BioChemistry, Nutrition

Fats (Lipids)

Fats (Lipids)

Fats, also known as lipids, are essential macronutrients. Unlike carbohydrates, these organic compounds are not soluble in water (hydrophobic). There are three major classes of fats. The most common are triglycerides. Triglycerides are found in most foods. They are involved in many structural functions of the body, as well as, a structural component of all cells. The second major class of fats is called phospholipid. The body manufactures these lipids, which maintain a structural role and give cells their integrity. Phospholipids are essential in the proper functioning of the body. Sterols make up the final class. The most prevalent of the sterols is cholesterol. This form of lipid is manufactured by living organisms of animal origin and is not found in plants. Although cholesterol is often considered unhealthy, it is needed (in constant supply) for proper health and functioning of the body.

Lipids are required for many independent functions, within the body. They play a major role in the body’s ability to absorb vitamins A, D, E, and K, which are considered ‘fat-soluble’. They are required for the proper growth and development of cells and because lipids are insoluble in water, they are the single most important component of the cellular membrane structure. Their involvement in the structure of the cell wall is essential to membrane permeability. Lastly, lipids provide insulation and protection to the body and organs and they provide fuel during strenuous activity. In athletic performance of endurance athletes, fats (in the form of triglycerides) are the primary source of energy.

Digestive Flow and Metabolism of Lipids

Lipids are unique in character; unlike other macronutrients, lipids are insoluble in water. It is this biochemical property that gives lipids their structural role within the cellular membrane. It is also this property that makes them less digestible than carbohydrates and proteins. Lipids can remain in the stomach for a period of up to four hours.

Digestion of lipids occurs primarily in the small intestine. Once in the small intestine, the breakdown process is initiated, whereby bile secretions from the liver are coupled with enzymatic secretions from the pancreas. Here, the glycerol molecule is cleaved from the fatty acids so that they can pass through the intestinal wall. Once the fatty acids pass through the intestinal wall, they become coated with a proteinecious substance, then pass into the lymphatic system where they are absorbed into the bloodstream. This causes the blood cells to form clumps in the arteries, slowing normal blood flow. The “clumping” often leads to lethargy because of decreased blood flow through the capillaries. The fatty acids are then transported to the liver, where their usage is determined. Fats are either metabolized for energy or the fatty acids are modified, as needed, for other cellular functions. Excess fatty acids, that are not immediately utilized for cellular functions by the body, will eventually become fat stores.  Fats can accumulate in adipose tissue, intramuscular stores, or liver stores.  During exercise, it was previously thought that fats (metabolized for energy) were derived from adipose tissue or blood cells but it is now understood that lipids, metabolized during endurance exercise, are primarily derived from intramuscular fat stores. For high-intensity exercise, the body is not efficient in using fat for energy. 


Triglycerides are the most prevalent class of lipids. They can be stored by the body or metabolized and used for energy. They consist of three fatty acids and one glycerol molecule. The different fatty acids vary in length and number of hydrogen atoms that are attached to the carbon sites within each individual chain. Short-chain fatty acids have four to five carbon atoms. Medium-chain fatty acids can contain six to twelve carbon atoms. Long-chain fatty acids can contain thirteen to nineteen carbon atoms. The degree to which the carbon chains are saturated is what determines their property. There are two types of triglycerides: saturated fats, solid at room temperature, and unsaturated fats (oils), which are liquid at room temperature. 


Unsaturated fatty acids


Unsaturated fatty acids are not saturated to the maximal extent and have available sites to which hydrogen atoms can bond to. These “unstable” fatty acids are liquid at room temperature and can differ in property, by the degree to which they are saturated.


Mono-unsaturated fats – are fatty acids that have one (double bonded) carbon atom in the fatty acid chain, and multiple (single bonded) carbon atoms. These include: olives, avocados, canola, and peanut oils.  

Poly-unsaturated fats – are fatty acids that have more than one (double bonded) carbon atom. These include: corn, safflower, and sesame oils.

