NAD+ and Gut Health: How NMN Reshapes Your Microbiome (2026)

For years, NAD+ research focused on what happens after the molecule enters your bloodstream: sirtuin activation, DNA repair, mitochondrial function. The gut was treated as a transit point – a tube NMN passed through on its way to "real" tissues.

That changed in 2026, when researchers at Nestl Research published a study in Nature Metabolism revealing that oral NAD+ precursors don't just pass through the gut. They are metabolized by gut bacteria, and in turn, they reshape the microbial ecosystem itself.

The finding creates an entirely new dimension of NAD+ biology. Your gut microbiome isn't a bystander in NAD+ supplementation – it's an active participant, and it changes in response to what you feed it.

This guide covers the science: how NMN is processed in the gut, which bacterial species respond, what happens to microbial NAD+ metabolism as you age, and what this means for anyone supplementing with NAD+ precursors.

TL;DR

• A 2026 Nestl Research study (Nature Metabolism) showed that oral NMN is partially converted to nicotinic acid (NA) by gut bacteria before absorption
• This gut-mediated pathway (the Preiss-Handler pathway) may account for a significant portion of NMN's NAD+-boosting effects
• NAD+ precursors promote the growth of beneficial bacteria including Akkermansia muciniphila and Lactobacillus species
• The gut microbiome's own NAD+ metabolism declines with age – mirroring the systemic NAD+ decline seen in human tissues
• Gut dysbiosis may reduce NMN efficacy by impairing the bacterial deamidation step that converts NMN to NA
• Supporting gut health through fiber, fermented foods, and avoiding unnecessary antibiotics may enhance NMN supplementation outcomes

The Discovery: NMN Doesn't Go Where You Think It Goes

For most of the last decade, the dominant model of NMN absorption went like this: you swallow NMN, it enters intestinal epithelial cells via the SLC12A8 transporter (identified by Grozio et al. in 2019, Nature Metabolism), gets converted to NAD+ inside those cells by NMNAT enzymes, and then NAD+ or its metabolites enter the bloodstream.

Clean and simple. Also incomplete.

In 2026, Cuenoud et al. published a study comparing three NAD+ precursors – NMN (nicotinamide mononucleotide – the direct precursor your body converts into NAD+), NR (nicotinamide riboside – another NAD+ precursor), and niacin – using isotope tracing in both mice and human subjects. The key revelation: a substantial fraction of orally administered NMN is first deamidated by gut bacteria into nicotinic acid (NA), which then enters the liver via the Preiss-Handler pathway to produce NAD+.

In other words, your gut bacteria are doing chemistry on NMN before your body even absorbs it. The molecule that enters your intestines is not necessarily the molecule that enters your bloodstream.

This wasn't a minor pathway. The Preiss-Handler route – previously considered a backup NAD+ synthesis mechanism – appears to be a primary route for orally consumed NMN, at least in the liver. The liver, in turn, is the central hub for systemic NAD+ distribution.

Watch: Huberman explains how the gut microbiome influences brain health, immune function, and overall longevity:

How Gut Bacteria Process NMN

The bacterial conversion of NMN follows a specific enzymatic cascade:

Step 1: Dephosphorylation. Gut bacteria express phosphatases that strip the phosphate group from NMN, converting it to nicotinamide riboside (NR). Multiple bacterial species carry these enzymes, making this step relatively robust.

Step 2: Cleavage to nicotinamide. Bacterial enzymes called purine nucleoside phosphorylases (PNPs) cleave the ribose sugar from NR, producing free nicotinamide (NAM). This step occurs rapidly in the gut lumen.

Step 3: Deamidation to nicotinic acid. This is the critical step. Bacterial nicotinamidases (encoded by the pncA gene in many species) convert NAM to nicotinic acid (NA). This enzyme is abundant in gut bacteria but absent in mammalian cells – meaning this deamidation step is entirely microbiome-dependent.

Step 4: Absorption and hepatic NAD+ synthesis. Nicotinic acid is absorbed in the intestine, travels to the liver via the portal vein, and enters the Preiss-Handler pathway: NA is converted to nicotinic acid mononucleotide (NAMN) by NAPRT, then to nicotinic acid adenine dinucleotide (NAAD) by NMNAT, and finally to NAD+ by NAD+ synthase (NADS).

