What is the DASH diet?

DASH stands for Dietary Action to Stop Hypertension and is recognised for reducing blood pressure. The diet calls for a reduction in fats, red meat, sweets and sugary drinks and an increase in whole grains, fruits, vegetables and low-fat dairy products. It also includes some fish, poultry and legumes and encourages a small amount of nuts and seeds a few times a week. 

Eating healthily is recommended to help lower high blood pressure readings, but more specifically, experts recommend following the DASH diet.

Interestingly, the success of the diet may be down to the action of the bacteria located in the mouth.

Mouth bacteria drives production of Nitric Oxide

The diet is rich in fruit and vegetables and low in saturated fat which in itself it recognised as having benefits to reducing cardiovascular disease and stroke. However it is the oral bacteria, mainly located at the back of the tongue, that is key to combating hypertension. The bacteria transforms dietary nitrate into nitrite which in turn leads to lower blood pressure via the production of nitric oxide (NO).

Professor Amrita Ahluwalia, co-director at the William Harvey Research Institute at the Queen Mary University of London says:

"The magnitude of the blood pressure reduction was found to be directly proportional to the rise in circulating nitrite levels."

Nitric Oxide is very important to the cardiovascular system

The finding is significant because loss of NO has been proven to be involved in the early stages of cardiovascular disease and the development of hypertension. Ahluwalia explains further:

"NO is important to the cardiovascular system. NO is produced in a healthy individual by the endothelium of all of our blood vessels. It exerts a range of beneficial, protective effects. It endows the blood vessels with an anti-hypertensive and anti-atherosclerotic phenotype."

An early warning sign of cardiovascular disease is when the endothelium malfunctions and this arises from a deficit in nitric oxide. Therefore replacing lost NO and increasing bioavailable levels in the body have the potential to treat those with cardiovascular disease.

The key is nitrate reducing bacteria in the mouth

Researchers fed volunteers dietary doses of nitrate and found that both blood and saliva concentrations of nitrate increased, but the latter was to to much greater degree.

Good sources of dietary nitrate include beetroot and green leafy vegetables.

Ahluwalia explains:

"We see 10 times higher concentrations of nitrate in the saliva in comparison to circulating levels and it is here that the nitrate comes into close contact with the bacteria.

There are bacteria which express nitrate reductase in the oral cavity and they convert nitrate to nitrite. You can't help swallowing your saliva and that's how it re-enters the body."

So the bacteria in the mouth reduce nitrate to nitrite and then the nitrite-rich saliva is re-ingested into the body where it's converted into the anti-hypertensive nitric oxide. The researchers were also able to confirm that blood pressure reduction effect came from the nitrite in the saliva, as patients who were made to spit out their saliva did not show lower blood pressure.

Ahluwalia concluded:

"Increasing consumption of fruit and vegetables provides sustained blood pressure lowering and I would like to suggest that it may be the nitrate content within that fruit and vegetable diet that is responsible for this."

"There have been a number of assessments showing the DASH diet contains between 6 and 20 millimoles per day of nitrate and we know absolutely that these kinds of doses will reduce blood pressure."