Not again! This time it is the simple potato that’s being demonised. This seems to never end in that scientists pick one food after another and try to find a bad apple in a complex diet. Sorry, so far there are no adverse effects reported for apples, but you just wait. Probably just a matter of time.
And the statistics used become more and more elaborate making it impossible to penetrate the reported findings. All based on dubious food frequency questionnaires in the first place.
So what’s new?
I have to give it to them that the researchers of the new report used an impressive number of people, overall over 187,000 men and women from three large US studies covering more than 20 years of follow-up. They all belonged to a cohort of health professionals, the same groups that have been used previously to report potential public health impacts of a range of different foods.
Unfortunately, the major shortcoming of all those reports is their dependence on food frequency questionnaires to capture dietary intake details.
In this case they analysed consumption of 130 foods and beverages, including the frequency of potato consumption. This might be fine for common foods, but what about all other minor foods we eat less regularly? If they aren’t captured you have no idea of their influence. Also you need a pretty good memory to recall all you ate during the past year.
Try it yourself. How often did you consume apples or ice cream? It will be more of a guesstimate and you might not even want to admit that you ate ice cream three times a week.
And also they asked participants to self report if they had been affected by hypertension as diagnosed by a health professional since their hypothesis was that eating a lot of potatoes would lead to an increase in blood pressure.
And the findings?
The researchers predictably found that higher intakes of boiled, baked, or mashed potatoes, and French fries were associated with an increased risk of developing high blood pressure. But now it gets more confusing.
After taking account of several other risk factors for hypertension, the researchers found that four or more servings a week of baked, boiled, or mashed potatoes was associated with an increased risk of hypertension compared with less than one serving a month in women, but not in men.
But higher consumption of French fries was associated with an increased risk of hypertension in both women and men.
And even more confusing, consumption of potato crisps (chips if you’re American) was associated with no increased risk.
And finally, replacing one serving a day of baked, boiled, or mashed potatoes with one serving a day of a non-starchy vegetable was associated with a lowered risk of developing hypertension.
So what to believe?
First the main rationale of the study. Potatoes are one of the world’s most commonly consumed foods – and have recently been included as vegetables in the US government healthy meals programs, due to their high potassium content. Not everyone agrees to this move. So the researchers set out to determine whether higher long term intake of potatoes could be linked to incident hypertension.
And they say their findings have potentially important public health ramifications, as they do not support a potential benefit from the inclusion of potatoes as vegetables in government food programs. Instead the findings support a harmful effect that is consistent with adverse effects of high carbohydrate intakes seen in controlled feeding studies.
But if you noticed that replacing a serving of potato with non-starchy vegetables lowered the risk of hypertension, the findings could actually be related to reduced vegetable consumption when consuming a lot of potatoes. Nitrate in vegetables is transformed to nitric oxide in the body. And nitric oxide is a vasodilator that reduce blood pressure.
Critics of the study
I am not the only critic of the study. In a linked editorial, other researchers argued that, although diet has an important part to play in prevention and early management of hypertension, dietary behaviour and patterns of consumption are complex and difficult to measure. Prospective cohort studies that examine associations between various dietary patterns and risk of disease provide more useful insights for both policy makers and practitioners than does a focus on individual foods or nutrients.
To be fair also the researchers acknowledge some study limitations and said that, as with any observational study, no firm conclusions can be drawn about cause and effect. But that didn’t deter the popular press to latch onto the findings, there are plenty of potato consumers to scare.