Quantity vs Quality: The Institute of Medicine recommends a total fat intake of 20% to 35% of total calories. Amounts in excess of this may be linked with greater total calorie intake and saturated fat, where as consumption below this may tip the balance towards excessive carbohydrate consumption. Excess carbs in turn, increase a form of fat in your blood called triglycerides and lowers your healthy cholesterol called HDL. Historically, there has been great emphasis on the total fat in the diet; however it is important to note that the balance of, and quality of various fats i.e. proportions of desirable (unsaturated) and undesirable (trans- and saturated) fats in the diet are equally important as we will be noting below.
Omega-3 vs Omega-6: As discussed in Types of fats, the 2 main types of fats in the diet include saturated and unsaturated fats. ( See Table I below). The unsaturated fats are further classified as monounsaturated (single double bond between carbon atoms) and polyunsaturated (as the name suggests, these fats have 2 or more double bonds). Based upon the location of the double bond, polyunsaturated fatty acids (PUFAs) may be further classified as omega-3 or Omega-6 fatty acids. The location of the double bond (on 3rd vs. 6th carbon, from the end of the carbon chain), can substantially influence how these fatty acids behave in your cells and tissues. Most importantly, these fatty acids cannot be synthesized by your body, which means you must obtain them from food and are hence considered essential.
Alpha linolenic acid, ALA and linoleic acid, LA: These omega fatty acids are also referred to as long chain fatty acids or triglycerides (LCTs) as they have 18 or more carbons in their chain. The precursors of omega -3 and omega-6 series in the diet are the 18 carbon alpha linolenic acid (ALA) and linoleic acid (LA) respectively. ALA can give rise to the 20 carbon all important EPA and 22 carbon DHA, while LA can be elongated to produce the 20 carbon arachidonic acid, AA). AA helps to maintain the structure and function of your cell membranes. Having said that, as a result of enzyme competition, dietary imbalances etc, in reality very small amounts of ALA convert to EPA and < 1% converts to DHA. What does this mean for you, the consumer? Your best bet to get adequate amounts of EPA and DHA is to get them directly from the consumption of fatty, cold water fish such as salmon, mackerel, tuna, herring, cod, scrod or bluefish.
Food sources of ALA and LA: ALA occurs only in plant foods, with the best sources from walnuts, flax and chia seeds.
Linoleic acid is found in soybean oil, corn oil, and safflower and sunflower oils. It should be noted that foods high in fats such as nuts and oils are often a combination of poly, mono as well as some saturated fats. For example, walnuts contain substantial amounts of ALA, (omega-3), but also contain some LA (omega-6 PUFA ) as well as small amounts of saturated fats. Olive oil is considered a mono-unsaturated fat or MUFA as it contains predominantly a mono-unsaturated fat called oleic acid, and contains only small amounts of saturated fats and PUFAs as highlighted in the table below:
So why are the omegas so important? The omega-3 and omega-6 fatty acids serve key functions in the body as they give rise to eicosanoids which are hormone- like substances that influence blood pressure, blood clotting mechanisms, the immune response and the inflammation response to name but a few. The eicosanoids produced from omega3s (EPA) and omega-6s (AA) vary structurally and functionally. While eicosanoids derived from omega-6s have pro-inflammatory properties, promote clot formation and vasoconstriction (narrowing of blood vessels), the omega-3s are known to have anti-inflammatory properties, serve as vasodilators ( dilate blood vessels), and have anti-clotting effects.
Omega-3 s: A great catch!: The news is good all-around when it comes to omega3s. Emerging evidence shows omega3 fatty acids are associated with lower risk of heart disease, stroke and fatal heart rhythms. The AHA recommends 2 servings of fish per week to provide 450-500 mg of EPA and DHA or roughly about 8 oz of fish per week.
LA ( Linoleic acid) and inflammation: Given the association between omega-6 LA and increased inflammation, concerns have been raised about the adverse effects of these fatty acids on overall health and risk of chronic disease. However, a 2012 systematic review did not establish any relationship between LA and increased inflammatory markers in healthy adults. At this time, the literature supports the replacement of saturated and trans fats in the diet with PUFAs (both omega3s and omega6s) and MUFAs. These oils do not raise LDL or harmful cholesterol in your body. The replacement of saturated fats with refined carbohydrates (think of foods with “white flour” as the first ingredient), however, has adverse effects on heart health by raising triglycerides and lowering HDL. So move over pretzels, and make room for nuts such as almonds as snacks.
Storage: Owing to their double bonds, dietary fats such as PUFAs are easily subject to oxidation triggered by heat, exposure to light and oxygen, causing them to turn rancid quickly. Hence they should be kept cold and stored in a dark place . This is especially true of chia and flaxseed oils.
Daily Reference intakes: The 2005 Daily Reference Intakes recommend 5% to 10% energy from omega-6 and 0.6% to 1.2% of energy from omega-3 fats. This translates to 100-200 calories from the omega-6 fatty acids on a 2000 calorie diet. (For e.g. 1 tbsp of vegetable oil provides 15 grams of fat and 120 calories)
Reference: J Acad Nutr Diet. 2014;114:136-153. “Position of the Academy of Nutrition and Dietetics: Dietary Fatty Acids for Healthy Adults”