The study included 20 people who were given food for three weeks that either contained the high-fibre supplement, a resistant starch called HAMSAB at 40g, or contained a placebo (corn starch or regular flour with no added resistant starches).
The group who ate the diet with the resistant starch had a clinically significant drop in their systolic blood pressure.
The HAMSAB diet also changed people's gut bacteria, and these changes are likely to be what helped to lower their blood pressure.
The authors say this drop in blood pressure is equivalent to taking a blood pressure-lowering drug and could reduce coronary death by 9% and stroke death by 14%.
Writing in the journal Nature Cardiovascular Research, they stated: “We hypothesized that increased production of gut microbiota-derived metabolites acetate and butyrate reduce BP in untreated patients with hypertension. To overcome the challenge of delivering these short-chain fatty acids (SCFAs) to the systemic circulation, we used high-amylose maize starch (HAMS), a type of resistant starch II that can be acetylated (HAMSA) and butyrylated (HAMSB).
“Intestinal microbial fermentation of HAMSAB releases high levels of acetate and butyrate in the colon, which are subsequently absorbed and delivered to the systemic circulation. Importantly, the levels of acetate and butyrate delivered by HAMSAB are significantly higher than achieved with non-acetylated and non-butyrylated HAMS alone.”
They added that the results provide clinical evidence that delivering SCFAs lowers home, 24-hour and central systolic blood pressure in patients with essential hypertension, independently of sex, age and BMI.
Microbiome impact
Furthermore, the HAMSAB diet also modulated the faecal microbiome, increasing SCFA producers and raising SCFA levels in the systemic circulation.
Specifically, three weeks on the HAMSAB diet was sufficient to shift the β-diversity and increase the relative abundance of two SCFA producers, Parabacteroides distasonis and Ruminococcus gauvreauii compared to placebo.
“Our findings suggest that HAMSAB modulated SBP by increasing SCFA production and prevalence of SCFA producers, such as Ruminococcus sp. and Parabacteroides sp. Further studies are needed to determine if these taxa are required for the SBP-lowering effect that we observed,” they added.
The main limitations of the study were the small sample size, lack of long-term follow-up and the differences in dietary fibre content between treated and control groups. To adequately conclude the benefits of supplementary delivery to control BP, larger and longer-term trials need to be conducted, they noted.
However, the paper concludes: “Our study provides evidence that delivering high levels of the microbial metabolites acetate and butyrate reduces SBP and total vascular resistance in patients with essential hypertension. Furthermore, HAMSAB enriched essential SCFA-producing microbes, which compounds the overall levels of SCFAs. Consumption of SCFAs directly, via the use of HAMSAB or other strategies, may represent a therapeutic option for patients with hypertension.”
The work was supported by a National Heart Foundation Vanguard grant, a National Health & Medical Research Council (NHMRC) of Australia project grant and NHMRC fellowships for several authors.
Source: Nature Cardiovascular Research
DOI: 10.1038/s44161-022-00197-4
“Prebiotic intervention with HAMSAB in untreated essential hypertensive patients assessed in a phase II randomized trial”
Authors: Francine Z. Marques, et al.