A question of RDA


This may sound silly but all RDAs seem to be based on an 18-25 year old subject with a “healthy” weight. My problem here is that I am not the average 25 year old man. I weigh a good 50lbs more than he does. I’m also a gym rat. Now I know I’m not a nutritional scientist, nor a biologist or chemist of any variety but it seems to me that what is fit for a man who is 3/4 of my weight may not quite enough for myself.

I’m probably not the biggest soylent fan either, there are almost certainly very large, very strong people out there interested in soylent but they don’t seem to be doing much posting other than asking questions about protein intake. I know I’m going to have to increase the protein by quite a bit if only to hit my calorific maintenance. My question is am I getting enough iron, or selenium, or zinc? Being that I am a much larger person are my nutritional needs not larger?

Can someone with some letters after their name help allay my fears that even with soylent I might have some issues with deficiencies?


I’m not sure anyone frequenting these forums have any nutritional or dietary qualifications including myself. Even Rob and Co don’t have any valid qualifications in nutrition but they have $272k for their campaign. With that said…

When body building they tell you to eat more protein and some others will say you need more carbs too as you need carbs to process proteins but they don’t tell you that you need more selenium or iron or zinc do they? Nope, just proteins and carbs. I read some articles about that eating more protein isn’t always the best option and that eating icecream would help more due to a specific mix of fats and proteins. Go figure.

So it all comes down to is which article you want to believe is right for you. One nutritionist can tell you one thing and another will say something different. Personally from what I have read and know I would just increase the protein and carb count to reach your calculated caloric intake or just have a bowl of icecream after a workout =] I like icecream.

Oh yeah… add creatine as well if you believe in it… I would.


One doesn’t reach 220lbs without knowing a little bit about macronutrient ratios, and for the record a whole lot of the biggest people out there recommend supplementing with zinc and magnesium specifically because they help regulate hormones that allow muscles to grow.

My question isn’t about the macronutrients. It’s about micronutrients. Is it not obvious (let’s be a little extreme here just to illustrate more efficiently) that a 300lb bodybuilder and a 150lb sedentary person have different micronutrient needs as well as macronutrient needs? Have any studies been done on this? How does someone go about calculating their daily needs of these things anyway? The original numbers didn’t just appear out of nowhere.


To be just guessing here, Id think that micronutrients related to digestion, nervous system functioning, bone growth would not need increasing much, however nutrients neccesary for blood, cell production/functioning, muscles and sinews obviously, hormones, neurochemicals would need increasing. Search for “nutrion RDA calculator” in google. You can then plot in weight, activity levels and such. How much they increase the nutrionlevels i dont know. Check it out with one sedentiary and on active persona :slight_smile:


The USDA has a DRI calculator, which you can use to calculate your nutrients needs based on sex, age, weight and activity level: here. Most nutrient requirements are just based on age and sex; they usually say that they’ll work for like 97% to 98% of all people; the exceptions are usually just people with special conditions that make them require a lot more or less of certain nutrients. Protein is adjusted for weight and calories are adjusted using all the factors. Generally people who are athletic tend to take a lot more protein than the recommended DRI (which is .8grams protein per kg of body weight), though some people think such excessive protein consumption is unhealthy.


I should also add, to what I said before. These are based on the 2006 DRI of the Institute of Medicine in the US.

Fiber is adjusted based on total calorie intake. The recommendation is 14 grams / 1,000 Kcal.

Iron is adjusted based on source. For people getting primarily their iron from non-animal sources (non-heme iron) it is recommended to get 1.8 times your regular iron that means 14.4mg/day for adult men and 32.4mg/day for adult women. Probably most soylent drinkers fall into this category.

People who frequently engage in intense workouts should also up their iron and additional 30-70%.

Smokers should consume an additional 35 mg Vitamin C above the RDA of 90 mg/day.


That’s very useful. I haven’t ready about those adjustments for iron before.

Do you have a source on those?


Here’s the pdf: http://www.nal.usda.gov/fnic/DRI/Essential_Guide/DRIEssentialGuideNutReq.pdf. Page 38



The Iron section starting on page 329 gives a bit more detail, but I was hoping to learn more about the increase for physical activity. I couldn’t find any more than what you stated though. The studies on that must be buried somewhere in their long list of uncited sources.


Just what I was looking for Joseph, wasn’t aware of the heme / non-heme issue, or the exercise. Makes it much easier to balance things now, appreciate your efforts :slight_smile:


I was hoping to learn more about the increase for physical activity

I was guessing that the increase in iron was due to people doing intense training having more hemoglobin-rich blood. It specifically says it’s for people doing lots of intense exercise, like professional athletes.

Unless, you fall into this category, you probably don’t need to worry about it. The DRI says that the RDA is meant to be sufficient for 97-98% of the population. That is, the RDA of 8 mg/day for men and 18 mg/day for women is greater than or equal to the daily needs of 97-98% of people. The RDA is calculated to be two standard deviations from the Estimated Average Requirement (EAR), which is the mean requirement for the population; that is, it’s greater than or equal to the needs of half the population. In short, unless you fall into that 2-3% that needs a lot of iron, the RDA for iron is enough, probably more than enough.

Note that this doesn’t apply to the AI (Adequate Intake), which is what they provide for most nutrients due to insufficient data.


Wait, if the RDA is set for +2 sigma (standard deviations, for non-stat-aware people) and it’s a standard bell curve (which if it isn’t then why are we using that measurement) then there’s a question of overdose for anyone whose needs are more than 1 sigma BELOW mean. For a lot of vitamins and minerals (but not all), the body clears overages very easily, but iron has some risks that are becoming more well known - excess iron is a free radical in the blood, it appears to contribute to formation of Alzheimer’s and other dementias, and it can mess with insulin sensitivity. It’s more common to have too much than too little iron.

I’d suggest not increasing iron significantly unless you find you have a deficiency from blood work, and you should be getting blood work done regularly if you’re doing this experimental diet. You may need more iron, but you probably won’t.


Thanks. I’ll stick to the standard for now.

I have a feeling that my exercise could be in the intense range they studied though. I don’t use steroids to decrease my recovery times and workout twice every day, but I do heavy weight lifting. It’s pretty much the definition of intense.