Fermented and Unfermented Whole-Grain Rye Modulate and Methylated Quaternary Ammonium Compounds Systemically in High-Fat Diet-Fed Mice

Whole-grain rye (WGR), a key component of the healthy Nordic diet, is linked to reduced metabolic disease risk. Gut-microbial metabolites and methylated-quaternary ammonium compounds (mQACs), such as betaines and acylcarnitines, are associated with WGR consumption and may drive these health benefits. These metabolites influence tissue-specific metabolic pathways (i.e., each tissue responds distinctively), with fermentation potentially enhancing their effects. Therefore, a comprehensive understanding of WGR’s role in whole-body metabolic response and how it modulates metabolic homeostasis is needed.

We conducted a dietary intervention in high-fat-diet (HF)-fed mice, comparing fermented (FRB) and unfermented rye bread (URB) using LC-MS-based metabolomics across key metabolically active tissues (heart, muscle, ileum, cecum, colon), along with plasma and stool.

Both WGR diets significantly (p<0.05) increased gut-microbial metabolites and mQACs-TMAO, 5-AVAB, trigonelline, and homostachydrine, confirming them as rye-associated biomarkers. FRB elevated TMAO—a cardiometabolic regulator—across plasma, muscle, and gut. FBR also reduced its precursor, trimethyllysine, linked to increased cardiovascular risk, suggesting microbial modulation may counterbalance TMAO production. FRB further increased 3-phenyllactate, indoles, and kynurenate (plasma, stool), hippurate (muscle, cecum), trigonelline (muscle), and long-chain acylcarnitines (gut), all associated with enhanced energy metabolism and immune function. Despite these beneficial shifts, FRB increased plasma insulin, glucose, and cholesterol; and correlated positively with plasma mQACs and gut-microbial metabolites (Ex:hippurate, indolelactate), suggesting an early-stage adaptive response to dietary shifts or potential metabolic stress. Conversely, URB increased antioxidant ergothioneine and reduced pro-inflammatory p-cresol sulfate, potentially reducing oxidative-stress and chronic inflammation commonly associated with metabolic diseases.

These findings highlight the role of WGR in shaping diet-microbe-host interactions that support metabolic health and gut function, with fermentation enhancing beneficial metabolic shifts, while URB reduces the levels of potentially harmful metabolites. The interplay between tissue-specific metabolic responses and gut-microbiota interactions highlights the need for integrative, whole-body approaches to improve dietary recommendations for managing metabolic diseases.