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The Nutrition InvestigatorThe health and nutrition blog by Dr. Roc Ordman.

CIS vs. Trans Fat Structures

by Roc (click here for full post)

1. Saturated fat, 2. Monounsaturated fat, 3. cis and trans fats

1. Saturated Fat

In this, all of the carbons are attached to each other by single bonds: C-C-C-C, with hydrogens attached so that each carbon forms a total of 4 bonds.

[see sat'd fatty acid below]

2. Monounsaturated Fat

Some of the carbons in fat can be attached by double bonds, for instance C-C=C-C. This is a monounsaturated fat, with the double bond being C=C.

[see double bonded fatty acids below, mono- and polyunsaturated]

This double bond does not allow rotation around the carbon-carbon bond axis, so the attached hydrogens can be on the same (cis) or opposite (trans) sides, producing cis-fats and trans-fats.

[all double bonds below are trans, actual double bonds are cis. See diagram at page bottom]

All naturally occuring fats are cis. Trans-fats are produced by industrial processing of vegetable oil to make them hard to make margarine. So our bodies do not know how to metabolize trans-fats. They muck up our metabolism, leading to a variety of health hazards. There are errors in Figure 1, because the double bonds are trans, and they ought to be cis. See 3. below if you do not know cis vs. trans configuration.

Figure 1: saturated fat,


Actual natural fats contain only cis double bonds, cis means same, trans means across from, referring to the attachment of the hydrogens (H) to the carbons on the double bond.

cis-double bond trans-double bond





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