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Energy and protein feed-to-food conversion efficiencies in the
US and potential food security
gains from dietary changes
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2016 Environ. Res. Lett. 11 105002
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Environ. Res. Lett. 11 (2016) 105002
doi:10.1088/1748-9326/11/10/105002
LETTER
Energy and protein feed-to-food conversion efficiencies in the
USand potential food security gains from dietary changes
AShepon1, G Eshel2, ENoor3 andRMilo1
1 Department of Plant and Environmental Sciences,Weizmann
Institute of Science, Rehovot 7610001, Israel2 Radcliffe Institute
for Advanced Study,HarvardUniversity, 10Garden Street,
Cambridge,MA02138,USA3 Institute ofMolecular Systems Biology,
ETHZrich, Auguste-Piccard-Hof 1, CH-8093 Zrich, Switzerland
E-mail: [email protected]
Keywords: livestock, food security, sustainability
Supplementarymaterial for this article is available online
AbstractFeeding a growing populationwhileminimizing
environmental degradation is a global challengerequiring thoroughly
rethinking food production and consumption. Dietary choices control
foodavailability and natural resource demands. In particular,
reducing or avoiding consumption of lowproduction efficiency
animal-based products can spare resources that can then yieldmore
food. Inquantifying the potential food gains of specific dietary
shifts,most earlier research focused on calories,with less
attention to other important nutrients, notably protein.Moreover,
despite thewell-knownenvironmental burdens of livestock, only a
handful of national level feed-to-food conversionefficiency
estimates of dairy, beef, poultry, pork, and eggs exist. Yet such
high level estimates areessential for reducing diet related
environmental impacts and identifying optimal food gain
paths.Herewe quantify caloric and protein conversion efficiencies
forUS livestock categories.We then usethese efficiencies to
calculate the food availability gains expected from replacing beef
in theUS dietwith poultry, amore efficientmeat, and a plant-based
alternative. Averaged over all categories, caloricand protein
efficiencies are 7%8%.At 3% in bothmetrics, beef is by far the
least efficient.We findthat reallocating the agricultural land used
for beef feed to poultry feed production canmeet thecaloric and
protein demands of120 and140million additional people consuming
themeanAmerican diet, respectively, roughly 40%of currentUS
population.
1. Introduction
The combination of ongoing population rise and the
increasing demand for animal-based products places a
severe strain on world natural resources (Smil 2002,Steinfeld et
al 2006, Galloway et al 2007, Wirsenius
et al 2010, Bonhommeau et al 2013). Estimates suggestthat global
meat demand would roughly double over
the period 20002050 (Pelletier and Tyedmers 2010,Alexandratos
and Bruinsma 2012, Pradhan et al 2013,
Herrero et al 2015). Earlier analyses (Steinfeldet al 2006,
Godfray et al 2010, Foley et al 2011, Herrero
et al 2015) of food supply chains identified
inefficiencyhotspots that lend themselves to such mitigation
measures as improving yield (through genetics andagricultural
practices), increasing energy, nutrient and
water use efficiencies, or eliminating waste. Others
focused on the environmental performance of specific
products, for example animal-derived (deVries and deBoer 2010,
Pelletier et al 2010, 2011, 2014, Thoma
et al 2013). A complementary body of work (Pimenteland Pimentel
2003, Eshel and Martin 2006, Eshel
et al 2010, Hedenus et al 2014, Tilman and Clark 2014,
Springmann et al 2016) quantifies the environmentalperformance
of food consumption and dietary pat-
terns, highlighting the large environmental impacts
dietary choices can have.Key to estimating expected outcomes of
potential
dietary shifts is quantifying the amount of extra foodthat would
become available by reallocating resourcescurrently used for feed
production to producinghuman food (Godfray et al 2010, Foley et al
2011,
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Cassidy et al 2013, Pradhan et al 2013, West et al 2014,Peters
et al 2016). One notable effort (Foley et al 2011,Cassidy et al
2013,) suggested that global reallocationto direct human
consumption of both feed and biofuelcrops can sustain four billion
additional people. Yet,most cultivated feed (corn, hay, silage) is
human ined-ible and characterized by yields well above those
ofhuman edible crops. Moreover, most previous effortsfocused on
calories (Cassidy et al 2013, Pradhanet al 2013), while other key
dimensions of human dietsuch as protein adequacy are equally
important.
