The perils of interpreting food composition

Thanks to Sodium Girl (see comments under Feedback) for giving me a chance to talk about one of my favorite nutrition topics: how do we know what’s in food.  Her question:

I am on a very low sodium diet…I am beginning to have less and less faith in the nutritional labels – who is regulating them and what process/research do they use to define the amounts? And it is not just produced goods. I find it hard to know what information to trust when it comes to whole foods as well. I know that the USDA reports nutritional values which are the standard. Even with their documents though, a raw egg is 70 mg of sodium while a boiled egg is upwards of 120 mg of sodium – are they taking salted water into account?

This comment sent me straight to the USDA’s nutrient composition data base.  Despite the daunting home page, it’s a lot of fun to use once you get the hang of it.  Start with where it says Search the data base online.  Type in Egg (not Eggs) at Keyword.  Click on Dairy and Egg where it says Select Food Group, pick what you are looking for (I checked “egg, whole, raw;” on the next round, I checked “egg, whole, cooked, hard boiled”), click on Submit, and then decide how you want the data presented.  I chose one large egg.  Bingo.

USDA reports large eggs as 50 grams.  A 50-gram raw egg has 70 mg sodium and a cooked one has 62.  My interpretation: no significant difference.

Here’s the deal on food composition tables: you have to consider these numbers as ballpark figures, not as something engraved in stone.

• Foods grown and raised in different places under different circumstances have different nutrient compositions, so the food you are eating is unlikely to be identical to the ones tested by USDA.

• Nutrient amounts depend on weight; if your egg is a little bit bigger or smaller, the nutrient numbers change accordingly.

So you need to interpret food composition numbers leaving a lot of wiggle room.  That’s why I think reporting calories the nearest calorie is silly.  A 50-gram hard-cooked egg is 78 calories?  Plus or minus 10 maybe.

The USDA figures are the most authoritative available.  The office in charge of the nutrient composition data base is an unsung treasure of American government.  The scientists who work there are first rate, but they struggle daily with two problems: (1) not enough money to do their own testing, and (2) food companies know quite well what is in their products but they won’t give the USDA any information about nutrient composition beyond what is on the food label; they consider that information “proprietary” and don’t have to.

When it comes to sodium, which we eat in gram amounts per day, the difference between 70 and 62 mg is trivial.  I use the USDA figures as ballpark estimates and don’t pay any attention to small differences.

Sodium Girl: unprocessed foods like eggs are all relatively low in sodium so you don’t have to worry about it if that’s what you routinely eat.   Things start getting salty when you eat foods like cheese, pickles, and soy sauce, or anything commercially processed or prepared for you by others.  That’s why I’m for getting food companies and restaurants to cut down on salt so it will be easier for you to follow your doctor’s orders.