What was our process for rating food groups?

We started by identifying 13 food categories, which allowed us to place all potential foods into common-sense and non-overlapping areas. We then chose seven foods to represent each food category, except for the egg category because Americans rarely eat eggs of fowl other than chickens. Once seven foods had been assigned to each of the 13 categories, we normalized the nutrient composition of each food to 2,000 calories. In other words, we asked how much of each nutrient a person would obtain if he or she consumed 2,000 calories’ worth of that food. Even though a person would not make a single food the source of all their daily calories, looking at the nutrients in 2,000 calories of a single food allows for a health-based comparison. The amounts of nutrients in foods are usually compared by weight, such as 100 grams of each food. We believe that comparing nutrient content based on calories instead of weight is a better guide to healthy eating. Everyone has a certain number of calories to ‘spend’ every day on the nutrients that will keep him or her healthy and energetic!

To calculate the individual nutrient scores: 1) We calculated the amount of nutrients a person would get from eating 2,000 calories of each of the 85 foods 2) We averaged the 28 nutrients individually by category 3) We took these nutrient averages and compared them to a real-life health standard, and in most cases, the Dietary Reference Intakes that have been established as public health guidelines in the area of nutrition; and 4) We turned this comparison into a percentage. Thus, every nutrient in a food category had a score. To calculate the total scores: we averaged each food category’s 28 nutrient scores together. Since lesser amounts of cholesterol, saturated fat and sodium are healthier, we subtracted their scores when we averaged them with the other nutrients instead of adding them.

How did we determine how much of each nutrient a person needs?

We used the Dietary Reference Intakes (DRIs) as established by the National Academy of Sciences for a 19-30 year-old sedentary woman whenever possible. The six specific publications we used in this context were:


  • Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. The National Academies. 2002/2005.
  • Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. The National Academies. 2004.
  • Dietary Reference Intakes for Calcium, Phosphorous, Magnesium, Vitamin D, and Fluoride. The National Academies. 1997.
  • Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6,Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. The National Academies. 1998.
  • Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. The National Academies. 2000.
  • Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. The National Academies. 2001.

DRIs were not available for saturated fat or cholesterol, so we used the widely-recognized recommendations for a 2,000 calorie diet which were established in the USDA Dietary Guidelines for Americans, 2005.


  • U.S. Department of Health and Human Services and U.S. Department of Agriculture. Dietary Guidelines for Americans, 2005. 6th Edition, Washington, DC: U.S. Government Printing Office, January 2005.

Since neither DRIs nor USDA Dietary Guidelines were available for monounsaturated fat, we used the American Heart Association’s recommendation as referenced below:


  • Krauss RM, Deckelbaum RJ, Ernst N, et al. Dietary guidelines for healthy American adults. A statement for health professionals from the Nutrition Committee, American Heart Association. Circulation. 1996 Oct 1;94(7):1795-800.

Since there was no established public health guideline of any kind for flavonoid intake, we used the following research articles to estimate average American intake at 175mg of flavonoids per day.


  • Gu L, Kelm MA, Hammerstone JF, et al. Concentrations of proanthocyanidins in common foods and estimations of normal consumption. J Nutr. 2004 Mar;134(3):613-7.
  • Manach C, Scalbert A, Morand C, et al. Polyphenols: food sources and bioavailability. Am J Clin Nutr. 2004 May;79(5):77-47.

How did we determine the amount of nutrients in each food?

Most of our nutrient amounts were derived from the USDA’s National Nutrient Database, Standard Reference, Release 18. A dash (-) in our food chart indicates that no data was available. The additional sources we used for the flavonoid content of foods are listed below. Since animals cannot synthesize flavonoids, we limited our analysis of food flavonoids to plant foods.


  • U.S. Department of Agriculture, Agricultural Research Service. USDA National Nutrient Database for Standard Reference, Release 18. 2005.
  • Nutrient Data Laboratory, Beltsville Human Nutrition Research Center. U.S. Department of Agriculture, Agricultural Research Service. USDA Database for the Flavonoid Content of Selected Foods. March 2003.
  • Nutrient Data Laboratory, Beltsville Human Nutrition Research Center. U.S. Department of Agriculture, Agricultural Research Service. USDA Database for the Proanthocyanidin Content of Selected Foods. August 2004.
  • USDA-Iowa State University Database on the Isoflavone Content of Foods. 1999.
  • Azevedo L, Gomes JC, Stringheta PC, et al. Black bean (Phaseolus vulgaris L.) as a protective agent against DNA damage in mice. Food Chem Toxicol. 2003 Dec;41(12):1671-6.