Here we quantify efficiencies of caloric and proteinfluxes in US
livestock production. We answer suchquestions as: How much feed
must enter the livestockproduction stream to obtain a set amount of
edibleend product calories?What is the composition of thesefeed
calories in the current US system? Where alongthe production stream
do most losses occur? We pro-vide the analysis in terms of both
protein and caloriesand use them to explore the food availability
impactsof a dietary change within the animal portion (exclud-ing
fish) of the American food system using the dietaryshift potential
method as described below. While diet-ary changes entail changes in
resource allocation andemissions (Hedenus et al 2014, Tilman and
Clark2014, Eshel et al 2016, Springmann et al 2016), here
wehighlight the food availability gains that can be realizedby
substituting the least efficient food item, beef, with
the most efficient nutritionally similar food item,poultry.
Because beef and poultry are the least andmost efficient livestock
derivedmeats respectively, thissubstitution marks the upper bound
on food gainsachievable by any dietary change within the meat
por-tion of the mean American diet (MAD). In this studywe focus on
substitution of these individual items, andplan to explore the
substitution of full diets elsewhere.As a yardstick with which to
compare our results, wealso present the potential food availability
gains asso-ciated with replacing beef with a fully
plant-basedalternative.
2.Methods and data
The parameters used in calculating the caloric andprotein Sankey
flow diagrams (figures 1 and 2) arebased on Eshel et al (2015,
2014) and references andsources therein. Feed composition used in
figures 1and 2 are derived from NRC data (National ResearchCouncil
1982, 2000). For this work, the MAD is theactual diet of the
average American over 20002010(United States Department of
Agriculture ERS 2015),with approximate daily loss-adjusted
consumption of2500 kcal and 70 g protein per capita (see SI
andsupplementary data for additional details).
Figure 1.ASankey flowdiagramof theUS feed-to-food caloricflux
from the three feed classes (left) into edible animal
products(right). On the right, parenthetical percentages are the
food-out/feed-in caloric conversion efficiencies of individual
livestockcategories. Caloric values are in Pcal, 1012 kcal.
Overall, 1187 Pcal of feed are converted into 83 Pcal edible animal
products, reflectingaweightedmean conversion efficiency of
approximately 7%.
2
Environ. Res. Lett. 11 (2016) 105002
2.1. Calculating the dietary shift potentialThe dietary shift
potential, the number of additionalpeople that can be sustained on
a given croplandacreage as part of a dietary shift, is
D =-
- -
( )( )
( )P P l ll l l
1a bUS a b
per capita land gain
MAD a b
updated per capita
MAD land requirement
In equation (1), the left-hand side (Pab) is thenumber of
additional people that can be fed onland spared by the replacement
of food item awith food item b. PUS300 million denotes the20002010
mean US population; la and lb denotesthe annual per capita land
area for producing a setnumber of calories of foods a and b. This
definitionreadily generalizes to protein based replacements,and/or
to substitution of whole diets rather than spe-cific food
items.
To derive the mean per capita land requirement ofthe MAD, l ,MAD
we calculate the land needs of each ofthe non-negligible plant and
animal based itemsthe MAD comprises. We convert a given per
capitaplant item mass to the needed land by dividing theconsumed
item mass by its corresponding nationalmean loss adjusted yield.
The land needs of thefull MAD is simply the sum of these needs over
all
items (see supplementary data). The per capita cropland
requirements of the animal based MAD cate-gories (e.g., l ,poultry
)lbeef are based on Eshel et al(2014, 2015).
