# 56% of McNugget Carbon is Corn

<br/>

I recently came across this stat in
[_The Omnivore's Dilemma_](https://bookshop.org/p/books/the-omnivore-s-dilemma-a-natural-history-of-four-meals-michael-pollan/586103?ean=9780143038580):

[![Amount of corn-derived carbon present in Pollan's McDonald's family meal, as measured by a mass spectrometer: 
Soda, 100%; milk shake, 78%; salad dressing, 65%; chicken nuggets, 56%; cheeseburger, 52%; and French fries, 23%.](/corn-percent.png)](https://newsarchive.berkeley.edu/news/media/releases/2006/04/11_pollan.shtml)

<br/>

My b\*llshit alarm went off, so I started doing a sniff test:

[![Mass Spectrometric Determination of Cane Sugar and Corn Syrup in Maple Syrup by Use of 13C/12C Ratio: Collaborative Study](/corn-abstract.png)](https://academic.oup.com/jaoac/article-abstract/67/1/22/5698839?redirectedFrom=fulltext)

<blockquote>
  <p>
  Use of C<sub>3</sub> carbon dioxide (CO<sub>2</sub>) fixation cycle by the
  sugar maple ... and C<sub>4</sub> carbon fixation cycle by 2 monocotyledenous
  plants, corn and cane, results in a physiological discrimination between
  <sup>13</sup>C and <sup>12</sup>C isotopes. Therefore, determination of
  <sup>13</sup>C/<sup>12</sup>C ratio of maple syrup by mass spectrometry can be
  used to detect adulteration with cane and corn sugars.
  </p>
</blockquote>

<br/>

H\*ly shit!

<p>
There are only a few distinct methods of fixing carbon from the air.
<sup>13</sup>C is only 1% of Earth's carbon, so it stands out. Not all plants
can grab <sup>13</sup>C equally. And once an organism has <sup>13</sup>C from
the air (or diet), no biochemical process is going to jettison those extra
neutrons.
</p>

<p>
The mass spec can't seem to differentiate between carbon from corn vs. sugar
cane because they're both C<sub>4</sub> plants, but the general idea totally
checks out.
</p>

One sec, I need more research...

Apparently fish show an
[isotopic signature](https://en.wikipedia.org/wiki/Isotopic_signature) from
their diet:

<blockquote>
  <p>
  Similarly, marine fish contain more <sup>13</sup>C than freshwater fish, with
  values approximating the C<sub>4</sub> and C<sub>3</sub> plants respectively.
  </p>
</blockquote>

A less dramatic effect (with poor p-values) can be seen
[in grass-fed vs. grain-fed beef](https://www.researchgate.net/publication/257473941_Food_authenticity_using_natural_carbon_isotopes_12C_13C_14C_in_grass-fed_and_grain-fed_beef):

<blockquote>
  <p>
  Natural carbon isotopes, 12C, 13C, and 14C, help to authenticate/trace foods
  and beverages. Levels of total carbon (TC), 13C (δ13C), and 14C in muscle and
  lipid tissues from grass-fed versus grain-fed steers are reported. The δ13C in
  muscle versus lipid of steaks were around 5‰ higher in grain over grass-fed
  (p<0.05).
  </p>
</blockquote>

<br/>

Corn isotopes everywhere! Has science gone too far?

![corn](/corn-diagram.jpg)