What is fat?

Fat is an essential energy source for humans. We eat fat and we also store energy in our bodies in the form of fat. Fat is utilized for energy, to build cell membranes, to transport fat-soluble vitamins and phytochemicals, to protect our organs from injury and our bones from pressure, and to insulate the body. Fats are also referred to as lipids.

Fats are named by their chemical structures

The simplest form of fat is the fatty acid (FA). 

Saturated fatty acids (SFA) have no double bonds between carbon atoms. Because of their structure, saturated fatty acids are able to pack closely together and are usually solid at room temperature. 

Monounsaturated fatty acids (MFA) contain one double bond between two carbon atoms. Double bonds create kinks in the shape of the molecule. Because of the kinking, unsaturated fatty acids are less able to pack tightly together and so are usually liquid at room temperature.

Polyunsaturated fatty acids (PUFAs) contain two or more double bonds between carbon atoms. For the same reasons as MFAs, they are also usually liquid at room temperature.

Triglycerides (TGs) are the storage form of fatty acids. They consist of three fatty acids joined to a glycerol side chain. Free fatty acids are rare in nature because they react readily with other molecules. Packaging fatty acids into triglycerides neutralizes their reactivity and prevents cell damage. Most of the fat we consume is in the form of triglycerides.

Fat in food

Contrary to what you might have been told, “You don't get fat from eating fatty foods just as you don't turn green from eating green vegetables.” - Gary Taubes

Dietary fat constitutes about 34% of the energy in the human diet. It could be more or less depending on how you eat. It is a source of energy and also a conveyance for fat-soluble nutrients, including vitamins, A, D, E and K. Naturally occurring fats are mixtures of different types of fats (saturated, monounsaturated, polyunsaturated), although one type usually predominates in a food.

Sources of dietary fat:

  • plant oils
  • meat
  • seafood
  • dairy
  • nuts and seeds

95-97% of ingested fat is absorbed. Fat increases the satiety of a meal, as fat is the slowest macronutrient to leave the stomach, other than fiber. The fatty acid content in the diet of an organism determines the proportion of fatty acid in the animal itself. The diet of a chicken determines the fats present in its eggs and meat and thus, the fats that we eat. The same is true for fish and all other types of meat and dairy.

Fat in the body

Fat in the body is found in: adipose tissue, blood as circulating triglycerides and lipoproteins, and in the liver. Body fat is categorized as either essential or storage.

Essential fat is necessary for normal physiologic functioning, is stored in small amounts in bone marrow, heart, lung, liver, spleen, kidney, muscles, and lipid-rich tissues in the nervous system.

  • In men, 3% body fat is essential.
  • In women, 12% body fat is essential because of sex-specific fat stores in breasts, pelvic regions and thighs.

Storage fat accumulates under the skin and around internal organs to protect them from trauma. Our reserves of stored fat can vary extensively, thus allowing for changing requirements of growth, reproduction, and aging as well as fluctuations in availability of food and physical demands.

The range of total body fat (essential + storage) associated with optimal health is 8%-24% in men and 21%-35% in women.

Fat-related buzz

Trans fats

Hydrogenation of unsaturated fat is the process whereby hydrogen atoms are added to liquid oils by chemical methods to form stable, solid fats, such as margarine. Hydrogenation is used by the food industry to change the properties of fats. The process produces trans-fatty acids. Trans is a reference to the location of hydrogens in relation to a double bond. Trans fats are harmful because their structure/shape allows them to pack tightly into bio-membranes.

Consumption of trans fat increases risk for coronary heart disease, cancer and other chronic diseases. Dietary sources of trans fats are hydrogenated margarine, shortening, commercial frying fats, high-fat baked goods, and salty snacks containing these fats.

Because of its harm, trans fat is noted on food labels; however, if a food contains less than 0.5 g trans fat per serving, the manufacturer doesn't have to mention it and can even label the food ias having “0 g trans fat.” A more reliable way to identify trans fat in a food is to look for “hydrogenated” in the ingredient list. If present, then the food contains trans fat, even if the label reads “0 g trans fat.”

Omega 3 fats and omega 6 fats

Omega 3 fatty acids and omega 6 fatty acids are both families of polyunsaturated fats. Their nomenclature is a reference to their chemical structures. Both omega 3 and omega 6 fatty acids are essential to humans, and unlike other types of fats, they cannot be synthesized in the body. Instead, they must be eaten.

Omega 3 fatty acids are known to have anti-inflammatory properties, which is beneficial. Our intake of omega 3 fatty acids has decreased over the years as our diet has changed from either fish-based (our predecessors living by the sea) or green plant-based (our predecessors living inland) to a largely meat and grain-based diet. Our modern diet is richer in omega 6 fatty acids from animal protein and grain oils. Omega 6 fatty acids, while essential to humans, can be inflammatory in large quantities. Omega 6 fatty acids are now over-abundant in our diets for our evolutionary preferences, while omega 3 fatty acids are too scarce.

Researchers believe the ratio of omega 6 fatty acids to omega 3 fatty acids is critical for optimal health. The optimal ratio of omega 6 to omega 3 fatty acids is between 2:1 and 3:1. To achieve this, try eating more omega 3 fatty acids and fewer omega 6 fatty acids.

Eat more sources of omega 3 fatty acids: 

  • wild-caught fish: salmon, mackerel, halibut, sardines, tuna and herring
  • nuts and nut oils: flax seeds, flaxseed oil, chia seeds, perilla oil
  • grass-fed meats
  • eggs from pastured chickens

Eat fewer sources omega 6 fatty acids:

  • meat, dairy and eggs from grain-fed animals
  • "vegetable" oil (usually a blend of some of the oils below)
  • sunflower oil
  • safflower oil
  • soybean oil
  • sesame oil
  • corn oil

Like to take a deeper dive into the world of fat and the new paradigm? Read Fat: The New Health Paradigm report by Credit Suisse. 

Need more evidence that Fat is Your Friend? Here's Dr. Aseem Malhotra to explain. 


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  • commented 2015-11-14 06:41:40 -0800
    I agree that the Fat Hypothesis was wrong. Fat is not the enemy with the exception of transfers, and saturated fats where the animals are fed corn or soy rather than pasture raised. WHY then, do you recommend low fat dairy in your recipes in the FatChance Cookbook?
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