Themodest land needs of poultrymean that repla-cing beef with an
amount of poultry that is caloric- orprotein-equivalent spares land
that can sustain addi-tional people on a MAD. We denote by citem
the kcal(person yr)1 consumption of any MAD item. The setnumber of
calories (or protein) consumed in theMAD is different for beef and
thus for the calculationof substituting beef with poultry, we
multiply the percapita land area of poultry by /c c ,beef poultry
the percapita caloric (or protein) beef:poultry consumptionratio in
the MAD, which is 1.2 for calories and 0.6 forprotein.
Using equation (1), the caloric dietary shift poten-tial of beef
is
D =
-
- -
P
P l lc
c
l l lc
c
.beef poultry
US beef poultrybeef
poultry
MAD beef poultrybeef
poultry
For the beef replacement calculation, the
resultantpost-replacement calories (light orange arrows infigure
3(a)) comprise (1) the poultry calories thatreplace the MAD beef
calories, plus (2) calories that
Figure 2.TheUS feed-to-food proteinflux from the three feed
classes (left) into edible animal products (right). On the
right,parenthetical percentages are the
food-protein-out/feed-protein-in conversion efficiencies of
individual livestock categories. Proteinvalues are inMt (109 kg).
Overall, 63Mt of feed protein yield edible animal products
containing 4.7Mt protein, an 8%weightedmeanprotein conversion
efficiency.
3
Environ. Res. Lett. 11 (2016) 105002
the spared lands can yield if allocated to the productionof
MAD-like diet for additional people (national feedland supporting
beef minus the land needed toproduce the replacement poultry). The
MAD caloriesthat the spared land can sustain is calculated
bymultiplying the spared land area by the mean caloricyield of the
full MAD with poultry replacing beef,1700Mcal (ac yr)1. The
national annual caloriesdue to substituting beef for poultry is
= +
-
- -
( )
C P c c
P l lc
c
l l lc
c
365 365
2
beef poultrynat.
US beef MAD
US beef poultrybeef
poultry
MAD beef poultrybeef
poultry
where c and l are the per capita daily caloric consump-tion and
annual land requirements of poultry, beef orthe full MAD,
respectively. The first and second termson the right-hand side of
equation (2) are terms (1)and (2) of the above explanation,
respectively.
To derive the difference between the above repla-cement calories
and the replaced beef calories (percen-tages in figure 3), we
subtract the original nationalconsumed beef calories P c365 US beef
from the aboveequation. The difference between replacement
andreplaced caloric fluxes is
-
=
-
- -
( )
C C
c
P l lc
c
l l lc
c
365 3
beef poultrynat.
beefnat.
MAD
US beef poultrybeef
poultry
MAD beef poultrybeef
poultry
As noted above, the quotient on the right-hand sidegives the
number of extra people that can be fed,reported in figure 3. An
analogous calculation repla-cing calories with protein mass, yields
the proteindietary shift potential shown in figure 3(b). Thecurrent
calculation of the dietary shift potential alsoenables calculating
the food availability gains asso-ciated with any partial
replacement. Figure S2 depictsthe relation between the dietary
shift potential (addi-tional people that can be fed a full MAD
diet) and thepercentage of national beef calories (from
MAD)replacedwith poultry.
2.2. The choice of poultry as the consideredsubstituteWe use
poultry as the replacement food in our foodavailability
calculations for several reasons. First, USpoultry consumption has
been rising in recent decadesoften substituting for beef (Daniel et
al 2011), suggest-ing it can serve as a plausible replacement. In
addition,poultry incur the least environmental burden amongthe
major meat categories and thus the calculation of
Figure 3.Dietary shift potential of substituting beef with
poultry in themeanAmerican diet (MAD). Percent change in
availablecalories due to substituting beef with poultry (panel
(a)),+520%. The number of additional people consuming 2500 kcal d1
thatthese calories can sustain (the dietary shift potential) is
116million (upper right parenthetical value). Caloric values are in
Pcal, i.e.1012 kcal. The protein gain due to dietary shift frombeef
to poultrywill increase by 380% (panel (b)), meeting the protein
needs of 142million additional people consuming 70 g protein d1 (as
in theMAD). Protein values are inMt (109 kg). The caloric loss
followingsubstitution is calculated based on the conversion
efficiency for poultry and theMAD. The loss of the plant-based
portion ofMAD iscalculated by assessing the loss of each individual
plant item throughout the supply chain (see supplementary data);
the loss of theanimal-based portion ofMAD is based on the caloric
efficiency conversion estimates shown in table 1. A similar
calculation isperformed for protein.
