Nutrition facts, glycemic index: tested, or estimated?

Do we have any idea how the nutrition facts are calculated? Did someone do the testing on some basic foods a long time ago, and then the way those foods are combined, formulas are done, and nutrition facts are estimated? Or is there some body out there that actually throws the food in a blender then runs it through whatever equipment actually burns the food and counts the calories?

And what about the glycemic index? Was there some mass data collection involved there, or is it being estimated based on some formula that extrapolates from a smaller pool of known values?

(i.e.: an apple is tested however they test for the GI value. Then, all other vegetables which share similar nutrition profiles to apples are assumed to have similar GI values, with whatever adjustments for fiber/water content, etc.)

Hell, how is the GI determined to begin wth (I shall consult The Google on that one, seems findable.)


Apples are fruit. I think wikipedia probably has a good article on the GI.

Through direct laboratory analysis, or through a nutrient database.

There are indeed labs where they essentially burn a food to see how much energy you can get from it. Most companies that use Nutrition Facts labels subscribe to a nutrient database service, which has information from these common laboratory results and combines them into a finished product.


If the manufacturer uses a nutrient database, they can look at their production process and say that an average 30g sampling of that above mix will have x % by weight of each of the ingredients. Using a nutrient database they can do a break down for how many calories by ingredient that equals out to and how many of each nutrients/vitamins.

The above is from a granola mix bag, and obviously with such a product it’s impossible to know with certainty what is in any individual 30g sampling of the product, but you can be fairly accurate over an entire batch.

(Capitalized to reflect capitalization you’d find on the label…)

I read the wiki on the GI and unfortunately it is as I suspected: it’s pretty much a very general guess which can change for many reasons:
[li]The glycemic index does not take into account other factors besides glycemic response, such as insulin response, which is measured by the insulin index and can be more appropriate in representing the effects from some food contents other than carbohydrates.[18][/li][li]The glycemic index is significantly altered by the type of food, its ripeness, processing, the length of storage, cooking methods, and its variety (white potatoes are a notable example, ranging from moderate to very high GI even within the same variety[19]).[20][dead link][/li][li]The glycemic response is different from one person to another, and even in the same person from day to day, depending on blood glucose levels, insulin resistance, and other factors.[20][/li][li]Most of the values on the glycemic index do not show the impact on glucose levels after two hours. Some diabetics may still have elevated levels after four hours.[20][/li][li]The GI of foods is determined under experimental conditions after an overnight fast, and might not apply to foods consumed later during the day because glycemic response is strongly influenced by the composition of the previous meal, particularly when meals are consumed within an interval of few hours. Indeed, it has been shown that a high-GI breakfast cereal (GI = 124) elicited a lower increase in blood glucose concentrations at lunch than at breakfast. Also, the difference in glycemic responses induced by the low- and the high-GI breakfast cereals at lunch were lower than that predicted by the large difference in their GI, which was determined at breakfast.[citation needed][/li][/ul]

Good article on the glycemic index: