Seaweed Sugars May Rewire the Gut to Fight Fatty Liver Disease

A sweeping new review argues that the ocean’s least glamorous exports—slippery polysaccharides extracted from seaweeds, sea cucumbers, and microalgae—could become powerful tools against metabolic dysfunction-associated steatotic liver disease, or MASLD, the most common chronic liver disorder worldwide. Writing in Food Science and Biotechnology, researchers Yuanjie Pan, Ruijie Zhang, and Yuping Chen synthesize a large body of evidence suggesting that marine polysaccharides act less like ordinary dietary fiber and more like precision instruments, selectively reshaping the gut microbiome in ways that ripple outward through the gut–liver axis to influence insulin resistance, dyslipidemia, adipose dysfunction, and chronic inflammation—the metabolic failures that drive MASLD.

MASLD is no longer a niche concern. It encompasses a spectrum running from simple hepatic steatosis to the inflammatory, fibrotic condition known as metabolic dysfunction-associated steatohepatitis, and it is tightly coupled to obesity and type 2 diabetes. Treatment options remain frustratingly thin. The recent approval of resmetirom, a thyroid hormone receptor-beta agonist that became the first FDA-approved medication for nonalcoholic steatohepatitis, marked a genuine milestone, but clinicians still lack cheap, safe, preventive strategies for the vast population of patients with early disease. That gap has pushed researchers toward nutraceuticals—food-derived compounds with drug-like activity—and toward the gut microbiome as a therapeutic target in its own right.

The gut–liver axis sits at the center of the new review’s argument. The liver receives the portal blood supply directly from the intestine, along with everything the gut microbes produce: short-chain fatty acids, bile acid derivatives, trimethylamine N-oxide, indole compounds, endotoxins, and ethanol made by bacteria themselves. When the microbial community falls into dysbiosis—a state that clinical studies have repeatedly linked to the severity of fatty liver disease—the balance of these metabolites tips. Barrier function in the intestine weakens, bacterial lipopolysaccharide leaks into circulation, hepatic inflammation and oxidative stress escalate, and hepatocytes accumulate fat. Some evidence even implicates high-alcohol-producing Klebsiella pneumoniae in driving fatty liver in non-drinkers, underscoring how directly microbial chemistry can become hepatic pathology.

What makes marine polysaccharides different from the plant fibers already celebrated in nutrition? The authors emphasize structural chemistry. Land-based fibers are built largely from neutral sugars, whereas marine polysaccharides—fucoidans from brown seaweeds, carrageenans from red algae, ulvans from green algae, agars and porphyrans from Porphyra, alginates from kelp, chitosan from crustacean shells, and sulfated glycans from sea cucumbers—carry sulfate groups and uronic acids, form complex glycosidic linkages, adopt diverse conformations, and span broad molecular-weight distributions. Those features mean that human enzymes cannot digest them, but specific gut bacteria can, using elaborate carbohydrate-active enzyme systems called polysaccharide utilization loci. The result is selective feeding: particular structures recruit particular microbial taxa, shifting community composition in reproducible, mechanism-linked ways.

Human populations provide a striking natural experiment. Japanese individuals harbor gut bacteria that acquired genes for digesting marine sulfated polysaccharides from marine Bacteroides via horizontal gene transfer, a discovery that revealed how the microbiome can expand its metabolic repertoire when the diet supplies novel glycans. Subsequent genomic work identified multiple independent transfer events that seeded seaweed-digestion genes into human gut bacteria. This capacity for adaptation is precisely what marine polysaccharide therapy hopes to exploit: by supplying glycans that only beneficial consumers can process, these compounds act as targeted prebiotics, enriching organisms such as Lactobacillus, Akkermansia muciniphila, and beneficial Bacteroides species while suppressing inflammatory lineages.

The downstream metabolic consequences are where the review gets technically ambitious. Fermentation of marine polysaccharides yields short-chain fatty acids—acetate, propionate, and butyrate—which nourish colonocytes, strengthen tight junctions, and engage G-protein-coupled receptors that regulate glucose homeostasis and appetite. Simultaneously, polysaccharide-driven changes in bile acid metabolism alter signaling through the nuclear receptor FXR and the membrane receptor TGR5, pathways now recognized as central to hepatic lipid handling, energy expenditure, and inflammation. At the hepatocyte level, marine polysaccharides and their oligosaccharide fragments activate AMPK and PPARα, the master switches of fatty acid oxidation, and engage the Nrf2 antioxidant program, directly countering the lipid accumulation and oxidative stress that define steatohepatitis.

Preclinical evidence illustrates the breadth of this approach. Fucoidan from Sargassum fusiforme alleviated high-fat diet-induced obesity and insulin resistance while improving the gut microbiota profile and hepatic oxidative stress. Alginate oligosaccharides relieved insulin resistance and fatty liver in mice through microbiota-mediated bile acid regulation. Iota-carrageenan tetrasaccharide reduced liver lipid accumulation via the bile acid–FXR–SHP/PXR pathway, and chitosan oligosaccharides attenuated steatosis, inflammation, and oxidative stress in diet-induced obese mice. Sea cucumber fucosylated chondroitin sulfate modified gut microbiota to prevent obesity, and oyster polysaccharide ameliorated hepatic oxidative stress through the bile acid–FXR–AMPKα axis. Porphyran from discolored nori prevented metabolic syndrome through a microbiota–bile acid–ceramide pathway, while ulvan oligosaccharides regulated lipid metabolism in high-fat diet-fed animals.

