Rounding up/down in calculating nutrition facts

[dpcalder]

I am calculating the nutritional content of a certain food per 100g. To simplify things a bit, I am rounding the data up and down to the nearest tenth. So for example, if it has 1.6 micrograms of selenium, I simply write 2 micrograms. If it has 4.3 milligrams of Vitamin C, I write 4 milligrams. Is this a legitimate way of going about it, or are there at least some vitamins, minerals, amino acids, fatty acids, etc. any sort of nutrient content where the smallest nuances in measurement matter such that total precision is required?

[Plantes Vertes]

What is the purpose of your calculation?

If you are doing this to improve your diet then there is no point in being more precise because the nutritional content of food varies enormously depending on its production conditions. The values on the box or wherever you are finding your information are averages and therefore often wrong.

Even if you could accurately measure the nutritional content of each of your foods, the body's requirements also differ widely depending on weight, type and degree of activity, other health conditions etc, so you wouldn't know whether you personally were getting the right amount of whatever it was.

Finally, the daily intake recommendations of different countries are quite various, so even if you could know the recommended amount for exactly your physical condition, the science could not reliably guide you (although of course following the guidelines is advisable in the absence of better information).

Edited August 12, 2013 by Plantes Vertes (log)

[heidih]

My first thought was "garbage in - garbage out" as in where you get the data matters. My second thought is that the person eating the food would need to be hyper careful about an accurate weight of the portion to make it matter. As asked above -what is this for? If it is a volume measurement for the portion you may as well not go past the first decimal if at all.

[Syzygies]

The only rounding that bothers me is "0 grams trans fat" which cost some serious lobbying dollars to manage in the U.S. Then look at the serving size, computed to be the fewest number of servings that succeeds in rounding to 0 per serving. This is generally a substantial multiple of the number of servings in practice.

(For example, my very athletic graduate student considered any cylindrical container of ice cream to be one serving.)

[dpcalder]

Well I am referring to some academic studies of the nutritional content of certain meats per 100g. I'm trying to provide a dietary guide for those interested in obtaining their nutrients from these meats.

[heidih]

Wow - meats are a tough one as there are so many variables, notably fat content, between samples of the same "cut". In addition, and please correct me if I am mistaken, I imagine the animal's diet also influences those trace minerals and other elements. A consistent and accurate number seems elusive.

[nickrey]

As Heidi says, no meat sample is going to be prototypical of the class. As a result, I'd be very surprised if the authors of the said articles didn't analyse a series of samples and then average to come up with their final results on content. As such your rounding is going to be well within the range of levels that they tested.

[Lisa Shock]

There are federal guidelines regarding how food packagers can label their foods. I agree with Syzygies that this system is flawed, in particular by the serving sizes allowed which give some foods a better profile than they would have if 'normal person' portions were given.

If it were me, I wouldn't round. You're taking already estimated material, why make it even more vague?

I personally am on a low methionine diet and would be pretty upset to discover that rounding had occurred in the generation of certain numeric values. (it's not so critical for, say, watermelon, but, super important when measuring pumpkin seeds)

[furzzy]

I have an app for bothiPhone & iPad called "FOODLE" from Pomegranate Apps that gives all that info. It's one of those "free" and then unlock a couple of features in-app for a pittance.