Fats

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Description and Use:

Fats or lipids are composed of carbon, hydrogen and oxygen. They are one of the three macronutrients, those nutrients needed in relatively large amounts to support normal function and health. The other two are proteins and carbohydrates. Fats are insoluble in water. They can be in a solid state, like animal fat, lard, butter etc. or in a liquid state, like vegetable oils. Their main functions in the body are to;

  • Provide fuel during rest or low to moderate activity.
  • Assist in the transport and utilization of fat-soluble vitamins; A, D, E and K.
  • Make lipid compounds; cell walls, hormones (eicosanoids).
  • Cushion vital organs.
  • Provide insulation. A layer below the skin can help protect from the cold.
  • Provide stores of energy when stored as adipose tissue.
When used for energy, fats can provide more calories per weight than carbohydrates or protein; 9 kcal/gm as oppose to 4 kcal/gm. That is because the fat molecule has a much higher ratio of hydrogen to carbon, for example C18H34O2. They are therefore less oxidized and require more oxygen to oxidize than carbohydrates.

Structure of Fats:

Knowing the different types of fats is important to understanding their health effects. Three types of lipids are commonly found in foods; triglycerides, phospholipids and sterols. 95% of they fats we eat are triglycerides.

  • Triglycerides are three fatty acid molecules attached to a glycerol backbone. A fatty acid is a long chain of carbon atoms with hydrogen attached to them. Fatty acids are characterized by their length (number of carbon atoms), saturation level (number of double bonds) and shape.
    • Saturated fats (saturated with hydrogen), SFA, are a fatty acid chain with no double bonds (weak points where an oxygen atom can attach). They are stable (resist going rancid) and are usually solid at room temperature. Examples are animal fats (meat, dairy products), coconut and palm (tropical) oils.
    • Monounsaturated fats, MUFA, are a fatty acid with one double bond. This double bond gives a slight curve to the molecule (cis shape) so that they do not fit compactly together like saturated fats. Therefore they are usually liquid at room temperature. Examples are olive oil, canola oil and peanut oil. Foods rich in MUFA include avocados, cashews, almonds, peanuts and most nuts.
    • Polyunsaturated fats, PUFA, are a fatty acid with more than one double bond. These are the least stable. If not stored properly, they are susceptible to oxidation and become rancid quickly. Examples are safflower, corn, soy and walnut oils. Foods rich in PUFA include walnuts and seeds (pumpkin, sunflower, sesame, flax).
    Keep in mind that fats, as found in foods, are a combination of several types, not just one. The examples given above represent fats where the majority component is of a certain type. For example the actual breakdown of olive oil is 74% MUFA, 14% SFA and 10% PUFA. So, in this case, olive oil is listed as a MUFA.
  • Phospholipids are two fatty acid molecules and one phosphate compound attached to a glycerol backbone. They are soluble in water, which makes them useful as emulsifiers and transporters of lipids in the body. The body can make them so they are not essential in the diet. Egg yolks, soybeans and peanuts contain phospholipids.
  • Sterols have a multi-ring structure quite different from triglycerides and phospholipids. The body can make them so they are not essential in the diet. Cholesterol is the most common example. It is part of every cell membrane and is needed to make sex hormones, adrenal hormones and vitamin D. It is only found in foods of animal origin; animal fats and egg yolks. Cholesterol does not contain any fatty acids (no saturated fat) and has no calories.

Food processing techniques can alter the properties of oils. Hydrogenation breaks the double bonds in MUFA's and PUFA's, and inserts hydrogen in a position to alter the shape of the molecule from cis to trans, making it straighter. They are therefore often referred to as trans fatty acids or just trans-fats for short. With this new shape, the oil becomes more solid at room temperature. This process is commonly used to make margarine from corn oil and shortening from plant oils. Hydrogenation is commonly used in the manufacturing of peanut butter in order to keep the oil from separating and to maintain a smooth texture. Hydrogenated oils are commonly used in processed foods to increase their shelf life. These trans fats, which will be discussed later, have been shown to have a negative effect on health. Update: On 18 June 2018, the U.S. Food and Drug Administration (FDA) officially banned the use of trans fats, or partially hydrogenated oils (PHOs), in all foods sold in American restaurants and grocery stores.

