Fats and Oils
|See Also||Clinical Nutrition|
Fats or lipids are essential macronutrients that play many different roles in the body including providing energy, helping to absorb fat soluble vitamins and assisting with growth and development. They can be classified as either fatty acids or triglycerides. Lipids are found in all cells in the body, with the highest concentration found in adipose (fat) and nerve cells, and the lowest concentration in muscle and epithelial cells.
Classifications of Fat
From a chemical perspective, fatty acids are carboxylic acids composed of a carboxyl (or carbon) group, methyl group, and a hydrocarbon chain. They are measured based on their length and are either short, medium or long chain. Short-chain fatty acids have fewer than six carbons, medium-chain fatty acids have 6-12 carbons and can form medium-chain triglycerides, long-chain contain more than 12 carbons and very-long-chain fatty acids contain 22 carbons.
Fatty acid chains are classified as either unsaturated or saturated. and as either essential or non-essential. Unsaturated fats are commonly referred to as good fats, saturated fats are the bad fats and trans fats are the one that you want to avoid completely. The type of fat you consume is more important than the quantity.
Unsaturated fatty acids are further broken down into monounsaturated, polyunsaturated or trans fatty acids. All dietary fats - butter, lard and vegetable oils - are a combination of monounsaturated, polyunsaturated and saturated. Trans fatty acids are made by processing liquid vegetable oils with hydrogen. This group is often referred to as partially hydrogenated oil and is by far the most harmful to health.
- Unsaturated Fatty Acids is a fat in which there is a least one double bond within the fatty acid chain.
- Monounsaturated Fatty Acids are liquid at room temperature and contain only one double bond.
- Polyunsaturated Fatty Acids are also liquid at room temperature and contain two or more double bonds. Examples of polyunsaturated fatty acids include Omega-3 Fatty Acids, Omega-6 Fatty Acid and Omega-9 Fatty Acid.
- Most vegetable oils are comprised of unsaturated fats. They can be divided into two main categories which are cooking oils and medicinal oils. The best known cooking oils include canola and olive oil. Medicinal oils include evening primrose oil, borage, flaxseed, and black currant oil.
- Evening primrose, borage, and black currant oil all belong to a class of omega-6, polyunsaturated, essential fatty acids that contain gamma-linolenic acid.
- Flaxseed oil is an omega-3, polyunsaturated, essential fatty acid that contains alpha-linolenic acid.
- Trans Fatty Acids have double-bonds between the fatty acids that can be converted to single bonds, hence the bonds are called unsaturated.
- Saturated Fatty Acids are solid at room temperature and contain long-chain carboxylic acids that contain only single hydrogen bonds.
- Coconut oil is a medium-chain fatty acid or triglyceride (MCT), that is saturated.
- Essential fatty acids are required by humans and must be obtained from food as they cannot be made in sufficiency quantity from other sources. The two essential fatty acids are widely available in plant oils and include linoleic acid which is an Omega 3 polyunsaturated fatty acid and alpha-linolenic acid which is an Omega 6 polyunsaturated fatty acids. The body has a limited ability to convert alpha-linolenic acid which is a short-chain fatty acid into long-chain fatty acids such as eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA).
Lipids are found in nearly every natural food stuff. Meats and poultry, whole milk and cheese and eggs generally have higher amounts of lipids while vegetables and fruits have much smaller amounts. The plant sources with the highest fat content include olives, avacodos, and nuts. More than half of the dietary fat consumed comes from processed foods, baked goods, whole grain cereals and milk.
