Despite popular belief, a diet high in fat is beneficial for your health. Fats, unlike carbohydrates are essential for our survival and take part in many vital functions in the body. The only function of carbohydrates is energy production.
If you are on a low fat diet, carbohydrates are the primary source of energy. However, if you switch to high fat diet and consume only a sufficient amount of carbohydrates to avoid keto-acidosis (around 50g), your metabolism switches to use fat as fuel.
Understanding the functions of fat, including which fats are bad and which are good, will help you to manage your diet better and take advantage of all the health and culinary benefits that fats can provide.
Dietary fat and fat in the body refer to a wide variety of lipids. Of these lipids, the most abundant are triglycerides – molecules composed of glycerol and three fatty acids.
Fatty acids are hydrocarbon chains and can be either:
- Unsaturated (polyunsaturated and monounsaturated). This also includes trans fatty acids.
For more details, see the article “Triglycerides – basic chemistry”.
Calories in fat
Fats are a high-energy macronutrient and an efficient way to store energy in our body. One gram of dietary fat is equivalent to 9 kilocalories, while the other two macronutrients, carbohydrates and proteins, only generate 4 kilocalories per gram.
“Dietary fats” refer to both fats and oils derived from animals or plants. They should ideally be called something like “dietary lipids” to avoid confusion. Read more on the differences between definitions of lipids, fats and oils here.
Dietary fats mainly consist (95%) of triglycerides, that combine various proportions of saturated and unsaturated fatty acids.
Saturated fats don’t necessarily consist of 100% saturated fatty acids. Fats are called saturated when they have a significant proportion of saturated fatty acids.
For instance, butter, although it is considered a saturated fat food, also contains polyunsaturated and monounsaturated fatty acids.
Similarly, monounsaturated fats usually mean a predominant proportion of monounsaturated fatty acids, such as in extra virgin olive oil. Olive oils also contain a small amount of saturated fatty acids.
When we think of fats from foods, we either think of saturated fats or unsaturated fats. This distinction is important, because each type of fat exerts different actions in our body.
Some are considered to be good and others bad. It is a controversial subject because the opinions on which fats are good and which are bad are divided.
- Fat as energy intake
Depending on your diet, the proportion of fat in your daily energy intake varies greatly.
If you are on a high carbohydrate diet, currently promoted by the mainstream nutrition authorities, you will most likely consume below 35% of your total calories from fat.
If you are on a high fat and low carbohydrate diet, such as the ketogenic diet, you may consume up to 75% of total calories from fat.
- Fat in cooking
Fat/oil are less dense than water and insoluble in water. Therefore, it always stays on top of watery liquids as a solid layer (due to its melting point being above fridge temperature), once they cool off after cooking (a good method to easily remove it from the liquid, if not desired).
Fats’ texture improves the palatability of foods. It contributes to food’s texture, flavor and aroma. Fat is essential in various cooking methods such as stir frying, pastry baking or deep frying. (1)
In high temperatures, fats and oils oxidize and become rancid, producing harmful compounds. Therefore, it is important to use the right fats or oils for cooking in high temperatures.
Carbon double bonds, which exist in mono and polyunsaturated fatty acids, are less stable and more vulnerable to chemical reactions, such as oxidation, than single bonds of saturated fatty acids.
The bottom line is, you need to know that the safest fats or oils to use in high temperature cooking methods are the saturated fats (no double bonds), such as coconut oil, or the monounsaturated fats (only one double bond), such as avocado oil.
- Vitamins in fats
Fats are an important part of our diet, because they are a source of four very important vitamins: A, D, E and K.
- Which fats are good and which fats are bad?
The healthiest fats are the monounsaturated fats and one type of polyunsaturated fats – the omega-3 fatty acids.
The most harmful fats are industrially produced trans fats (can be polyunsaturated or monounsaturated). They are generated during partial hydrogenation process in the production of some margarines and shortenings. Industrial trans fats have a clear link to an increased risk of developing heart diseases and cancers. (read more..)
The naturally occurring ruminant trans fats are considered as safe for human consumption in their natural form – milk or meats of ruminant animals. (read more..)
