mets

food_energy.tex

@@ -39,30 +39,33 @@ Everyone eats, maybe not 3000 kcals per day, but at least something every day.
 
 To introduce Food Energy, I ask the students to work through a few questions:
 
-\subsection{food converted into body heat}
+\subsection{Converting food into body heat}
 Planning to save money, one college student decides to go to an all-you-can-eat buffet each day at 11am.  If he brings homework and stretches the meal out for a few hours he can get all $3000~kcals$ with only one meal bill.  Food is fuel for the human body -- could too much fuel make his body feel sick? If his body burned all this food at once, how much warmer would he get? 
 Useful information: the student has a mass of 80kg and is made mostly of water.  A Calorie heats 1 kg of water $1^{\circ}C$. 
 
-Possible Answer:
+Here's a possible answer:
-We'll equate food energy with calorimetric heating and assume human bodies have the same heat capacity as water, about $1kcal/kg\cdot\degC$. This allows us to calculate the body's temperature increase.
+equate food energy with calorimetric heating and assume human bodies have the same heat capacity as water, about $1kcal/kg\cdot\degC$. This allows us to calculate the body's temperature increase.
 \bea
 3000kcals &=& 80kg\cdot1 \frac{kcal}{kg\cdot \degC}\cdot\Delta T\\
 \Delta T &\approx& +37.5\degC
 \eea
-Students are normally quite surprised at this answer.  Although it's unrealistic, there is a related phenomena of diet-induced thermogenesis\cite{meat_sweats} known informally as ``the meat sweats''. Some students connect this to feeling quite hungry after a cold swim in the pool (a similar effect).  On a larger scale, talking about what's wrong with this estimate is useful.  The main storage mechanism for storing food energy is fat tissue, which the calculation completely ignores.  Infants are generally born with little fat, and an infant sleeping through the night often coincides with the baby growing enough fat to store enough kcals to make it though a night without waking up ravenously hungry.  A related follow-up is that if a person is stranded in the wilderness, they should immediately start walking downstream (ie, towards civilization) as they likely won't be able to harvest an amount of kcals equivalent to what they already have stored on their hips and abdomen.\cite{trout}  The contrast of bear hibernation \cite{fat_bear} and songbirds constatly eating through the winter are related connections to investigate.
+Students are normally quite surprised at this number.  Although wildly unrealistic, $\Delta T \approx +6\degC$ is typicaly fatal, there is a related phenomena of diet-induced thermogenesis\cite{meat_sweats} known informally as ``the meat sweats''. Some students connect this calculation to feeling quite hungry after a cold swim in the pool (a similar effect).  On a larger scale, discussing what's wrong with this estimate is useful.  The main storage mechanism for storing food energy is fat tissue, which the calculation completely ignores.  Infants are generally born with little fat, and an infant sleeping through the night often coincides with the baby growing enough fat tissue to store sufficient kcals to make it though a night without waking up ravenously hungry.  A related follow-up is that if a person is stranded in the wilderness, they should immediately start walking downstream (ie, towards civilization) as they likely won't be able to harvest an amount of kcals equivalent to what they already have stored on their hips and abdomen.\cite{trout}  The contrast of bear hibernation \cite{fat_bear} and songbirds constatly eating through the winter are related connections to investigate.
 
-Section{Biophysical Power}: 
+\subsection{Biophysical Power}: 
 A more realistic question to follow up with relates to the average \textit{power} given off by a person over a day.  
 Again, assuming 3000kcal is burned over 24 hours, with useful information: $1 kcal \approx 4200J$ and $1 J/s=1W$.
 \be
 \frac{3000kcal}{24hours}\frac{4200J}{1kcal}\frac{1hour}{3600sec}\approx145W
 \ee
-Most students still remember $75Watt$ lightbulbs, but given the spread of LED lighting, ``A person is two 75W light bulbs'' will probably only make sense for a few more years.  Desert or cole-weather camping, alone or with friends, and survival swimming are also examples for students to make sense of this answer.  If you can take advantage of other people's waste body heat, you'll sleep more pleasantly.  
+Most students still remember $75Watt$ lightbulbs, but given the spread of LED lighting, ``A person's body heat is two 75W light bulbs'' will probably only make sense for a few more years.  Desert or cold-weather camping, alone versus with friends, and survival swimming are also examples for students to make sense of this answer.  If you can take advantage of other people's waste body heat, you'll sleep more pleasantly and survive longer in cold water.  
+
+Another connection to make is that of ``brown fat,'' a sort of biological space heater that humans and other mammals develop in response to cold weather.  This tissue's mitochondria can burn lipids and carbohydrates in a useless proton pumping scheme, which produces metabolic heat \cite{Brown_fat}.  Most common in rodents and infants, this mechanism can be stimulated by extended exposure to cold temperatures.  The idea of a biological space heater that takes a month to turn on and a month to turn off matches the lived experience of college students in Minnesota, who wear down jackets in $4\degC$ weather in November, and beachwear in the same $4\degC$ weather in March.  Additionally, transplants to northern climates often take a few years to ``get used to'' the colder weather up north. It seams just as easy to say that transplants' bodies take a few years to develop the brown fat cells which allow them to be comfortable in cold weather.
+
+One other connection to emphasize at this question is the difference between power and energy.  A graph of a human body's ``kcal content'' over the course of a day can be a useful illustration.  When sedentary, this graph probably has the slope of $-150W\approx 125kcals/hour$.  If the $3000kcal$ meal at the buffet takes an hour, this period corresponds to an energy-time slope of $+3000kcal/hour\approx +3500W$.  
+
+In medicine, these slopes are related to ``Metabolic Equivalent of Task'' (METS) and are commonly discussed in cariology and exercise physiology.  METS is power normalized by mass, $1METS=1\frac{kcal}{kg\cdot hour}$ and common METS levels are available for many different physcial activities. \cite{METS}
 
