We are always being urged to ‘Eat up your greens!’ and it has been thought that the beneficial effects of our greens was due to the high levels of antioxidants in them; people who ate a high vegetable diet were generally healthier and had lower blood pressure than those who did not. But no research seemed to be able to back up the antioxidant claim. Then, in 2008, there was a study done on the effects of beetroot juice on blood pressure which cleared up the mystery.1 The study was done on 14 healthy volunteers who drank 500ml beetroot juice in 30 mins.
What was found was that leafy green vegetables, spinach and lettuce are the most frequently quoted, and root veggies, particularly beetroot contain a high level of nitrates, particularly when grown in low light conditions. Now nitrates are rather controversial, being used to preserve food and so we are usually advised to lower consumption. In the study there was no mention made of nitrates as a preservative as a source of nitrate. However, nitrates in veggies seem to be a good thing. And this is why.
OK, it is a bit diddly, but if you click on it, it should expand alarmingly – a bit like the waistline after Christmas. Put simply for the moment, nitrates convert to nitric oxide in the body. It has been known for a while that nitric oxide reduces inflammation and blood clotting and that in cardiovascular illnesses, the patients make less nitric oxide and this is associated with high blood pressure, atherosclerosis (fatty plaques on the artery walls) and strokes. Increasing the amount of nitric oxide gives protection against ischemia reperfusion which is the restoration of blood flow to tissues which were starved of blood flow – this causes damage to the tissues, and the areas of the body concerned are the heart, liver, kidneys, lungs and brain. In the healthy, nitric oxide is protective of various heart diseases.
The study used beetroot juice and what it found was that when we drink the juice, about 25% of it is absorbed through the stomach wall and recirculated in the saliva; this is in the picture above left. In this form when it comes into contact with more beetroot juice it converts it into nitrite which goes into the stomach, where the stomach acid converts it into nitric oxide which then passes to the liver and on into the body where it does its good things of reducing blood pressure, increasing blood flow and, as we shall soon see, increasing glucose uptake by the muscles. Essentially beetroot and leafy veggies work like aspirin, but without the nasty side effects of destroying our stomachs.
The study compared drinking beetroot juice with drinking water (the control group) and it was found that after drinking the juice, the nitrate concentration went up rapidly in the first 30 mins, peaking at about 1.5 hours, where it remained stable for about 6 hours. It then slowly declined, but was still a little higher after 24 hours than the nitrate levels of the water drinkers.
The study recommended increasing intake of nitrate rich foods in the healthy for their protective effects. Another study was done by Stephen Bailey of Exeter University on how beetroot juice improves sporting performance. Click on the link to hear a radio interview with him. In light of the above study, it is hardly surprising to learn that he found that the drink increased blood flow and glucose uptake into the muscles and reduced their oxygen needs, resulting in an increase of 20% in endurance and a 1 – 2% increase in race times.
In the interview, he does say that eating leafy vegetables should have the same effect – so we don’t all have to start drinking beetroot juice, as far as I can tell. Which is a relief since it isn’t to everybody’s taste.
So developing a taste for curly Kale will help prevent heart attacks, strokes and other good things. It will help us rush along for further without feeling quite so exhausted. As a final point, athlete’s coach Charles Poliquin reckons that a dislike of green vegetables is due to a lack of omega 3 which gives the vegetables a bitter taste. So to avoid the risk of taking beta blockers – or suffering a stroke – but the thought of eating a cabbage or a pile of beetroot is appalling, then taking a heavy dose of high quality fish oil for a few months will be hugely beneficial, solve the problem and help weightloss.
- Webb AJ, Patel N, Loukogeorgakis S, et al. Nitric Oxide, oxidative stress. Acute blood pressure lowering, vasoprotective and anti-platelet properties of dietary nitrate via bioconversion to nitrite. Hypertension 2008; 51:784-790 [↩]