The burning of fossil fuels such as coal and oil are doing more than just changing our climate — they are changing the atomic structure of our food. Nature has reported that human-induced carbon emissions are leading to changes in the natural occurrence of carbon isotopes in the environment, and the changes could make it more difficult to keep processed food manufacturers from increasing levels of artificial sweeteners.

The study, performed by geochemist William Peck of Colgate University, began as a lab demonstration to teach students how isotope analysis works. Peck and his students collected maple syrup samples from different parts of the northeastern United States to see if the carbon isotopes in the syrup varied by geography.

"Our intent was really just to see if isotope values varied by geography or if anyone was putting in sweeteners," Peck said.

Carbon isotope analysis is particularly important for tracking the origins of processed foods, since regulatory agencies use discrepancies in isotope variations to determine if low-cost sweeteners, such as corn syrup, have been added to foods.

The two most important carbon isotopes for food analysis are carbon-12, which has six neutrons, and carbon-13, which has seven. Carbon-13 is the rarer of the two since it is heavier, but it occurs more frequently in plants such as maize and sugar cane because they utilize a different type of photosynthesis than most other food plants. By testing the ratios of carbon-12 compared to carbon-13 in our food products, regulatory bodies can identify the source of the ingredients.

At first, Peck and his class didn't discover anything out of the ordinary from the maple syrup samples they collected. But they got a surprise when they compared the samples against isotope values of maple syrup in papers from the late 1970s and early 1980s. The relative amount of carbon-13 in maple syrup seems to have gone down since the 1970s, which means it's possible baseline isotope ratios are shifting over time because of environmental changes.

The largest source of those environmental changes relative to carbon isotope levels could be human-induced carbon emissions. Carbon released from the burning of oil or coal has very little carbon-13, significantly less than naturally occurring levels. So as excess fossil fuels are burned, environmental ratios of carbon isotopes should shift accordingly.

To confirm the hypothesis, Peck obtained 246 actual maple syrup samples covering the period of 1970–2006 and compared changes in carbon isotope levels against atmospheric data over the same time period. The atmospheric data showed that isotope ratio changes correlate directly with the changes in the maple syrup isotopes over the course of the 36 years studied.

The findings are significant for food regulation, particularly because regulatory agencies could be misidentifying levels of artificial sweeteners being added to our food. And now that these findings are public, it could leave loopholes open for food manufacturers to add sweeteners without being caught.

"We've known that atmospheric carbon isotope values were changing, but nobody was applying this to food science," said geochemist John Valley at the University of Wisconsin-Madison. "Clearly, food-monitoring studies need to start taking atmospheric isotope data into account."