Good question(s). I can't answer all of it by I'll try to en light.
Your body obviously needs vitamins, minerals, proteins etc.
First of all, it needs those in different quantities at different times. Example, need more water if its hot and your exercising. You need more folic acid when you are pregnant (because the new forming child needs it for DNA synthesis).
Secondly, some of those can be stored very in large quantities and for a long period, while others can't. Example, if you have a normal diet your body has a storage of vitamine B12 to last 2 years. As you pointed out, you only last a few days without water intake.
Thirdly, your body can synthesize some nutrients by itself. Vitamine D3 is produced in the skin from cholesterol using UV light. Some aminoacids are synthesized by your body (non-essential amino acids), while others need to be supplied by diet (essential amino acids).
Then another factor of the DRI is how well your body can absorb those nutrients. Example, iron absorption from meat is much better than iron absorption from vegetables. However, water is absorbed for almost 90%.
Also important: There is a huge difference in how well your body can tollerate shortage (deficiency) or overdosis (intoxication) of different nutrients. Example, you can handle enormous amounts of vitamine C, glucose (sugar), fats, proteins and more. However, it can't handle large quantities of iron or tablesalt (actually, the body can regulate its salt levels very well, but eat 6 tablespoons of salt and you need medical care) can be very bad for health.
And last but not least, most of those factors are very different per individual.
So there are numerous factors (and i hardly described them all) that play a role in how much nutrients you can and should take in.
Similarly, what are the absorption limits so that if someone tries to cheat by not taking a nutrient for a few days and then trying to make up for it every so often?
As said, that depends on which nutrient. Some you can skip for months (years!) and some you don't.
Assuming Vitamin-A requirements are weekly, does this mean that I'm
getting about 2.68 times of it? OR (the more likely scenario) that
some of the carrot vitamin-A is not being absorbed and I'm just
Your body can store vitamine A very well. I can't tell how much days you can "skip". The DRI are "avarage intake" over a period.
What I'm ultimately interested in is finding the "time period" of each nutrient.
This can't be answered. You would need to know for every (which is unknown) nutrient you need:
- how much you as a person need, which differs per individual
- how much of every nutrient is in all foodstuff (which is unknown and differs per appel/tomato/carrot etc)
- how well your individual body absorbs those nutrients
and then calculate it for every nutrient, which are very much.
I'm not a health professional nor diet guru. But my advise: do not worry to much. Wanting to know what you need to eat and what is healthy is a very good custom. But I think you want to calculate everything and that is unhealthy, since it will take you too much time and stress.
Your national dietary guidelines are based on the latest knowledge and research. Try to keep up with them and you will be safe. And have a varied diet! Always eating tomatoes and carrots is not necessarily healthy, as you could miss some less well known proteins and minerals.
While it is not very scientific, this article seems to answer a lot of your questions and seems quite accurate:
Webmd has some excellent content on living healthy
Wikipedia has some pretty good articles on different vitamines:
My doctor asked me to take one Vitamin-D supplement (cholecalciferol) every 10 days, so I'm assuming Vitamin-D requirement is not daily.
In the Netherlands (where I'm from) it's common to take Vitamin-D everyday. A 10 day supplement is very uncommon, since you would forget to take it in. So i'm quite surprised..