The food you eat really becomes you

Have you ever thought that your teeth hold many secrets besides helping you chew your food?

You may remember from high school or college chemistry class that elements often exist in a variety of atomic states with different masses.

A classic example is carbon, which occurs as isotopes with mass numbers 12, 13, and 14, represented by 12C, 13C, and 14C, respectively, and pronounced "carbon 12," "carbon 13," and "carbon 14."

In the natural environment, the first two isotopes are stable, while carbon 14 is a radioactive isotope that changes its atomic structure at a constant rate after the organism dies. This process of radioactive decay forms the basis of carbon 14 dating, that is, the less carbon 14 left, the older the object.

To interpret certain food signals, we need to understand that the carbon 13 content in plants varies, depending on their photosynthesis process.

Photosynthesis of plants, image source: pexels

Certain tropical and subtropical plants, including many grasses, papyrus, and corn, obtain carbon from the air to produce energy through a water-saving mechanism called the C4 pathway.

Temperate or cold-climate plants use another energy-producing mechanism, called the C3 pathway. C3 plants are more numerous and make up the majority of the world's plants. Although their photosynthesis process is less efficient in the tropics, they are still found there.

The key point here is that the carbon 13 content in C4 plants is much higher than that in C3 plants. This difference will also be reflected in the bodies of insects and animals that feed on these plants, even including animals at the top of the food chain.

So if an animal feeds exclusively on C4 plants, like an antelope, its teeth and bones will have a higher C13 content than an animal that eats C3 shrubs and trees, like a giraffe.

Ancient humans were also part of this food web, but it's still unclear when our ancestors made it to the top of the pyramid and became top meat eaters. Isotopes in teeth are helping scientists pinpoint the timing of this transition.

Paleoanthropologists have spent the past few decades carefully measuring the carbon isotope values ​​of African hominid teeth and have found that human diets showed surprising differences over millions of years.

The oldest species dated so far is Ardipithecus ramidus, which shows a carbon-13 signature dominated by carbon-3 plants, and is closer to living chimpanzees than to later primitive humans.

Similar results were found in two Australopithecus sediba individuals, even though they were separated from Ardipithecus by more than 2 million years and thousands of kilometers.

In contrast, the East African flat-faced, robust Australopithecus, Paranthropus boisei, showed a strong tropical C4 plant signature, meaning that it largely ate grasses, tubers, and sedges.

Grass, image source: pexels

However, scientists cannot rule out the possibility that they ate a lot of insects or animals that ate C4 plants. Other hominids of the period, such as early Homo, Australopithecus africanus and Paranthropus robustus, all showed a comprehensive diet.

The famous Taung child was an Australopithecus africanus, and different members of the species had different ratios of C3 to C4, making simple generalizations more complicated. Since it is impossible to distinguish whether an individual consumed plants or ate animals that fed on plants, other methods are needed to delve deeper into these clues in order to determine when early hominids switched from a plant-based diet to one that added large amounts of meat.

Those searching for a "paleo diet" may be a little lost. Our early ancestors and relatives tried a variety of different diets as they spread out of Africa. One particularly striking result was found in two robust Australopithecus species, Paranthropus boweni and Paranthropus robinsii.

Their teeth and heads were nearly identical, but their diets were very different. These eastern and southern African species show differences in both carbon-13 and dental microwear, though the details of the various lines of evidence don’t quite agree. Paleoanthropologists studying the morphology of their teeth, jaws, and skulls found that something seemed to be wrong, as both species had a fairly strong bite, but only Paranthropus robustus seemed to really use its huge incisors. The debate among scholars involving microwear, dental chemistry, and facial size morphology shows how reasonable people can come to very different conclusions about ancient behavior.

What can tooth chemistry tell us about hominids who left Africa?

Unfortunately, we have very little information about the diets of the earliest migrating hominids. Studies of diets in Africa and Eurasia differ by almost a million years, in part because of the environmental history of these regions.

For example, temperate Europe is almost entirely populated by native C3 plants, so comparing C13 values ​​is not very meaningful and cannot determine the intake of different types of plants.

Instead, scientists studying European hominids have focused on the carbon and nitrogen isotope combinations in food proteins, which can help distinguish between carnivores, herbivores, and omnivores.

The problem is that these analyses require organic material, especially collagen, an important protein found in dentin and bone. Unfortunately, water, heat, microorganisms, and chemicals in the soil all accelerate the breakdown of collagen, ultimately causing this important dietary evidence to be lost forever.

The best hope for collagen is from individuals less than 100,000 years old in cool climates. Most of the samples studied have come from the bones and teeth of Neanderthals, the robust hominids who were at home in cool Eurasia.

Scientists think they obtained a lot of dietary protein by hunting large herbivorous mammals. The menu of prehistoric Europe included mammoths, bison, rhinos and wild horses, most of which are now extinct. Neanderthals' isotope values ​​are roughly consistent with most mammals living at the same time, including high-level carnivores such as wolves or hyenas.

Towards the end of the Neanderthal reign, modern humans living in Europe had even higher nitrogen isotope values, suggesting a similar carnivorous diet that even included foods from freshwater or marine ecosystems.

Meat, image source: pexels

So, do these species only eat meat?

Some have pointed out that it is unlikely that any hominin species consumes as much meat as carnivorous mammals, because high levels of animal protein could be dangerous to humans, especially pregnant women and infants.

One limitation of these tooth chemistry studies is that meat-derived proteins can mask plant-derived signatures that are barely visible in traditional collagen analyses.

A new method that focuses on nitrogen isotopes in amino acids, the building blocks of proteins, may provide higher resolution, and the team that pioneered the method reports that Neanderthals may have gotten 20% of their dietary protein from plants.

Our teeth can reveal a lot about our behavior and health; food particles, bacteria, and DNA all tell a story.

END