The efficiency of this entire pathway depends on your gut bacteria's ability to perform Step 3. If your microbiome lacks sufficient nicotinamidase activity – due to dysbiosis, antibiotic use, or age-related microbial shifts – the conversion efficiency drops.

Key Takeaway: The 2025 Cuenoud et al. study in Nature Metabolism revealed that a significant portion of oral NMN is converted by gut bacteria into nicotinic acid, which then enters the Preiss-Handler pathway to produce NAD+ in the liver. This means your gut microbiome directly affects how efficiently NMN works — gut health and NAD+ supplementation are more interconnected than previously understood.

NAD+ Precursors Reshape the Microbiome

The relationship between NAD+ and gut bacteria isn't one-directional. NAD+ precursors don't just get metabolized by bacteria – they actively alter microbial composition.

Akkermansia muciniphila Expansion

Multiple preclinical studies have demonstrated that NAD+ precursor supplementation increases the abundance of Akkermansia muciniphila, a mucin-degrading bacterium associated with:

• Improved gut barrier integrity
• Better glucose metabolism
• Reduced inflammation
• Lower body fat in overweight individuals

A 2019 study in Nature Medicine (Depommier et al.) showed that Akkermansia supplementation itself improved metabolic markers in overweight humans – it's one of the most therapeutically promising commensal bacteria identified to date.

The mechanism linking NAD+ precursors to Akkermansia expansion likely involves nicotinamide's role as a bacterial growth substrate. Akkermansia species encode nicotinamidase genes, meaning they can directly metabolize NAM as a nutrient source. When you supplement with NMN, some of the NAM generated during bacterial metabolism feeds Akkermansia growth.

Lactobacillus and Bifidobacterium Effects

Animal studies supplementing with NR (a closely related NAD+ precursor) have shown increases in Lactobacillus and Bifidobacterium species – both associated with improved gut health, immune modulation, and reduced intestinal permeability.

A 2022 study in Cell Reports (Ear et al.) found that NR supplementation in mice on a high-fat diet partially reversed the microbiome shifts caused by the diet, restoring microbial diversity toward the composition seen in lean, healthy controls.

Reduced Pathobiont Abundance

The same studies showed decreases in potentially harmful bacteria, including certain Proteobacteria species associated with gut inflammation. The proposed mechanism: NAD+ precursors shift the metabolic environment of the gut in ways that favor saccharolytic (fiber-fermenting) bacteria over proteolytic (protein-fermenting) species that produce inflammatory metabolites.

Key Takeaway: NAD+ precursors do not just pass through the gut — they reshape it. NMN supplementation has been shown to alter gut microbial composition, increasing beneficial species and SCFA production. This creates a positive feedback loop: NMN improves gut health, and improved gut health enhances NMN metabolism. Supporting gut health may amplify the benefits of your NAD+ supplementation.

The Aging Gut: Where NAD+ Decline Meets Microbiome Decline

Here's where the story gets particularly relevant for longevity. Two parallel declines happen as you age:

1. Systemic NAD+ levels drop – substantially in key tissues during middle age (Camacho-Pereira et al., 2016, Cell Metabolism).

2. Gut microbial diversity decreases – with loss of beneficial species and expansion of inflammatory taxa. A 2021 study in Nature Aging (Wilmanski et al.) showed that microbial uniqueness increases with age in healthy individuals but collapses toward a shared, less diverse profile in those with declining health.

These two declines are not independent. They interact in a vicious cycle:

Lower NAD+ reduces gut barrier integrity. NAD+-dependent sirtuins (a family of seven NAD+-dependent enzymes that regulate aging and cellular repair), particularly SIRT1 (the most-studied sirtuin – regulates DNA repair, metabolism, and stress response) and SIRT3, maintain intestinal epithelial cell function. When NAD+ declines, sirtuin activity drops, tight junction proteins are downregulated, and intestinal permeability increases – "leaky gut" in common parlance.

Leaky gut increases systemic inflammation. Bacterial endotoxins (lipopolysaccharides) that cross the compromised gut barrier trigger immune activation. This drives the chronic low-grade inflammation ("inflammaging") that characterizes aging.

Inflammation increases CD38 expression. CD38 (an enzyme that consumes NAD+ – its activity increases with age) – the enzyme most responsible for consuming NAD+ in aging tissues – is upregulated by inflammatory signals. More inflammation means more CD38 activity, which means less NAD+.

Less NAD+ further damages the gut barrier. And the cycle repeats.

