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The Basics of EFAs

Article

by Robin Koon -

While knowledge of essential fatty acids (EFAs) is growing among marketers and consumers, reviewing the comprehensive lipid category provides a point of references to delve further into the structure and function of these beneficial fats.

Dietary lipids are an essential constituent of the human diet along with carbohydrates, proteins and fiber. Fats are a source of energy, supplying about 9 calories per gram, and make up approximately 40 percent of the body’s normal caloric intake. Lipids are a large and diverse group of naturally occurring organic compounds related by their solubility in non-polar organic solvents (e.g., ether, chloroform, acetone, benzene, etc.) and insolubility in water.

In the human diet, triglycerides are the most abundantly consumed form of edible dietary lipids and normally constitute approximately 95 percent of total fat ingested. The remaining 5 percent is in the form of cerebrosides, phospholipids, fatty acids, fatty alcohols, cholesterol, sterols, terpenes, etc. The average human being consumes between 50 and 200 g/d of fat.

Triglycerides (TG) are comprised predominantly of fatty acids (present in the form of esters of glycerol), although they are technically a combination of glycerol and three fatty acids, sometimes referred to as triacylglycerol. Glycerol is a three-carbon chain alcohol molecule with chemical formula of C3H803. When combined with one, two or three fatty acids, it forms a monoglyceride, diglyceride or triglyceride, respectively. Triglycerides are generally not well-absorbed in the gut and are enzymatically hydrolyzed, which splits the TG into its components by removing the fatty acids from their glycerol base, so all of these components can be easily absorbed.

Fatty acids (FAs) are substances typically found in plant and animal lipids. Natural fatty acids commonly have a hydrocarbon chain of four to 28 carbons (usually unbranched and even numbered), terminating at one end with a carboxylic acid group (-COOH), and the other end with a methyl group (-CH3). The differences between many of the fatty acids are the length of the chain and the positions of their bonds, which may be either saturated or unsaturated.

FAs are divided into two basic groups, classified upon their degree of saturation. Saturated and unsaturated fats are designated by the presence of double bonds within the chain of carbon atoms in the fatty acid. Saturated fats have only single bonds, while unsaturated fats have one or more double bonds. Unsaturated fats with only one double bond are known as monounsaturated fatty acids (MUFAs) and those with more than one double bond are called polyunsaturated fatty acids (PUFAs). Normally at ambient room temperature, saturated fats are solid (fats) and unsaturated fats are liquid (oils).

Fatty acid chain lengths from two to six are called short-chain, from six to 10 are medium-chain, and 12 to 28 are long-chain. The length of the “tail” determines water solubility and amphipathic characteristics.

Designations using the Greek alphabet (α, β, γ, ..., ω) are used to identify the location of the double bonds in unsaturated FAs. The “alpha” carbon is the carbon closest to the carboxyl acid group (-COOH), and the “omega” is the last carbon of the chain (methyl group, -CH3), as omega (ω) is the last letter of the Greek alphabet.



The EFA Category

EFAs are polyunsaturated fatty acids that cannot be made by man endogenously, but must be derived or ingested from dietary sources, exogenously. There are two families of EFAs: ω-3 (omega-3) and ω-6 (omega-6). Omega-3 EFAs are a class of fatty acids with the double bond in the third carbon position from the methyl terminal (ω- omega end), while the initial double bond in omega-6 EFAs occurs in the sixth carbon position from the methyl group (ω- omega end). Both families have parent compounds, which are short-chain polyunsaturated fatty acids (SC-PUFA): the omega-3 family comes from alpha-linolenic acid (ALA) and the omega-6 family comes from linoleic acid (LA).

ALA and LA are considered to be “essential,” as the body can convert one omega-3 to another omega-3, but cannot create an omega-3. Human metabolism cannot create EFAs from other fatty acids because the human body is unable to add a double-bond to a fatty acid that is more than nine carbons away from the acidic end (-COOH). Humans lack the necessary enzymes (desaturase) to insert a cis double bond at the ω-3 or ω-6 position of a fatty acid. This also means the body cannot convert an omega-3 to an omega-6 fatty acid, or vice-versa.

