How do you find out energy required per day?

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Discussion Overview

The discussion revolves around the methods for determining the energy requirements of the human body, specifically focusing on daily caloric needs and energy expenditure during various activities. Participants explore experimental approaches and theoretical models used to quantify these energy values.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that the human body requires about 2000-2500 calories per day and questions how this number is determined through experiments.
  • Another participant suggests several methods for measuring energy expenditure, including heat production, oxygen consumption, long-term food intake measurements, and muscle models.
  • A participant expresses skepticism about the feasibility of accurately calculating energy requirements for activities, citing the complexity involved.
  • It is mentioned that while approximations are possible, actual energy expenditure can vary significantly based on individual differences and activity specifics, along with measurement uncertainties.
  • One participant provides an example calculation for the energy required to climb stairs using the formula E = m.g.h., questioning its validity as an approximation.
  • Another participant responds that the calculation represents a lower limit due to the inefficiency of the human body.
  • Further complications are raised regarding individual fitness levels, which can affect recovery time and metabolic state after physical activity.
  • A question is posed about the similarities between measuring heat in biological processes and other calorimetric measurements, suggesting historical methods used in early experiments.

Areas of Agreement / Disagreement

Participants express a mix of skepticism and interest regarding the accuracy and feasibility of measuring energy expenditure, indicating that multiple competing views remain on the topic.

Contextual Notes

Participants acknowledge the presence of measurement uncertainties and individual variability, which complicate the determination of energy requirements. There are also references to the efficiency of the human body and the impact of fitness levels on energy expenditure.

Avichal
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Human body needs about 2000-2500 calories per day. How do you find out this number?
What sort of experiments do people do to figure out this number?

Also, in general how do you find things like - energy spent while walking, talking, blinking? It almost seems impossible to find out these things but I find numbers in books.
 
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Some things you can try:
- measure the produced heat of the body during those activities (and at rest)
- measure the required oxygen, as this is related to the consumed energy
- measure the required food (long-term measurement)
- use some model of the muscles to find an estimate
- probably some concepts I forgot or do not know
 
I find it extremely hard to believe that you can actually calculate energy we require for doing activities. There are just too many things involved. Does this actually work?
 
It is possible to find approximations. The actual power/energy will vary a bit between different persons, details of the activity and other circumstances. And you always have a measurement uncertainty, of course.
It is just interesting how precise those values are. To find some values is easy.
 
Just for the sake of an example, say I want to calculate energy it takes for an average man to climb 30 stairs (30 steps).
I just calculated using E = m.g.h. Will that be a correct approximation? Why/why not?
 
It is a lower limit. The human body is far away from 100% efficient.
 
There will also be other complications like the fitness of the person in question. An unfit person will take longer to return to a basal (resting) metabolic state so in addition to the energy expended climbing the stairs there's the period after characterised by faster heart rate, heavy breathing etc.
 
How is it different from measuring heat of any process? Technically you just use a larger calorimeter (think thermally isolated room). I believe that's how the early experiments were designed.
 

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