NAD+ precursor supplementation may interrupt this cycle at multiple points: by restoring sirtuin activity in gut epithelial cells, by promoting beneficial bacterial growth, and by reducing the inflammatory signaling that drives CD38 expression.

The Bacterial NAD+ Metabolome

Bacteria don't just process your NAD+ precursors. They have their own NAD+ metabolism, and it matters for your health.

Gut bacteria use NAD+ for the same fundamental reasons your cells do: electron transfer in energy metabolism, enzymatic reactions, and signaling. Bacterial NAD+ biosynthesis pathways include:

• De novo synthesis from tryptophan or aspartate
• Salvage pathways using nicotinamide or nicotinic acid
• The Preiss-Handler pathway from nicotinic acid

When you supplement with NMN, you're essentially providing your gut bacteria with a rich source of NAD+ precursor material. The bacteria that can most efficiently metabolize this resource gain a competitive advantage – which is likely why beneficial species with robust NAD+ salvage pathway enzymes (like Akkermansia) expand in response to supplementation.

This has an important implication: your gut microbiome composition may influence how well NMN supplementation works for you. A microbiome rich in nicotinamidase-expressing species will more efficiently convert NMN-derived NAM to nicotinic acid, enhancing the Preiss-Handler contribution to systemic NAD+ levels. A depleted microbiome may leave more of this conversion potential on the table.

What Impairs the Gut-NAD+ Axis

Several common factors can disrupt the microbiome's role in NAD+ metabolism:

Antibiotics

Broad-spectrum antibiotics don't distinguish between harmful and beneficial bacteria. A single course of antibiotics can reduce microbial diversity for months, potentially impairing the bacterial deamidation step that converts NAM to nicotinic acid.

A 2018 study in Nature Microbiology (Palleja et al.) tracked gut microbiome recovery after a single 4-day antibiotic course and found that while most species recovered within 6 months, some beneficial species hadn't returned even at the 6-month mark.

If you're supplementing with NMN after recent antibiotic use, the gut-mediated pathway may be temporarily impaired. This doesn't mean NMN won't work – the direct SLC12A8 transporter pathway still functions – but the Preiss-Handler contribution may be reduced.

Low-Fiber Diets

Fiber is the primary fuel source for saccharolytic gut bacteria. Diets low in diverse plant fibers starve beneficial bacteria, reducing both their abundance and metabolic activity. Since many of the bacteria responsible for NMN processing are fiber-fermenting species, a low-fiber diet may indirectly reduce NMN's gut-mediated efficacy.

Chronic Stress

The gut-brain axis runs bidirectionally. Chronic psychological stress alters gut microbial composition through cortisol-mediated changes in gut motility, immune function, and mucus production. A 2019 review in Frontiers in Psychiatry documented consistent microbiome disruption across multiple stress models.

Excessive Alcohol

Alcohol disrupts the gut barrier and shifts microbial composition toward dysbiotic profiles. Even moderate chronic alcohol intake has been associated with reduced Akkermansia abundance and increased intestinal permeability.

Watch: Sonnenburg and Huberman dive deep into the gut microbiome, fermented foods, and how to support microbial diversity:

Key Takeaway: NAD+ decline and microbiome decline accelerate together after age 40 — and they worsen each other. Lower NAD+ impairs intestinal stem cell renewal and gut barrier integrity. A degraded gut barrier increases inflammation, which upregulates CD38 and destroys more NAD+. Breaking this vicious cycle requires addressing both sides simultaneously.

Practical Implications: Optimizing the Gut-NAD+ Connection

Based on the current evidence, here's how to maximize the gut-microbiome component of NAD+ supplementation:

1. Take NMN Orally, Not Sublingually

Some NMN products market sublingual (under-the-tongue) delivery as superior because it "bypasses the gut." In light of the Cuenoud et al. findings, bypassing the gut may actually reduce total NAD+ elevation by skipping the Preiss-Handler pathway. Oral swallowed delivery allows both the direct SLC12A8 pathway and the gut-bacterial pathway to contribute.

2. Support Microbial Diversity

• Eat 30+ different plant foods per week. The American Gut Project found this to be the strongest dietary predictor of microbial diversity.
• Include fermented foods daily. A 2021 Stanford study (Wastyk et al., Cell) showed that 10 weeks of high-fermented-food intake increased microbial diversity and reduced inflammatory markers – more effectively than a high-fiber diet alone.
• Prebiotic fibers matter. Foods rich in inulin (garlic, onions, leeks), resistant starch (cooked and cooled potatoes, green bananas), and pectin (apples, citrus) specifically feed beneficial bacterial populations.

