The edible oils perform multiple cooking/processing roles: as food constituents, as cooking/processing aids (which also makes them a part of the food) and as value-adders to consumption experience. That is how they reach our stomach. Their physiological role begins when they reach the blood after digestion into fatty acids and glycerol and the release of its micronutrients. This ‘fat entering the blood’ looks like an impending disaster; fact is: we would be crippled without its physiological functions.

We already know from Post 17, Edible oils: An introduction, The multifaceted personality of cooking oils, that refining makes oil good-looking but robs them of crucial micronutrients. In India, some unrefined oils (apart from corresponding oilseeds themselves) have traditionally been a part of daily diet. Hence the food functionalities of oils must include the roles of the non-oil useful constituents – micronutrients – that unrefined oils carry. It is logical, therefore, to separate the functionalities of the oil (or glycerides) and non-oil components. Obviously, a diet using only refined oils would be depriving itself of the aforesaid micronutrients, most of which are natural anti-oxidants and vitamins. Hence a diet lacking fruits and vegetables and using only refined oils to cook, would invite the risk of some serious nutritionally mediated disease conditions including cancers and vascular and heart diseases.

The role of glycerides or acylglycerols – the bulk of all oils

They carry the ‘bulk’ responsibilities unlike trace constituents which have crucial, special roles.

Energy for doing work and maintaining body temperature:

Oils and fats are energy-dense, immiscible with water (and hence immune to being washed out) and can be stored in large quantities. Glucose, equivalent to about 4.2 calories per gram, remains the primary and preferred source of energy to do everything we do and comes mainly from digested starch and sucrose or sugar (which also releases fructose) and milk sugar (lactose, which also releases galactose) in the diet. Fructose and galactose, close cousins of glucose in the first place, are easily converted to glucose in the liver. It is ‘picked up’ from the blood stream and its level can drop in presence of intense work and absence of dietary input.

As soon as this happens, intricate mechanisms swing into action to release it from stored sources till they last, which is not for long because such stores are limited. In that event, stored fats or triglycerides coming in at about 9.2 cals/gm, start being ‘burnt’ to release energy.

Fats are stored in a larger quantity because they are spread all over the body and don’t need water to ‘stay’ unlike glycogen – the glucose storage form. This, combined with their greater energy density, gives them a serious capacity to compensate for lowered chemical energy supply. Stranded on an island with just water to drink, it is your bodily fat supply that will bail you out till you are bailed out. Proteins or amino acids remain the primary sources for growth and repair of body tissue and synthesis of hormones and enzymes; they are drawn into the energy release play only as the last resort. Interestingly, all three are stored in the body in re-combined, insoluble forms.

Body’s adipose tissue as fat carriers: We know that dietary oils or fats are digested in the small intestine into fatty acids (and glycerol), absorbed into blood and re-synthesized into triglycerides for storage. (Coconut oil and its close cousin palm kernel oil are exceptions; they go straight to the liver.) They are stored in the fat or adipose tissue which are spread throughout the body and which rob you of the ‘six packs’ but save you from energy scarcity. Equally importantly, they ‘cushion’ vital internal organs from shocks.

Caution: Indiscriminate oil/fat consumption combined with sedentary  lifestyle promotes hyperlipidemia (raised blood triglyceride, cholesterol and, in some cases, fatty acids) levels and obesity. This is essentially continued fat deposits without much withdrawal for combustion. This can be further aggravated by flawed consumption in terms of types of fatty acids and oxidized MUFA and PUFA. This invites a plethora of disease conditions and is abuse of champions called oils.

Non-energy functionalities of glycerides: Among  PUFA, omega 3 and 6 fatty acids (alpha linolenic and linoleic acid respectively) are considered essential as our body cannot synthesize them in vivo. Hence edible oils bringing them in must be thanked for that. They are precursors to bio-synthesis of even longer chain omega PUFA (EPA, DHA). However, disease-causing deficiencies of essential fatty acids is rare and oils in general can cope adequately.

Eicosanoids are a group of powerful bio-active compounds synthesized copiously in our body from essential fatty acids. They have influence in almost all our physiological systems and hence edible oils must be credited with far-reaching essentialness.

The role of non-glyceride constituents:

Let us now check out the roles of the aforesaid minor constituents.

Phytosterols and phytostanols are plant origin micronutrients (phyto – plant) and, being oil-soluble, become part of the unrefined oil that is extracted from the source. Since, they survive refining to a large extent, this applies to refined oils also. Though available at ‘parts per million’ (ppm) levels, they reduce colonic absorption of cholesterol (the human equivalent of phytosterol) thru their close structural similarity with it. This obviously helps reduce serum total and ldl cholesterol – a major triumph but applicable more to meat eaters who send dietary cholesterol to the colon.

Oil-soluble vitamins A, D, E and K are found mainly in animal source oils (along with cholesterol). Refined oils do retain small parts of these vitamins but consuming unrefined oils in moderation remains a good tool to get these vitamins naturally.

Anti-oxidants, in a wide variety are found, more in unrefined oils than the refined ones. (Visit the post nos. 2, 15 and 16 to understand their importance.) The oxidation of ldl-cholesterol in the arterial walls (along with arterial endothelium malfunction and/or injury) is believed to trigger the formation of an obstinate blockage (atherosclerosis) – the vascular disease and its serious downstream effects. Such oxidation can be mediated by oxygen-carrying molecules and highly reactive ‘free radicals’ which can come in thru burnt food – the main reason to avoid fried bought-outs and burnt food. Such reactive species have also been marked for onset of cancers. Anti-oxidants coming in thru oils can neutralize these reactive oxidative species, within limits.

Phosphatides are natural compounds found at relatively higher levels e.g. samples of unrefined soybean oil can have as much as 2.5 % of them, though refining must necessarily remove all of it. They resemble glycerides closely but are differentiated by phosphoric acid in their make-up which imparts some serious attributes to it. Phospholipids (mainly ‘lecithin’ as one of its types) is a very common emulsifier (that allows intimate mixing of oils with water and similar food molecules) and finds extensive uses in ice-creams, baked goods, chocolate, margarines and spreads, brown powder beverages, etc. Indeed, it is mostly derived from the crude phospholipids that are removed during soybean oil refining.  Almost every one of the billions of our body cells contain phosphatides and they perform so many varied functions (including that of an anti-oxidant) that it is convenient to simply acknowledge them as versatile friends.

Cholesterol is scarce in plant origin foods and, in a loosely vegetarian diet, can come in only thru eggs and milk, in small quantities. Our body can synthesize its requirement from the food we eat and hence cholesterol-deprivation is rare even for vegetarians. If your diet is vegetarian with only milk as the dietary cholesterol source, ease into even eggs gradually. Liver cannot dispose of sudden dietary cholesterol bursts and blood levels can rise. Cholesterol is essential for healthy tissue development and growing children must get dietary cholesterol support.

Conclusion: As we can see, the physiological roles of edible oils are a bit complex which probably explains our paranoia about them. Bottomline: Adopt a low fat diet rich in fruits and vegetables and ensure the ‘low fat’ part is smartly chosen – both in quality and quantity. Guidance on that, ‘coming soon’.

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