POTATOES &Their GI

GI POTATOES AND THE GLYCAEMIC INDEX

We all know that vegetables are rich in health-promoting nutrients, and the potato, which is both a starch and a vegetable, is nutrient-dense and very good for us.

So why have so many diets and consumers given potatoes such a bad rap?

It’s because they have been lured in to believing the controversial physiological measure known as the Glycaemic Index (GI) is at the root of our health and weight management.

WHAT DOES THE GI MEAN?

The GI is a ranking of carbohydrates (on a scale from 0 to 100) based on their immediate effect on blood glucose (blood sugar) levels. The importance of this is that high blood sugar levels lead to the production of insulin, a hormone that leads the body to store excess carbohydrates as fat.

It was originally developed as a tool for the dietary management of diabetes, and has now been promoted to the general public as a dietary management and disease prevention tool.

However, a general lack of understanding of what the GI actually measures, as well as its limitations, has produced widespread confusion regarding carbohydrates and an erroneous perception that certain starchy carbohydrates are ‘BAD’ and should be eliminated from the diet. The index alone is not perfect in making day to day food choices because it does not take into consideration portion sizes.

POTATOES VARY ON THE GI

According to the low GI diet philosophy, all carbohydrate-rich foods that have a high GI should be eliminated from the diet. However, the fact is that the GI of many foods doesn’t fall neatly into low, medium or high GI categories.

A study reported in the British Journal of Nutrition1 (2005), indicated that the GI response to eight potato varieties varied considerably and exhibited a wide range of GI values from 54 to 94.

In 2011 the University of Pretoria screened two potato varieties for the GI. The GI values for the two cultivars ranges from intermediate to high, which dispels the myth that potatoes only have a high GI.

A number of factors influence the GI:

  • Ripeness: as a vegetable ripens the GI tends to decrease.
  • Preparation method:The GI of starchy foods can be significantly reduced by cooking and then cooling. That is why cooked and the cooled potatoes have a lower GI.
  • Variety and origin:The GI can vary greatly upon the variety as well as their origin. The research conducted on British potatoes showed that potatoes with a waxy texture produced medium GI values, whilst those with a floury had higher GI values*.
  • Testing methodology:There is same debate about the validity of the methodology used to test GI and there is speculation that the GI of potatoes may not be as high as predicted based on incorrect methodology used in same of the studies. This makes it impractical to assign a blanked GI value to potatoes2,3.
    For example, the GI of potatoes may be medium to low when eaten cooled, rather than hot, and when boiled and consumed whole, rather than mashed.
  • Inclusion of other foods or condiments:The addition of protein and/or fat or increasing the acidity (i.e. with vinegar) also lowers the GI. So this emphasises that baked potatoes make a perfectly balanced meal when topped with protein and a little fat.

IDEAL TOPPINGS FOR THE PERFECT LOW GI BAKED POTATO SPUD

Fill your baked potato with:

  • Low fat cheese
  • Tuna or chicken mayonnaise
  • Cottage or cream cheese
  • Lean meats
  • Minced meat

And enjoy these condiments with your spud:

  • Butter
  • Salsa
  • Vinegar

WHAT ABOUT NUTRIENT DENSITY?

The GI does not correspond to nutrient density. For example the GI of potatoes is considered higher than that of ice-cream or chocolate, yet few would disagree that potatoes are a far more nutrient-dense choice.

So go on, reach for that hot steamy potato spud. But if you follow the GI approach, let it cool down and combine it with a good fat and lean protein.

(Perhaps we could have a picture of ice-cream and chocolate VS potato – nutrient density? Let me know and I can give you values.

References:

1. Henry CJ, Lightowler HJ, et al. Glycaemic index value for commercially available potatoes in Great Britain. Br J Nutr. 2005 Dec; 94(6):917-21. 2. Fernandes G, Velangi A, Wolever TMS. Glycemic index of potatoes consumed in North America. 2005;105:557-562. 3. Pi-Sunyer FX. Glycemic index and disease. Am J Clin Nutr. 2002;76(suppl):266S-273S.

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