Our Insatiable Appetite for Sugar
Sugar has been one of the most impactful drivers of societal inequality and medical challenges in the modern world. Sugar (originally from sugar-cane) was first produced in New Guinea some 10,000 years ago, and brought to Europe as crystalized “honey powder” from the Indian Territories by the armies of Alexander the Great. By the late 19th century, millions of Africans had been enslaved and shipped across the Atlantic to farm sugar-cane.
In 1800 the average American consumed approximately 7 pounds of sugar a year. Today, the average American consumes well over 100 pounds of added sugar annually, and accordingly the world has experienced catastrophic increases in obesity, metabolic syndrome and diabetes.
Our craving for sugar is rooted in brain circuits dedicated to reward the recognition of high energy food sources -a mechanism essential for animals in the wild, and most certainly critical in our own evolutionary trajectory, but terribly misused and abused by humans today -in essence by hijacking this pathway for our own pursuit of pleasure (17).
Recently, we have shown that sugar acts in the gut to activate a neural circuit that communicates to the brain the presence of sugar (18). Importantly, this gut-to-brain communication axis is activated by sugar but not artificial sweeteners, and functions as the principal conduit driving preference for sugar. Indeed, we engineered animals where synaptic activity in this gut-to-brain circuit was genetically silenced, and prevented the development of behavioural preference for sugar. Furthermore, we showed that hijacking this circuit by chemogenetic activation can create preferences to novel stimuli.
Together, these findings revealed a gut-to-brain post-ingestive sugar-sensing pathway critical for the development of sugar preference. In addition, they explain the neural basis for the differences in the effects of sweeteners versus sugar (i.e. why they have failed to substitute for sugar’s behavioral effects), since unlike sugar, they do not activate this preference circuit.