Niki Bezzant: Headlines mash study results

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The subject line read, "Swap the spuds, chuck the chips to lower blood pressure". It referred to a British Medical Journal study that was made for a clickbait headline.

This sounds like bad news for potatoes. And it is, if you just read the headline and the couple of lines that show up in your Facebook feed. If I were a potato-grower, I'd be cringing.

The study did indeed report an association between higher intakes (four or more servings a week) of boiled, baked or mashed potatoes and French fries, with an increased risk of developing high blood pressure (hypertension) in adults.

Before we throw out all the spuds, let's look carefully at that language. It's classic science-speak that is especially common when we look at studies about diet.

The key phrase to note: "is associated with". Association (or correlation) is very different from causation, a fact that can get lost in science reporting.

Any time you see the words "linked with", it's talking about association. (Google "spurious correlation" and you'll find lots of silly examples, like the rate of violent crime being associated with higher sales of icecream).

The potato researchers are clear: they're not saying eating potatoes causes high blood pressure. They also note the limitations of the study. People's potato intake and their diagnosis of hypertension were self-reported. No one in this study had their blood pressure measured.

There are also what is known as confounding factors. Other things could be going on that might contribute to the result. In this case, there's the obvious fact that potatoes are usually not served naked, but very often with their friends: salt and saturated fat.

Salt is known to have an effect on hypertension. It is also mentioned in passing that "participants who consumed four or more servings a week of any type of potatoes were, in general, less physically active and smoked more than participants whose consumption was less than one serving a week".

The researchers worked to allow for these factors but they can't be ruled out. Further research would hopefully reveal more.

Despite its limitations, this study adds to what we know about potatoes. The Heart Foundation's Angela Berrill says: "Past advice grouped all vegetables together but current dietary advice has moved on from this. The Heart Foundation's Healthy Heart Visual Food Guide recognises the difference between non-starchy vegetables and starchy vegetables, such as potatoes. We recommend that people eat mostly non-starchy vegetables but starchy vegetables fall into the 'eat some' category."

Another common mistake is cherry-picking results that fit our own view or singling out results we like (see almost any study about chocolate).

In this case there was one unexpected result I'm tempted to cherry-pick: eating potato chips was not associated with high blood pressure. I'm putting my hand up to take part in the potato chip study.

Niki Bezzant is editor in chief of Healthy Food guide.

- Herald on Sunday

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