(12) High Blood Pressure
Other dietary help
Will eating a low-fat, high fruit and vegetable diet help to reduce my BP?
Healthy eating is a broad term for a change of diet to increased intake in fresh fruit and vegetables as well as an increase in low fat foods. In terms of reducing BP there is good evidence that a low-fat, high fruit and vegetable diet does reduce BP in people with no history of cardiovascular disease. Reductions in BP have been in the region of 3 mmHg diastolic and 5 mmHg systolic BP.
Although these are not as large reductions as for other nondrug activities such as exercise, if you keep to this diet they will be worthwhile and reduce your chance of suffering a stroke or heart attack.
Should I eat more fibre?
‘Dietary fibre’ usually means everything in your food that you cannot digest, and therefore is excreted. It includes lots of important materials that are not fibrous at all, such as gums, which affect both the way in which food is absorbed, and the quantity you want to eat before you begin to feel full and tired of chewing. As well as breakfast cereals and wholemeal bread, all fruit and vegetables have high fibre content, although how much you actually get depends on whether you cook them or eat them raw. Routine addition of sodium bicarbonate to keep vegetables green rapidly destroys their fibre content, as does prolonged boiling.
Steaming and microwaving vegetables are the best cooking methods. Fresh fruit and raw salads are ideal. Pulses (peas, beans, lentils, etc.) have the highest fibre content of any cooked vegetables. Increasing the fibre content of your diet by eating more whole meal bread, fruit and vegetables is one of the most effective steps you can take in any reduced-fat, weight-reducing, and cholesterol-lowering diet.
The nurse in our practice said that I should try and eat a ‘healthy diet’. What is meant by a healthy diet? Should it include foods that are eaten in the Mediterranean region?
Most of the good results in studies have been due to changes in diet involving eating a minimum of five portions of fruit and vegetables per day. Often these studies have been delivered through health promotion advice from nurses so that people’s new eating habits are monitored and reinforced.
There have been no studies specifically addressing the issue of BP lowering by increasing fish intake or changing your diet to a Mediterranean-type diet. However, the benefits of high fish diets have been demonstrated in other situations, particularly in the lowering of risk for heart attack (myocardial infarction).
The benefit of changing to a Mediterranean diet, which consists of bread, fruit, vegetables and fish, with less meat and replacement of butter and cream with olive or rapeseed oils, has not been shown to be associated with reductions in BP levels but there is good evidence that diet does reduce your risk of heart attack or stroke.
So, are there any particular types of fish that could help to reduce BP?
Fatty fish, such as mackerel, herrings, salmon and trout, have an important protective effect against coronary heart disease, and are an important part of any prudent diet for people with high BP. The effect is probably through what are known as omega-3 fish oils, which can be taken as capsules. They reduce blood levels of triglyceride, the form in which fat is transported from the gut to the liver.
I have heard that eggs and dairy foods are bad for you, but I am a non-meat eater and like eggs and milk. Are these OK?
Strict vegetarian diets can easily become deficient in protein, which is essential for building new cells. Fish, eggs, and cheese are important possible sources of protein as well as variety for most vegetarians. They are not eaten by strict vegetarians (vegans), who must rely on pulses (beans and peas) and nuts as their most protein-rich foods.
Egg yolks are high in cholesterol, but as a source of high blood cholesterol they are no more important than other foods containing animal fats, which, when digested, are changed into body cholesterol. A good diet should contain not more than two eggs a week, but if you cut down on other fats, you can eat more.
All cheeses except cottage cheese contain large amounts of salt, so cheeses have to be virtually eliminated from any serious low-salt diet. They also contain a lot of saturated fat, which raises blood cholesterol.
The same applies to butter, except that you can easily get low-salt butter. For reasons that so far remain unexplained, people who drink a lot of milk tend to have lower blood cholesterol levels than people who drink little or none. Evidence for this is consistent and apparently reliable. However, milk does contain a lot of salt, and has to be restricted in low-salt diets.
What about increasing my potassium intake? I’ve been told that bananas and other fruits are the most effective way of doing this. Will they decrease my BP?
You are correct. The best way to increase potassium is to eat more fresh fruit and vegetables. However, a potassium balance is maintained within a fairly narrow range by physiological mechanisms in the kidney.
There is some evidence that increasing your potassium intake by about 200 mg, roughly equivalent to the amount contained in five bananas, does reduce BP by small amounts.
Our advice to people is that increases in potassium intake are consistent with increasing a fruit and vegetable intake.
Somewhat like the salt issue, we think that there is unlikely to be any harm in increasing your fruit and vegetable intake, but you should be realistic about the size of benefit in terms of lowering your BP.
Increasing the potassium intake in the form of bananas or other fruits to a substantial extent should be cautioned in people with a history of kidney problems. In these people, excretion of excessive potassium can sometimes become impaired.
Non-pharmacological treatment What about taking multivitamins and antioxidants, do they help?
Until recently there was a great deal of excitement about the potential for taking vitamin supplements and antioxidants in reducing risk for heart attacks and strokes both in people with and without high BP. Unfortunately, randomized trials of vitamin supplementation and antioxidants have been disappointing and have failed to show substantial benefit. We routinely tell people who ask whether vitamin supplementation is worthwhile that there is no evidence to suggest that it will reduce either their BP or their risk of having a stroke or heart attack.
My wife is a vegetarian. Would a vegetarian diet help me to lower my BP?
Yes it would. BP is on average lower in vegetarians than in meat eaters, and BP falls in people on a vegetarian diet who have BP high enough to need treatment, though rarely enough to avoid any need for BP-lowering drugs. We have good evidence that potassium (which comes mainly from fruit and vegetables) reduces BP, and this may be the main way in which a vegetarian diet works.