When you have high blood pressure, following a plant-based diet may help to bring it down. A vegetarian diet is one that excludes or only rarely includes meat, and focuses on eating vegetables, grains, beans/legumes and fruits. Some vegetarian diets include dairy products and eggs, while some people who avoid meat will eat fish.
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Vegetarian diet and blood pressure
Following a mainly plant-based diet is associated with having a lower blood pressure. An American study compared blood pressure and dietary patterns in 500 people and found that those following a vegetarian diet (meat, fish and dairy product less than once a month) were 64% less likely to have high blood pressure (defined as greater than 139/89 mmHg) or to take prescribed antihypertensive drugs than those followed an omnivorous diet.
Among vegetarians who ate eggs and dairy products (lacto-ovo vegetarians) the risk of having hypertension was 33% less than for omnivores. But, when the researchers adjusted these figures to take weight and body mass index into account, the blood pressure lowering effect of following a vegetarian diet was no longer statistically significant. In these 500 people, at least, most of the benefit of following a vegetarian diet came from the fact that they were less likely to be overweight or obese.
A UK study compared blood pressure and dietary patterns in 8,663 people and found that blood pressures were significantly lower in vegans than in meat eaters, fish eaters or lacto-ovo vegetarians. But again, when they adjusted for body mass index, the relationship was no longer statistically significant. Other dietary factors such as saturated and polyunsaturated fat intakes had a stronger relationship in both sexes.
In a third study, involving 35,372 women in the UK, vegetarians had a lower risk of hypertension than meat eaters (11.4% versus 19.6%) and also had a lower body mass index (BMI 23.3 kg/m2 versus 25.0 kg/m2) and were less likely to drink alcohol (45% vs 54%).
Based on these three studies alone, it seems that following a vegetarian diet does lower your risk of hypertension but this is mostly because you are more likely to achieve a healthy weight for your height. If you are a meat eater who is within the healthy weight range, you may be just as likely to have a healthy blood pressure as a fellow vegetarian.
By how much does a vegetarian diet lower blood pressure?
Researchers decided to investigate these findings further, using the results from 7 clinical trials, some of which asked participants to follow specific dietary guidelines, and some of which actually provided the food for volunteers to eat, rather than just asking people if they were vegetarian or not.
These studies showed that following a vegetarian diet was associated with an average blood pressure reduction of 4.8/2.2 mmHg compared with an omnivorous diets.
The researchers then analysed the results from 32 observational studies (in which dietary patterns were recorded for 21,604 people) and found that following a vegetarian diet was associated with a blood pressure that was, on average, 6.9/4.7 mmHg than for those who ate meat.
While this may not seem like much, a reduction of 5 mmHg systolic blood pressure (upper reading) is expected to lower the risk of a fatal stroke by 14% and the risk of a fatal heart attack by 9%.
How might a vegetarian diet lower blood pressure?
People who follow a plant-based diet tend to have a lower intake of saturated fat and cholesterol than meat eaters, and a higher intake of dietary fibre, magnesium, potassium, vitamin C, vitamin E, folate, carotenoids and other antioxidants, especially flavonoid polyphenols.
Salt: There are no clear differences in salt intake among vegetarians, and some studies show sodium intakes are higher in vegetarians. In the studies above, however, overall salt intake was lower in those following a vegetarian diet.
Potassium: Vegetarian diets provide high intakes of potassium, which flushes sodium from the body and promotes blood vessel dilation.
Plant protein: The protein found in plant and dairy foods has a different blend of amino acids than those found in meats, and is higher in glutamic acid, which can be converted into arginine – an amino acid with a powerful blood pressure lowering effect. Some research suggests that mainly eating vegetable rather than meat proteins is associated with a 2.1/1.35 mmHg reduction in blood pressure, although this reduced to 1.11/0.71 mmHg reduction when height and weight were taken into account.
Antioxidants: Plants are the main dietary source of antioxidants, which have protect effects on the circulation which increase blood vessel elasticity and dilation, and reduce hardening and furring up of the arteries.
Fibre: Plants are our only dietary source of fibre. Data from 25 studies suggest that those with the highest dietary fibre intake have a blood pressure that is, on average, 1.15/1.65 mmHg lower than those with the lowest intakes. The effect is stronger in people with hypertension, in whom increasing dietary fibre can lower blood pressure by 5.95/4.20 mmHg.
Gut bacteria: A plant-based diet changes the balance of bacteria in the gut and is associated with the production of fewer bowel toxins (eg p-cresol sulfate, indoxyl sulfate trimethylamine N-oxide) which are, on average, 60% lower than when following an omnivore diet. These toxins have been associated with vascular disease.
Should you go vegetarian?
While the blood pressure benefits of a vegetarian diet may be partly explained by weight reductions, most of us would benefit from eating more vegetables and plant protein, and cutting back on intakes of meat.
Tips for following a healthy vegetarian diet include:
- Select whole-grain cereals rather than refined cereals (eg brown bread, brown rice, wholemeal pasta, buckwheat, polenta) for calories, protein, fibre, B vitamins, calcium and iron.
- Tofu and soy beans are a good source of protein, calcium, iron, zinc, thiamine, riboflavin and niacin.
- Mycoprotein, derived from the fungus Fusarium graminosum, is a good source of protein but is low in iron and calcium. Some products contain egg white.
- Mock meat substitutes are a useful protein source and available in the form of veggie mince, burgers, sausages, bacon and fillets, if you want to carry on eating familiar looking dishes.
- Eat at least 5 and preferably more servings of vegetables/fruit per day, including one of citrus fruit.
- Eat plenty of dark green leaves (eg spinach, watercress, broccoli, greens) for folate, calcium and iron.
- Dried fruits such as apricots, dates and figs are a useful source of fibre and iron.
- Wash down iron-containing fruit and veg with fresh orange juice, or similar, as vitamin C increases absorption of plant-based iron.
- Carrots and sweet potato provide protein, energy, fibre, calcium, iron, zinc and vitamin E.
- Nuts, seeds, beans, lentils and cereals all contain protein but not all contain all the essential amino acids, so eat a variety.
- Nuts and seeds are good source of minerals and essential fatty acids.
- Semi-skimmed milk (or fortified soy or almond milk)
- Cheeses provide protein, calcium and minerals.
- Eggs are a great source of protein, vitamins A, B12 and D, and are a useful source of iron and magnesium.
- Vitamin B12 is found in fortified soy milk, fortified breakfast cereals, fortified yeast extracts, Protoveg or supplements.
- Zinc is found in wholegrains, beans, eggs and cheese.
- Olive, rapeseed, flaxseed, walnut and hemp oils are good sources of healthy fats.
Public Health England advise that everyone takes a vitamin D supplement in winter – whatever your diet. You may also consider taking a multivitamin and mineral designed for vegetarians or vegans to support your intakes of vitamin B12, zinc, iron and calcium.
There is more good information on the Vegetarian Society website.