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Dr Chris van Tulleken sets out to test the health claim made for three foods – beetroot, garlic and watermelon. It’s said they can all reduce our blood pressure but what’s the truth? High blood pressure is a major risk factor for heart disease, the U.K.’s biggest killer, so if such claims are true then these three foods could be lifesavers.

Dr Andy Webb of Kings College London helped run an experiment to find out what effect these foods really have.

Each volunteer measured their blood pressure twice a day - morning and evening. Each time they took 3 measurements to calculate an average. It was then possible to see which foods made the biggest difference to blood pressure.

• Full experiment protocol

The baseline blood pressure for the group—the average reading taken when everybody was eating and drinking normally - was 133.6 mmHg. On the beetroot diet, this went down to 128.7 mmHg and the garlic gave a similar result (129.3 mmHg). The result in this small study is in agreement with what Dr Webb and others have found in larger studies.

Studies on the links between high blood pressure and heart disease suggest that, if such a drop in blood pressure is maintained, this roughly translates into a reduction of the risk of stroke and heart attack by 10%! Watermelon didn’t have such a strong effect - it reduced systolic blood pressure to 129.8mmHg. This may be because water melon is mainly water- there isn’t much of the active ingredient.

What does the experiment tell us?

Our small study adds to a growing number which suggest that eating beetroot and garlic regularly may help reduce your blood pressure. But these aren’t the only foods that can do this. The active ingredient in beetroot, nitrate, is present in plenty of green vegetables: celery; lettuce; watercress; rocket; spinach; chard; broccoli; for example.

And the active ingredient in garlic – allicin – is also present in onions, shallots, leeks, chives and spring onions.

It turns out there are several foods which can help keep our blood pressure low. But, crucially, how good they are depends on how they’re prepared.

• Eat salad and vegetables raw. Nitrate is intact in the vegetable in their uncooked states but can be reduced by processing and cooking. It is also water soluble and so if your boiling, steaming beetroot or spinach some of the nitrate will be lost in the water. Pickling also reduces the amount of nitrate in beetroot as it’s lost in the picking vinegar.
• If you do boil beetroot, leave it as it is: don’t peel or top and tail it before boiling.
• Have beetoot juice (why not try juice with other flavours such as apple, celery and a little ginger). In juice, you retain most of the beetroot in its raw state.
• Make soup – the nitrate lost in the water will remain in the soup.
• Steam spinach and other vegetables rather than boiling (you use less water so you’ll lose less nitrate in the water).
• Use the water from cooking in soups and stews.