How can this be?
A lot of you have written with questions about nutrient information here on ND that doesn't seem to make sense. For example, one user noticed that cooked red peppers have more vitamin C than raw red peppers. How can this be? Vitamin C is generally lost in cooking so it should be the other way around, shouldn't it?
Other user reported that cooked rutabagas had higher amounts of omega-3 and omega-6 fats than raw rutabagas. Yet another wrote to ask why frozen blackberries have less fiber than fresh blackberries. Both perfectly valid questions. Cooking vegetables shouldn't increase the amount of fat they contain and freezing shouldn't reduce the amount of fiber.
Maybe you've run into similar nutrient data on NutritionData and thought to yourself, "How can this be?"
In some cases, it's because the quantities that are being compared aren't quite identical. Take the rutabaga, for example. Both listings were for a cup of cubed rutabaga. But you'll notice that the calorie count for the cup of raw rutabaga (50) is less than for a cup of cooked rutabaga (66).
Think about it: If you were to take a cup of raw rutabaga, cook it, drain it, and put it back in the cup, you wouldn't quite have a full cup because as the vegetable cooks, some water is lost and it gets softer. To get a full cup of cooked rutabaga, therefore, you'd have to start with slightly more than a cup of raw rutabaga. Judging by the percentages, the difference in omega-3 and omega-6 fatty acids appears to be due to the difference in the quantities involved.
But that doesn't seem to adequately explain the red peppers or the strawberries. Something else is going on here.
Keep in mind that the nutrient content of fruits and vegetables varies considerably from harvest to harvest, region to region, even from piece to piece. As time and budget permit (government funding for this work has been slashed in recent years), the USDA gathers nutrient information on multiple samples from various locations and in different years. As time goes on and more samples are analyzed, the different values are averaged together.
So it could be that some of the red peppers that were cooked and then analyzed by the USDA just happened to have slightly more vitamin C to start out with than the red peppers that were analyzed raw.
But what's the point of all this super-accurate nutrient analysis, then? If the pepper you're eating might have less or more vitamin C than the peppers analyzed for this database, what good does it do you to look them up and calculate their nutritional content?
Here's why I think it's still useful to use Nutrition Data (and USDA nutrient composition data) to analyze your diet, using our red pepper as an example:
1. While any one pepper might be higher or lower in vitamin C than the number in the database, chances are good that the average vitamin C content of all the peppers you eat will be fairly close to the amount reported in the database. That's how averages tend to work. The more peppers you eat (and the more samples the USDA analyzes), the closer the two averages are likely to be.
2. The database shows that 1 raw red pepper contains 209.4 mg of vitamin C. The pepper you ate today might only have contained 194.8 mg. When you're measuring things to the tenth of a milligram, it seems like a pretty big discrepancy. But let's zoom out for a moment. Whether it contains 209 or 194mg of C, a red pepper is indesputably an excellent source of vitamin C (containing about three times as much vitamin C as the same sized orange, for example). You can be confident that eating red peppers will help you meet (or exceed) your daily requirement for his nutrient.
In other words, these small discrepancies, as perplexing or frustrating as they may be, don't take away from the overal value and usefulness of the USDA nutrient database. While not perfect, it is still impressively detailed and accurate. When paired with ND's unique analyses and reports, you've got an invaluable tool for planning, analyzing, and improving your diet.
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Posted by: Chuck Franklin | Jul 18, 2008 5:30:42 AM
Yes! I've found a bunch of these myself: my favorite: If you freeze cauliflower and then cook it with salt(has to be with salt though!) the net carb count goes down to almost nothing, literally it's almost all fiber in the cauliflower frozen cooked with salt entry.
Now compare it to all the other cauliflower entries: You don't freeze it first and then cook it with salt and you apparently according to the databases are getting 50% less fiber.
