Dietary fats and oils

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 calories/gm. Nuts and oil seeds are good sources of fat. Beside rich in energy, dietary fats are incredible sources of essential fatty acids, vitamin E in addition to act as the transport vehicle for fat-soluble vitamins/hormones.

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 chemical structure. They exist in a solid state at room temperatures, and, usually derived from animal sources, although some of them obtained from plant sources. Examples: butter, lard, palm kernel oil, coconut oil, etc.
  
• Unsaturated fats contain one or more double bonds in their chain. They are liquid at room temperatures and in general, derived from plant sources. Examples include soybean oil, safflower oil, etc. Fish oil, however, is composed of major proportion of unsaturated fats to saturated fats.
  

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 α-linolenic acid. α-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 α-linolenic acid must be present in the diet at a ratio of 5:1 to 10:1.
  
• The important derivatives of α-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 through 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 the good source of plant sterols, especially β-sitosterol and campesterol. 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 across 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 during the times of starvation, illnesses and cold-weather conditions.
  
• In fact, fats and oils high in mono-unsaturated fats as in olive, canola, peanut, sesame...etc., help lower LDL-cholesterol in the blood.
  

Limitations of fats and oils

Apart from the need for fat-soluble vitamins and essential fatty acids, there is no specific requirement for dietary fats and oils as long as the diet provides adequate nutrients for energy. Excess carbohydrates in the form of glucose ultimately convert into fatty acids under the influence of insulin hormone. Those who consume omega-6 and omega-3 fats at the ratio of more than 10:1 should compensate by consuming omega-3 rich foods like fish, greens and algae.

Excess fats in the diet circulate as triglycerides and cholesterol in the blood. These components deposit at various proportions in different 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:-

Item	SFA%	MUFA%	PUFA% ω-6    ω-3	ω-6  to  ω-3 ratio	Remarks
Canola oil	8	61	21       10	2:1	Recommended
Flax seed oil	9	18	16       57	1:3.5	Recommended
Safflower oil	10	13	77         0	77:0	Somewhat recommended
Sunflower oil	11	20	69         0	69:0	Somewhat recommended
Corn oil	13	25	61         1	61:1	Somewhat recommended
Olive oil	14	77	8           1	8:1	Highly recommended
Soybean oil	15	25	53         7	8:1	Recommended
Sesame oil	15	42	43         0	43:0	Recommended
Peanut oil	18	49	33         0	33:0	Recommended
Salmon fat	24	34	0         42	0:42	Somewhat recommended
Cotton seed oil	27	19	54        0	54:0	Somewhat recommended
Chicken fat	32	47	21        0	21:0	Somewhat recommended
Palm oil	40	48	11        1	11:1	Somewhat recommended
Pork fat	41	48	11        0	11:0	Not Recommended
Beef tallow	47	53	0          0	0:0	Not Recommended
Cocoa butter	64	36	0          0	0:0	Not Recommended
Butter	69	31	0          0	0:0	Not Recommended
Cheese	70	30	0          0	0:0	Not Recommended
Hydrogenated- vegetable oil	76	19	0          0	0:0	Not Recommended
Coconut oil	92	6	1.6      0.4	4:1	Not Recommended

SFA= Saturated fatty acids

MUFA= Mono-unsaturated fatty acids

PUFA= Poly-unsaturated fatty acids

ω-3= Omega 3 fatty acids

ω-6= Omega 6 fatty acids