The body requires two essential fatty acids (EFAs) for proper function, growth and structure. Poly-unsaturated fats are required by the body when the primary EFA, linoleic acid, is in limited availability.  


Essential Fatty Acids (EFAs)

Fatty acids vary in form. Essential fatty acids (EFAs) are known by their poly-unsaturated properties, and are often referred to as vitamin F. Essential fatty acids are those that cannot be manufactured by the body and therefore must be ingested in the diet. EFAs are helpful in lowering cholesterol levels and blood pressure. They are also known to reduce the risk of heart disease and stroke. EFAs are found in high concentrations in the brain and are necessary for the proper function of the brain and nerves. There are two essential fatty acids that the body requires for optimal health, and one that is considered conditional. 


Linoleic acid – is the primary essential fatty acid needed for proper growth and good health. The recommended daily intake of EFAs is between 10 to 20 percent of the macronutrient ratio.  Diets that maintain the recommended portions of EFAs and are low in saturated, nonessential fatty acids are found to increase the metabolic rate, which in turn reduces the body’s need to store fat.  Diets that are higher than the recommended amounts are not healthy and will tend to be a factor in overweight individuals.

Linoleic acid occurs naturally in vegetables and vegetable oils.  When these oils are heated, they are converted to trans-fatty acids. Fats in this form no longer contain functional health benefits.

Alpha-linoleic acid – is the second essential fatty acid. Alpha-linoleic acid is important for growth and development. In addition, it is a known precursor to EPA (eicsapentaenoic acid) and DHA (decosahexaenoic acid). 

Arachodonic acid – is an essential fatty acid and is only needed when there is a deficiency of linoleic acid.  It is considered the conditional EFA. This fatty acid is derived from linoleic acid within the body. It is said to have a sparing effect on linoleic acid, thus preserving the body’s supply of linoleic acid. 

Omega-3 Fatty Acids

EPA (eicsapentaenoic acid) and DHA (decosahexaenoic acid) are both omega-3 fatty acids. They are manufactured in the body and derived from the essential fatty acid, linoleic acid.  Omega-3 fatty acids can also be obtained by consuming certain cold-water fish such as salmon, trout, sardines, mackerel, cod and tuna. Researchers believe omega-3 fatty acids assist the body in lowering cholesterol levels, when coupled with a diet low in saturated fat. They can also minimize the prevalence of heart disease, because omega-3s help the body disperse fatty acids and cholesterol.

Omega-3s have also been known to enhance athletic performance by increasing strength and aerobic capabilities.

Trans-fatty acids

Trans-fatty acids (trans fat) have been gaining attention because of their links to heart disease, diabetes, clogged arteries, and high cholesterol. Trans fats are unsaturated fatty acids that have been partially hydrogenated through a manufacturing process (hydrogenation) to increase the stability of their structure. With the use of heat, hydrogen atoms are added to vegetable oil and pressure is applied so the hydrogen atoms can attach themselves to altered sites within the carbon chain. Hydrogenation, thus, increases the shelf-life and palatability of the fatty acid by changing the properties and structure of the fatty acids so that the oil becomes solid at room temperature.


Hydrogen trans fats are also called “partially hydrogenated oils”. Hydrogenated fats are more highly saturated and therefore more solid at room temperature. Margarines and shortenings are unsaturated fats that have been hydrogenated. Hydrogenated fats are no healthier than saturated fats.     

Hydrogen trans fats can be found in dairy and meats, in small amounts, and they can also be found (artificially) in processed foods. The major sources of trans fats are in fried foods, packaged snack foods, microwave popcorn, piecrust, pizza dough, doughnuts, cookies, margarine, and crackers.  The RDA (recommended daily allowance) is less than 1 percent of  total caloric intake.

On July 25, 2008, California became the first state to ban trans fats from all restaurants and baked goods.  New York City has passed a similar ban.  Twelve other states have similar bills pending. 

