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What are Fats?

Fats are a highly varied macronutrient group, and they're present in both animal and plant-derived foods.  At nine calories per gram, fat is the most dense source of calories required by the human body.  However, not all fats are created equal and it's crucial to pay attention to which types of fat you include in your diet.  Some fats are healthy, some are fairly neutral, while others are actively detrimental to you health.

What Fats Do in the Body

Fats perform a number of duties in your body, such as helping absorb certain micronutrients and keeping your skin and hair healthy. The process of creating, storing, and using fat is how energy is kept in balance. Fats enable your body to absorb and hoard fat-soluble vitamins in the liver and fat tissue. Vitamins A, D, K, and beta-carotene typically have an absorption rate of about 80%, while vitamin E is absorbed at a rate of about 20%. In one study, vitamin D absorption increased simply by adding fat to the meal. When the fat content of the meal was 30% of the calorie count, the vitamin D3 absorption improved significantly. Fat is responsible for setting off basic metabolic processes that regulate growth, immune function, and reproductive development. If you’re trying to limit fat intake, obtain no less than 6% of your calories from fat to keep these systems functioning properly.At the other end of the spectrum, cap your fat intake at 20-35% of your total daily calories. Since fat contains more than twice the calories of protein or carbohydrates, excessive consumption can lead to weight gain.


Absorption and Storage of Fats

Most dietary fats are “triglycerides.” These are composed of three fatty acid hydrocarbon chains bonded to a glycerol backbone. During the digestive process, bile breaks down triglycerides in the small intestine so they can be absorbed into the bloodstream via the liver and either directed into cells for immediate use or sent to lipocytes (fat cells) to be stored and used later.

Metabolism of Fat Reserves

When your body taps into its energy reserves, the

reserves used are carbohydrates, which are stored

as branched chains of glycogen in the muscles and

liver. Humans only store enough carbs to fuel about

20-30 minutes of vigorous activity.After that, your body switches its energy resource to fat reserves. Lipases are the enzymes that break down fat stores to release energy for mitochondria. The metabolism of fat is aerobic (it requires oxygen molecules) and occurs in the mitochondria. The metabolism of carbohydrates is anaerobic (it does not require oxygen) to release energy.

In addition to providing a calorie-dense source of energy, visceral fat protects organs in the abdominal cavity from damage. Subcutaneous fat insulates the muscles and helps regulate body temperature.

Types of Fat

Dietary fat can be essential or non-essential. Essential fatty acids, like omega-6 (linoleic acid) and omega-3 (alpha-linoleic), cannot be produced by the human body—they need to be consumed. There are several subclassifications of these fats, like ALA and DHA, which are distinguished by their chemical structure. The body relies on essential fatty acids for blood clotting, neural development, and managing inflammation.

Non-essential fatty acids are still important to the body but can be produced internally with the proper resources. Saturated fat is not essential in a nutritional sense but is important for hormone regulation in the body.


Whether a fat is saturated or unsaturated depends on the number of the hydrogen atoms bonded to the carbon chain that makes up the triglyceride. If a fatty acid is saturated, there are no double bonds between the carbon atoms. The fatty acid chain is fully saturated with hydrogen atoms. If there are double bonds between two carbons in the chain, the fatty acid is either monounsaturated or polyunsaturated depending on the number of double bonds in the chain. Saturated fats are solid at room temperature because the hydrocarbon chains are closer together. These straight chains can stack together at the molecular level to become more viscous. Mono- and polyunsaturated fats are twisted or kinked at their double carbon bonds, preventing the chains from packing closely together.

All naturally occurring classifications of fats are composed of a mixture of polyunsaturated, monounsaturated, and saturated fatty acids. The physical state of any fat at room temperature is determined by which type of fatty acid is the most prevalent.


In olive oil, the dominant fatty acid is monounsaturated, so it is liquid at room temperature. Butter is primarily made up of saturated fatty acids, so it is solid at room temperature.

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