De novo synthesis of milk triglycerides in humans

Am J Physiol Endocrinol Metab. 2014 Apr 1;306(7):E838-47. doi: 10.1152/ajpendo.00605.2013. Epub 2014 Feb 4.


Mammary gland (MG) de novo lipogenesis contributes significantly to milk fat in animals but little is known in humans.

Objective: To test the hypothesis that the incorporation of (13)C carbons from [U-(13)C]glucose into fatty acids (FA) and glycerol in triglycerides (TG) will be greater: 1) in milk than plasma TG, 2) during a high-carbohydrate (H-CHO) diet than high-fat (H-FAT) diet, and 3) during feeding than fasting. Seven healthy, lactating women were studied on two isocaloric, isonitrogenous diets. On one occasion, subjects received diets containing H-FAT or H-CHO diet for 1 wk. Incorporation of (13)C from infused [U-(13)C]glucose into FA and glycerol was measured using GC-MS and gene expression in RNA isolated from milk fat globule using microarrays. Incorporation of (13)C2 into milk FA increased with increased FA chain length from C2:0 to C12:0 but progressively declined in C14:0 and C16:0 and was not detected in FA>C16. During feeding, regardless of diets, enrichment of (13)C2 in milk FA and (13)C3 in milk glycerol were ∼ 3- and ∼ 7-fold higher compared with plasma FA and glycerol, respectively. Following an overnight fast during H-CHO and H-FAT diets, 25 and 6%, respectively, of medium-chain FA (MCFA, C6-C12) in milk were derived from glucose but increased to 75 and 25% with feeding. Expression of genes involved in FA or glycerol synthesis was unchanged regardless of diet or fast/fed conditions. The human MG is capable of de novo lipogenesis of primarily MCFA and glycerol, which is influenced by the macronutrient composition of the maternal diet.

Keywords: GC-MS; fatty acid; gene expression; glycerol; lipogenesis; stable isotopes.

Publication types

  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adult
  • Blood Chemical Analysis
  • Carbon Isotopes / pharmacokinetics
  • Diet, High-Fat
  • Dietary Carbohydrates / pharmacology
  • Eating / physiology
  • Fasting / metabolism
  • Female
  • Glucose / metabolism
  • Humans
  • Lipogenesis*
  • Mammary Glands, Human / metabolism*
  • Milk, Human / chemistry
  • Milk, Human / metabolism*
  • Triglycerides / analysis
  • Triglycerides / biosynthesis*


  • Carbon Isotopes
  • Dietary Carbohydrates
  • Triglycerides
  • Glucose