.
The researchers used urinary sodium and potassium to determine compliance with the conditions of the study. The subjects were supplied with packets of salt to use at each meal. They were to use only these packets with their food. The control group of subjects was given a set amount of normal table salt in the packets. The experimental group was given the same total amount in the packets, but the packets contained a 3 to 1 mixture of potassium salt with normal salt.
The amount of sodium and potassium excreted in the urine showed that the control group participants did not use just the assigned salt. They used additional salt. The control group had more than the expected excretion of sodium. The amount of sodium in the urine was higher than would have resulted from the amount of salt they were provided daily.
On the other hand, the experimental group probably did not use the entire amount of the potassium salt they were given. And although the sodium in the urine fell as expected, the potassium also fell. It would be expected that the potassium in the urine would have increased if they were actually consuming a salt that added a thousand milligrams per day to their diet.
However, the experimental group's ratio of potassium to sodium in the urine changed favorably, which can explain the favorable change in blood pressure. This favorable change in potassium sodium ratio indicates that the salt they used was the potassium salt. But because they did not get the entire amount of potassium salt, the fall in blood pressure may have been due to a reduction in sodium intake rather than due to the addition of potassium or due to the improved ratio.
The Taste Change Of Potassium Salt
The second problem with the study was the change in taste of the food. 89.5% of the participants using the potassium salt complained of a change in taste of the food. Pure potassium salt usually is described as having a metallic or bitter taste. To avoid the taste change, the change in concentration of potassium in salt needs to be gradually done over a period of time rather than suddenly, as was done in this particular study. More than a 25% concentration of potassium in salt is noticeable when done suddenly.
This points out a problem, not with the study, but with the potential to use a potassium salt throughout a nation's population. Long-term compliance with using a strong potassium salt rather than a sodium salt would be unlikely. Because of these taste changes few people would continue to use the potassium salt.
Because the patients were living their normal routine, there was not the control of the diet that was present in the Taiwanese study discussed last week. In the Taiwanese study the subjects were in a retirement home and their diets were provided by chefs. The salt that was provided was the only salt available. In the present study the control subjects used additional salt that they had obtained on their own.
Also in the Taiwanese study, the change in salt composition was gradual. This allowed the change in taste to be undetectable to the participants. The sudden change in composition in the present study meant the taste changed suddenly.
This study shows some of the difficulties with dietary studies. But because the researchers examined the sodium and potassium in the urine they were able to determine the degree of compliance. Many researchers do not include ways to determine compliance and thus cannot detect such weaknesses in their studies. These researchers did an excellent job of being able to determine the noncompliance. The result is a better ability to evaluate the findings of the study and weigh the role of potassium and sodium.
1. Impact of light salt substitution for regular salt on blood pressure of hypertensive patients. Barros CL, Sousa AL, Chinem BM, Rodrigues RB, Jardim TS, Carneiro SB, Souza WK, Jardim PC. Arq Bras Cardiol. 2015 Feb;104(2):128-35. doi: 10.5935/abc.20140174. Epub 2014 Nov 18.