Karela juice is an extract of pure Karela or Bitter Gourd or Bitter Melon. Bitter gourd is popular for its ability to regulate blood sugar levels. Scientifically, Bitter gourd reduces the amount of glucose that is released into the blood by inhibiting the enzymes that break down disaccharides to two monosaccharides (e.g. glucose)
Bitter Melon has a distinct warty exterior and an oblong shape. It is hollow in cross-section, with a relatively thin layer of flesh surrounding a central seed cavity filled with large, flat seeds and pith. The fruit is most often consumed while it bears its green color. At this stage, the fruit's flesh is crunchy and watery in texture. The skin is tender and edible. Seeds and pith appear white in unripe fruits; they are not intensely bitter and can be removed before cooking.
Bitter Melon contains several biologically active compounds, chiefly momordicin I and momordicin II, and cucurbitacin B. The plants contains several bioactive glycosides (including momordin, charantin, charantosides, goyaglycosides, momordicosides) and other terpenoid compounds (including momordicin-28, momordicinin, momordicilin, momordenol, and momordol). It also contains cytotoxic (ribosome-inactivating) proteins such as momorcharin and momordin.