The potato is a versatile vegetable, and can surface in our diet in a variety of guises. Some of these, such as crisps and chips, are not held in high regard from a nutritional perspective. However, less fat-packed forms of potato are generally seen as healthy fare. Of all the sorts of spuds that may grace our plates, the jacket potato is oft-regarded as the pick of the crop. Naturally low in fat and high in fibre, these starch-filled orbs are often seen a wholesome and slimming food, an ideal for filling our stomachs, but not our trousers or skirts.
At least some of the baked potato’s healthy allure seems to come from the vitamin C and fibre it reputedly has to offer. Actually, potatoes tend not to compare well with other vegetables in the nutritional stakes. For instance, weight for weight, baked potatoes contain significantly less fibre than broccoli, and offer only a fraction of the vitamin C. Another of the potato’s supposed selling points is the ability of the starch contained within it to provide a source of sustained fuel for the body. Here again, however, it appears as though the potato does not stack up at all well.
The speed and extent to which a standard quantity of food increases blood sugar levels is referred to as its glycaemic index. Glucose, a sugar that is absorbed very rapidly from the gut, is assigned an arbitrary glycaemic index of 100. In comparison, baked potatoes have a hefty glycaemic index of 85. While conventional wisdom dictates that baked potatoes release sugar slowly and steadily from the starch they contain, the reality is that their effect on blood sugar levels is disturbingly similar to that of pure sugar itself.
In response to the sugar surge that a baked potato may induce the body will tend to make copious quantities of the hormone insulin. Insulin’s prime job is to keep blood sugar levels from rising too high, but too much of it can be a bad thing. In excess, insulin can drive blood sugar to subnormal levels, which can lead to a variety of undesirable symptoms. In my experience, a baked potato had for lunch will tend to precipitate a distinct slump in energy in the mid to late afternoon, and is often accompanied by an urge to raid the biscuit tin or vending machine. In the longer term, a glut of insulin can have dire consequences for our body. Insulin stimulates the conversion of sugar into fat, which then has the propensity to dump itself around the midriff. Plus, high levels of insulin can cause the body to become relatively immune to the effects of this hormone in time, helping pave the way for diabetes in later life.
While baked potatoes have the capacity to destabilise the body’s chemistry, this is not so true for other forms of potato. New potatoes, for instance, have a much more measured effect on blood sugar balance which is reflected in a glycaemic index of 57. Also, it’s worth bearing in mind that the sugar-releasing effects of potatoes can be tempered by eating them in moderation and combining them with more stabilising foods such as meat, fish and non-starchy vegetables. In this way, a piece of salmon accompanied with some broccoli and a few new potatoes represents a well-balanced and healthy meal for most. As for big baked potatoes, however, I don’t dig them at all.