Fats, also known as triglycerides, are organic molecules composed of three fatty acid chains and the alcohol glycerol. There are many different kinds of fats, but each is a variation of the same chemical structure.
The simplest unit of fat is called a fatty acid – which is made from hydrocarbon chain with a methyl group on one end and a carboxyl group on the other. Saturation can occur when hydrogen atoms bond to the hydrocarbon – the more hydrogen, the more saturation.
A fat is classified as saturated fat when all of the available bonding spots are occupied by hydrogen. This structure usually leaves the saturated fat solid at room temperature.
If all of the bonding spots are not occupied by hydrogen, the fatty acid is classified as unsaturated.
A monounsaturated fatty acid occurs when only one of the carbons is not saturated, and a polyunsaturated fatty acid occurs when more than one of the carbons is not saturated.
Fat has several functions in the diet:
Omega-3 fatty acids are polyunsaturated fatty acids with a double bond at the third carbon atom from the end of the carbon chain. There are several omega-3 fatty acids, but in human physiology our focus is on three: alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). These fatty acids are important for normal human metabolism, and while we can’t synthesize them, we can obtain ALA from our diet to help form EPA and DHA. Unfortunately, this conversion occurs at a very low percentage (slightly higher in women than men).
Omega-3 fatty acids are often considered to have anti-inflammatory effects. They will help dilate blood vessels, decrease pain, and reduce systemic inflammation.
Omega-6 fatty acids are polyunsaturated fatty acids with a double bond at the sixth carbon from the methyl end. There are several omega-6 fatty acids, but the most talked about are linoleic acid (LA), gamma-linolenic acid (GLA), and arachidonic acid (AA).
Contrary to the omega-3 fatty acids and their anti-inflammatory nature, omega-6 fatty acids have a pro-inflammatory effect on the human body. They promote eicosanoids that will increase inflammation, cause blood clotting, and can increase pain. While this sounds pretty bad on the surface level, also understand that we need them – and that without them we wouldn’t be able to recover from training and/or injuries.
Because our bodies lack the enzyme omega-3 desaturase, we can’t breakdown omega-6 fatty acids to omega-3 fatty acids. This is important to understand, because both fatty acids are competing for the same enzymes internally. For this reason, it is recommended that we consume a diet that is balanced at minimum 1:1 omega-3 to omega-6. Unfortunately, the current North American diet provides a ratio closer to 10:1, and european diet providing a ratio of 20:1.
Food quality can typically help bring this ratio back closer to 1:1. Once you have addressed food quality, supplementation can also help.
Food sources that are highest in saturated fats are:
Food sources that are highest in monounsaturated fats are:
Food sources that are highest in polyunsaturated fats are:
When viewing digestion of fats, it is important to understand that lipids are hydrophobic, and are therefore poorly soluble in the digestive tract. Instead, bile will emulsify triglycerides mostly in the small intestine. Emulsification is the breaking up of fat globules into much smaller emulsion droplets.
The pancreas then secretes pancreatic lipase into the small intestine where fatty acids and glycerol are separated.
Once inside the enterocyte and mucosa (intestinal cell layer), the fatty acids are repackaged into chylomicrons. Chylomicrons will then carry these triglycerides into the blood, where they are again broken down into free fatty acids and glycerol. This breakdown occurs with the help of lipoprotein lipase, so that they can pass through more cell membranes into other tissues of the body.
From there, two things can happen:
As discussed above, chylomicrons are the are the largest lipoprotein, and they are involved in transport of fatty acids. There are several other lipoproteins that exist, but in your work you will likely discuss two of them on a regular basis:
You may recognize these numbers associated with cholesterol in your blood work. For the purposes of this text, we will not go into great detail about the physiology of lipoproteins (beyond your scope). However, because these numbers are indicators of health, it is important to create a brief understanding.
LDL – often referred to as – bad cholesterol, have the ability to transport their content INTO artery walls, causing things like atherosclerosis.
HDL – often referred to as – good cholesterol, have the ability to remove these same contents OUT OF artery walls, contributing to better health and decreasing cardiovascular risks.
It is important to understand that fat is the most calorically dense macronutrient, at 9kcal/g. And while fats have several health benefits, eating them in excess will not contribute to positive physical changes.
As discussed earlier, quality of fat intake is also extremely important. Creating a minimum ratio of 1:1 omega-3 to omega-6 should be the goal when viewing fat consumption.
The overall recommendation of fat intake will vary from individual to individual. The USDA has provided the following guidelines:
Remember, USDA guidelines are NOT created with any specific populations in mind.
In the athletic and aesthetic world, we have found that the percentage of fat intake will vary to a much greater degree, ranging from 20-70% of total calories.
The lower end of this range is typically seen in populations focussed on extreme aesthetics, or high volume aerobic work, whereas the the higher end of this range is used in ketogenic diets. We will discuss this in greater detail in the “application” portion of this course.
A few things to consider when prescribing fat intake:
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