title: Effects of low carbohydrate diets on energy and nitrogen balance and body composition in rats depend on dietary protein-to-energy ratio.
abstract: OBJECTIVE
  Truly ketogenic rodent diets are low in carbohydrates but also low in protein. The aim of this study was to differentiate effects of ketosis, low carbohydrate (LC) and/or low-protein intake on energy and nitrogen metabolism.
  
  
  METHODS
  We studied the nitrogen balance of rats fed LC diets with varying protein contents: LC diets consisted of 75/10, 65/20 and 55/30 percent of fat to protein (dry matter), respectively, and were iso-energetically pair-fed to a control (chow) diet to 12-wk-old male Wistar rats (n = 6 per diet). Previous studies demonstrated only LC75/10 was truly ketogenic. Food, fecal, and urine samples, as well as carcasses were collected and analyzed for heat of combustion and nitrogen (Kjeldahl method). Blood samples were analyzed for plasma protein, albumin, and triacylglycerol.
  
  
  RESULTS
  All LC groups displayed less body weight gain, and the degree of reduction was inversely related to digestible crude protein intake (daily weight gain compared with chow: LC75/10: -50%; LC55/30: -20%). Nitrogen excretion by urine was related to digestible protein intake (chow: 0.23 ± 0.02 g nitrogen/d; LC75/10: 0.05 ± 0.01 g nitrogen/d). Renal energy excretion was closely associated with intake of digestible crude protein (r = 0.697) and renal nitrogen excretion (r = 0.769). Energy-to-nitrogen ratio in urine was nearly doubled with LC75/10 compared with all other groups. Total body protein was highest with chow and lowest with LC75/10. Rats fed with LC75/10 displayed features of protein deficiency (reduced growth and nitrogen balance, hypoproteinemia, depletion of body protein, and increased body and liver fat), whereas the effects with the non-ketogenic diets LC65/20 and LC55/30 were less pronounced.
  
  
  CONCLUSIONS
  These results suggest that truly ketogenic LC diets in growing rats are LC diets that are also deficient in protein for growth.
authors.affiliation: Animal Nutrition, Ludwig-Maximilians University, Munich, Germany.
authors.forename: Lena
authors.initials: L
authors.lastname: Frommelt
authors.affiliation: Endocrine Research Unit, Medizinische Klinik und Poliklinik IV, Klinikum der Universität, Ludwig-Maximilians University, Munich, Germany.
authors.forename: Maximilian
authors.initials: M
authors.lastname: Bielohuby
authors.affiliation: Endocrine Research Unit, Medizinische Klinik und Poliklinik IV, Klinikum der Universität, Ludwig-Maximilians University, Munich, Germany.
authors.forename: Dominik
authors.initials: D
authors.lastname: Menhofer
authors.affiliation: Endocrine Research Unit, Medizinische Klinik und Poliklinik IV, Klinikum der Universität, Ludwig-Maximilians University, Munich, Germany.
authors.forename: Barbara J M
authors.initials: BJ
authors.lastname: Stoehr
authors.affiliation: Endocrine Research Unit, Medizinische Klinik und Poliklinik IV, Klinikum der Universität, Ludwig-Maximilians University, Munich, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Bidlingmaier
authors.affiliation: Animal Nutrition, Ludwig-Maximilians University, Munich, Germany. Electronic address: Kienzle@tiph.vetmed.uni-muenchen.de.
authors.forename: Ellen
authors.initials: E
authors.lastname: Kienzle
mesh_terms: D000818:Animals; D001823:Body Composition; D050528:Diet, Carbohydrate-Restricted; D055423:Diet, Ketogenic; D018753:Diet, Protein-Restricted; D004040:Dietary Carbohydrates / Q000008:administration & dosage; D004041:Dietary Fats / Q000008:administration & dosage; D004044:Dietary Proteins / Q000008:administration & dosage; D002149:Energy Intake; D004734:Energy Metabolism; D007662:Ketosis; D008297:Male; D009584:Nitrogen / Q000378:metabolism* / Q000652:urine; D017208:Rats, Wistar; D015430:Weight Gain
chemical_list: D004040:Dietary Carbohydrates; D004041:Dietary Fats; D004044:Dietary Proteins; D009584:Nitrogen
keywords: Body composition; Ketosis; Low-carbohydrate high-fat diets; Nitrogen balance; Rats