Nature: The burning of fossil fuels such as coal and oil releases carbon dioxide that alters the balance of carbon isotopes naturally found in the environment — an effect that is now being found in food, reveals a US study. Modern methods for tracking the origins of processed foods use isotopes — atoms of the same element that have different numbers of neutrons. Of the most common naturally occurring isotopes of carbon — carbon-12, with six neutrons, and carbon-13, with seven — the …