Saturated fatty acids


Saturated fatty acids have no available sites for hydrogen atoms to bond and are thus considered to be at maximum saturation. These ‘stable’ fatty acids are solid at room temperature; and therefore have a long shelf life. The sources of saturated fatty acids are typically from animals, but palm oil and coconut oil are also highly saturated and are solid at room temperature.  Butter and dairy products can also contain high levels of saturated fatty acids. 

Medium-Chain Triglycerides

Medium-chain triglycerides (MCTs) are saturated fatty acids and can have six to twelve carbon atoms within the fatty acid chain. They are found in milk fat, coconut oil, and palm oil. MCTs are digested quicker than most fatty acids because of their medium-chain carbon properties. Long-chain triglycerides (LCTs) absorb across the intestines and then into the lymphatic system before entering the bloodstream, but MCTs tend to enter directly into the bloodstream after passing across the intestines. Thus, they become more readily available and a useful source of energy.

MCTs are found to be beneficial for endurance athletes and bodybuilders. They are a quick source of fuel and appear to be more efficient than fatty acid stores. For endurance athletes, MCTs can be a good source of high-energy fuel. 

Many bodybuilders believe a large consumption of MCTs (400 calories/day) can help increase muscle definition and improve muscle separation. This understanding is based on the fact that MCT consumption has a muscle sparing effect, when the diet is restricted to foods low in calories. The body may prefer the use of MCTs in the bloodstream for energy, over that of muscle glycogen.


The second major class of lipids is the phospholipids.  Phospholipids are manufactured by the body and are an integral part of all cells and their constituents. Due to the hydrophobic nature of lipids, they can coexist in the body, thus, they are the foundation that provides the rigidity and structure to the cellular membrane. They are made up of two fatty acids, a three-carbon glycerol, and a phosphate compound. Like most compounds within the body, they serve multiple functions. The primary function of lipids is in the structural integrity that they give to the cellular membrane. They are also involved in the digestive process, in which they assist in distributing fats throughout the blood stream. Phospholipids also play a metabolic role. In addition, they contain a major structural role in the nervous system and the conductivity of the neurons within. 

Phospholipids work in conjunction with biochemical compounds such as choline and inositol, which have lipotropic purposes within the body and therefore serve a very important role in the metabolism of fatty acids and carbohydrates.


Lecithin is a phospholipid that works with choline and inositol. Every living cell in the body requires lecithin to sustain itself. The cellular membrane is largely composed of this fatty substance. The presence of lecithin helps to protect the cell from oxidative damage, thus preventing hardening.

Lecithin is an important emulsifying agent.  It helps to remove fats from the liver along with its constituents, choline and inositol. Lecithin is important in brain function and memory.  It is the major component within the protective sheath surrounding the brain and neurons. It is highly concentrated in the protective layer surrounding muscular bundles. 


Choline is a lipotropic nutrient that is involved in the metabolism of fatty acids and cholesterol. It helps rid the liver of fat and aids in hormone production. Choline is also important in brain function and memory.


Inositol is a lipotropic nutrient that is important in the metabolism of fatty acids and cholesterol.  It helps in the removal of fats from the liver. In addition, inositol is essential in the production of lecithin.



Sterols are manufactured in the body, but can also be obtained from animal food products.  Cholesterol is the main group of sterols. 


Cholesterol is the most prevalent group of sterols. Produced in the liver, the body requires cholesterol for proper health. Upon secretion from the liver, cholesterol moves throughout the bloodstream and an uptake into cells occurs, where it is needed for various functions.  It assists the body in the digestive process, as it helps in the absorption of fatty acids across the intestines. It helps facilitate the distribution of fatty acids in the blood. Cholesterol, not needed by the cells, remains in the bloodstream. It can lead to plaque formations on the walls of the arteries.

LDLs (low-density lipids) – are the “bad” form of cholesterol and are consumed in the diet by eating animal meat and shellfish.  This form is not beneficial to the body and is often harmful to good health, due to the accumulation of plaque formations on the artery walls. In addition, the amount of cholesterol the body will produce and secrete is not dependent on the amount of cholesterol ingested. The body will maintain its normal production of cholesterol, even if levels are high due to excessive fat consumption.

