Provided are methods for preparing chemically modified lipids. The lipids are obtained from heterotrophically cultured microalgae and are subjected to a transesterification or interesterification reaction. The microalgae include those from the genus Parachlorella, Prototheca, Chlorella, or strains having at least 85% nucleotide sequence identity in 23S rRNA sequences to a Parachlorella, Prototheca, or Chlorella strain that are cultured in a bioreactor substantially in the absence of light.