Biochemistry of Fats and Oils

Chapter summary

• Fat chemistry is complex but needs fewer than five concepts.
• Be wary of omega fatty acid myths. They are vital, but science is still uncertain on many points.
• You probably consume enough essential fatty acids without supplements.

Five concepts

• Fats and oils are the same chemistry. Liquid oils and solid fats are all fats.
• Fats versus fatty acids: A fat (triglyceride) is glycerol with three fatty acids attached, shaped like the letter E.
• Fatty acid: a chain of carbon atoms, usually 4 to 28, with an acid group at one end.
• Saturation: Saturated fats have no double bonds (lard, coconut oil). Monounsaturated have one (olive oil, canola, nut oils). Polyunsaturated have two or more (vegetable oils, seafood).
• Bonds: Cis-fats are natural. Trans-fats come from partially hydrogenated oils. Modern manufacturing now avoids creating them.

Essential fatty acids

• Humans must eat only two fatty acids because the body cannot make them. The body builds the rest.
• Triglycerides break down into glycerol, which can be turned into glucose, and free fatty acids for heart and muscle fuel.

The omega families

• Omega-3 (n-3): ALA from flaxseed, walnuts, canola, soybean and green vegetables such as kale and spinach. EPA and DHA come mostly from fish.
• Omega-6 (n-6): Linoleic acid is the shortest. Main sources are palm, soybean, rapeseed and sunflower. Global production is about 32 million tonnes of omega-6 against 4 million tonnes of omega-3 ALA.
• Omega-9: Oleic acid (olive and macadamia oils) and erucic acid (rapeseed and mustard).
• Omega-6 and omega-3 are converted into eicosanoids, which signal inflammation and other processes.

Where views differ

• Heart organisations: The Australian Heart Foundation and others recommend polyunsaturated fats in place of saturated fat.
• Harvard (Sacks): Omega-3 is beneficial for the heart, though supplement evidence is mixed.
• The author: The omega story is oversold. Many people already get enough, and the science is uncertain about how much more helps.
• Trans-fats: Ascherio and Willett (1997) showed harm, and there is wide agreement they should be avoided.

Take-away points

• Know the difference between saturated, mono- and polyunsaturated fats.
• Do not buy omega supplements without a clear need.
• The next chapters explain why the author recommends avoiding seed oils.

References

• Sacks, F. (2014) Ask the Expert: Omega-3 fatty acids. Harvard School of Public Health, The Nutrition Source.
• Ascherio, A. and Willett, W. (1997) Health effects of trans fatty acids. Am J Clin Nutr 66(4):1006S-1010S.
• Wikipedia entries: Fat; Essential fatty acids; Omega-3, Omega-6 and Omega-9 fatty acids; Eicosanoid.