Serving Size, Calories, Daily Values, and Food LabelsDate: 05/26/2005 at 15:35:52 From: joe Subject: how to determine the serving size and % DV I'm trying to figure out the equations used for values that are displayed on a food label. I can't figure how they determine the serving size and the grams involved. For example: serving size 1 cup (228g) calories 250 %DV Total Fat 12g 18% Saturated Fat 3g 15% I can't come up with an equation nor the possible variables that might be used to determine these results. Date: 05/27/2005 at 09:48:12 From: Doctor Wilko Subject: Re: how to determine the serving size and % DV Hi Joe, Thanks for writing to Dr. Math! Good question. I'd say you'd probably get more insight into food labels and nutrition by going to the Internet and searching for some good websites that discuss "nutrition" or "nutrition labels". One good starting point might be the FDA's site: http://www.fda.gov As I saw your question come through, I was sitting here eating a bag of Famous Amos Chocolate Chip Cookies and thought, "Perfect, let's try it!" The label looks as follows: ----------------------------------------------- Serving Size 1 package, 1 serving per container Calories 280, Calories from Fat 120 ----------------------------------------------- Total Fat 13g 20%DV Sat Fat 4.5g 23%DV Total Carbs 38g 13%DV Fiber 1g 4%DV Protein 3g -- ------------------------------------------------ If you notice, the labels will usually say, "Percent Daily Values are based on a 2,000-calorie diet." Then the legend below will be listed. This legend is how you calculate the %DV: ------------------------------------------------ For a 2,000-Calorie Diet: Total Fat should be less than 65g Saturated Fat should be less than 20g Total Carbs should be less than 300g Dietary Fiber should be 25g ------------------------------------------------ Let's calculate the %DVs and see if we are close to the label. The way we do this is just make a ratio of the amount of nutrient in one serving size over the recommended daily amount (based on a 2000- calorie diet). Total Fat: 13g/65g = 0.20 = 20% DV Sat Fat: 4.5g/20g = 0.225 = 22.5% DV (Label rounded to 23%) Total Carbs: 38g/300g = 0.126.. = 12.7% DV (Label rounded to 13%) Dietary Fiber: 1g/25g = 0.04 = 4% DV Our calculations look good. Remember the %DVs are not recommended intakes, but just reference points to help people gauge what their overall dietary needs should be. Again, most labels calculate the %DV from a 2,000-calorie diet. If you calculated these values from a 2,500-calorie diet, the %DV would be different from what's listed on the package. The only other math I can think of from the label is to see how they calculate the "Total Calories" and the "Calories from Fat" at the top of the label. You do need some additional information that is not on the label to do this. You need to know: 1g Fat = 9 calories 1g Protein = 4 calories 1g Carb = 4 calories From here we can calculate the calories from fat. From the label, we were given the following: Total Fat 13g Since 1g fat = 9 calories, then 13 * 9 = 117 calories from fat. The label said 120 calories were from fat, so there may be some rounding going on here, but we're still close. Let's calculate the calories from protein and carbs to find the total calories: Total Carbs 38g Since 1g Carb = 4 calories, then 38 * 4 = 152 calories from carbs. Protein 3g Since 1g Protein = 4 calories, then 3 * 4 = 12 calories from protein. If we add these calories, we get: 117 calories from fat 152 calories from carbs 12 calories from protein + -------------------------- 281 calories total (Label said 280 calories total) This should give you some good insight into understanding nutrition labels. Now the challenge is for you to take something from your fridge and see if you can calculate the values like we've done above! Does this help? Please write back if you have further questions. - Doctor Wilko, The Math Forum http://mathforum.org/dr.math/ Date: 06/06/2005 at 14:26:09 From: joe Subject: Thank you (how to determine the serving size and % DV) I want to thank you for this very helpful response. A million thanks! |
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