-Another connection to make is that of ``brown fat'' a sort of biological space heater that humans can develop in response to cold weather.  For example, this tissue's mitochondria can burn lipids and carbohydrates in a useless proton pumping scheme, which produces metabolic heat \cite{Brown_fat}.  Most common in rodents and infants, this mechanism can be stimulated by extended exposure to cold temperatures.  The idea of a biological space heater that takes a month to turn on and a month to turn off matches the lived experience of college students in Minnesota, who wear down jackets in $4\degC$ weather in November, and beachwear in $4\degC$ weather in March.  Additionally, transplants to northern climates often take a few years to ``get used to'' the colder weather up north. It seams just as easy to say that transplants' bodies take a few years to grow the brown fat that allows them to be comfortable with cold weather.
 
-Power is the slope of energy-time
-METS
 Imagine that after eating a $600~kcal$ bacon maple long-john (donut), you decide to go for a hike to work off the Calories.  Winona State  is in a river valley bounded by 200m tall bluffs.  How high up the bluff would you have to hike to burn off the donut?  
 Useful information: human muscle is about $30\%$ efficient and gravitational energy on Earth's surface has a slope of about $10~Joules/kg\cdot m$.
 
@@ -106,25 +109,9 @@ The work was prompted in part by discussions with John Deming, Carl Ferkinhoff,
 %a simple heading of ‘Appendix’ use the code \section*{Appendix}. If it contains
 %numbered equations, figures or tables the command \appendix should precede it and
 %\setcounter{section}{1} must follow it
-\appendix
+%\appendix
-\section{Introductory Food Energy Questions}
+\%section{Introductory Food Energy Questions}
 
-Planning to save money, one college student decides to go to an all-you-can-eat buffet each day at 11am.  If he brings homework and stretches the meal out for a few hours he can get all $3000~kcals$ with only one meal bill.  Food is fuel for the human body. If his body burned all this food at once, how much warmer would he get? 
-Useful information: the student has a mass of 80kg and is made mostly of water.  A Calorie heats 1 kg of water $1^{\circ}C$. 
-
-Answer
-\bea
-3000kcals &=& 80kg\cdot1 \frac{kcal}{kg\cdot C^{\circ}}\cdot\Delta T\\
-\Delta T &\approx& +37.5^{\circ}
-\eea
-Fat tissue serves a valuable purpose, brown fat, babies, songbirds
-
-What power does the body give off in the more realistic case that the 3000kcal is burned over 24 hours? 
-Useful information: $1 kcal \approx 4200J$ and $1 J/s=1W$.
-\be
-\frac{3000kcal}{24hours}\frac{4200J}{1kcal}\frac{1hour}{3600sec}\approx145W
-\ee
-Survival swimming, putting all the kids in one bed on a cold winter night.
 
 
 \section*{References}
@@ -143,15 +130,14 @@ ISBN 9780122270550,
 https://doi.org/10.1016/B0-12-227055-X/01188-3.
 (https://www.sciencedirect.com/science/article/pii/B012227055X011883)
 
-\cite{trout}
+\bibitem{trout}
 The wilderness river might be full of trout, but if they're 300kcals each, you'll have to catch, clean, and smoke $10$ of them to store up a day's food. \url{https://fdc.nal.usda.gov/fdc-app.html#/food-details/175154/nutrients}
 
-\cite{fat_bear}
+\bibitem{fat_bear}
 Some sources claim that bear metabolism can vary between 4000 to and 20,000 kcals per day, \url{https://bear.org/5-stages-of-activity-and-hibernation/}, comically illustrated by the National Park Service at \url{https://www.nps.gov/katm/learn/fat-bear-week-2022.htm} .
   
 \bibitem{brown_fat}
-A space heater
+Huttunen P, Hirvonen J, Kinnula V. The occurrence of brown adipose tissue in outdoor workers. Eur J Appl Physiol Occup Physiol. 1981;46(4):339-45. doi: 10.1007/BF00422121. PMID: 6266825.
-\url{https://hms.harvard.edu/news/research-brown-fat-heats}
 
 Brown and Beige Fat: Molecular Parts of a Thermogenic Machine
 Paul Cohen1 and Bruce M. Spiegelman2
@@ -168,6 +154,9 @@ Himms-Hagen J. Nonshivering thermogenesis. Brain Res Bull. 1984 Feb;12(2):151-60
 
 https://www.nih.gov/news-events/nih-research-matters/uncovering-origins-brown-fat
 
+\cite{METS}
+Jetté M, Sidney K, Blümchen G. Metabolic equivalents (METS) in exercise testing, exercise prescription, and evaluation of functional capacity. Clin Cardiol. 1990 Aug;13(8):555-65. doi: 10.1002/clc.4960130809. PMID: 2204507.
+
 \bibitem{Aztec_Cannibalism} for crop productivity
 
 \bibitem{USDA_1917_yields}