4
Environ. Res. Lett. 11 (2016) 105002
the dietary shift potential presented here serves as anupper
bound on possible food gains achievable by anysubstitutionwithin
themeat portion of theMAD.
Plant-based diets can also serve as a viable replace-ment for
animal products, and confer larger meanenvironmental (Eshel et al
2014, 2016) and food avail-ability gains (Godfray et al 2010).
Recognizing that themajority of the populationwill not easily
become exclu-sive plant eaters, herewe choose to present the less
radi-cal and perhapsmore practical scenario of replacing
theenvironmentally most costly beef with the moreresource efficient
poultry. We also augment this calcul-ationwith a plant-based
alternative diet as a substitute.
Finally, poultry stands out in its high kcal g1 and gprotein g1
values and its desirable nutritional profile.Per calorie, it can
deliver more protein than beef whiledelivering as much or more of
the other essentialmicronutrients (figure S1).While it is tricky to
comparethe protein quality of beef and poultry, we can use
thebiological value (modified essential amino acid indexand
chemical score index Ihekoronye 1988) and theprotein digestible
corrected amino acid score, the pro-tein indicator of choice of the
FAO. Within inevitablevariability, the protein quality of poultry
is similar tothat of beef using both metrics (Sarwar 1987,
Ihekor-onye 1988, Lpez et al 2006, Barrn-Hoyos et al 2013).While
the FAOhas recently introduced anupdated pro-tein quality score
(DIAASdigestible indispensableamino acid score) (FAO Food and
Nutrition paper No.92 2011), to our knowledge no reliable DIAAS
datacomparing beef andpoultry exists.
3. Results
The efficiency and performance of the animal portionof the
American food system is presented in table 1(see detailed
calculations in supplementary files),highlighting a dichotomy
between beef and the otheranimal categories, consistent with
earlier environmen-tal burden estimates (Eshel et al 2014).
The calories flow within the US from feed to live-stock to human
food is presented in figure 1. From leftto right are primary inputs
(concentrated feed, pro-cessed roughage and pasture) feeding the
five second-ary producer livestock categories, transformed
intohuman consumed calories. We report energy fluxes inPcal=1012
kcal, roughly the annual caloric needs of amillion persons.
Annually, 1200 Pcals of feed fromall sources (or 800 Pcals when
pasture and bypro-ducts are excluded) become 83 Pcals of loss
adjustedanimal based human food. This is about 7% overallcaloric
conversion efficiency. The overall efficiencyvalue arises from
weighting the widely varied categoryspecific efficiencies, from 3%
for beef to 17% for eggsand dairy, by the average US consumption
(rightmostpart of figure 1). Concentrate feed consumption, suchas
maize, is distributed among pork, poultry, beef anddairy, while
processed roughage and pasture (50% oftotal calories) feed almost
exclusively beef. The con-centrated feed category depicted in
figure 1 alsoincludes byproducts. We note that because
detailedinformation on the distribution of byproducts as feedfor
the different animal categories is lacking, we can-not remove them
from the feed to food efficiency calc-ulation. Yet, our analysis
shows that for the years20002010 the contribution of byproducts to
the totalfeed calories (and protein) was less than 10% (see
SIspreadsheet) and so their effect on the values is quanti-tatively
small. The results reported in all figures arecorrected for
import-export imbalances, such that thepresented values refer to
the feed used to produce theanimal-derived food domestically
consumed in theUS(i.e., excluding feed used for livestock to be
exported,and including imported feed, albeit quite minor in theUS
context).
