Effects of ketogenic diet on rat bone δ13C values and their implications for dietary reconstruction studies

Abstract

Few controlled feeding experiments have investigated the degree to which dietary lipids contribute carbon to structural tissues and influence isotopic signatures, and most studies have focused on soft tissues. This study utilizes a rodent model to examine the effects of a ketogenic diet (high fat, low carbohydrate) on the δ¹³C values derived from bone tissue (bone collagen and bone apatite). Femora were opportunistically harvested upon conclusion of an unrelated study, where adult rats had received either ketogenic diet (KD) or a micronutrient, protein, and calorie-matched standard diet (SD) for 6 months. Bone samples were prepared for stable isotope ratio analysis and δ¹³C_collagen, δ¹⁵N_collagen, δ¹³C_apatite, and Δ¹³C_{apatite−collagen} values were determined. Observed differences in δ¹³C_collagen values between KD and SD groups indicate significant assimilation of lipid-derived carbon among the KD animals. KD-fed rats recorded lower δ¹³C_apatite values and smaller Δ¹³C_{apatite−collagen} values than those fed the SD, reflecting the respective dietary energy macronutrient profiles. Incomplete equilibration with the experimental diets precluded determination of Δ¹³C_{apatite−diet} values, and possible group differences in isotopic discrimination associated with the metabolic shift from glycolysis to ketosis among the KD rats could not be evaluated. Experimental outcomes highlight the influence of dietary lipids on metabolic routing and suggest that sampling bone collagen alone could lead to inaccurate dietary interpretations among past human populations where access to carbohydrates was limited and lipids supplied the majority of daily energy needs. Implications for stable isotope analysis (SIA) and dietary reconstruction studies based on archaeological and neontological materials are discussed.