Combining a Mediterranean diet with a periodic long fast leads to a sustained reduction in blood pressure and to healthier gut microbes and immune system, according to a recent study from the Max Delbrück Center for Molecular Medicine and the Experimental and Clinical Research Center.  

The research included obese, hypertensive patients who were on a Mediterranean-style diet consisting of fish, lean white meats, fruits, vegetables, and nuts and seeds. Before starting the diet, a randomly-selected group of participants did a 5-day modified fast, which consisted of up to 350 kcal per day of veggie juices and veggie broth.

5 days of fasting before following a Mediterranean diet for 3 months led to a sustained reduction in systolic blood pressure that did not occur in those who followed the diet without a prior fast. 

The improvement in blood pressure seems to be attributable to changes in the bacteria that live in the gut and that occur during and after fasting. Those who had the biggest benefit initially lacked gut bacteria capable of producing anti-inflammatory metabolites known as short-chain fatty acids, but a 5-day fast led to a sustained increase in gut bacteria capable of producing them.  

Short-chain fatty acids help control inflammation in the gut and can ameliorate symptoms of gut inflammatory conditions such as inflammatory bowel syndrome. They also cause blood vessels to dilate, which lowers blood pressure.

The researchers think that fasting might ‘prime’ the gut to regrow short-chain fatty acid-producing gut bacteria following the Mediterranean diet. “I think the ones who were responding had a less healthy microbiome to start with,” says the study’s corresponding author Dr. Sofia Forslund. “We were able to help them overcome this disadvantage by doing a one week fast before shifting to an overall healthy diet.” 


A 5-day fast followed by a Mediterranean diet leads to improvements in blood pressure that may be the result of changes in the gut microbiome and the immune system, according to a recent study.

There were also changes in cells of the immune system during and after the 5-day fast that did not occur with a Mediterranean diet alone and that also could explain the effect on blood pressure. For example, fasting reduced Th1 cells (a type of immune cell that helps other cells of the immune system mature and become activated) whose activation is linked to hypertension

The researchers also reanalyzed data from a similar study that examined the effect of a 10-day modified fast on gut microbiome composition in healthy men, and compared it to their own data from obese and hypertensive patients. Bacteria that produce short-chain fatty acids increased after refeeding in both groups, indicating that even if you’re healthy, your gut could benefit from an extended break from eating. “We see many of the microbiome changes replicate, which is lending support to the idea that this is a specific and generalizable set of alterations that happen when one goes into a fast,” Forslund says. 

Fasting has already been linked to multiple health benefits, including improved blood sugar control and improved insulin sensitivity. This study points to combining periodic fasting with a Mediterranean diet to potentially manage inflammatory conditions in the gut, or to maintain your colony of healthy gut bacteria that can produce beneficial short-chain fatty acids.