While calories are widely used to quantify foodsystem
performance, proteinwhich is often invokedas the key nutritional
asset of meatoffers an impor-tant complementary dimension (Tessari
et al 2016).The flow of protein in the American livestock
produc-tion system, which supplies 45 g protein person1
Table 1.Key parameters (std. dev.)used in evaluatingUS feed
allocation and conversion among animal categories (Eshelet al 2015)
and energy (caloric) and protein efficiency.
Parameter Units Beef Poultry Pork Dairy Eggs
Feed intake per LW kg/kg LW 144 1.90.4 3.11.3 N/A N/AFeed intake
per EW kg/kg EW 3613 4.20.8 62.5 N/A N/AFeed intake perCW kg/kgCW
499 5.41.4 94 2.60.6 2.41.2Feed caloric content kcal g1 2.30.6
3.41.4 3.62 2.80.9 3.42.4Food caloric content kcal g1 3.20.3 2.30.1
2.80.2 1.20.1 1.40.1Caloric conversion efficiency % 2.90.7 134 94
174 179Feed protein content % 123 177 1711 155 1712Food protein
content % 152 202 141.4 60.6 131.3Protein conversion efficiency %
2.50.6 217 94.5 144 3116
Note: LW=live weight (USDA reported slaughter live weight);
EW=edible weight (USDA reported retail boneless edibleweight);
CW=consumed weight (USDA reported loss-adjusted weight). N/A,
denotes not applicable as the parameter isrelevant only for CW.
Feed caloric content refers to metabolizable energy and feed
protein content refers to crude protein. For
further information on all data sources and calculations see SI
and supplementary data.
5
Environ. Res. Lett. 11 (2016) 105002
d1 to theMAD, is shown in figure 2. Overall, 63Mt (1Mt=109 kg)
feed protein per year are converted byUS livestock into 4.7Mt of
loss-adjusted edible animalbased protein. This represents an
overall weighted-mean feed-to-food protein conversion efficiency
of8% for the livestock sector. Protein conversion effi-ciencies by
individual livestock categories span an11-fold range, more than
twice the correspondingrange for calories, from 31% for eggs to 3%
for beef(see SI formore details).
By isolating visually and numerically the contribu-tions from
pasture, which are derived from land that isunfit for production of
most other foods, figures 1 and2 quantify expected impacts of
dietary shifts. Of those,we choose to focus on substituting beef
with poultry.Because these are themost and least resource
intensivemeats, this substitution constitutes an upper
boundestimate on food gains achievable by any meat-to-meat shift.
Lending further support to the beef-to-poultry substitution choice,
poultry is relatively nutri-tionally desirable (see the methods
section and figureS1), andjudging by its ubiquity in the
MADpala-table tomanyAmericans.
We quantify the dietary shift potential (a term wefavor over the
earlier diet gap Foley et al 2011), thenumber of additional people
a given cropland acreagecan sustain if differently reallocated as
part of a dietaryshift.While here we estimate the dietary shift
potentialof the beef-to-poultry substitution, the
methodologygeneralizes to any substitution (see methods sectionfor
further information and equations). The beef-to-poultry dietary
shift potentials are premised on reallo-cating the cropland acreage
currently used for produ-cing feed for US beef (excluding
pastureland) toproducing feed for additional poultry
production.Subtracting from beefs high quality land require-ments
those of poultry gives the spared land thatbecomes available for
feeding additional people.Dividing this spared acreage by the per
capita landrequirements of the MAD diet (modifying the latterfor
the considered substitution) yields the numberof additional people
sustained by the dietarysubstitution.
We calculate the dietary shift potential for beef (asdefined
above and in the methods section) by quanti-fying the land needed
for producing calorie- and pro-tein-equivalent poultry
substitution, and theirdifferences from the land beef currently
requires. Wederive the number of additional people this land
cansustain by dividing the areal difference thus found bythe per
capita land demands of the whole modifiedMAD,0.5 acres (2103 m2)
per year.
