Fat spatial geometry

Fatty acid is a chain of carbons. In the case of unsaturated fat (ie, MUFA or PUFA), there is at least one site in the chain with double bond (and the adjacent carbons both bind only one hydrogen atom each, instead of two). The double bond secures the bonding of these carbons so that they remain mutually fixed in one position.

In this case, the remaining two hydrogens (bonded to the adjacent carbons) may be located in space in two ways:

  • on the same side opposite to each other (cis in latin), so as a result, the chain is bent (toward the “hole” where the hydrogens are missing)
  • each on the opposite side (trans), they do not block each other, and the chain is stabilized in (unnatural) straight position

When there is at least one point in the chain in the trans configuration, we talk about trans fat. When all double bonds are in the natural cis configuration, it’s a case of cis fat. The bent cis fats naturally occur in the diet and they are (generally) healthy. Conversely, trans fat should be avoided in the diet.

Saturated fats cannot be trans because they do not have double bonds and thus do not stabilize in space. In this case the entire chain is fully saturated with hydrogen and the individual carbons are more loosely linked by single bonds, so it makes no sense to talk about spatial orientation of the chain. Also, from both trans and cis unsaturated fat, the same saturated fat is created after saturation with hydrogen (complete hydrogenation).

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