Researchers have successfully tuned a particular compound in brown algae that appears to have powerful anti-obesity potential — not by suppressing appetite or burning fat, but by targeting your gut microbiome, allowing your body to fight weight gain naturally and long-term, without the need for drugs or dietary changes.
In a study at Zhejiang University of Technology, scientists extracted fucoidan, a sugar-rich sulfated polysaccharide found in Japanese sweet kelp (Saccharina japonica), a brown algae widely consumed in Japan and South Korea. While fucoidan (which is widely found in brown algae) is known for its antioxidant, anti-inflammatory and immune system-modulating properties, scientists have proven difficult to tap into its full bioactive potential.
To explore how to increase the bioavailability of fucoidan and thus its biological activity, the researchers used chemical methods to break it down into smaller fragments with different molecular weights and sulfate contents, resulting in four low molecular weight fucoidans (LMWF). The lower molecular weight means it interacts better with gut flora than larger, complex polysaccharides, which are often less easily broken down by microbial enzymes.
Among the four drug candidates, one called LMWF4 stood out. This engineered compound has the lowest molecular weight yet the highest degree of sulfation. Lowering the molecular weight makes the compound more easily absorbed and interacted with by the body, while increasing the number of sulfate groups enhances the molecule's ability to influence gut bacteria.
Essentially, by making fucoidan smaller and more chemically active, the researchers turned a naturally beneficial compound into a targeted gut-modulating tool that not only travels through the digestive system but also works within its composition to support metabolic health.
"Structural differences in low-molecular-weight fibers can significantly influence their regulatory effects on gut microbiota and their impact on obesity outcomes," the researchers wrote. "We used fucoidan and four of its derivatives, each with varying molecular weight and degree of sulfation, in mouse experiments."
As mentioned above, LMWF4 has a very low molecular weight (mW) of 2.6 kilodaltons (kDa), is highly sulfated (37.7%), and has a high fucose content (92.9%) - essentially retaining all the good things about fucoidan, but specifically engineered to allow the gut to reap benefits that it cannot naturally get.
In this study on mice, the researchers divided the mice into groups, with one group fed a low-fat diet (LFD) as a control group and the other group fed a high-fat diet (HFD) to simulate diet-driven obesity. LFD mice serve as a health baseline to assess normal body weight, metabolic health, and gut microbiota under a "normal" mouse diet. However, the real tests were conducted on mice fed a high-fat diet.
After four weeks of high-fat diet (HFD), the mice were again divided into several groups: one group continued without any intervention; another group received natural (crude) fucoidan extracted directly from brown algae; and the remaining mice received one of four low molecular weight dietary fibers (LMWF). After another four weeks, the researchers measured the HFD mice's weight gain, fat accumulation, blood sugar and cholesterol levels, and analyzed their gut microbiota.
They found that all fucoidan-treated mice gained less weight than mice fed a high-fat diet (HFD) without any intervention. But the most significant effect came from LMWF4, which not only reduced weight gain and fat accumulation, but also improved blood sugar and cholesterol levels. The mice also had a healthier and more balanced gut microbiota, with increased numbers of microbes associated with metabolic health and reduced numbers of microbes associated with obesity.
This suggests that LMWF4 regulates the gut ecosystem and helps the body resist weight gain—even in the presence of a high-fat diet. In fact, LMWF4 restored the diversity of the gut microbiota, bringing species richness to near-normal levels. Specifically, this molecule increased populations of Akkermansia bacteria, known to help prevent obesity, and elevated levels of Blautia and Eubacterium species, as well as Muribacterium species that promote the production of short-chain fatty acids (SCFA). This is also a sign of improved metabolic health.
Notably, there was also a decrease in the abundance of an as-yet-unclassified bacterial group known as Rikenellaceae_RC9_gut_group, which is associated with inflammation- and obesity-related microbiome changes in mice. These flora are usually increased through HFD (high frequency meals). Populations of Helicobacter pylori, which is associated with inflammation and obesity, were also reduced.
Overall, the changes in the mice were not due to direct effects of fat metabolism, but rather to changes occurring in the microbial community. By DNA sequencing the microbial community, the research team found that LMWF4 reshaped the intestinal flora, increasing the number of beneficial bacteria while suppressing obesity-related flora. The findings suggest that LMWF4 can reshape the gut environment in a way that makes the body more resistant to weight gain and metabolic dysfunction.
Of course, a key limitation of the study is that it was conducted in mice, but the findings suggest that rather than trying to force the body to lose weight through drugs or restriction, the same goal could be achieved by promoting the right army of fat-fighting microbes.
And because LMWF4 is derived from a safe, edible source—kelp, which is often used as cold pickles or dried as snacks or in umami-rich soups—it could be developed into a functional food ingredient or supplement to maintain long-term gut health.
The researchers added: "The analysis of the structural characteristics of different fucosan and the corresponding changes in intestinal bacteria provides valuable insights into their impact on the intestinal microbiota and lays the foundation for the further development of fucoidan-based therapies."
A growing body of research supports the health properties of fucoidan, a substance found in the cell walls of brown seaweed. In a 2024 study, researchers studied fucoidan extracted from Sargassum binderi (Malaysian seaweed) and found that rats fed this compound had a 36% reduction in weight gain and an 18% reduction in visceral fat compared with untreated HFD rats. In 2022, kelp (S. japonica, formerly Laminaria japonica) fucoidan studied how this compound improved fat and blood sugar profiles in mice treated with antibiotics, suggesting beneficial interactions with gut microbiota. Last year, scientists discovered that crude polysaccharides from Sargassum thunbergii (including fucoidan) have fat-inhibiting effects.
While further human studies are needed, this new study opens the door to a new natural obesity treatment that could make the gut resistant to weight gain and promote long-term weight loss. Additionally, it shows that not all fucoidans are created equal and can be better targeted through biohacking.
The researchers added: "Studies on intestinal flora at both the phylum and species levels have shown that ingesting the polysaccharide LMWF4 through gavage can alleviate the HFD-induced decrease in the overall number and diversity of the intestinal flora. Our findings indicate that modifications with relatively lower molecular weights and higher sulfation degrees have more significant anti-obesity effects. In addition, these modifications also show a stronger ability to regulate intestinal flora disorders and are therefore expected to become potential candidates for anti-obesity treatment."
The research was published in the journal Carbohydrate Polymers.