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Half-baked coverage of potatoes
Recent media headlines have linked consumption of potatoes with high blood pressure following a study published in the British Medical Journal.
We know that there are nutritional factors that increase the risk of developing high blood pressure. These include:
- Being overweight;
- Eating too much salt;
- Not eating enough fruit and vegetables;
- Drinking too much alcohol.
But should we be concerned about the regular appearance of the spud on our menus?
The study looked to investigate whether there was an association between potato consumption and hypertension in three large cohorts of women and men (around 187 000 participants) in the United States. Dietary intake over a 25-30 year period was assessed using a food frequency questionnaire that included the frequency of potato consumption in the form of baked, boiled, or mashed potatoes, French fries (chips), and potato chips (known here as crisps). Assessment of hypertension was self-reported by participants but based on diagnosis by a health professional.
What did the study report?
Comparing high consumers (consuming 4 portions a week or more) with those reporting consumption less than once a month, the authors found:
- An increased risk (11%) of hypertension for baked, boiled, or mashed potato in women, but no association in men;
- An increased risk (17%) for French fries (chips) in both men and women;
- No association with potato crisps.
Whilst these results are interesting and the media was flooded with suggestions that eating potatoes is linked to high blood pressure, there are some important factors that should be considered.
Firstly this type of study can only show association and not cause and effect. We cannot conclude from this study that potatoes cause high blood pressure.
There are also findings that are difficult to explain. Why for example was an association noted with baked, boiled, or mashed potato in women but not in men? And why should a higher consumption of French fries yet not crisps be associated with hypertension?
Could there be other factors rather than potatoes that are explaining these findings?
It is possible that other factors in the diet or lifestyle are affecting the results. For example, it could be what people are eating with potatoes – salt and fats – rather than the potatoes themselves.
Prevention and early management of hypertension is important. Diet has an important part to play. However dietary behaviours are complex and difficult to measure. Although observational studies like the one we are discussing here provide some insights, we are increasingly aware that looking at dietary patterns rather than single foods or nutrients may be more useful. The DASH (Dietary Approach to Stop Hypertension) recommended by the US National Institute of Health is a pattern rich in fruit, veg, wholegrains, low fat dairy, and includes fish, poultry meat nuts and beans. It also includes potatoes.
The recent Scientific Advisory Committee on Nutrition report Carbohydrates and Health recommends starchy carbohydrates as a key part of a healthy, balanced diet, and this is reflected in government recommendations, where potatoes particularly cooked with skins on to increase fibre, form part of this important food group. Potatoes are also useful contributors of vitamin C and potassium. Interestingly potassium contributes to the maintenance of normal blood pressure.
So on the basis of this evidence, keep the spud on the menu but keep the salt you put on them to a minimum.
Ayela Spiro, British Nutrition Foundation – QCS Expert Nutrition Contributor