Omega-6 fatty acids are a type of polyunsaturated fats that, like omega-3, are essential to our good health. However, our modern diet consists of excessive amounts of these fats. Therefore, in this context, omega-6 fatty acids are considered unhealthy and should be limited in order to reduce the ratio of omega-6 to omega-3. Polyunsaturated fatty acids are high in vegetable oils, margarines and shortenings. (4)
- Best food sources of fat
The best sources of dietary fat don’t necessarily mean foods with the highest fat contents. It rather means the best combination of quantity and quality of the fats and high nutritional value of those foods.
For this reason, partially hydrogenated fats (with high trans fats contents), high omega-6 fats (such as vegetable oils, margarine spreads and shortenings), or genetically modified oils (GMOs) are not good sources of fat.
The definite, good, polyunsaturated fats are the omega-3 fatty acids that you can get from small fatty fish, flaxseeds, chia seeds and walnuts. These foods not only contain high amounts of fat but are very nutritious. Our modern diet requires more of these fatty acids and less omega-6. (5)
Saturated fats, such as dairy and meat, are also good sources, despite the continuing anti-saturated fat campaign. Red meats (such as beef or lamb), however, are a still a grey area, due to their possible connection to cancer.
Foods high in fat, increase the satiety level after a meal. They are slower to digest and effectively trigger the satiety signal in your brain, making you feel full quicker.
Functions of fats in our body
Fat is produced in the body not only from the components of the dietary fat itself, but also from other energy nutrients, such as carbohydrates.
- Fat is an energy source
Fat is used as a source of energy in the body. Each gram of fat provides more than double the number of calories compared to carbohydrates and proteins.
However, if you are on a high carb diet, your metabolism utilizes carbohydrates as a main source of fuel and fat as a secondary source. If you are on high carbohydrate diet you are more likely to have a lower insulin sensitivity, which means that you don’t burn fat as efficiently and therefore may find it harder to lose weight.
When you are on a high fat/low carb diet, your metabolism switches and starts burning fat first as a fuel choice. It also triggers the fatty cells to release more fat for energy use. This is why this diet is so effective in losing weight.
- Back-up energy storage
Fat can be stored or released, when your diet doesn’t provide enough energy nutrients (macronutrients).
NOTE: The visceral fat stored in the abdomen area is important to protect the organs. However, when stored in excess, it is linked to various diseases, such as metabolic syndrome and type 2 diabetes, may lead to heart diseases and is associated with an increased mortality rate.
Fat is stored around major organs to protect them from sudden movements and outside impacts. Stored fat is also used as a thermal insulation to maintain a normal core body temperature.
- Hormone production
The adipose tissue is used to produce hormones, such as leptin, estrogen and resistin. These hormones are vital for a good body function.
Fat is also used in the production of sex hormones and of prostaglandins (hormone-like particles that control several body functions).
- Fat is used to absorb, transport and store fat-soluble vitamins
The vitamins A, D, E and K, which are essential for our health and crucial in some important body functions, are soluble in fat.
All of these vitamins are needed for good skin and hair health. Individually, they are also crucial for various functions: vitamin A (eye health), vitamin D (bone health), vitamin E (antioxidant) and vitamin K (blood clotting).
This means that fat is important to absorb these vitamins from food and to store and transport them within the body. Restricting the fat intake, for instance by following a low-fat diet (e.g. fruitarianism), may also decrease the daily intake of these vitamins and, in some cases, cause a deficiency.
- Fat is essential in the cell structure
Fat is an essential part of the cellular membranes of all cells in the body. Without it, the integrity of the cell would be compromised, which could lead to the self-destruction of the cell.
- Fat is used in the brain structure and protects the nerve fibers
Fat is a crucial part of the brain structure and protects the nerve fibers by forming an insulating layer around them. At the same time, it helps the nerves to carry messages faster.
- Fat is required for skin protection
In addition to its function in absorbing essential vitamins for good skin health, the fat layer under the skin (subcutaneous fat) makes it looks rounded and healthy.
- Essential fatty acids
Essential fatty acids, such as omega-3 and omega-6, are required for a normal body function. Omega-3 fatty acids are an integral part of the cell membranes and affect how the receptors on these cells function. They are involved in the hormone production, regulate blood clotting and inflammation, are essential in the artery wall contraction and relaxation and prevent many inflammatory related diseases. (9)