Despite being the most popular vegetable in the United States, potatoes have fallen out of favour somewhat with nutritionists over the last few decades due to a relatively low nutrient density and high levels of quickly absorbed carbohydrates. Many diabetics avoid potatoes altogether for fear of exacerbating their condition. Fortunately the news is not all bad when it comes to diabetes and potatoes and most diabetics can include a modest level of potatoes in their diet.
The main reason diabetics are cautious when it comes to potatoes is their very high glycemic index (GI) value. The glycemic index is important for diabetics because it is a measure of the impact a particular food has on blood glucose levels once it has been digested. Eating large amounts of foods with high GI values results in a large increase in blood sugar levels which would normally result in a corresponding rise in insulin to bring blood sugar levels back to a normal level within a few hours. Because diabetics have an impaired insulin response, blood sugar levels can remain very high for quite some time leading to the typical symptoms of diabetes such as excessive thirst, frequent urination, tiredness, and nerve problems.
Potatoes have a GI value that ranges from 65 to 80 which is considered high. By comparison table sugar (sucrose) has a GI of 63, white bread has a GI of 71, wholemeal bread a GI of 60, and brown rice a GI of 55.
Interestingly the method of cooking and variety of potato can affect the GI value of potatoes greatly. Newer potatoes tend to have lower GI values than older potatoes. Waxy potato varieties such as Red Norland, Yellow Finn, and Red Pontiac have lower GI values than floury potato varieties such as Russet Burbank and Norgold Russet.
A 2005 study published in The Journal of the American Dietetic Association looked at the effect of cooking method on the GI index of potatoes. The researchers found that mashed and boiled potatoes had the highest GI values (85-90). Baked, roasted, or microwaved potatoes had moderate GI values (70-80), while boiling red potatoes, refrigerating overnight, and eating them cold the following day resulted in a GI value of just 56.
Diabetics may also benefit from eating potatoes with the skin on. Potatoes with skin have almost twice the amount of fibre as the flesh by itself. Fiber is important for diabetics because it helps slow the digestion of food, preventing large spikes in blood sugar. Furthermore, although not a significant source of nutrients itself, the potato skin can help prevent the leeching of nutrients into the water when potatoes are boiled.
If you’re feeling adventurous, try adding a small amount of avocado to mashed potato instead of margarine or butter. The avocado will impart a slight greenish tinge to the mashed potato but will not alter taste significantly. The avocado is a rich source of fibre with an impressive 13g of fibre per avocado. In addition to this, avocados are a rich source of oleic acid which has been linked to increased insulin sensitivity in some studies.
French fries are one form of potatoes that should definitely be eaten sparingly. One study, published in the American Journal of Clinical Nutrition in 2006, looked at the effects of potato and french fry consumption on the risk of diabetes in women. The study found that while consumption of both french fries and other forms of potato increased diabetes risk, french fries had a larger effect. Women in the top vs bottom quintile for consumption of french fries had a 21% increased risk of developing diabetes compared to a 14% increased risk for other forms of potato. The researchers suggested that the trans-fat often present in the frying oil might be responsible for the additional diabetes risks associated with french fries.
Fortunately most restaurants and fast food chains are moving towards using trans-fat free oils to fry with. If you choose to eat fries, stick with thick cut fries or wedges as these have a lower ratio of oil to potato (almost half the calories in shoestring fries come from the oil they are fried in).
To sum up, diabetics should be able to incorporate small servings of potatoes into their meals (up to 150g or 1 medium potato) without any adverse health affects. When possible, potatoes should be cooked the night before, then reheated the next day (or eaten cold) with the skin still on. New potatoes should be selected when available while waxy varieties are preferable to floury ones.
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