3. Avoid Unnecessary Microbiome Disruption

• Use antibiotics only when medically necessary
• Limit processed food (emulsifiers like polysorbate-80 and carboxymethylcellulose have been shown to disrupt the mucus layer and microbial composition)
• Moderate alcohol intake

4. Consider the Timing

NMN's gut-bacterial processing likely varies with the diurnal rhythm of microbial activity. Gut bacteria show circadian patterns in composition and metabolic output. Taking NMN with your first meal – when gut motility and bacterial metabolic activity are ramping up – aligns with both the circadian NAD+ rhythm and gut microbial activity cycles.

5. Track Gut Health Biomarkers

If you're serious about optimizing this axis, periodic gut microbiome testing can provide useful data points. Look for:

• Microbial diversity scores – higher is generally better
• Akkermansia muciniphila abundance – one of the key responders to NAD+ precursor supplementation
• SCFA (short-chain fatty acids – beneficial compounds produced by gut bacteria) production – markers of healthy bacterial fermentation
• Calprotectin levels – a marker of intestinal inflammation

The Short-Chain Fatty Acid Connection

There's another dimension to the gut-NAD+ relationship: short-chain fatty acids (SCFAs). Gut bacteria produce SCFAs – primarily butyrate, propionate, and acetate – by fermenting dietary fiber. These metabolites have direct relevance to NAD+ biology:

Butyrate activates SIRT1. Butyrate, produced by Faecalibacterium prausnitzii and other colonic bacteria, inhibits histone deacetylases (HDACs) and activates SIRT1 in intestinal epithelial cells. Since SIRT1 is NAD+-dependent, butyrate-mediated SIRT1 activation effectively increases NAD+ demand while supporting the sirtuin activity that maintains gut barrier function.

SCFAs reduce intestinal inflammation. Butyrate is the preferred energy source for colonocytes (colon epithelial cells). Adequate butyrate production maintains the integrity of the colonic lining, reduces NF-κB activation in intestinal immune cells, and supports the anti-inflammatory environment that keeps CD38 expression in check.

Propionate improves systemic metabolic health. Chambers et al. (2015, Gut) showed that colonic propionate delivery reduced visceral fat accumulation and improved insulin sensitivity in overweight adults – metabolic effects that parallel those seen with improved NAD+ status.

The practical implication: a fiber-rich diet that promotes SCFA production doesn't just support gut health directly – it supports the gut-barrier integrity and anti-inflammatory environment that protects systemic NAD+ levels from CD38-mediated degradation.

This creates a virtuous cycle: dietary fiber feeds SCFA-producing bacteria, SCFAs maintain gut barrier integrity and reduce inflammation, lower inflammation preserves NAD+ levels, and adequate NAD+ supports the sirtuin activity that maintains epithelial function. NMN supplementation adds exogenous NAD+ precursor substrate to this cycle, amplifying its benefits.

What We Don't Know Yet

Scientific honesty requires acknowledging the gaps:

Human data is limited. The Cuenoud et al. study confirmed the gut-bacterial processing of NMN in humans, but the microbiome-reshaping effects of NMN have primarily been demonstrated in animal models. Large-scale human trials measuring microbial composition changes during NMN supplementation are still needed.

Individual variation is huge. The composition of your gut microbiome is as unique as your fingerprint. Two people taking the same NMN dose may have very different gut-bacterial processing efficiencies. We don't yet have practical tools to predict individual responses.

Causation vs. correlation. While NMN supplementation is associated with beneficial microbial shifts in animal models, it's not yet clear whether the microbial changes are directly caused by NMN metabolites, or indirectly caused by NMN's systemic effects on host metabolism and immune function.

Dose-response in the gut. The optimal NMN dose for systemic NAD+ elevation (600mg/day per Yi et al. 2023) was established without considering gut microbial effects. It's possible that different doses optimize for systemic vs. gut-microbiome outcomes.

The Bigger Picture: NAD+ as a Gut-Systemic Integrator

The emerging picture positions NAD+ metabolism as a key integrator between gut health and systemic aging. NAD+ precursors entering the gut influence bacterial ecology; those bacteria process precursors into forms the body can use; the resulting NAD+ supports intestinal barrier function; and the barrier integrity, in turn, modulates the systemic inflammation that drives NAD+ decline.

