Do potatoes have fewer usable calories than advertised?

Thursday, June 3, 2010 19:42
Comments Off on Do potatoes have fewer usable calories than advertised?


MP900177942[1] Q. I was wondering if the calorie counts are accurate for raw
potatoes.  I've heard they have a lot of
"resistant starch." Does this mean that some of the calories listed do
not get fully digested and pass through our system?

[ANSWER UPDATED: June 4, 2010]

A. Are the effects of resistant starches accounted for in the calorie counts? My tentative answer is: probably not.

(For more about resistant starches,
see this recent episode of my weekly podcast.)

As most of you know, the nutrient data displayed here on NutritionData.com (and virtually everywhere else) comes from the USDA's National Nutrition Database, the largest and most complete database of its kind in the world. Nonetheless, it is not perfect.

Efforts are made to adjust for digestibility. For example, you'll see that foods that are high in fiber provide fewer calories per carbohydrate gram than low fiber foods. (For more on how the calculations and adjustments are done, explore the USDA's Nutrient Data website.) But as far as I can tell, the formation of resistant starches does not appear to be accounted for.

When potatoes are cooked and then cooled, for example, some of the
starches are converted into a form that is more resistant to
enzymatic digestion. As a result, a few of those starches might indeed
pass through the system undigested. The digestibility of the carbohydrates in potatoes has been evaluated. But cooked potatoes are assumed to provide the same amount of calories per gram of carbohydrate as raw potatoes.

I suspect that the formation of resistant starches was not on the radar screen when the digestibility research was originally done. It's possible that that the calories for cooked (and cooled) potatoes, pasta, and rice may be slightly over-estimated in the National Nutrition Database. But I seriously doubt that the difference is large enough to make a meaningful difference. Being off by a small amount in your portion size would have a much bigger impact on the accuracy of the calorie count.

So, I'd encourage you to think of it as a margin of error that might work (slightly) in your favor if you're trying to limit your calorie intake.

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