Digestion of Fats:

Digestion and absorption of lipids occurs primarily in the small intestine. Foods containing fats pass fairly intact to the stomach where they are mixed and broken up into droplets. They are then passed into the small intestine where they are mixed with bile secreted from the gall bladder. Bile emulsifies the lipids into smaller and smaller droplets that can be acted upon by enzymes secreted from the pancreas. There are specific enzymes for the three different types of lipids. Enzymes for triglycerides, break the fatty acid chains off the glycerol backbone. Absorption happens through the villa (enterocyte cells) of the small intestine. Short and medium chain FA (less than 14 carbons) attach to a transport protein (like albumin) or phospholipid and pass directly into the bloodstream. Long chain FA are reconstructed into trigylcerides and together with cholesterol and some phospholipids are packaged into a water soluble lipoprotein, chylomicron. Chylomicron is absorbed into the lymph system where it is eventually delivered into the bloodstream. In this way, fat consumed in a meal can be transported throughout the body via the bloodstream.

Chylomicrons can be picked up by various cells throughout the body. The three main fates of these lipoproteins are:
  • Used as an immediate source of energy, especially by muscle cells.
  • Used to make lipid compounds; cell walls, eicosanoids (prostaglandins etc.)
  • Stored in muscle or adipose tissue for future energy use.
People who are physically active, will have fat stored in the muscles first so it can be available for future activity. Excess after that is then stored in adipose tissue. To use energy stored in adipose tissue, it must first be broken down then transported to the muscle cells. Chylomicrons are cleared from the blood within 6-8 hours of a meal with moderate fat content. This is why people fast before a blood serum test, so that the lipids in the blood reflect regular ongoing bodily functions rather than the after affects of a particular meal.

Effects on Health:

The amount and type of fats that we consume in our regular diet can have a significant effect on our health. Not all fats are bad. Some fats are good for you. In fact, there are two essential fatty acids, EFA's that the body cannot make for itself and are required in the diet. These are the omega-3 and omega-6 EFA's which will be discussed later. Fats are needed to build sound cell membranes and to perform numerous physiological functions. The best strategy is to eat fats in moderation, i.e. in proportion to the total calories consumed, to avoid the bad fats (saturated and trans) and to consume the good fats (MUFA and PUFA). Too much fat can be a factor leading to obesity and all the problems that can come with it, high blood pressure, diabetes, heart disease etc. Eating the wrong types of fat can lead to heart disease, the number one killer in the U.S.

Doctors often use a blood serum lipid profile to check for the likelihood of heart disease. Atherosclerosis is the leading cause of most heart disease. It is a condition where artery passages become narrowed or blocked due to the accumulation of fatty deposits or plaque that over time can become fibrous and calcified (hardening of the arteries). The lipid profile indicates total cholesterol, LDL (low-density lipoproteins) often referred to as the bad cholesterol, HDL (high-density lipoproteins) referred to as the good cholesterol and the ratio of LDL to HDL. High LDL levels are a factor in causing arterial damage. They can oxidized with free radicals in the bloodstream and cause an inflammation reaction to start on the arterial wall. HDL on the other hand removes excess cholesterol from the blood. Healthy targets levels are: total cholesterol < 200 mg/dL, LDL < 130 mg/dL, HDL > 40 mg/dL and a ratio of total-cholesterol/HDL < 4.5.

Though other factors can contribute to atherosclerosis (obesity, smoking, stress, lack of exercise, high blood pressure etc.) diet remains the major factor. High levels of saturated fat will, in most people, cause LDL and total cholesterol levels to rise. Studies have shown that trans fats are even more harmful than saturated fats, raising LDL and lowering HDL. MUFA's, on the other hand, provide a healthy source of fats for use as fuel and the transport of fat-soluble vitamins while having a relatively neutral effect on LDL levels. However, they are not a source of the EFA's. It is the PUFA family though that includes the two EFA's. Linoleic acid has a double-bond in the 6th position (between the 6th and 7th carbon) and so is referred to as an omega-6 FA. Alpha-linolenic acid has a double-bond in the 3rd position and is referred to as an omega-3 FA. These EFA's play a very important role in forming the eicosanoid compounds that regulate many important cellular functions (reduce blood clotting, contraction and relaxation of artery walls, reduce inflammation response, gastrointestinal tract motility, vascular permeability, secretory activity, etc.). Omega-3 oils have been shown in many studies to have the beneficial effect of lowering LDL, raising HDL and lowering blood pressure in people with high blood pressure. It is important to include some good sources of omega-3 in the diet. The effectiveness of omega-3 can be inhibited by too much omega-6. It is therefore recommended that the ratio of omega-6 to omega-3 stay in a range between 4:1 to 10:1. Canola and soy oils have a ratio in this range. However, corn, safflower, sunflower, peanut, and sesame oil have a good portion of omega-6 but do not have any omega-3. Since they do not maintain good ratio, they are not the best choices for a staple oil in the diet.

