Sugar in the gut and body is introduced to infants in mothers' breast milk and formula, and from there it seems like we humans have a love/hate relationship with it. The taste of sweetness is compelling, and is hardwired into our genes.
Interestingly, studies show that mice and humans prefer real sugar over artificial ones. How does this happen?
You may remember learning that sweet receptors are found in the front of
the tongue. Forget that, please. While some parts of the tongue are
more sensitive to certain tastes than others, sweet receptors are, in
fact, spread out across all taste areas in the mouth.
Losing your sense of taste should then reduce your desire for sweets, right? Wrong. You may be surprised to learn that not only do we have sweet taste receptors, T1R receptors, that function as carbohydrate sensors in taste buds, but they have also been found in various mammals in surprising places such as the nasal passage, gut, pancreas, brain, liver, kidney, testes, bladder, and adipose (fat) tissue.
The sweet taste receptors are heavily involved in nutrient sensing, monitoring changes in energy stores, and triggering metabolic and behavioral responses to maintain energy balance. As such, T1R receptor cells are involved in detecting sweetness and stimulating sensory cells, and their main neurotransmitter to do this is ATP. (Yes, it’s the same ATP that is involved in energy production.)
Aside from the local effects of sugar in the gut that are discussed in this article, I would be remiss if I did not mention the role of other senses and the brain in your desire for sweets. It is known that taste is only one of several sensations that affect our perception as to whether a food or drink is desirable or undesirable.
Taste falls in the category of the gustatory system, the system responsible for taste and flavor. The gustatory system works in concert with the somatosensory system and olfactory systems, which detect the odors, textures, and temperatures of foods. We know that smelling freshly baked chocolate chip cookies, for example, can make us want them. If we expect a warm, chewy cookie and instead feel a cold, mushy cookie, our desire may weaken.
You also have monitors in your body that detect the internal state of affairs, such as fullness and blood glucose levels, that may alter the results from the gustatory, somatosensory, and olfactory systems.
Additionally, your brain plays an important role in your desire for sweets. It has multiple areas that are involved in reinforcement learning and the development of automatic behaviors found in formations of habits, compulsions, and addictions. Importantly for this article, one of those areas is called the striatum.
The substance we commonly call "sugar" is a two-part molecule composed of the simple sugars glucose and fructose. Although we sense sweetness in the mouth, we tell the difference between sugar and artificial sweeteners in the gut. The sensors for sugar are concentrated in the duodenum, the first part of the small intestine attached to the stomach. It is in this area that the post-consumption rewarding effects of glucose happen. Fructose, on the other hand, passes through the intestinal wall rather uneventfully.
In the past, scientists figured if they silenced the sweet taste receptors in mice that the mice would not be able to detect sugar. They were wrong. A fascinating study published January, 2022 shows that T1R sweet taste receptors are not the only drivers of the desire for sugar in mice and humans. Your gut detects sugar and it does so very specifically without the use of taste receptors.
Some enteroendocrine cells (entero, meaning intestines; endocrine, meaning hormone-releasing) are known to release the hormone CCK, which is involved with satiety, digestion, and gallbladder contractions, among other things. What was surprising to learn was that these CCK-releasing cells were able to form synapses with underlying mucosal nerves, including the vagus nerve. They were labeled CCK neuropods. Not only did they release hormones, but they also acted as neurons!
What also was surprising is that sweet taste receptors in the gut were not involved in transmitting data about sugar in the gut of mice to the brain, which is the opposite of what happens in the mouth. Additionally, not all neuropod cells were able to respond to sugar. Instead, the CCK neuropods sensed the sugar and used glutamate to transduce a glucose stimulus from the gut to the brain via the vagus nerve. This happened in thousandths of a second!
The moral of the story of sugar in the gut is that oral sweet taste is not essential to make us want sugar. You don’t have to taste sugar to want it. We are hardwired through our genes to detect sugar via taste receptors throughout the body, and this new study showed that specialized small intestinal neuropod cells are involved, also.
Also, our brain biochemistry can make us want sugar. The neurotransmitter dopamine is involved in reward and motivation. Sugar ingestion is known to be associated with significant dopamine releases in the dorsal striatum of the brain, one of the main areas known to influence habits, compulsions, and addictions.
We also know that sugar in the gut can influence dysbiosis by allowing pathogenic or opportunistic microbes to become major influencers in the gut. Many pathogenic microbes can utilize the simple sugars to outcompete the beneficial microbes in your gut causing inflammation and other undesirable consequences.
We also now know that neuropod cells are scattered throughout the small intestine, and once they have the stimulus of sugar imprinted on them, they, along with our gustatory, somatosensory, and olfactory systems, neurotransmitter status, genes and receptors, and internal monitors, guide our food and drink choices.
Avoiding all sugar is not possible if you eat a balanced diet, however, as even the least sweet vegetables like broccoli have some sugars in them. Additionally, your liver and kidneys can create glucose when it is needed since glucose is a main fuel for generating energy in the body.
What can you do then to resist the craving for sugar? It is NOT hopeless. You have to work on all the aspects involved, from balancing neurotransmitter chemistry in the brain as well as the gut, to changing behavioral clues, to avoiding the smell and feel of sugary goods, to making sure you aren't hungry when you are around sweets, to not reinforcing the neuronal signals from sugar in the gut or mouth by eating it.
Gut health and its microbiome are known to play roles in neuron
transmissions, inflammation, and satiety, so balancing your gut is critical. Beneficial microbes such as probiotics can digest sugars and other carbohydrates, including complex sugars in plant foods, that may ultimately be fermented and converted into helpful lactic acid and short-chain fatty acids. Simple sugar in the gut like sucrose, however, can upset the ecological balance in your gastrointestinal tract.
You may think that artificial sweeteners such as saccharin, acesulfame K, and sucralose are the answers to your cravings. No, they are not because they come with their own sets of disadvantages that I address in one of my books.
The goal is to decrease the traffic on the superhighway of expectations and reward signals that come from consuming sugar, and to do that, you have to decrease/eliminate sugar. It gets easier over time, especially if you have worked on all the aspects of sugar craving.
Should you want help with taming the sugar beast and supporting your body from the damages sugar causes, please consider nutritional consultations with me.
Main reference: https://www.nature.com/articles/s41593-021-00982-7
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