This is not a linear pathway. It's a feedback loop – and it means that approaches to NAD+ supplementation should consider gut health as a fundamental variable, not a secondary concern.

For anyone taking NMN to support NAD+ levels, the practical implication is clear: your gut microbiome is part of the delivery system. Treat it accordingly.

References:

1. Cuenoud B, et al. (2026). The differential impact of three different NAD+ boosters on circulatory NAD and microbial metabolism in humans. Nature Metabolism, 8(1), 62-73.
2. Grozio A, et al. (2019). Slc12a8 is a nicotinamide mononucleotide transporter. Nature Metabolism, 1, 47-57.
3. Depommier C, et al. (2019). Supplementation with Akkermansia muciniphila in overweight and obese human volunteers. Nature Medicine, 25(7), 1096-1103.
4. Chini CCS, et al. (2020). CD38 ecto-enzyme in immune cells is induced during aging and regulates NAD+ and NMN levels. Nature Metabolism, 2(11), 1284-1304.
5. Wilmanski T, et al. (2021). Gut microbiome pattern reflects healthy ageing and predicts survival in humans. Nature Aging, 1, 274-283.
6. Wastyk HC, et al. (2021). Gut-microbiota-targeted diets modulate human immune status. Cell, 184(16), 4137-4153.
7. Palleja A, et al. (2018). Recovery of gut microbiota of healthy adults following antibiotic exposure. Nature Microbiology, 3(11), 1255-1265.
8. Yi L, et al. (2023). The efficacy and safety of NMN supplementation in healthy middle-aged adults. GeroScience, 45(1), 29-43.

Frequently Asked Questions

Q: Does NMN improve gut health?

Preclinical evidence suggests NMN supplementation promotes beneficial gut bacteria, including Akkermansia muciniphila and Lactobacillus species, while reducing potentially inflammatory taxa. However, human clinical trials specifically measuring NMN's effects on gut microbiome composition have not yet been published. The mechanistic rationale is strong – NAD+-dependent sirtuins maintain gut barrier integrity – but direct human evidence is still accumulating.

Q: How does NMN get absorbed in the gut?

NMN uses two parallel absorption pathways. First, it can enter intestinal cells directly via the SLC12A8 transporter and be converted to NAD+ intracellularly. Second, gut bacteria can process NMN through a series of enzymatic steps, ultimately producing nicotinic acid, which is absorbed and converted to NAD+ in the liver via the Preiss-Handler pathway. Both pathways contribute to the total NAD+ elevation from oral NMN supplementation.

Q: Should I take probiotics with NMN?

There is no direct clinical evidence that adding probiotics enhances NMN's efficacy. However, maintaining a diverse, healthy gut microbiome – through diet, fermented foods, and prebiotic fiber – supports the bacterial enzymes (particularly nicotinamidases) that process NMN in the gut. If your microbiome is compromised (e.g., after antibiotic use), supporting microbial recovery makes biological sense.

Q: Does gut health affect NAD+ levels?

Yes. Gut dysbiosis increases intestinal permeability, which allows bacterial endotoxins into the bloodstream. This triggers systemic inflammation, which upregulates CD38 – the primary NAD+-consuming enzyme in aging tissues. A compromised gut can therefore accelerate NAD+ decline independently of age. Conversely, a healthy gut barrier helps maintain the low-inflammation state that preserves NAD+ levels.

Q: Is sublingual NMN better than oral NMN?

Based on the 2026 Cuenoud et al. study showing that gut bacteria play an active role in converting NMN to nicotinic acid (which then produces NAD+ via the Preiss-Handler pathway), sublingual delivery may actually reduce total NAD+ production by bypassing this gut-mediated pathway. Oral swallowed delivery allows both the direct intestinal absorption pathway and the bacterial conversion pathway to contribute.

Related Reading

• What Is NMN? The Complete Guide to Nicotinamide Mononucleotide
• NAD+ Decline by Age: The Complete Decade-by-Decade Timeline
• Gut Microbiome and Longevity: What Your Bacteria Have to Do With Aging
• NAD+ Precursors Compared: NMN vs NR vs Niacin vs Tryptophan
• Berberine and Longevity: The Nature's Metformin Claim, Examined
• NMN vs NR: Which NAD+ Precursor Should You Take?

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