Polyphenolic compounds exhibit pronounced lipid-lowering effects, and their absorption in the human gastrointestinal tract varies considerably, which critically influences their bioavailability. Buckwheat, a natural food being rich in polyphenols, has been suggested to possess unique lipid-lowering potential.

This study aimed to investigate the differential absorption of buckwheat polyphenols using an MKN28/Caco-2 sequential transport model, and to systematically evaluate their lipid-lowering effects and underlying mechanisms through cellular assays and gut microbiota fermentation experiments.

Buckwheat polyphenol extract was characterized by ultra-high-performance liquid chromatography coupled with quadrupole Orbitrap mass spectrometry (UHPLC-Q-Orbitrap MS). Based on the MKN28/Caco-2 transport model, the extract was fractionated into readily absorbable and poorly absorbable components. The lipid-lowering effects of the absorbable fraction were assessed in adipocytes using Oil Red O staining and intracellular lipid quantification. In addition, the impact of the non-absorbable fraction on gut microbiota composition was evaluated in vitro fermentation.

Component analysis revealed that there are 23 kinds of polyphenolic compounds rutin and protocatechuic acid exhibited relatively high signal intensities. The absorbable fraction significantly reduced lipid accumulation in adipocytes, with triglyceride (TG), total cholesterol (TC), and low-density lipoprotein cholesterol (LDL-C) levels in 3T3-L1 cells decreased by 17.8%, 28.6%, and 15.2%, respectively. Furthermore, in vitro fermentation demonstrated that the poorly absorbable fraction (BWP-AP) modulated gut microbiota composition by increasing the relative abundance of Bacteroides and Bifidobacterium, while decreasing Escherichia-Shigella and Alistipes.

Buckwheat polyphenol extract contained 23 identified phenolic compounds. The readily absorbable fraction exerted significant intracellular lipid-lowering effects, whereas the poorly absorbable fraction regulated metabolic homeostasis via modulation of gut microbiota. These findings revealed a dual-pathway mechanism involving direct host absorption and microbiota-mediated regulation, providing a theoretical basis for the development of functional foods based on buckwheat polyphenols.

At present, relevant animal experiments have confirmed that buckwheat had a good intervention effect on obesity and lipid metabolism disorder caused by high-fat diet. At the same time, studies have shown that the adaptive thermogenesis of brown fat could effectively improve the body’s energy metabolism. Therefore, increasing the activity of brown fat and promoting the browning of white fat could be used as an effective way to prevent obesity and improve energy metabolism diseases.

The raw buckwheat and four kinds of main polyphenols identified from buckwheat were prepared according to the content proportion to study the lipid-lowering effects of buckwheat polyphenols in high-fat diet-induced obese mice via browning of white adipocytes.

Phenolic compounds in buckwheat polyphenol extract were identified by UHPLC-Q-Orbitrap mass spectrometry combined with database. And the main polyphenol compound was prepared according to the content proportion in the raw buckwheat. In order to explore the regulating effects of buckwheat on body weight, organ index and blood lipid level in C57BL/6J mice, the dietary intervention was carried out with 10%, 20% and 40% proportion of buckwheat to replace basic feed and the 2.5 mg∙mL^-1 of mixture buckwheat polyphenol standard substance. Last but not least, Western-blot and q-PCR were used to investigate the effects of buckwheat feed and polyphenol intervention on the expression of heat-producing proteins and genes in white and brown fat in mouse subcutaneous adipose tissue.

Twenty phenolic compounds in buckwheat polyphenol extract were identified by UHPLC-Q-Orbitrap mass spectrometry, and the content of four phenolic compounds with the highest content (hydroxycinnamic acid, quercetin，scoparone, and rutin) accounted for more than 80% of the total phenolic compounds, which were the main polyphenols in buckwheat. The results showed that after 39 d in the diet intervention, compared with high-fat diet group, adding buckwheat feed and buckwheat polyphenol intervention on body weight in mice, the liver index and serum triglyceride (TG), total cholesterol (T-CHO), low-density lipoprotein cholesterol (LDL-c), aspartate aminotransferase (ALT) and third transaminase (AST) increased significantly inhibitory effect; with the increase of amount of buckwheat, the inhibition increased. At the same time, adding buckwheat feed and buckwheat polyphenol could protect and improve the decrease of renal index and HDL-c in mice. It was also the high dose 40% buckwheat and polyphenol group that had the best effect, which showed that phenolic substances played a major role in the improvement of abnormal lipid metabolism in high-fat diet-induced obese mice. UCP1, PRDM-16, and PGC-1α protein and gene expression levels were significantly decreased in the high-fat diet group compared with the normal diet group, while Tcf21 and HOXC8 expression levels were significantly increased (P<0.05). After dietary intervention, protein expression levels of UCP1, PRDM-16 and PGC-1α in the buckwheat intervention group were significantly up-regulated, while protein expression levels of Tcf21 and HOXC8 were significantly decreased (P<0.05). In addition, the 40% buckwheat and polyphenol intervention group significantly increased the expression of UCP1, PRDM-16 and PGC-1α genes in mouse visceral adipose tissue (P<0.05), and which down-regulated the expressions of Tcf21 and HOXC8 genes.

Buckwheat intervention could effectively improve the lipid metabolism disorder in high-fat diet-induced obese mice, and it was confirmed that buckwheat polyphenols played a major role. The mechanism was mainly buckwheat polyphenols could significantly improve the thermogenic activity of brown fat, reduce the content of white fat, and regulate the energy metabolism balance. This study provided a new idea and theoretical basis for the utilization of buckwheat and the development of functional foods about lipid-lowering products.