Interesting historical and cultural notes:

Unfortunately, the modern diet has become low/deficient in EFA's. They are intentionally removed from commercial oils and processed foods to increase shelf life. Omega-3 oils cannot be made by animals and originate in plants. Fish have high levels due to algae in their diet. In the past, meat from free range grazing livestock had more omega-3 due to a diet of grass, wild plants and seeds in contrast to today's grain and corn fed livestock. This may explain why heart disease in America was rare prior to 1900 even though diets included a good amount of saturated fat. In the mid 1900's with the reduction of EFA's in the food supply, introduction of trans-fats and still a good amount of saturated fat (red meat, dairy) in the diet, heart disease really took off. In contrast, the traditional Japanese diet included a good amount of fish (omega-3 rich), little red meat or dairy and no trans-fat. Heart disease was very rare. Today, as they and other cultures move toward a typical Western diet, a corresponding increase in heart disease can be observed. So, this reinforces some basic points for good health; include a good source of omega-3 & omega-6 in the diet, reduce saturated fat intake and eliminate trans-fats.

Recommended Intakes:

A good recommendation for the total amount of fat in the diet is about 15-25% of total kcal. The low-fat groups (mostly in the Vegan community) prefer a lower level, 15-20% while other groups (American Dietetic Association) will accept a higher level 20-35%. The lower level, is a bit rigid and may require some self-discipline (like being on a diet all the time), may increase the risk of essential FA deficiency and taste will be sacrificed. A healthy individual can safely enjoy more. The higher level runs the risk of obesity. Again, the type of fat is more important than the total fat. Cretans eat about 40% total fat, mostly from olive oil, but have little heart disease. On the other hand, Scots also consume a high total fat but mostly from SFA and therefore have the resulting high levels of heart disease.

Assuming the average person has about 2000 kcal/day, this would mean 300-500 kcal should be from fats. At 9 kcal/gm this is approximately 35-55 gm. The mix of this total is important.

  • According to the AHA, less than 7% should be from saturated fat. In our example of 2000 kcal/day, this would mean 140 kcal or less than 16 gm of saturated fat per day. That's about 2 Tbsp of butter (butter is 50% saturated fat by weight), 5 glasses of 2% milk (3 glasses of whole milk) etc.
  • The remaining 20-40 gm should be from MUFA and PUFA. 1 Tbsp of oil is about 14 gm so this comes out to about 2-3 Tbsp.
  • The AI, adequate intake, for omega-6 is 17 gm for an adult male, 12 gm for an adult female and for omega-3, 1.6 gm for an adult male, 1.1 gm for an adult female.
  • Sources of omega-6 are more common than omega-3, so to maintain a good ratio (4:1), be moderate with the omega-6 sources and put a little more emphasis on finding a good source of omega-3. Sources of omega-6 include; sunflower, safflower, corn, soy and peanut oils and products made from them (like mayonnaise). Sources of omega-3 include; dark green leafy vegetables, flaxseeds, chia seeds, soybeans, pumpkin seeds, walnuts and canola oil. So, using canola oil for cooking and soy oil for mayonnaise/salad dressing can be a good choice. They include both omega-3 and omega-6. 1 Tbsp of canola oil has about 1.3 gm omega-3, soy oil about 1 gm.
  • 1 tsp of flaxseed oil (2.4 gm omega-3), 1 Tbsp of ground flaxseed meal (1.8 gm omega-3) or 1 Tbsp of chia seeds (2.3 gm omega-3) taken as a daily supplement, provide excellent sources of omega-3.

Keep in mind that in the average diet, the majority of fats consumed are in the form of "invisible fats". Cookies, crackers, chips, fries, bread, cakes, pastry and ice cream are typical examples. Unlike "visible fats", cream, butter, oil, mayonnaise etc. where you can see how much you are adding to your food, it is difficult to judge how much of the "invisible fats" you are getting when you consume processed foods. So, eat more whole foods and less processed foods. For the processed foods you do buy, find brands that use natural vegetable oils with no trans-fats.