The body can synthesize longer omega-3s and omega-6s—known as long-chain polyunsaturated fatty acids (LC-PUFA)—from these “parent” fatty acids. ALA can be converted into the longer-chain omega-3s eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Similarly, LA can be converted into long-chain omega-6s gamma-linolenic acid (GLA) and arachidonic acid (AA). However, this biochemical-physiological process is slow and inefficient; it is estimated that only 5 to 7 percent of ingested ALA is converted into omega-3 LC-PUFAs.

Fortunately, there are many dietary sources of omega-3 and omega-6 EFAs, which can be consumed in foods/beverages, functional foods or dietary supplements. Omega-6s are found primarily in plant oils, including corn oil, safflower oil, soybean oil, black currant seed oil and evening primrose oil, among others. ALA can be found not only in plants (e.g., canola, chia, flax, hemp, pumpkin seed), but also from marine sources (e.g., algae, fatty fish). Pre-formed EPA and DHA are found in marine sources.



EFAs in the Body

EFAs are involved in several key bodily functions, including cardiovascular function; eicosanoid formation/synthesis; prostaglandin production; cellular membrane structure/function (e.g., fluidity, flexibility, permeability); brain/nervous system activity; gene expression (activating or inhibiting transcription factors); and vision. In addition, EFAs are substrates for the endogenous synthesis of other fatty acids that are needed for many physiologic processes. Deficiency is rare, occurring most often in infants fed diets deficient in EFAs; however, it is possible to develop an EFA insufficiency. Reported clinical signs of EFA deficiency run the gamut from skin conditions (acne, dermatitis, wound healing) to cardiovascular dysfunction (angina, hypertension, stroke), and neurological dysfunction into inflammation and cancer.

In addition, the balance between dietary intake of ω-3 and ω-6 can strongly affect their functions. The typical western diet is low in EFAs in general, and tends to be much higher in omega-6s than omega-3s, with typical consumption ratios of omega-6 to omega-3 in excess of 10-to-1.

Many researchers believe this imbalance is a significant factor in the rising rate of inflammatory disorders or related diseases. There is much evidence that several so-called “lifestyle” diseases—such as arthritis, heart disease, cancer, diabetes and obesity to name just a few—are reduced by increasing dietary intake of omega-3s.

That said, there is still no consensus on the “ideal” amount of omega-3 consumption, particularly of the longer-chain EPA and DHA. For example, the American Heart Association (AHA) recommends 0.5 to 1 g/d of EPA/DHA. The USDA Nutrient Data Library lands on the higher side of that recommendation (1.0 g/d), the UK Department of Health goes much lower (0.2 g/d), and the World Health Organization (WHO) lands in the middle (0.7 g/d). Another guideline is the Dietary Reference Intake (DRI) system issued by the U.S. Institute of Medicine (IOM), which offers varied recommendations on Adequate Intakes (AI) of total EFAs.

Dietary Reference Intakes (DRIs)∗
Macronutrient Children 1-3 yrs Children 4-18 yrs Adults
n-6 polyunsaturated fatty acids (linoleic acid) 7 10 17
n-3 polyunsaturated fatty acids (alpha-linolenic acid) 0.7 0.9 1.6
Source: National Academies Institute of Medicine (IOM)

Notes: 1. Approximately 10 percent of the total can come from longer-chain ω-3 or ω-6 fatty acids. 2. DRI for adult shown above is for males aged 19-30 years.
∗Consumption amounts shown in g/d.



Robin Koon is senior vice-president at Best Formulations and has more than 25 years of pharmaceutical experience in clinical pharmacy as a drug chain executive overseeing operations and managed-care, and in retail mass market.

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