How pre-diet fasting can remodel microbiome and improve blood pressure
Two new studies investigating the relationship between fasting and the microbiome are offering fresh insights into the way our gut bacteria composition can be remodeled by short-term dietary alterations, and how this can benefit cardiovascular health. The research suggests fasting is not only beneficial for reshaping the microbiome, but a short fast before beginning a new diet can amplify the diet’s beneficial effects.
A number of prior studies have pointed to the community of bacteria living in our gut as playing a major role in the way the food we eat influences our general health. A pair of studies last year, for example, highlighted the significant associations between diet, gut microbiome composition and healthy aging.
Fasting before DASH diet
Newly published research is now offering more granular insights into these relationships, looking at how dietary interventions, specifically fasting, can catalyze blood pressure improvements via microbiome alterations. The first study, published in the journal Nature Communications, demonstrated how a short-term fast offered acute improvements to blood pressure when followed with a longer-term Mediterranean diet.
One of the first treatments often offered to patients suffering hypertension is a dietary intervention known as DASH (Dietary Approach to Stop Hypertension). The DASH diet is an effective first-line treatment for hypertension, however it is still unclear exactly how it directly improves blood pressure. It is hypothesized that dietary alterations to the microbiome could be causing the improvements.
To investigate this hypothesis a team of researchers recruited 71 subjects with hypertension. The cohort were randomly split into two groups, both tasked with following the DASH diet for three months. One group was also tasked with a five-day fast preceding the DASH diet.
Tracking immune biomarker and microbiome changes, the researchers discovered greater blood pressure improvements in the cohort preceding their dietary change with a stretch of fasting. Interestingly, the immune and microbiome changes seen in the fasting cohort were notably different to those detected in volunteers only following the DASH diet.
The researchers hypothesize the fasting diet may be rapidly altering microbiome composition and increasing the availability of short-chain fatty acids. This short-term change could subsequently alter how the body responds to the DASH diet.
"Body mass index, blood pressure and the need for antihypertensive medication remained lower in the long term among volunteers who started the healthy diet with a five-day fast," notes Dominik Müller, one of the researchers working on the project.
The microbiome link
Another newly published study, led by researchers from Baylor College of Medicine, looked to better understand how gut microbes could be influencing blood pressure. The researchers were also interested whether this outcome could be achieved without fasting, either through a dietary supplement or by directly manipulating microbiome composition.
The researchers conducted a series of studies using a particular animal model engineered to study hypertension, known as SHRSP rats (spontaneously hypertensive stroke-prone). The first test was whether fasting-induced changes to the microbiome effected blood pressure improvements.
For nine weeks one group of SHRSP rats were only fed on alternate days. At the end of this period the intermittently fed animals displayed significantly lower blood pressure compared to the animals eating a normal diet. Using fecal transplant experiments the researchers then established that the microbiomes of the fasting rats seemed to be directly responsible for the blood-pressure improvements.
"It was particularly interesting to see that the germ-free rats that received microbiota from the fasting SHRSP rats had significantly lower the blood pressure than the rats that had received microbiota from SHRSP control rats," says David Durgan, one of the researchers working on the study. "These results demonstrated that the alterations to the microbiota induced by fasting were sufficient to mediate the blood pressure-lowering effect of intermitting fasting."
So what exactly is going on here? Close analysis of the microbiota from the fasting animals revealed higher levels of bile acids than those hypertensive animals eating a normal diet.
"We applied whole genome shotgun sequence analysis of the microbiota as well as untargeted metabolomics analysis of plasma and gastrointestinal luminal content,” explains Durgan. “Among the changes we observed, alterations in products of bile acid metabolism stood out as potential mediators of blood pressure regulation. Supporting this finding, we found that supplementing animals with cholic acid, a primary bile acid, also significantly reduced blood pressure in the SHRSP model of hypertension.”
Taken together these new studies offer greater insights into how the gut microbiome helps catalyze beneficial metabolic outcomes from dietary interventions. A lot more work is still needed to understand whether frequent intermittent fasting cycles could improve hypertension while on the DASH diet, but in the short-term it seems a short bout of fasting preceding a dietary change may help beneficially reshape the microbiome.
The DASH study was published in the journal Nature Communications.
The animal study was published in the journal Circulation Research.