Carbohydrate is the most controversial food group for people with hypertension who also need to lose weight. Do you follow the traditional advice to cut back on fats and count calories or do you instead cut back on carbohydrates and follow a low-carb diet?
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The DASH diet and blood pressure
The Dietary Approaches to Stop Hypertension (DASH) diet is widely recommended to manage blood pressure as it is low in salt and follows the Mediterranean way of eating. The DASH diet is low in saturated fat, but it can be relatively high in carbs, especially if you opt for pasta.
In fact, the results from ten studies show that, if the saturated fat that’s cut from a DASH diet is replaced with carbohydrates, then within 3 to 14 weeks blood pressure tends to creep up to become 2.6/1.8 mmHg higher than in people who replaced the saturated fat with healthier monounsaturated fats, such as those found in olive oil, macadamia nuts and avocados.
Low carb diets and blood pressure
One study asked 20 overweight women to follow a low carbohydrate diet for 8 weeks, in which they reduced their carbohydrate intake from an average of 232 grams per day to 71 grams per day. At the same time, their total energy intakes was reduced by an average of 632 kcals (2,644 kJ) per day. Over the course of two months, they lost 5 kg in weight and their blood pressure fell by an average of 9/7 mmHg. Their cholesterol and triglyceride levels also decreased to significantly reduce their predicted risk of a heart attack or stroke.
Low carb diets and kidney disease
There has been concern that following a low carb, high protein diet may worsen kidney disease which can accompany high blood pressure. This concern arose from that fact that people with chronic renal failure are treated with a low protein, fluid-restricted diet. This does not mean that protein (or fluids) cause kidney disease, however. For people with healthy kidneys, there is minimal risk from eating more protein as part of a low carb diet.
A recent study involving 162 overweight or obese adults without diabetes or kidney disease compared the effects of following a DASH diet, a high carbohydrate diet (58% energy from carbs, 16% from protein), or a low carb diet (40% energy from carbs, 23% from protein) with different variations providing either a high or a low glycemic index based on the quality of the carbs. Each person followed each type of diet, separated by 2-week intervals of normal eating. The aim was to maintain a constant weight rather than to lose weight, as this was purely designed to see what happened to kidney function.
The results clearly showed that reducing the percentage of carbohydrate in the diet and increasing the percentage of protein and fat increases kidney function. Lowering the glycemic index of the diets also improved kidney function. The researchers believed that dietary protein increased production of nitric oxide in the kidneys to relax arteries so more blood reached the kidneys for filtering.
Low fat diets can lower blood pressure too
If you don’t want to follow a low carb diet, and prefer to follow usual advice and a low-fat diet, rest assured that these can lower blood pressure if you successfully lose weight.
For example, a study involving 31 overweight and obese men and women compared the effects of following either a low-fat diet or a low-carbohydrate diet for ten weeks.
Those on the low fat diet obtained an average of 17.8% of their energy from fat – half their usual intake of 36.4%, with a resulting 607 kcals (2540 kJ) per day reduction in energy intake. Those on the low carb diet ate an average of 15.4% energy in the form of carbohydrate – less than a third of their usual intake of about 50% carbohydrate, resulting in a 763 kcals (3195 kJ) per day reduction in calories.
Over the ten weeks, both groups lost significant amounts of weight – 6.8 kg for those on the low-fat diet, and 7.0 kg for those on the low carb diet. Both diets were equally effective in reducing blood pressure by around 10/5 mmHg.
Whichever type of diet appeals to you best, the important thing is to follow it and to lose at least some excess weight. I’ve known patients who were able to come off their antihypertensive medication completely after losing weight and they felt much better in themselves as a result.
Some people will continue to have high blood pressure despite losing weight, of course, and some have hypertension despite always maintaining a healthy weight. Everyone is different, but if you are overweight, then losing at least some excess fat will improve your overall health.
NB Only reduce or stop your medication under the supervision and advice of your own doctor.
Have you improved your blood pressure by losing weight?