News Author: Lisa Nainggolan
CME Author: Désirée Lie, MD, MSEd
CME Author: Désirée Lie, MD, MSEd
Clinical
Context
According
to He and colleagues, hypertension is highly prevalent, and a 2-mm Hg reduction
in systolic blood pressure (BP) could lead to a 6% reduction in stroke
mortality rates, a 4% reduction in coronary artery mortality rates, and a
3% reduction in all-cause mortality rates. A diet rich in dairy products has
been shown to reduce BP in clinical trials, perhaps because of the high content
of potassium and calcium in these diets.
This
randomized, double-blind, crossover trial compares the effect of soy protein,
milk protein, and refined carbohydrates on systolic and diastolic BP in adults
with prehypertension or stage I hypertension.
Study
Synopsis and Perspective
Both soy
protein and milk reduce systolic BP compared with carbohydrates, according to
the first randomized controlled trial to directly compare the effects of these
two proteins with carbohydrate [1].
The trial
found that 40 g/day of soy protein and 40 g/day of milk protein both
reduced systolic BP by approximately 2 mm Hg compared with
40 g/day of carbohydrate over eight weeks. While this is a small change
for an individual, at a population level such a drop would translate into a 6%
reduction in stroke mortality, a 4% cut in coronary heart disease deaths, and a
3% fall in all-cause mortality, say Dr
Jiang He (Tulane University
School of Public Health and Tropical Medicine, New Orleans, LA) and colleagues
in their paper published inCirculation.
"Our
study suggests that partially replacing carbohydrate with soy or milk protein
might be an important component of nutrition intervention strategies for the
prevention and treatment of hypertension," He told heartwire. He added that increasing intake of
low-fat milk and other low-fat dairy products, soy milk, and beans would help
achieve this goal.
First
Study to Show Milk Lowers BP in Pre- and Early Stage Hypertension
He, an
epidemiologist, and colleagues note that prior observational epidemiologic
studies that looked at the relationship between dietary protein intake and BP
have reported inconsistent findings. They also note that there are very limited
data from randomized controlled trials to assess the effect of dietary protein
on BP, and in most of these trials, change in BP was not the primary outcome
and sample sizes were small.
In their
study, they compared the effect of soy protein, milk protein, and complex
carbohydrate supplementation on BP in a randomized, double-blind crossover
trial in 352 adults with pre- or stage 1 hypertension between 2003 and 2008.
Participants
were randomized to 40 g/day of soy protein, milk protein, or carbohydrate each,
taken as powder supplements dissolved in water, for eight weeks in random
order, and with a three-week washout period between interventions. The
supplements used were formulated in a way that ensured they had the same
sodium, potassium, and calcium content, so that the changes observed were not
due to changes in the intake of these minerals.
BP
readings were taken three times at each of two clinic visits--two before and
two after each eight-week phase--to give a net BP change for each supplement
period.
Compared
with carbohydrate controls, soy protein and milk protein were significantly
associated with a 2.0 mm Hg (p=0.002) and 2.3 mm Hg
(p=0.0007) net decrease in systolic BP, respectively.
"The
present study provides further evidence that soy protein supplementation
reduces BP [and] to the best of our knowledge, this is the first clinical trial
to document that milk protein lowers BP in prehypertension and stage 1
hypertension," the researchers note.
Despite
these encouraging findings, further long-term randomized controlled trials are
needed to examine the effects of various dietary proteins on BP, and to make
specific recommendations for dietary changes, they conclude.
The
authors report no conflicts of interest.
References
- He J, Wofford
MR, Reynolds K, et al. Effect of dietary protein supplementation on blood
pressure. A randomized controlled trial. Circulation 2011;
doi:10.1161/circulationaha.110.009159. Available at:http://circ.ahajournals.org/
Study
Highlights
- The Protein and
Blood Pressure study was a randomized, double-blind, placebo-controlled
phase 3 clinical trial to test whether soy or milk protein supplementation
would reduce BP compared with a complex carbohydrate.
- A crossover
design was used with 3 intervention phases.
- Between 2003 and
2008, participants were allocated to either 40 g of soy protein, 40 g of
milk protein, or 40 g of complex carbohydrate, each for 8 weeks,
after a 2-week washout, with random sequence and 3 weeks between each
intervention.
- 3 groups of
participants received the 3 dietary interventions in 3 different orders.
- Inclusion
criteria were age 22 years or older, and a mean systolic BP of 120 to 159
mm Hg and a diastolic BP of 80 to 95 mm Hg at 6 readings during
2 screening visits.
- Excluded were
patients receiving antihypertensive medication; those with a systolic BP
of 160 mm Hg or higher or a diastolic BP of 95 mm Hg or higher; those who
reported kidney disease, diabetes mellitus, or cardiovascular disease;
those with body mass index of more than 40 kg/m2; those who
consumed more than 14 alcoholic drinks per week; or those with a current
or intended pregnancy.
- The participants
were recruited by mass mailing, worksite, and community-based BP
screenings in 2 cities.
- The soy protein,
milk protein, and complex carbohydrate supplements were provided by a
single producer. There were comparable amounts of sodium, potassium, and
calcium in each supplement.
- 2 baseline and 2
termination visits were made for each of the phases of intervention and 3
BP measurements at each visit.
- Mean age of the
participants was 47 years, 58% were men, one third were black, 45%
reported alcohol intake, and 5% to 11% were current smokers.
- Mean
systolic/diastolic BP was 126.7/82.4 mm Hg.
- 18.5% of
patients had hypertension.
- 80.7% had BP
measured at the end of supplementation with soy protein, 81.3% after
supplementation with milk protein, and 81.5% after carbohydrate
supplementation.
- On average,
dietary protein intake was significantly increased in both the soy (30.5
g/day) and milk protein (32.8 g/day) groups but not in the carbohydrate
group.
- Carbohydrate
intake was significantly decreased in the soy protein (by 30.7 g/day) and
milk protein (30.6 g/day) supplementation phases but was increased in the
carbohydrate phase.
- Urinary
excretion of urea was significantly increased during the soy and milk
protein phases but not in the carbohydrate phase.
- Mean systolic BP
was reduced by 1.5 mm Hg from baseline during the soy protein phase and by
1.8 mm Hg during the milk protein phase but not during the carbohydrate
phase.
- Diastolic BP was
not significantly different during the 3 phases.
- Compared with
the carbohydrate phase, the soy protein phase was associated with a 2.0-mm
Hg reduction in systolic BP (P = .002), and the milk protein
phase was associated with a 2.3-mm Hg lower systolic BP (P = .0007).
- No significant
difference in BP reductions were seen for the soy protein phase vs the
milk protein phase.
- Adverse effects
were similar among the 3 phases and consisted of appetite change, nausea,
and stomach pains.
- The authors
concluded that dietary supplementation with soy or milk protein compared
with complex carbohydrates was associated with a clinically significant
reduction in systolic BP in patients with prehypertension or stage I
hypertension.
Clinical
Implications
- Supplementation
with soy protein or milk protein compared with complex carbohydrates is
associated with a reduction of 2 to 2.3 mm Hg in systolic BP in patients
with prehypertension or stage I hypertension.
- Supplementation
with soy protein or milk protein compared with complex carbohydrates is
not associated with a reduction in diastolic BP in patients with
prehypertension or stage I hypertension.
regards, taniafdi ^_^
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