Purple potato power

Although vegetables generally have a positive, and deserved, reputation for being healthy there is one vegetable that is the black sheep of the bunch; the potato. It has a reputation for being fattening and lacking many of the health-giving phytochemicals that make other vegetables such healthy foods. A new study though, might have something to say about the potato’s tarnished reputation.

In the new study eighteen people who were overweight or obese and with high blood pressure were put on a regime that involved eating six to eight purple potatoes (each about the size of a golf ball) with skins twice daily for a month.

The researchers monitored the subjects’ blood pressure, both systolic (the higher number in a blood pressure reading) and diastolic (the lower number). The average diastolic blood pressure dropped by 4.3 per cent and the systolic pressure decreased by 3.5 percent. This is especially significant since increases in diastolic pressure are even more significant and worrying than systolic increases, although both are significant for health. The majority of people in the study took anti-hypertensive pharmaceutical drugs and still had a reduction in blood pressure. None of the study participants gained weight.

So it is all looking good for potatoes but there are a few things worth noting about the research.

The study was funded by the United States Department of Agriculture Agricultural Research Service (USDA-ARS) State Cooperative Potato Research Program. This does not invalidate the findings, but it should be kept in mind.

The researchers used purple potatoes because the purple pigment in fruits and vegetables is especially rich in beneficial phytochemicals. According to the researchers the results will probably also apply to red and white potatoes but given the reasoning behind choosing purple potatoes for the study, then that assumption may be optimistic.

Of course, even if you did use purple potatoes with the skin on, the news is bad for fans of hot chips or potato chips. High cooking temperatures seem to destroy most of the healthy substances in a potato, leaving mainly starch, fat and minerals. Potatoes in this study were simply microwaved, without oil.

Despite the results of this study potatoes still do tend to be in the high, or high end of medium, range for glycaemic index and glycaemic load. Figures for microwaved potatoes in their skin are not available but 150g of red potato boiled with the skin on has a glycaemic index of 89 (high) and a glycaemic load of nineteen (twenty is high in glycaemic load). To put that in context, a 250ml can of Coca Cola has a glycaemic index of between 53 and 60 and a glycaemic load of fourteen. A 30g portion of homemade white bread has a glycaemic index of 66 and a glycaemic load of nine.

The other problem for potatoes is that they are rarely presented simply with skin on and microwaved. Usually there are additions like mayonnaise, sour cream, or vinegar, even if they have not been cooked in fat under high temperature in the first place.

It’s true then that the potato in its best form probably does not deserve its lowly position in the vegetable pantheon. In reality though, it is equally not time for purple potatoes to be added to the superfood list.