腸の健康と人工甘味料
Hello everyone, welcome to SCIENSPOT. SCIENSPOT is a podcast that shines the spotlight on the
latest scientific technology from Japan. Your host is REN from SCIEN-TALK.
Today I want to talk about artificial sweeteners. Have you ever heard of conditions like
Irritable Bowel Syndrome and Inflammatory Bowel Disease?
There are gut disorders characterized by painful symptoms like abdominal pain and bloating.
For people living with these conditions, diet plays a crucial role. A dietary approach
called the low FODMAP diet has gained attention because it limits certain types of carbohydrates
that can worsen symptoms. FODMAP is an acronym for fermentable oleosaccharides, disaccharides,
monosaccharides, and polyols. These are carbohydrates that are poorly absorbed in the
small intestine, reaching the large intestine, where they are fermented by gut bacteria,
potentially causing gas and abdominal pain. Among the FODMAPs, we want to focus particularly
on polyols, which are known as sugar alcohols. This group includes the barely familiar name
sorbitol. Sorbitol is widely used as a low-calorie sweetener in many products like candies and soft
drinks. Interestingly, reports have shown that in patients, particularly during the active
disease period, sorbitol concentrations in these tools are higher compared to healthy individuals
or those in remission. This has long suggested a connection between sorbitol and gut inflammation.
ソルビトールと大腸炎の関係
However, what wasn't clear until now was whether sorbitol directly induced gut inflammation
and how gut bacteria and immune cells might be involved in this process.
From Kitazawa University and Keio University in Japan has shed light on this mystery.
In this research, the scientists first investigated how sorbitol affects the
colitis using mice. They fed mice sorbitol for two weeks and then induced colitis.
The results were significant. Mice that consumed sorbitol showed greater weight loss,
increased inflammatory markers in their faces, and more severe tissue damage in their large
intestines compared to control mice. This confirmed that sorbitol indeed worsened colitis.
So why does sorbitol make colitis worse? The research team further examined the
cellular changes in the mice's large intestines. They found that sorbitol intake promoted the
production of inflammatory cytokines called IL-1 beta and also increased the number of
inflammatory immune cells known as M1-type macrophages. Let's use an analogy here.
Think of our body's immune system as a defense force. Among these cells, macrophages are like
the body's cleanup crew or scavengers. They have two main forms, M1 and M2.
M1-type macrophages are like the attack squad. They fight off bacteria and viruses that cause
inflammation. On the other hand, M2-type macrophages are more like the recovery team,
サルビトールと炎症の関係
suppressing inflammation and helping tissue repair. This study found that sorbitol increased
disease among attack squad macrophages and also intensified the call to arms signal IL-1 beta.
The crucial role of M1 macrophages and IL-1 beta in worsening inflammation was further
supported by experiments using mice that lacked IL-1 beta. In these IL-1 beta deficient mice,
colitis did not worsen and their survival rate improved even with sorbitol intake.
This is like saying that even if the attack squad grows in number,
without the call to arms signal, inflammation is less likely to escalate.
Furthermore, it became clear that gut bacteria are deeply involved in this inflammatory mechanism.
When antibiotics were given to mice to eliminate the gut bacteria,
the increase in M1 macrophages due to sorbitol intake was suppressed.
This indicates that the presence of gut bacteria is essential for sorbitol to exert
its harmful effects. Then, a specific type of gut bacteria came into focus,
the Prevoteraceae family bacteria. In mice that consumed sorbitol, the proportion of these
bacteria significantly increased and their abundance showed a strong positive correlation
with the proportion of M1 macrophages. What's even more surprising is that
this type of bacteria were confirmed to grow by utilizing sorbitol as a nutrient.
It's almost as if sorbitol acts as a special fertilizer for these specific bacteria,
ソルビトールの影響
promoting their growth. And the final piece of this research puzzle is in a substance called
tryptamine. In the feces of sorbitol-fed mice, tryptamine concentrations were significantly
elevated. And when tryptamine was added to culture macrophages, it promoted their
differentiation into M1 type macrophages and also enhanced IL-1 beta expression.
So the chain of inflammation revealed in this study is as follows. Firstly, ingestion of
artificial sweeteners, sorbitol, and then an increase in the Prevoteraceae bacteria in the gut
and proliferating these bacteria produced large amounts of tryptamine.
And next, tryptamine activates the immune cell's attack squad. This is the M1 type macrophages and
issues the call to arm. And finally, resulting in exacerbated gut inflammation.
This research has indeed identified a new inflammatory pathway where gut bacteria,
their metabolites, and immune cells work in concert to trigger gut inflammation.
This study demonstrated that a common artificial sweetener, especially sorbitol,
can influence gut inflammation and worse condition by interacting with our gut environment.
This suggests that certain FODMAPs may contribute to the propagation of colitis.
And at the same time, it further strengthens a scientific basis for the low FODMAP diet
as an effective nutritional intervention for some patients.
Of course, not all components within the FODMAPs are detrimental. Some like soluble dietary fiber
can be beneficial for maintaining the gut microbiome diversity and function, so a balanced diet is crucial.
Moving forward, by precisely analyzing how each FODMAP component affects the gut microbiome
and has immunity, we can look forward to the development of precision nutrition
tailored to each individual's patient's condition and gut environment.
That's all for today's SciencePod. This podcast is broadcasted every weekday morning
in both Japanese and English. I'd love for you to listen to the podcast and post your thoughts
with the hashtag SciencePod. Thank you for listening and see you next time.
