When it comes to food science, the numbers we use are nothing more than guesstimates. The number of calories in one apple isn't necessarily a predictor of the number of calories in another. The same with nutrient values, which vary based on where, when, and under what conditions food is grown, and how far it traveled from source to mouth. The longer an apple sits in transit, in the supermarket, or in your kitchen, the more nutrients it loses.
To make matters even more confusing, the kinds of numbers used for measuring nutrients have changed. When I was growing up, we had the RDA, or Recommended Daily Allowance. In addition to RDAs, we now have DRIs, AIs, ULs, IUs, DVs, and EARs, each used by different people for different reasons. RDA was used by the Food and Nutrition Board of the National Academy of Sciences for about 50 years, from 1941-89, and measured the average amount of a nutrients needed by healthy people of a certain age and gender, but it was not meant for individual diets. DRI, Dietary Reference Intake, came into use in 1997 to prevent deficiencies and lower risk of chronic diseases like osteoporosis, cancer, and heart disease, but is intended for scientists, not consumers. AI stands for Adequate Intake and is used when there isn't enough information to compute an RDA. UL stands for Tolerable Upper Intake Level and measures the maximum amount of a nutrient a person can ingest for an extended period of time. EAR stands for Estimated Average Requirement and estimates the appropriate amount of a nutrient for half of all healthy people of a certain age group and gender. DV stands for Daily Value. Determined by the Food and Drug Administration, it calculates percentages of specific nutrients in foods for 2,000- and 2,500-calorie diets, but it does not take into account age or gender.
Relatedly, some of you have commented that you are having a hard time figuring out what counts as a serving. How do you translate cups of dairy into ounces of cheese?
I'm having the same problem. When it comes to servings, there are certain useful ways to figure it out.
- You can buy a kitchen scale, though this brings back too many bad memories of Weight Watchers for me.
- MyPyramid gives some equivalents, if you are willing to click around to find them.
- MyPyramid also offers a menu planner and dietary analysis , though I found them a bit frustrating to use.
- WebMD teaches you how to eyeball serving sizes.
Of course this only matters sometimes. Certain foods are important to measure: meats, fats, dairy products, and definitely sweets. But if you are eating fruits and vegetables? I wouldn't worry about it too much, unless you are planning to eat them by the bushel.
What's your secret when it comes to portions? Do you have a method of measuring or an app or Web site that you use? Please share below.