From: hubermanlab
Understanding the biological underpinnings of sugar craving involves delving into the concepts of “liking” versus “wanting”. These phenomena, while often related in human experience, are distinct processes mediated by separate mechanisms in the brain and the body.
The Role of Taste in Sugar Liking
The taste system is responsible for the immediate perception of sweetness and other flavors. This system is well designed to detect the basic taste qualities: sweetness, sourness, bitterness, saltiness, and umami ([00:11:06]).
Sweet receptors are located throughout the oral cavity, primarily on the tongue. When these receptors detect sugar, an appetitive response is triggered, which is described as “liking”. This is an innate and hardwired response (Sugar sensing and the gut-brain axis) ([00:26:04]).
Wanting: The Gut-Brain Axis of Sugar Craving
The concept of “wanting” is primarily mediated by the Gut-brain axis rather than taste alone. This axis comprises a communication pathway where the gut informs the brain about the satisfaction of nutritional needs. This process happens below the level of conscious detection and involves a different set of biological responses than liking ([01:19:02]).
Post-Ingestive Effects
When sugar is ingested, its recognition doesn’t stop at the taste receptors. The gut contains special sensors that detect the presence of glucose and other sugars, which then send signals to the brain via the vagal nerve—a crucial component of the gut-brain axis. These signals reinforce sugar consumption behaviors by activating specific brain regions associated with reward and motivation Dopamine system and its role in reward and addiction ([01:49:01]).
Dissociation of Liking and Wanting
A pivotal discovery in distinguishing between liking and wanting comes from studies where the sugar taste receptor was knocked out in mice. Mice lacking these receptors could not taste sweetness (and therefore had no liking response to sugar), yet over a period of time, they still developed a preference for sugar solutions based on the post-ingestive rewarding effects (Mechanisms of sugar cravings) ([01:48:09]).
Implications for Artificial Sweeteners
Artificial sweeteners activate the sweet taste receptors, mimicking the liking response. However, they fail to activate the gut-brain pathways responsible for true satisfaction and the reduction of cravings. This is why artificial sweeteners might not reduce sugar cravings effectively, as they do not fulfill the wanting component mediated by the gut-brain axis ([01:53:06]).
Conclusion
The dissociation between liking and wanting in the context of sugar intake highlights the complexity of dietary behaviors and their regulation. While taste drives the initial preference (liking), the gut-brain axis fundamentally controls the craving (How the nervous system regulates sugar intake) (wanting) for sugar. Understanding these mechanisms opens potential avenues for addressing problems related to overnutrition and obesity by modulating the gut-brain signaling pathways to manage sugar cravings without relying solely on taste receptors.