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I'm trying to lose weight, and to that end, I've started logging my meals. 90% of the time it's very straightforward, except for one scenario: food that changes volume significantly.

For example,

  • Dry rice, when cooked with water, grows quite substantially. A single cup of dry rice might become 2-3 cups or more of cooked rice.
  • Alternatively, a single serving of cooked (and thus wilted) spinach is often sold in containers that require moving equipment to get out to my car.

When reading nutrition tables and other statistics about food, should volumes be understood as pre-preparation, or post? And is the answer standardized across all (or at least most) platforms and info sources, or does it change from place to place?

If I cook 1 cup of dry rice with water and it becomes 3 cups of cooked rice, and I eat it all, did I just eat 1 cup of rice, or 3?

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  • Common sense says dry food measurements are reflected in the nutrition labels, since that is the form it is sold in. For example how would a cornflakes producer know how much milk or yoghurt etc you use? Ideally though labels should use weight, not volume for solids.
    – jiggunjer
    Jun 2 '15 at 3:24
  • Though if you are logging meals you should log caloric intake, not just the amount of cups/grams/whatever of a food you eat.
    – jiggunjer
    Jun 2 '15 at 3:30
  • @jiggunjer Agreed on both points, but not what I'm looking for: in the app I'm using, you input how much you ate and it gives you all the calories/sugar/carbs/protein, etc. So I just need to know how much I ate. Which should be easy, but when I go to input Rice, I stop. "I ate one cup of rice," I say to myself, "but that was half of the one cup of dry rice that I cooked. Did I eat one cup of rice, or half a cup of rice?" I can't figure out the carbs until I know how much I ate, and because the app is independent of the packaged food, I don't know if they're assuming cooked or uncooked.
    – Nerrolken
    Jun 2 '15 at 5:57
  • And in that situation, using weight is no different: rice gains a LOT of weight from water. Is that "5 ounces of rice" supposed to be uncooked rice, or cooked rice? The stats will be wildly different, because the calories-per-ounce gets skewed when the water weight is added to the equation.
    – Nerrolken
    Jun 2 '15 at 5:59
  • 1
    In that case your app documentation should mention it. Though my guess is the dry/pre-cook amount, because that data is easier available to app programmers.
    – jiggunjer
    Jun 2 '15 at 7:21
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In the US, 21 CFR 101 provides reference amounts for serving sizes, which are usually followed somewhat closely (I wasn't able to determine if they are required by law) by food manufacturers.

In the specific case of rice, the standard serving size is "140 g prepared; 45 g dry" listed in the format "_ cup(s) (_ g)".

Usually, the nutritional label on the actual product package (no comment on databases on random websites and apps) will provide information about whether it is referring to prepared or "raw" state, or will provide both. The prepared state may include ingredients not provided in the package.

For example, Cheerios has a serving size of "1 cup (28 g)", dry, and additionally provides a column with values for "with 1/2 cup skim milk".

Kraft Macaroni & Cheese Dinner gives the serving size as "2.5 oz (70 g / about 1/2 box) (Makes about 1 cup)", and provides columns for "as packaged" and "as prepared". Different pictures I found of the nutrition information and directions varied widely as to the calories of the "as prepared" column and the amount of butter called for; presumably these will match on any given box.

I wasn't able to find any pictures of real nutrition labels for packages of plain rice.

Google allows you to specify "raw" or "cooked" when searching for the nutrition information of rice - according to it, 100 grams of cooked long-grain brown rice has 111 calories, and 100 grams of raw long-grain brown rice has 370 calories. When the measure is switched to one cup, the calories are 216 and 684 respectively, with the weights being 195 and 185 grams. So, if your app doesn't say, it should be easy to figure out which numbers track better with how many calories it actually says a cup of rice has.

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There is no standard for calculating "food volumes". The nutrition data of all foods is only consistent by weight. Standardized nutrition data labels all give nutrients per 100 g, frequently also adding the nutrient amount calculated for other weights, for example for one unit of packaging, or one piece when the food is in discrete pieces.

When somebody is talking of nutrition units (e.g. calories, grams of carbs, or whatever) per volume, they are probably using some volume conversion formula. But for most foods, there is no really good formula. Food volume changes a lot in preparation, and frequently it's not as predictable as the change in rice volume you describe - if you have chopped walnuts, the final volume depends on how finely they are chopped, and also how they were handled afterwards. Also, volume measurement of foods is imprecise to the point where it's useless (for example, a "cup" of flour can be anywhere from 100 to 160 grams for the same type of flour).

The conclusions: 1) there is no way to predict what formula they are using (e.g. whether they are using the average for cooked or raw rice), because there is no standard for that, and 2) even if you happen to use their formula, you can't achieve precision. If you need precision, you'll have to switch to an app which lets you measure your food by weight.

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  • How would using weight make more sense? It's got exactly the same problem: one cup of rice weighs X when dry, but it weighs Y when cooked with water. You're still confronted with the question of "I just ate 100g of cooked rice. Should I input 100g, or 50g because that's how much it weighed dry?"
    – Nerrolken
    Jun 2 '15 at 21:11
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    @nerrolken My point was less about your specific rice conundrum and more about your app by itself. It is either not intended to calculate calories with any precision, or it wants to but fails. The usual nutrient database treats "cooked rice" and "raw rice" as different foods and lists them separately. A less-complete database may only list one of them, but will make sure to spell out which one it lists. There is no answer to the question "is it calculated pre- or post preparation" because both calculations are common, they need to be labelled.
    – rumtscho
    Jun 3 '15 at 8:17
  • @nerrolken because if you put your cup of rice in a blender it will be half a cup of rice, but still weigh the same.
    – jiggunjer
    Jun 3 '15 at 17:06
  • @jiggunjer I'd argue it won't be rice anymore, but will be ricemeal or rice flour.
    – Random832
    Jun 3 '15 at 17:34
  • @Random832 the semantics are irrelevant, the nutritional content is given for an ingredient and just changing the shape does not affect that, but the point was it may change the volume. Ergo using weight is superior, in practically all cases.
    – jiggunjer
    Jun 4 '15 at 7:32

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