HDLs (high-density lipids) – are the “good” form of cholesterol.  They help to remove and lower the levels of LDLs in the blood and tissues.  They are typically associated with lower risks of heart disease.

Sources of Fats

Mono-unsaturated fats:

Common sources: olives, avocados, canola oil, and peanut oil

Poly-unsaturated fats:

Common sources: corn oil, safflower oil, and sesame oil

Omega-3 fatty acids:

Common sources: cod fish, salmon, sardines, trout, and mackerel

Trans-fatty acids:

Common sources: fried foods, packaged snack foods, microwave popcorn, piecrust, pizza dough, doughnuts, cookies, margarine, and crackers. 

Gamma Linolenic acid:

Common sources: evening primrose oil, borage oil, and black currant oil

Saturated fats:

Common sources: whole milk, creams, butter, whole- milk cheeses, ice cream, lard, animal fat


Common sources: meats, egg yolks, dairy products, organ meats, poultry, fish, and shellfish

Fat Consumption and Weight-loss

To achieve weight loss, it is first recommended that the total daily caloric intake be reduced. It is important to focus on reducing the amount of fat calories to 20 percent of the daily intake, or lower in some cases. For the average person, it is not recommended to go below 15 percent of total calories because the body requires fatty acids for proper function and overall good health.

An individual on a reduced calorie diet, high in fat, will tend to store more fat than an individual on an identical caloric intake with a lowered dietary fat percentage. Therefore, reducing the fat calorie intake to 20 percent (or close to it) will be more effective than just a reduced calorie plan alone. It is recommended that a reduced calorie meal plan be coupled with an exercise program to maintain weight loss.

Fat consumption, for average healthy individuals and those looking to maintain their weight, should be no more than 30 percent of their daily calories. The intake of saturated fats should be monitored and kept below 10 percent. It is therefore recommended that the greatest amount of fat intake should come from unsaturated fats, focusing on polyunsaturated fats being the greater of the two. Essential fats should be consumed at the amounts of 1 to 2 percent of the daily caloric intake. 

Calculating Fat Calories

Conversion factors for calculating percentage of fat calories:

1 g fat = 9 calories

1 teaspoon fat = 5 grams (g)

5 g fat = 45 calories

1 tablespoon fat = 15 grams (g)

15 g fat = 135 calories

How to calculate the percentage of fat calories per food item:

Example:  250 calories, 9 grams (g) fat

1. Multiply the number of grams of fat in a serving by 9.

9 x 9 = 81

2. Divide the result by the number of calories in a serving.

81 ÷ 250 = 0.324

3. Multiply the result by 100.

0.324 x 100 = 32.4

32% of the total calories are from fat.

How to calculate total fat calories consumed:

2,000 total calories/day:

20% of calories from fat = 400 calories

      (45 g fat/day)

      (3 tablespoons fat)

30% of calories from fat = 600 calories

      (67 g fat/day)

      (4.5 tablespoons fat)

3,000 total calories/day:

20% of calories from fat = 600 calories

      (67 g fat/day)

      (4.5 tablespoons fat)

30% of calories from fat = 900 calories

      (100 g fat/day)

      (7 tablespoons fat)

* Keep in mind, the total grams or tablespoons per day is the maximum, not the minimum. Try to keep the fat calories to amounts less than the calculated portions per day.

Fat Intake for Athletic Performance

For endurance athletes, it is recommended that an average of 20 to 25 percent of their daily caloric intake come from lipids. A primary source of fuel for endurance athletes will be derived form fat stores. In general, athletes should try to minimize their daily intake to less than 20 percent of their total calories.  Bodybuilders usually try to lower their fat intake to around 15 percent of their total calories per day. All athletes require greater amounts of essential fatty acids (EFAs). It is also important for all athletes to reduce the amount of saturated fats, to help maintain higher levels of energy and improve athletic performance.


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