Intermittent fasting may do more than just slim your waistline.
Diets like the 5:2 – based on eating normally for five days and drastically cutting your calorie intake for the rest of the week – have gained popularity for helping people lose weight without completely overhauling their lifestyle.
Far from weight loss being the only benefit, fasting has been linked to reduced inflammation, improved brain health and even a longer life.
Scientists from the Baylor College of Medicine in Houston have now found feeding rats every other day helped lower the rodents' blood pressure by changing the bacteria in their gut.
This comes after a University of Oxford study found blood pressure-lowering drugs could reduce the risk of heart disease, even in those who appear healthy.
Around a third of British adults have high blood pressure, which occurs when the force of blood against artery walls is dangerously elevated.
Also known as hypertension, the condition rarely causes symptoms, with most cases being diagnosed during a routine check-up.
Left untreated, high blood pressure raises the risk of heart attacks and strokes. It can be reduced, however, via medication and lifestyle choices, like quitting smoking and cutting back on salt.
Research also increasingly suggests that disruption to gut bacteria may cause blood pressure to rise.
"Previous studies from our lab have shown the composition of the gut microbiota ["the community of microorganisms" in the gastrointestinal tract] in animal models of hypertension, such as the SHRSP (spontaneously hypertensive stroke-prone rat) model, is different from that in animals with normal blood pressure," said study author Dr David Durgan.
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The scientists previously found transplanting a disrupted microbiota from a rodent with hypertension into a healthy animal caused the latter's blood pressure to rise.
"This result told us gut dysbiosis [imbalance] is not just a consequence of hypertension, but is actually involved in causing it," said Dr Durgan.
"This ground work led to the current study in which we proposed to answer two questions: First, can we manipulate the dysbiotic microbiota to either prevent or relieve hypertension?
"Second, how are the gut microbes influencing the animal's blood pressure?"
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Past studies have suggested fasting influences a person's microbiota and their heart health. How gut bacteria relates to blood pressure, however, was less clear.
Drawing on previous research, the Baylor scientists analysed SHRSP rats and rodents without high blood pressure. Some of the animals were fed every other day, while the remainder had unrestricted access to food.
As expected, the SHRSP animals had higher blood pressure than their healthier counterparts in both groups after nine weeks, as published in the journal Circulation Research.
Those that were made to fast, however, fared significantly better than the SHRSP animals with unlimited food.
"Next, we investigated whether the microbiota was involved in the reduction of blood pressure we observed in the SHRSP rats that had fasted," said Dr Durgan.
The scientists transplanted the microbiota of the experimental rats into "germ-free" rodents; laboratory animals with no gut bacteria.
"It was particularly interesting to see the germ-free rats that received microbiota from the fasting SHRSP rats had significantly lower blood pressure than the rats that had received microbiota from SHRSP control rats," said Dr Durgan.
"These results demonstrated the alterations to the microbiota induced by fasting were sufficient to mediate the blood pressure-lowering effect of intermitting fasting."
To answer the second question of their experiment – how does microbiota regulate blood pressure? – the scientists analysed the entire genetic sequence of the various animals' gut bacteria, as well as molecules within their blood and gastrointestinal tract.
"Among the changes we observed, alterations in products of bile acid metabolism stood out as potential mediators of blood pressure regulation," said Dr Durgan.
The SHRSP rats that were fed normally had lower bile acids in their blood than the rodents without high blood pressure. Bile acids are critical for digestion, helping the body to absorb fats. Intravenously administering bile acids has been shown to significantly reduce blood pressure.
The Baylor results also reveal the fasting SHRSP animals had more bile acids in their circulation.
"Supporting this finding, we found supplementing animals with cholic acid, a primary bile acid, also significantly reduced blood pressure in the SHRSP model of hypertension," said Dr Durgan.
"This study is important to understand fasting can have its effects on the host through microbiota manipulation.
"This is an attractive idea because it can potentially have clinical applications.
"Many of the bacteria in the gut microbiota are involved in the production of compounds that have been shown to have beneficial effects as they make it into the circulation and contribute to the regulation of the host's physiology.
"Fasting schedules could one day help regulate the activity of gut microbial populations to naturally provide health benefits."
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