Endocrine Abstracts

We previously reported the impact of low-carbohydrate/high-fat (LC–HF) diets on different endocrine systems in rats. To unravel metabolic pathways involved, we now studied if pair-feeding isoenergetic amounts of three different diets – all composed of macronutrient from the same sources but at different relative abundance, – leads to specific changes of the plasma metabolic profile.

Methods: Plasma was collected from male Wistar rats (n≥7/group) which were pair-fed for 4 weeks either a control chow diet (CH), or two LC–HF diets (LC–HF-1: high in fat and matched in protein content to CH; LC–HF-2: very high in fat, but low in protein). ¹H-NMR spectra were recorded on a DRX-600 NMR spectrometer (Bruker BioSpin). OPLS-DA models were carried out between diet groups. Statistical analyses were performed with SIMPCA P+12.0 (Umetrics AM, Sweden).

Results: The best separation was found between LC – HF-2 and CH. The OPLS-DA model had a predictive ability Q2Y=94.9% and explained a total variance of R2X=61.0%. Furthermore, the model showed that the variance related to the class separation was R2pX=24.5%. As expected, NMR spectra revealed the ketone metabolite 3-hydroxybutyrate as one major metabolite allowing clear discrimination of the groups. After exclusion of 3-hydroxybutyrate corresponding ppm-regions the OPLS-DA model still showed a Q2Y of 91.9% and a R2X of 73.6% (R2pX was 20.3%). Also LC–HF-1 and CH groups were clearly distinguishable, although no differences in 3-hydroxybutyrate were detected. When comparing spectra from LC–HF-1 and LC–HF-2 groups and excluding the metabolite 3-hydroxybutyrate, the OPLS-DA model showed a Q2Y of 72.3% and a R2X of 81.0%.

In conclusion, NMR-spectroscopy and OPLS-DA allowed precise discrimination between dietary groups. As expected, 3-hydroxybutyrate is one major metabolite differing between LC-HF-2 and LC-HF-1 or CH fed rats. However, even exclusion of this metabolite allows good group separation paving the way to indentifying previously unexpected metabolic pathways.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.