Clinical data, though still early, are encouraging. A randomized, double-blinded, placebo-controlled trial found that chitosan supplementation improved liver function, hepatic steatosis predictors, and metabolic indicators in adults with non-alcoholic fatty liver disease. Chitooligosaccharides rebalanced gut microorganisms and their metabolites in NAFLD patients, and Icelandic trial data showed that chitosan supplementation favorably altered the gut microbiota in healthy women. A fucoidan extract improved insulin resistance and cardiometabolic markers in obese, nondiabetic subjects in a randomized controlled trial, and fucoidan has also demonstrated clinical efficacy as an adjunct in Helicobacter pylori eradication, hinting at broad microbiome-modulating potential. Trials combining Laminaria japonica with probiotics improved intestinal microbiota in human volunteers, and fecal microbiota transplantation protocols now being tested in steatohepatitis underscore how central microbial manipulation has become to the field.

The review is candid about the obstacles between laboratory promise and clinical reality. Marine polysaccharides are structurally heterogeneous, and batch-to-batch variation in sulfation pattern, molecular weight, and monosaccharide composition makes standardization difficult—yet those same variables appear to determine biological activity, as shown by recent synthetic fucoidan libraries that enabled systematic structure–function comparisons. Safety questions also persist, particularly for carrageenan, a widely used food additive whose degraded forms have been associated with intestinal inflammation in some animal and human studies, even as food-grade material appears benign in others; clarifying this controversy is essential for consumer confidence. Contaminant burdens in macroalgae, including arsenic, cadmium, lead, and mercury, require careful regulatory alignment between producing and consuming regions. Dosing, bioavailability, and long-term effects remain underexplored.

Nevertheless, the authors position marine polysaccharides as uniquely advantaged relative to terrestrial fibers: their unusual chemistries reach microbial niches that common fibers cannot, and their pleiotropic effects—spanning short-chain fatty acid production, bile acid signaling, barrier protection, endocrine modulation, and direct hepatic pathway activation—map precisely onto the multi-organ pathophysiology of MASLD. As sequencing technologies make it possible to identify exactly which bacteria consume which glycans, and as controlled synthesis enables reproducible materials, the field is converging on a rational design framework: engineer polysaccharide structures to recruit defined beneficial communities and thereby steer the gut–liver axis away from disease. If clinical trials confirm the early human signals, the humble slime of the seashore may prove to be one of the most practical liver medicines of the coming decade—harvested not from a pharmaceutical plant, but from the wrack line.

The scale of the unmet need gives this research agenda its urgency. Population studies suggest that roughly a third of adults in many industrialized countries carry hepatic steatosis, with prevalence climbing in children and adolescents, yet most affected individuals are identified only incidentally or through rising cardiometabolic risk factors. Because early-stage disease is largely asymptomatic, an intervention that could be delivered safely as a dietary supplement—and taken for years—would address a far larger population than any prescription drug realistically can.

The prebiotic framing deserves careful attention. Classic prebiotics such as inulin and fructooligosaccharides are fermented broadly by common saccharolytic organisms, which can limit how precisely a community can be steered. Sulfated marine glycans, by contrast, demand specialized enzyme machinery, so only microbes equipped with the appropriate sulfatases and carbohydrate-active enzymes can access them. This substrate specificity is the theoretical basis for precision microbiome editing through diet, and it explains why the authors treat structural chemistry rather than fiber content as the decisive design variable.

Molecular weight emerges as a recurring theme in the preclinical literature. High-molecular-weight polymers are often poorly soluble and difficult for microbes to process, while controlled depolymerization into oligosaccharides frequently enhances water solubility, bioactivity, and fermentability. Several of the most striking animal results cited in the review involve oligosaccharide fragments rather than intact polymers, suggesting that processing technology—enzymatic degradation, controlled hydrolysis, or even synthetic chemistry—will be as important as source selection for future products.

Practical considerations also favor the field. Many marine polysaccharides already hold food additive or generally recognized as safe status in major jurisdictions, and industrial supply chains for carrageenan, alginate, and agar are mature, which could shorten the path from bench to consumer. Seasonal and geographic variation in seaweed composition remains a genuine hurdle, but cultivation of defined macroalgal strains under controlled conditions offers a route to more consistent raw material than wild harvest alone.

What remains most persuasive is the convergence of mechanisms: microbial selection, metabolite generation, barrier reinforcement, and direct hepatic signaling all point in the same direction. Few nutraceutical candidates offer that degree of mechanistic coherence, and few target a disease with such a large and growing affected population.

Subject of Research: Marine polysaccharides as nutraceutical modulators of the gut microbiome and gut–liver axis in metabolic dysfunction-associated steatotic liver disease

Article Title: Marine polysaccharides: promising nutraceuticals for metabolic dysfunction-associated steatotic liver disease as unique and potent modulator of gut microbiome

Article References: Pan, Y., Zhang, R., & Chen, Y. (2026). Marine polysaccharides: promising nutraceuticals for metabolic dysfunction-associated steatotic liver disease as unique and potent modulator of gut microbiome. Food Science and Biotechnology. https://doi.org/10.1007/s10068-026-02283-w

Image Credits: AI Generated

DOI: 10.1007/s10068-026-02283-w

Keywords: marine polysaccharides, MASLD, gut microbiome, gut–liver axis, fucoidan, carrageenan, ulvan, chitosan, short-chain fatty acids, bile acid signaling, nutraceuticals, fatty liver disease