Is it because of a sweet tooth?… A controversial hypothesis emerges: sugar, not protein, fueled brain growth 최근 학술지 네이처에 발표된 연구에 따르면 인류의 뇌는 단백질이 아닌 당분의 공급으로 커졌을 수 있다는 가설을 제기했다. A recent study published in the journal Nature suggests that the human brain may have grown due to the supply of sugar, not protein. 진화생물학자 존 데스마이스터르(John Dehmel)와 카를로스 부에차(Charles Bouchaud) 스위스 로잔 연방 공과대학 연구진은 인류의 뇌가 커진 이유에 대해 기존의 가설을 반박하는 연구 결과를 내놓았다. Evolutionary biologists John Dehmel and Charles Bouchaud of the Swiss Federal Institute of Technology in Lausanne presented research results that contradict existing hypotheses about why the human brain grew. 지금까지 인류의 뇌가 커진 이유에 대해서는 단백질의 섭취가 많았기 때문이라는 가설이 널리 받아들여졌다. Until now, the hypothesis that increased protein intake was the reason for the growth of the human brain has been widely accepted. 그러나 이번 연구에서는 단백질의 섭취는 인류의 뇌 성장에 큰 영향을 미치지 못했다고 주장했다. However, this study argues that protein intake had little impact on human brain growth. 연구진은 인류의 뇌 성장에 영향을 미친 것은 당분이라고 주장했다. The researchers claimed that sugar was what influenced human brain growth. 인간이 섭취한 당분의 양이 늘어나면서 에너지 효율성이 높은 뇌 조직이 커졌을 수 있다는 것이다. As the amount of sugar consumed by humans increased, energy-efficient brain tissue may have grown. 연구진은 영장류의 뇌 크기와 당류, 단백질의 섭취 비율을 분석했다. The researchers analyzed the brain size of primates and the intake ratio of sugar and protein. 그 결과 뇌가 큰 영장류는 당류의 섭취량이 많았고, 단백질의 섭취량은 상대적으로 적은 것으로 나타났다. As a result, it was found that primates with larger brains consumed more sugar and relatively less protein. 이에 대해 연구진은 "뇌 조직은 에너지 효율성이 높은 조직"이라며 "에너지 공급원으로서 당분이 단백질보다 뇌 성장에 더 많이 기여했을 것"이라고 말했다. In response, the researchers said, "Brain tissue is a highly energy-efficient tissue," and added, "As an energy source, sugar may have contributed more to brain growth than protein." 다만 이번 연구 결과에 대해 과학계에서는 여전히 논쟁이 이어지고 있다. However, there is still debate in the scientific community about the results of this study. 영국 케임브리지 대학의 진화생물학자 앤디 코프(Andy Cuff) 교수는 "뇌 성장과 당류의 상관관계에 대한 가설은 흥미롭지만, 이번 연구는 설득력이 없다"고 말했다. Andy Cuff, an evolutionary biologist at the University of Cambridge, said, "The hypothesis about the correlation between brain growth and sugar is interesting, but this study is not convincing." 코프 교수는 "영장류의 뇌 성장에는 다양한 요인들이 작용한다"며 "단백질 섭취가 뇌 성장에 영향을 미치지 않는다는 결론은 너무 성급한 결론"이라고 말했다. Cuff added, "Many factors are at play in primate brain growth," and said, "The conclusion that protein intake does not affect brain growth is too hasty." 이번 연구는 학술지 네이처에 지난달 29일 발표됐다. This study was published in the journal Nature on the 29th of last month.

Around 400,000 years ago, the human ancestor known as Lucy from Africa had a brain weighing just 300 grams, similar to a modern-day chimpanzee. However, about 30,000 years later, the modern human brain (Homo sapiens) had grown to weigh a massive 1,500 grams. To support the activity of such a large brain, considerable energy was required.

Additionally, human brains, despite making up only 2% of our body weight, consume 20% of our total energy intake, even more for growing children. Traditionally, the academic community attributed brain capacity growth to the consumption of meat (protein and fat) and the discovery of cooking. However, this explanation has its flaws, as the brain primarily uses sugar, not protein, for energy.

An international team of researchers from the University of Sydney in Australia and the University of Glasgow in the UK published a study in the journal Science, suggesting that sugars from fruits, honey, and starch may have played a more significant role in human brain evolution than previously thought. Their analysis of human nutritional and metabolic models showed that over half of the total energy required by the human body came from carbohydrates, with the majority coming from fruits and honey during the early stages of human evolution, and starch later on.

Today, our craving for sweet foods can be traced back to this evolutionary history. A 2017 study by researchers at New York University sparked interest after discovering that fruit-eating primates have larger brains on average than leaf-eating primates and even larger brains than omnivorous primates that eat meat. Dr. Jennifer Brandel-Miller, the lead author of the current study from the University of Sydney, nutrition department, said she was inspired by the research, likening it to turning on a light bulb in her mind.

She pointed out that converting protein to sugar in our bodies is not only energy inefficient but also insufficient to meet the high demand for sugar during pregnancy and lactation. The researchers divided the 4 million-year evolution of our ancestors into six stages and created models of their hominin diets based on fossil records.

They calculated the total sugar needs of key organs and tissues, as well as the additional sugar requirements during pregnancy and lactation. Their findings suggest that early humans primarily obtained sugar from fruits and honey in the African tropical rainforest, with natural sugars accounting for over two-thirds of their total energy intake.

The discovery of fire around 100,000 years ago allowed humans to cook roots and grains, providing a secondary burst of energy to further drive brain growth. However, as humans migrated to cooler, drier regions after leaving Africa, carbohydrate intake became insufficient, leading to selective evolution of genes that help better absorb sugars.

For example, humans have up to 20 amylase genes involved in starch digestion, compared to just one in chimpanzees. The researchers point out that these genes that raise blood sugar levels may also contribute to modern-day conditions like type 2 diabetes and cardiovascular diseases. However, this study is not without its limitations, as it is based on assumptions and not definitive evidence.

Critics, such as Dr. Matthew Spornheimer from Colorado State University, argue that the study presents a valuable analysis based on unverified assumptions. They note that while the role of diet in human evolution is speculative, objective evidence like eye color, tooth shape, and isotopic ratios suggest that early humans primarily consumed fruits for sugar.

The researchers acknowledge that while our ancestors likely had a diet rich in fruits, the exact nature of their diet remains uncertain.