If the amount of protein in our diets goes up at the expense of the amount of carbohydrates, our blood pressure goes down. But the amount of protein in itself does not seem to make a difference. This conclusion was drawn by Dr. Susanne Tielemans of Human Nutrition in the thesis for which she received her doctorate on 14 June.
In order to reach this conclusion, Tielemans analysed the results of 29 studies, including 17 clinical trials. Her meta-analysis reveals that replacing 40 grams of carbohydrate in the daily diet with 40 grams of additional protein produces a drop in blood pressure of 2 mm. ‘But we don’t know whether this happens because you consume more protein or because you consume less carbohydrate,’ comments Tielemans. The findings are therefore not sufficient basis for dietary advice.
In a previous epidemiological study Tielemans had already found a link between a higher consumption of plant protein and lower blood pressure, but she could not confirm that with the meta-analysis. Tielemans: ‘My guess is therefore that plant protein does not have a different effect on blood pressure to animal protein. It is possible that the link we found earlier has to do with more plant-based eating habits in general.
A drop in systolic blood pressure of 2 mmHg through more protein and less carbohydrate may not sound much but is quite significant, according to Tielemans. ‘The projection is that it would mean 6 percent fewer deaths by stroke and 4 percent fewer deaths by cardiovascular disease such as heart attacks.’
The difference blood pressure can make to life expectancy was made clear by Tielemans in another part of her doctoral research. She used two datasets about old men who were monitored until their deaths: one from Minnesota in the US, and one from Zutphen. She grouped the men on the basis of their blood pressure history. The group with the lowest baseline blood pressure was the reference group. ‘The men in the third group lost four to eight years of life compared to the reference group. That indicates that people in that group have a considerable risk of an earlier death.’