Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Perfect food with no need for excretion?

  1. Oct 7, 2017 #1
    Perfect Food :
    Is it possible to design our daily food/meals in such a way that it has all the nutrients (100% absorb-able) but no waste parts, thus removing the necessity for the body to excrete anything at all? (This will reduce the food quantity making it cheaper; I understand that fiber must be eaten and must be excreted.)
    Last edited by a moderator: Oct 7, 2017
  2. jcsd
  3. Oct 7, 2017 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    While you may be able to reduce the total amount of waste excreted, you cannot eliminate it completely, as at least part of that waste consists of byproducts of normal cellular activity and cannot be eliminated.
  4. Oct 7, 2017 #3
    A related question is, "Are there any forms of life that do not excrete?".
  5. Oct 7, 2017 #4

    jim mcnamara

    User Avatar

    Staff: Mentor

    Short answer: no.
    Urination cannot stop - as an example, potassium (K) is required in your diet. Your body excretes K as part of electrolytic balance, a part of homeostasis. If you cannot excrete K normally in urine it builds up in the blood serum and becomes fatal. Excretion requires water. If you do not consume potassium it has fatal effects on heart rhythm. The only way to get low K with enough in the diet is to eat foods that are low in K, what people on dialysis have to do.

    Leaching root vegetables is interesting, IMO

    Same thing is true with defecation. Unless you can eliminate feces it becomes impacted. You can research that one.

    NASA has had problems feeding astronauts in orbit, in part because it is hard to create a perfect diet that healthfully minimizes excretion of waste. Prepared foods that are complete (I guess that is what you mean by perfect) do exist, example: canned infant formula. However lots of research indicates that breast milk, for a variety of reasons, remains a preferred choice.

    See table 1 in the link about increased risks of formula feeding. This link is a much abbreviated version of 'The Importance of Breastfeeding':


    Bottom line: currently it is a very difficult task to design a perfect food. DO NOT listen to the garbage in advertisements from supplement vendors.
  6. Oct 7, 2017 #5


    User Avatar
    Gold Member

    Done all the time, for patients on medical treatment.
    And that's about as perfect a food one could get, in either case.

    For certain cases of individuals who have a non-functional gastrointestinal tract.
    for a not so bad write up, at least it gives a breakdown of the constituents of the liquid.
    or TPS for total parenteral nutrition.
    Nevertheless complications can and do arise.
    That's one way.

    Then there is enteral feeding
    for example, ICU units in hospitals normally choose this for their patients, who cannot chew, swallow, etc.
  7. Oct 7, 2017 #6

    jim mcnamara

    User Avatar

    Staff: Mentor

    @256bits The point is that waste products and normal nutrient cycling still have to occur. Yes, formulated foods work for people who would otherwise die, but they are not really perfect, simply because there is such thing in Biology. Close maybe.

    The original Q asked about greatly reduced waste. If waste is removed via dialysis it still has been removed. You cannot change human metabolic pathways like that. And I do understand feeding tubes - I kept my wife alive via a feeding tube at home for her last six months.
  8. Oct 10, 2017 #7


    User Avatar
    Gold Member

    @jim mcnamara
    I was going for who could provide a near to perfect food but none other than the medical community itself, where nutrition would be achieved and attention to the elimination of excretion would be a somewhat desirable feature ( for those that have to do the cleanup so to speak ).
  9. Oct 10, 2017 #8
    How much perfectly good nutrition gets wasted simply because we eat more than necessary?

    A way to quantify this question somewhat: If I ate the same amount of food over a longer time period, would there be less total waste?
  10. Oct 10, 2017 #9

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor

    I think this is the wrong question: all of us have a gut populated with bacteria ('gut flora'), and we have a symbiotic relationship with those bacteria:


    Because our gut is literally an ecosystem, there is no real meaning to the phrase "perfect food for the body".
  11. Oct 11, 2017 #10
    Just for fun:

    There was an animated series on MTV in the 1990s called Beevis and Butthead, created and produced by Mike Judge.

    On one episode, our heroes had the following exchange (from memory):

    Butthead: I heard that in the future, food will be so advanced and efficient that you'll be able to eat and never have to poop,

    Beevis: Ya know, I think I'd kinda miss it....

  12. Oct 11, 2017 #11


    User Avatar
    Gold Member

    I've often thought that @Drakkith is one such. :oldlaugh:
  13. Oct 26, 2017 #12
    I recall when I was a child (more years than I like to recall) I used to read Isaac Asimov science fiction books. I don't recall which novel it was, but I do remember him describing intelligent beings on an exoplanet who had photosynthetic patches on their skin. When they needed food, they just went outdoors and exposed themselves to their "sun". But even with that, you still have to lose moisture (transpiration) and CO2 (like plants do). I wonder if millennia from now we can change our genome to become photosynthetic beings (plant animal hybrids, like Euglena!). The genetic engineering behind this must be mind blowing, but the tiny Euglenas did it hundreds of millions of years ago.
  14. Oct 27, 2017 #13


    User Avatar
    Science Advisor
    2017 Award

    Fun exercise in Fermi estimation (all figures from quick google searches): A typical human needs to consume 2000 kcal per day. The average human male has a surface area of ~ 1.9 m^2. Average peak solar radiance is ~ 1kW/m^2 = 860 kcal m^-2 hr^-1. Photosynthetic efficiency is ~ 5%. So, sunbathing (exposing ~ half of one's surface area to sunlight at its peak) for 1 hr would be the equivalent of eating 43 kcal (similar to the amount of calories one would obtain from eating a single oreo cookie). One would need to sunbathe for 47 hours per day in peak sunlight to subsist solely on photosynthesis.

    There is a reasons why animals are not photosynthetic!
  15. Oct 27, 2017 #14
    True, but I am not sure if that is good news for plants.
  16. Oct 27, 2017 #15


    User Avatar
    Science Advisor
    2017 Award

    Plants are fine as long as they do not need to perform energy intensive tasks like move around, maintain body temperature, or think.
  17. Oct 27, 2017 #16
    Thank you for the input, great calculation.
  18. Oct 31, 2017 #17
    Perhaps one issue to consider is that human dietary needs vary and for all sorts of reasons, for some micronutrients our body simply absorbs what it needs and discards the rest. It can get complicate when our needs vary and the way in which we manage these needs also vary, you can't design a standard formula with no waste when we don't have standard needs. There are also risks involved in long term changes which render the gut unnecessary because it doesn't become non functional and the efficiency of certain organs may be dependent on their role in digestion, the liver might be a good example.
  19. Oct 31, 2017 #18
    Good insight. During hibernation, this whole physiological function, and others, shut down. Will be interesting to research the underlying mechanisms that prevent atrophy of the digestive organs during hibernation.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted