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I'm looking at the nutrition facts label on my protein shake bottle and it says:

  • Protein 42g - 84% DV
  • Vitamin C - 100% DV
  • Vitamin A - 40% DV
  • Vitiman D - 50% DV
  • etc...

I know the 84% daily value for 42g of protein an overestimation for bodybuilders. Most reputable sources say protein intake should be proportional to your target body weight (2g protein per kg of body weight) and how much you work out. 42g of protein yielding 84% DV would only be sufficient for puny 5 year olds that lift weights.

Now lets move from talking about macronutrients and start talking about vitamins. Would the amount of vitamin C in this example protein shake be 100% DV for everyone, or do bodybuilders require more or less? I would like to know how to calculate any vitamin daily requirement based off of physical fitness goals.

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1 Answer 1

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If you look closely, you will notice that at the bottom of the label it says "Percent Daily Values are based on a 2,000 calorie diet. Your daily values may be higher or lower depending on your calorie needs." So that clarifies the DV value for protein.

As for micronutrients, the DV is based on the RDI (recommended daily intake) value, which represents the "average daily nutrient intake level that meets the requirements of 97-98% of healthy individuals in every demographic in the United States". So even for most bodybuilders, the micronutrient DVs should be sufficient.

Note, however, that these RDI values are not based on the current RDA (recommended daily allowance) values, but the older RDA values from 1968. As such, they are not very accurate.

The newer RDA values are not printed on food labels, but can be found online, and they are listed separately based on age and gender, but not weight or activity. The RDA is based on the "requirements of 97-98% of healthy individuals in each life-stage and gender group". Differences between RDI and RDA are substantial, e.g. the RDI recommends 60mg of Vitamin C per day, while the RDA for males ages 19-30 recommends 90mg per day. The "97-98%" are not arbitrary, by the way: it captures people up to 2 standard deviations above the average, assuming adequate intake is normally distributed.

The reason for the confusion is that the RDI values (on food labels) are regulated by the FDA, while the (more accurate) RDA values are regulated by the Institute of Medicine (IOM), and these two don't always agree. Generally speaking, and this is purely subjective, the FDA is much more influenced by political pressure and corporate interests, while the IOM is considered to have higher scientific credibility.

Of course there are studies claiming that certain micronutrients have an added value beyond both the RDI and RDA, but the evidence for these claims has generally not been considered strong enough to increase either value. Whether it makes sense to take a certain micronutrient at a dose above the RDA should be carefully considered on an individual basis, based on current research.

If you believe that scientists have an exact model describing how factors such as physical activity, weight, muscle mass, etc. affect the recommended intakes of any micronutrient, I have to disappoint you. In most cases, these relationships are simply unknown, and you have to make do with the RDA values. For many micronutrients, not even an RDA is known, but only an AI (adequate intake), which is not much more than an educated guess how much people should take.

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