Dietary fats and oils

Dietary fats and oils are the most concentrated form of energy as they yield 9 calories/g, whereas, carbohydrates and proteins yield only 4 cal/gm. Nuts and oil seeds are good sources of fat. Besides providing calories, dietary fats sources of essential fatty acids, vitamin E and acts as transport vehicle for fat-soluble vitamins.

There are two types of dietary fats, visible and non-visible fat. Visible fats include oils, butter, animal fat etc. Invisible fat, not visible to naked eyes, is present in food items like wheat, rice and pulses etc, in small amounts.  In general, the fats and oils we use are mainly composed of either saturated OR un-saturated fatty acid chains.

• Saturated fats contain no double bonds in their chain, exist in solid form at room temperatures, and, usually, derived from animal sources and some vegetable oils. Examples: butter, palm kernel, coconut oil etc.

• Unsaturated fats contain one or more double bonds in their chain, are liquid at room temperatures and in general, derived from plant sources. Examples include soybean oil, safflower oil etc.

Why fats and oils?

• The significance of dietary fats and oils is that they provide essential fatty acids (EFA), as their name defines, they are absolute essential nutrients required by the body. EFAs are linoleic acid and ?-linolenic acid. ?-Linolenic acid (ALA) is known as omega-3 and linoleic acid is called as omega-6 essential fatty acids. Both linoleic acid (omega-6) and ?-linolenic acid must be present in the diet in the ratio of 5:1 to 10:1.

• The important derivatives of ?-linolenic acid are ecosa-pentaenoic acid (EPA) and docosa-hexaenoic acid (DHA). 1-3% of calories should come from EFA.  Deficiency of EFAs results in impaired brain growth, mental retardation and learning difficulties, dermatitis (dryness of skin), hair loss, and poor wound healing.

• The four fat-soluble vitamins namely vitamin A, D, E and K are, in fact, require fats and oils in the food to be absorbed in the gut. Inadequate fats may results in the deficiency of these vitamins leading to serious metabolic derangements with subsequent manifestations like night blindness, osteoporosis, bleeding from skin and mucus membranes, dry skin (phrenoderma) and susceptibility to infections.

• Furthermore, vegetable oils are good source of plant sterols, especially ?-sitosterol and campesterols. The FDA has approved the following claim for phytosterols: "Foods containing at least 0.4 gram per serving of plant sterols, eaten twice a day with meals for a daily total intake of at least 0.8 gram, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease." Phyto-sterols competitively inhibit cholesterol absorption in the gut and thereby can reduce cholesterol levels by 10% to 15%.

• Fats are also high in calories. On an average 100 g of cooking oil provides 900 calories. Fats are functions like reserve energy that is readily available for use at the times of starvation, illnesses and cold weather conditions.

• In fact fats and oils high in mono-unsaturated fats like olive, canola, peanut, sesame...etc help lower LDL-cholesterol in the blood.

Limitations of fats and oils

Apart from the need for essential fatty acids, there is no specific requirement for dietary fats and oils as long as the diet provides adequate nutrients for energy. Those who consume omega-6, omega-3 fats in a ratio more than 10:1 should compensate by consuming omega-3 rich foods like fish, greens and legumes.

Excess fats in the diet circulate as triglycerides and cholesterol in the blood. Both of these agents deposit in various organs and tissues inside our body leading to obesity, coronary artery disease, diabetes, peripheral vascular disease, stroke...etc.

Although the average American diet contains 35-40% of calories as fat, most current recommendations are to limit dietary fat to 30% or less of total calories. No more than 5-10% of energy should come from saturated fats, 10% should be from mono-unsaturated and another 10% from poly-unsaturated fatty acids.

Below is the table with in-depth analysis of some of commonly used dietary fats and oils:-

SFA= Saturated fatty acids
MUFA= Mono-unsaturated fatty acids
PUFA= Poly-unsaturated fatty acids                               
?-3= Omega 3 fatty acids
?-6= Omega 6 fatty acids