Effect of dietary proteins on blood pressure

Lowering blooedpressure in humans with high-normal or untreated type 1
hypertension can contribute significantly to a reduction of morbidity and
mortality due to cardiovascular diseases, because of the high incidence within
the population. Food could play an important role in this. From previous
studies it has been shown that food rich in protein, can reduce bloodpressure.
It is however still unknown if the proteins itself are responsible for this
reducion and also the underlying mechanism is still not yet clear.

The primary objective of the study is to demonstrate a difference in changes in
fasting blood pressure and 24-hour ambulatory blood pressure after 4 weeks on a
diet with a high protein content or a diet with a high carbohydrate content.
Secondary objectives are to explore potential mechanisms of the blood pressure
effect of dietary proteins by studying the postprandial responses of
potentially relevant variables to high protein and high carbohydrate meals, on
the first day of the intervention as well as after 4 weeks. The secondary
objectives will be studied in a subgroup of the total study population.

The study has a double-blind randomised two-arm parallel design.
After screening, subjects will enter a 2 week run-in phase, where they will
consume a standard diet (30% fat, 55% CHO, 15% protein). At the end of this
run-in period, subjects will be randomised to one of the dietary groups for 4
weeks: a high-protein group (30% fat, 45% CHO, 25% protein) and a high
carbohydrate group (30% fat, 55% CHO, 15% protein). Primary outcome variables
(fasting blood pressure and 24-hour ambulatory blood pressure) will be measured
at the end of the run-in phase, at the start of the randomised phase and at the
end of the randomised phase. In the subgroup the secondary outcome measures
will be assessed at the beginning and end of the randomised phase.

The intervention will consist of a fixed diet for 6 weeks, whereas there will
be supplements provided after 2 weeks.
During supplementation, the high-protein group will have a 60 gr reduction of
carbohydrates in their diet, that will be replaced by 60 gr protein supplement.
This protein supplement consists of milk, egg (60%) and soy and pea proteins
(40%) (3 x 20gr supplement).
The diet of the high-carbohydrate group will also be reduced with 60 gr of
carbohydrate and this will be replaced by maltodextrin equal to 60 gr of
carbohydrate (3 x 20gr supplement).
Bloodpressure will be taken every week. In a subgroup there will be
measurements determining mechanisms involved in the regulation of
bloodpressure. These will be forearm bloodflow, kidney blood flow & filtration
rate, heart rate volume, cardiac output and arterial stifness. Subsequently
there will be several bloodsamples taken. These measurements will take place
after two and six weeks.

Subjects will be asked to strictly adhere to a diet, partly through
supplements, for 6 weeks and to adhere to physical activity recommendations on
2-3 days during this period. The measurements are easily sustainable and are
very low risk. Bruising from blood sampling may occur. The duration of the
study is 6 weeks and requires 9 visits to the lab, ranging between 30 and 60
minutes, including screening. In the subjects participating in the full
protocol with measurement of secondary parameters, an extra two whole days at
the lab are required.