Many of the various health organizations recommend eating more fruits and vegetables. Study after study has shown that those who eat more fruits and vegetables have less cardiovascular disease and hypertension. There are multiple theories bandied about – antioxidants, harm from animal protein, low fat, alkalinity, and even an occasional “I don't know,” such as offered by the DASH researchers. Which makes this week's article even more interesting. It reports that one of the places with a higher fruit and vegetable intake than the US has just about as much hypertension and cardiovascular disease as the US.
A recent report (1) out of Korea has demonstrated how you can eat a lot of fruits and vegetables, and still be hypertensive. Korea has a 27% (29% men, 24% women) prevalence of hypertension despite the average Korean eating a much higher percentage of their diet from fruits and vegetables than the average Westerner.
Kimchi – Pickled Vegetables
The big difference is how they prepare their vegetables. The national dish of Korea is kimchi – pickled vegetables. The vegetable used may vary, but it is highly seasoned. There is a lot of variation in the type and amount of spice and herbs added. But consistently a great amount of salt is added. Kimchi forms a major part of the daily Korean diet.
Kimchi accounted for more than 20% of potassium intake, and more than 50% of sodium intake in the study. Rather than the 1.13 ratio that vegetarians typically have, the Koreans in this study averaged a potassium to sodium dietary ratio of 0.72 for males and 0.78 for females. This is about the same as the ratio of a typical Western diet.
Blood Pressure And Kimchi
The researchers found that for men, a poor potassium sodium ratio was strongly correlated with blood pressure. Dividing the participants into 5 groups, the researchers looked at sodium intake, potassium intake, and the sodium to potassium ratio. They also looked at fruit intake, fruit and non-pickled vegetable intake, and kimchies (kimchi) intake. They found a strong correlation with kimchi intake, and an inverse relation with fruit and non-pickled vegetables.
The study did not find any correlation for the women, though. However, in contrast to the men, the fruit intake of the women increased as their kimchi intake increased. With the men, fruit intake decreased as kimchi intake increased. So for the women, the potassium sodium ratio may not have varied as much as the researchers estimated.
Problems With Food Frequency Questionnaires
The researchers felt because they used food frequency questionnaires that a more accurate study could be obtained. They plan to use a prospective trial using a more objective measurement of sodium and potassium (such as urinary measurements).
The problems with using a food frequency questionnaire to estimate potassium and sodium intake are that the memory of the participants may be inaccurate, and the estimates of how much sodium is in the food may be considerably inaccurate. Sodium content of kimchi can be off considerably because each individual uses different methods to prepare kimchi. The researchers used a standard estimate (Food Composition Table of Korea) to determine the amount of sodium in the participants' diet.
Nonetheless, this is a study that shows it is not just getting more fruit and vegetables that lowers blood pressure. It also matters how the fruit and vegetables are prepared. Specifically if sodium is added to the vegetables, they will lose much of their ability to lower blood pressure.
This is one problem with canned vegetables in the US. Most canned vegetables have salt added as a preservative.
Done right, having plants as the basis of your diet will reduce blood pressure, and reduce the possibility of hypertension's complications. But adding salt to the plants is not the right way to add them to your diet.
And Korea is not alone. As we will see next week, there is another country where they eat more plants than Americans do. In this country, vegetarians have worse blood pressure than non-vegetarians.
1. The relationship of dietary sodium, potassium, fruits, and vegetables intake with blood pressure among Korean adults aged 40 and older. Kim MK, Kim K, Shin MH, Shin DH, Lee YH, Chun BY, Choi BY. Nutr Res Pract. 2014 Aug;8(4):453-62. doi: 10.4162/nrp.2014.8.4.453. Epub 2014 Jul 17.