Evaluating this substitution, and taking note of fullsupply
chain losses, we obtain the overall dietary shiftpotential of beef
to poultry on a caloric basis to be120 million people (40% of
current US popula-tion; figure 3, panel (a)). That is, if the
(non-pasture)land that yields the feed US beef currently consumewas
used for producing feed for poultry instead, and
the added poultry production was chosen so as to yieldexactly
the number of calories the replaced beef cur-rently delivers, a
certain acreage would be spared,because of poultrys lower land
requirements. If, inaddition, that spared land was used for growing
a vari-ety of products with the same relative abundance as inthe
full MAD (but with poultry replacing beef), theresultant human
edible calories would have risen to sixtimes the replaced beef
calories (figure 3, panel (a)).For protein-conserving dietary shift
(figure 3, panel(b)), the dietary shift potential is estimated at
140million additional people (consuming 70 g proteinperson1 d1 as
in the full MAD). As the protein qual-ity of poultry and beef are
similar (see the methodssection and references therein), this
substitutionentails no protein quality sacrifices.
As a benchmark with which to compare the beef topoultry results,
we next consider the substitution ofbeef with a plant based
alternative based on themetho-dology developed in Eshel et al
(2016). In that study,we derive plant based calorie- and
protein-conservingbeef-replacements. We consider combinations of
65leading plant items consumed by the average Amer-ican
thatminimize land requirements with themass ofeach plant item set
to 15 g d1 to ensure dietarydiversity.We find that these
legume-dominated plant-based diets substitute beef with a dietary
shift potentialof190million individuals.
4.Discussion
In this study we quantify the caloric and proteincascade through
the US livestock system from feed toconsumed human food.
Overall,
sustained individuals, respectively. This potentialproduction
increase can serve as food collateral in faceof uncertain food
supply (e.g. climate change), orexported to where food supply is
limited. In the case ofenvisioning various scenarios resulting in
only partialsubstitution to poultry consumption, the
currentcalculation also enables to deduce the food gainsassociated
with substituting only a certain percentageof national beef
calories with poultry (see figure S2).Our purpose here is not to
endorse poultry consump-tion, nor can our results be construed as
such. Rather,the results simply illustrate the significant food
avail-ability gains associated with the rather modest andtractable
dietary shift of substituting beef with lessinefficient animal
based alternatives. Substitution ofother food items with other
nutritionally similaranimal food items is also plausible (e.g.,
pork for beef),yet the food gains expected from such
replacementsare considerably lower (see supplementary
data).Substitution of beef with non-meat animal basedproducts
(dairy and eggs) is possible on a caloric orprotein basis (see
supplementary data), yet given theirdissimilar nutritional profile,
amore elaborate metho-dology is required to construct and analyze
such a shift(Tessari et al 2016). The dietary shift potential
ofreplacing beef with a plant based alternative (domi-nated by
legumes) (Eshel et al 2016) amounts to190million additional people.
Thus while plant basedalternatives offer the largest food
availability gains,poultry is not far behind.
We note that the substitution of beef for eitherpoultry or
plants also entails vast reductions indemand for pastureland. The
effects of dietary shiftson demand for agricultural inputs (such as
fertilizer orwater) for the production of food on the land
sparedfrom growing feed for beef requires furtherinvestigation.
This paper offers a system wide view of feed tofood production
in the US, and introduces the dietaryshift potential as a method
for quantifying possiblefood availability gains various dietary
shifts confer.Building on this work, future work can quantify
thedietary shift potential of full diets (e.g. Peterset al 2016),
enhance the realism of various considereddietary shifts, and better
integrate nutritional con-siderations, micronutrients in
particular, in the assess-ment of expected outcomes.
Acknowledgments
We thank David Canty, David St-Jules, Avi Flamholz,Avi Levy,
Tamar Makov, and Lisa Sasson for theirimportant help with this
manuscript. This researchwas funded by the European Research
Council (Pro-ject NOVCARBFIX 646827). RM is the Charles
andLouiseGartner professional chair.
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1. Introduction2. Methods and data2.1. Calculating the dietary
shift potential2.2. The choice of poultry as the considered
substitute
3. Results4. DiscussionAcknowledgmentsReferences