The table below displays the percent fat in 100g portions of common foods.
|Food||Total Fat % by Weight||% Saturated Fat of Tot FA|
|Bread, whole wheat||2.6%||0.4%|
|40% Bran Cereal||2.8%||Trace|
The following chart looks at different salad and cooking oils and their composition.
|Oil||Omega 6 to Omega 3||% monounsaturated fat||% polyunsaturated fat||% saturated fat|
|Mustard seed oil||2.60||59.2%||21.2%||11.6%|
|Almond oil||no Omega 3||69.9%||17.4%||8.2%|
|Apricot kernel oil||no Omega 3||60.0%||29.3%||6.3%|
|Coconut oil||no Omega 3||5.8%||1.8%||86.5%|
|Hazelnut oil||no Omega 3||78.0%||10.2%||7.4%|
|Peanut oil||no Omega 3||46.2%||32.0%||16.9%|
|Rice bran oil||20.9||39.3%||35.0%||19.7%|
|Safflower oil||no Omega 3||14.4%||74.6%||6.2%|
|Sunflower oil||no Omega 3||19.5%||65.7%||10.3%|
|Tomato seed oil||22.1||22.8%||53.1%||19.7%|
|Wheat germ oil||7.9||15.1%||61.7%||18.8%|
Lipids play an integral role in maintaining health including:
- Important energy source and fuel for the body. Lipids are calorically rich, with an energy density of 9 kcal/g, in comparison to protein and carbohydrates which both have an energy density of 4kcal/g.
- Structure and function of cell membranes
- Precursors to some hormones
- Act as cell signalling intermediates.
- Provide the sense of being satiated or full when eating.
- The benefits of dietary intake and supplementation of polyunsaturated fatty acids, specifically Omega-3 Fatty Acids, with respect to Cardiovascular Disease (CVD), auto-immune disease, Cancer, diabetes, Psoriasis, and mental illness are well studied and regularly emphasized in the practice of Clinical Nutrition.
- While studies in the 1960's and 1970s suggested increased fat intake was correlated with increased risk of coronary heart disease (CHD), more recent evidence suggests decreased fat intake has no appreciable effect on CHD.
- Lower fat intake may lower LDL Levels, but it also seems to decrease HDL and increase triglycerides. The lack of appreciable benefit to lower fat intake may be correlated to the associated increase in carbohydrates. If the carbohydrates replacing dietary fat are largely refined with low fiber intake, this will adversely affect glucose-insulin homeostasis and its correlating negative health affects.
- Increased dietary intake of trans fatty acids has been shown to increase LDL, triglycerides, and lipoprotein a levels, and decrease HDL levels. Unlike saturated fatty acid intake, these negative effects are observed regardless of the macronutrient replaced. Studies have also demonstrated trans-fatty acids may promote inflammation, insulin resistance, visceral adiposity, and endothelial dysfunction.
Traditionally dietary fat intake is recommended not to exceed 30% of total energy in the diet, with unsaturated fatty acids accounting for at least 70% of total lipid intake. Many cell types can use either glucose or fatty acids as an energy source. Heart and skeletal muscle prefer fatty acids.
- 'Rancid fats and oils. Fats, oils and lipids are prone to rancidification, which means that there is a chemical decomposition that occurs due to oxidation and produces undesirable odours and flavours. At times, such as with aged cheese, this process may be intentional.
- Antioxidants are added to fats and oils to reduce the risk of rancidification.
- Different fats and oils oxidize or become rancid at different rates.
- At the grocery store
- Read labels to ensure that you are avoiding saturated and trans fats.
- Choose leaner cuts of meat, skinless chicken and turkey. Or remove the skin before cooking.
- Choose lower-fat dairy products.
- Choose soft margarines that are low in saturated and trans fat.
- Buy fewer pre-packaged foods and "ready-to-eat" meals.
- Buy vegetables, fruit and whole grain products with no added fat.
- Berdanier CD, Zempleni J. (2009) Advanced Nutrition: Macronutrients, Micronutrients and Metabolism. CRC Press.
- Cordain Loren (2011) The Paleo Diet, Revised Edition, Lose Weight and Get Healthy by Eating the Foods You Were Designed to Eat, John Wiley & Sons, New Jersey.
- Hoffer A, Prousky J. Naturopathic Nutrition: A Guide to Nutrient-Rich Food and Nutritional Supplements for Optimum Health. CCNM Press 2006
- Mozaffarian D. (2011) Nutrition and Cardiovascular Disease: Chap 48 Braunwald's Heart Disease - A Textbook of Cardiovascular Medicine, 9th ed. Saunders.