Eating four or more servings of white potatoes a week is associated with a significantly increased risk of hypertension, according to three studies, which followed over 187,000 doctors and nurses for more than 20 years.
The results showed that eating baked, boiled or mashed potatoes at least four times a week appeared to increase the risk of hypertension by 11%, while eating French fries increased the risk by 17% compared to those who ate less than one serving of these per month. These statistical associations remained, even after adjusting for total dietary intakes of sodium, potassium, magnesium, calcium, fibre and dietary fats, and after taking people’s weight and age into account.
The researchers concluded that replacing one serving a day of baked, boiled or mashed potatoes with one serving a day of a non-starchy vegetables could reduce the risk of developing hypertension by 7% – but what does this mean if you already have a high blood pressure? The likelihood is that eating too many potatoes is ‘bad’ for you, too.
Eating potatoes may raise your blood pressure
Although potatoes are a good source of potassium, (at least 300mg/100g) which helps to flush excess sodium from the body, they also have a high starch content. This causes a rapid spike in blood glucose levels after eating which, in turn, triggers the release of insulin hormone from the pancreas.
The rapid rise in blood sugar levels after eating – known as postprandial hyperglycemia – has many harmful effects on the circulation which stops blood vessel linings from reacting as they should, (endothelial dysfunction), increases damage from oxidative stress and sets up a low-grade inflammation all of which are involved in the development of hypertension.
There’s also another factor, which the researchers surprisingly did not consider in this paper. Insulin has a direct effect on kidney function that reduces sodium excretion – even in healthy people, let alone those with hypertension.
A study involving 8 healthy volunteers, with an average age of 27, showed that, as insulin levels increased after eating a carbohydrate-rich meal, less and less sodium was flushed via the kidneys into the urine. Insulin appears to have an effect on the kidney tubules that tells them to reclaim as much sodium as possible back into the circulation.
So, all in all, it seems that eating too many potatoes is not good for you whether or not you have hypertension. Certainly you don’t want to eat four or more servings a week. It makes sense to reserve boiled, baked, or mashed potatoes for an occasional treat. Instead, replace them with non-starchy vegetables that have less of an effect on blood glucose levels, which is described according to their glycemic load (GL).
- Foods with a GL of 10 or less are classed as having a low GL (great for health)
- Those with a GL of 11-19 are classed as having a medium GL (don’t over-indulge)
- Foods with a GL of 20 or more have a high GL and will cause the highest blood glucose spikes (restrict your intake).
The glycemic load of a variety of vegetables is shown below.
|Baked white potatoes||33|
|Broad (fava) beans||13|
|Sweet potato (boiled)||11|
|Corn on the cob||8|
|Baby sweet corn||2|
With that much choice there is no reason not to restrict potatoes to just once or twice a week – if at all – they don’t have to feature within a good, blood-pressure-lowering DASH diet.
The good news is that sweet potatoes, including purple-fleshed varieties have a relatively low glycemic load. They offer numerous health benefits that make them a natural alternative to white potatoes.
If your blood pressure is raised, self-monitoring is key to maintaining good control.
Click here for advice on choosing a blood pressure monitor to use at home.
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