Deficiency symptoms: Dry skin, mucous membranes, damaged hair, fat-soluble vitamin deficiency and gall stones. The symptoms can be vague and varied due to the widespread use of fats in functions of the body including numerous hormones and all cell membranes.

Excess symptoms: Too much total fat can lead to obesity. A high ratio of the wrong types of fat can lead to heart disease and possibly cancer (prostate).

Summary:

Based on the above information, here are some general (vegetarian) guidelines;

  • Minimize the amount of saturated fat in the diet. Use butter sparingly. Use low-fat dairy products as much as possible, 2% milk, low-fat yogurt and cheeses. Where practical, substitute some oil for butter in baking recipes, use milk instead of cream and frozen yogurt instead of ice cream.
  • Avoid trans-fats. Read labels on any processed foods. If there are any trans-fats or hydrogenated oils, pass on it. Look for other products from natural food companies that strive to keep their ingredient list clean. (Kashi, Amy's, Cascadian Farms, Cedarlane, to name a few)
  • Use MUFA oils for cooking. They are more stable. Use olive oil for sautéing vegetables. Use canola oil for frying when an olive oil taste is not desired, like for eggs and omelettes. Canola is also a good choice for baking. Peanut oil can be used for some Asian dishes.
  • Never heat an oil to the smoking point, the oil becomes damaged. Never breath the smoke from oil, it is toxic.
  • Do not heat PUFA oils. These are better used for cold oils, mayonnaise, salad dressing etc. Soy and safflower are good choices. Mayonnaise is a healthy addition to the diet. Use in sandwiches, potato salad, coleslaw etc.
  • Refrigerate PUFA oils and only keep small amounts of cooking oil out at a time. Oils are sensitive to light, air and heat. Discard any oil you think is rancid. It will have a bad smell.
  • Buy unrefined, cold/mechanically pressed, organic oils.
  • Eat a handful of raw nuts or seeds (pumpkin, sunflower) every day. Nut butters are good for toast, sandwich spreads or in recipes. Eat from a variety of different nuts and seeds. Walnuts are high in omega-3 oils.
  • Flax oil is an excellent source of omega-3 oils. 1 tsp per day with food can be very beneficial. Or using a coffee grinder, flax seeds can be ground into a meal then added to some dish. Whole flax seeds are not recommended, as they will pass through the system undigested.
  • Flax oil can go rancid quickly so buy small amounts, keep refrigerated and watch expiration dates.
  • Eggs are OK. Even though the yolks have some cholesterol, eggs are very low in saturated fat and have other beneficial nutrients. Studies have shown, that when eaten in moderation, there is no significant affect on LDL levels. Moderation is recommended though; not more than two at a time and not everyday. Choose the free-range variety. They will be higher in omega-3 and it's kinder to the chickens.
  • If you deep-fry foods at home, discard the oil after use. Deep-frying should be a very rare event, not something done on a regular basis. Avoid deep fried foods at restaurants. There's no telling the type and condition of the oil.
  • Coconut when eaten as a whole food, is healthy and safe. It is generally eaten in small amounts. Coconut oil which can raise blood cholesterol, may not be the best choice for cooking and baking when there are other monounsaturated vegetables oils (canola, olive) that are known for their abilities to lower LDL.

Disclaimer:

The contents of this Web site are not intended to offer personal medical advice. You should seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this Web site.

References:

  1. Thompson, Janice L., Melinda M. Manore and Linda A. Vaughn. "Lipids: Essential Energy-Supplying Nutrients" The Science of Nutrition San Francisco, CA : Pearson Benjamin Cummings 2008
  2. Duyff, Roberta L. "Fat Facts" American Dietetic Association Complete Food and Nutrition Guide Hoboken, NJ : Wiley 2006
  3. Weil, Andrew. "Fat Revisited: The Best Part of Food or the Worst?" Eating Well for Optimum Health New York : Quill 2001
  4. Willet, Walter C. "Surprising News About Fat" Eat Drink and Be Healthy New York : Free Press 2001
  5. Melina, Vesanto, and Brenda Davis. "Fat Feuds: Who's Winning?" Becoming Vegetarian Summertown, TN : BPC 2003
  6. Craig, Winston J. "Focus on Fat" Nutrition and Wellness Berrien Springs, MI : Golden Harvest Books 2008
  7. Murray, Michael T. and Jade Beutler. Understanding Fats & Oils Encintas, CA : PHP 1996
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