Lipids: All about lipid metabolism


Although they have been singled out for many years, dietary lipids or fats are essential for good health. These provide the human body with “essential” fatty acids that cannot be synthesized by the body. Lipids are an important source of energy for the human body.

Characteristics of lipids:

  • There are saturated fats and unsaturated fats
  • Omega-3 and 6 are said to be essential because the body cannot manufacture them.
  • Lipids are mainly found in vegetable oils, butter, industrial products, etc.     
  • Constituents of all cell membranes in the body
  • A deficiency or an excess can have serious consequences

Why eat foods that contain fat?

Definition of lipids

Some fatty acids are called essential because the body cannot synthesize them. These are omega-6 (linoleic acid) and omega-3 (alpha-linolenic acid) fatty acids. They play an important role in the membranes of cells in the human body. The ratio between omega-3 and omega-6 fatty acids is very important because an imbalance between these two types of fatty acids can be harmful. For example, omega-6s consumed in excess prevent omega-3s from exerting their beneficial effect at the cardiovascular level.

Monounsaturated fatty acids are not essential fatty acids but are a key component of nervous system cells. They are mainly found in olive oil, avocado, and nuts and seeds.

Saturated fats and trans fats are not essential fatty acids and are even recognized in various studies as having harmful effects on LDL cholesterol levels and cardiovascular risk. They should therefore be limited as much as possible.

Roles of lipids in the body


Unlike proteins and carbohydrates which provide 4 kcal per gram, fat provides 9 kcal per gram. They therefore participate in covering energy needs.

Structural role

Lipids, and especially unsaturated fatty acids, are the major constituents of cell membranes and cells of the nervous system. They also ensure the plasticity and elasticity of the skin because they are important constituents of the cells of the dermis.

Transport of fat-soluble vitamins

In the body, some vitamins can only be transported with the help of lipids. They are called fat-soluble vitamins: vitamins A, D, E and K.

Synthesis of hormones

Fatty acids allow the synthesis of certain steroid hormones, directly derived from cholesterol: estrogen, testosterone and cortisol. Prostaglandins are also derived from lipid molecules.

Lipid assessment and exploration of a lipid abnormality

A lipid balance allows to make an inventory of the lipids present in the blood and to know if they are in excess or not. LDL cholesterol, HDL cholesterol and triglyceride levels are the most studied lipid levels. The results of the lipid profile give a good idea of ​​the cardiovascular risk. Indeed, too high a level of total cholesterol or triglycerides is a risk factor for cardiovascular accidents that must be taken seriously.

Digestion of lipids

Once ingested, lipids will be emulsified and mixed with bile salts in the intestine. They form micelles capable of entering the cells of the small intestine. They then come out in the form of chylomicrons. Chylomicrons release lipids into the blood, where they circulate bound to lipoproteins: HDL, LDL, etc. It is the presence of these lipoproteins that is measured during a blood test in order to detect any lipid abnormality.

Foods high in fat

The main sources of lipids are butter, margarine, vegetable oils, fried foods, pastries, and certain prepared meals. As they enhance the flavor and texture of food, they are widely used for the development of industrial foods.

Here is in detail the lipid content of certain foods:

Food Servings Quantities (g)     
Donut, cake type, sweet coating                          


Commercial Chocolate Cookies

Regular Ground Beef

Cream 35%

Ice cream


chicken nuggets

Cheddar-type cheese

Vegetable oil (all varieties)

Egg yolk

Whole milk (3.25% MF)


Pecan nuts


Whole milk yogurt

1 (57g)


2 cookies (20g)


15 ml (1 tbsp)

125 ml (1/2 cup) or 70 g

1 medium 60g

6 (110g)


5ml (1 teaspoon)

1 (17g)

250 ml (1 cup)


125ml (75g)

100 g or ¼ pâté

175 g (3/4 cup)

















Sources of omega-3s are fatty fish, flax and chia seeds, enriched eggs, canola oil and walnuts. Omega-6 fatty acids are mainly found in vegetable oils such as grapeseed, corn, safflower or sunflower oil.

How to properly use lipids?

Use of lipids

How much fat should you consume per day to lose weight or maintain a stable weight?

For the healthy adult, here are the nutritional recommendations relating to the consumption of lipids:

Recommended dietary allowance (ANC) for healthy adults              
Total lipids                                      35-40% of Total Energy Intake (TEI)
Saturated fatty acids < 12% of TEI
Palmitic, lauric and myristic acid < 8% of TEI
Oleic acid (monounsaturated) 15-20% of AET
Omega-6 4% of TEI
Omega 3 1% of AET
DHA 250 mg/d
EPA + DHA 500 mg/d

Lipid-based dietary supplements

Certain food supplements based on Omega-3, 6 and 9 may be indicated in the preventive or curative treatment of certain cardiovascular or neurodegenerative pathologies. In any case, before considering lipid supplementation, it is essential to seek the advice of your doctor.

Lipids and bodybuilding

For athletes and in bodybuilding in particular, a good supply of quality fatty acids is essential. Lipids make it possible to synthesize hormones, accelerate metabolism and promote muscle gain. A varied and balanced diet is enough to cover the needs. however, supplementation with essential fatty acids can, in some cases, be a good solution.

Adverse effects of lipids

Lipid deficiency

Inadequate intake of dietary fat can lead to impaired growth and increased risk of chronic diseases. If the insufficient intake of fat is also accompanied by an insufficient intake of carbohydrates and proteins and therefore of energy, this can lead to malnutrition. Adequate fat intake is especially important during childhood and during pregnancy. In addition, a diet that is low in fat but very high in carbohydrates could reduce HDL cholesterol levels, in addition to increasing the glycemic and insulin response after food ingestion.

Excess fat

It is recognized that a diet high in fat that exceeds energy requirements can lead to obesity. There is also a link between high fat intakes and an increased risk of cardiovascular disease, cancer and insulin resistance leading to type 2 diabetes. The type of fatty acid consumed in excess plays a determining role in this relationship.

Interactions with other nutrients

Lipids slow down the digestion and absorption of carbohydrates, so they have the effect of reducing the glycemic index of a meal. Between them, some lipids can compete. This is the case of Omega-6 and 3. Omega-6 consumed in excess block the beneficial action of Omega-3 and have a pro-inflammatory effect. Finally, lipids are essential for the absorption of fat-soluble vitamins A, D, E and K.

Chemical properties

Lipids constitute fat mass. Depending on their molecular structure, they can be solid or liquid in their natural state. Saturated fatty acids are solid fats because they do not have double bonds, which makes them particularly stable and hard. On the contrary, mono and polyunsaturated fatty acids are liquid fats at room temperature, their double bonds makes them unstable and particularly sensitive to oxidation. Lipids can be hydrophobic or amphiphilic, ie they have a hydrophilic group and a hydrophobic group.


Nutrient history

in the 1850s, scientists began to discover the role of the pancreas in the digestion of lipids. It was only at the end of the 1920s that the first studies demonstrated the more or less serious consequences of deficiencies in various lipids: reproductive disorders, hormonal disorders, etc. Researchers then begin to understand the essential nature of certain fatty acids, which the body is not capable of synthesizing. However, it was not until 1965 that lipid metabolism interested biochemists. For a long time, lipids will be demonized and held responsible for the mechanisms of weight gain. Fortunately, we know today that this is not the case and that certain fats want us much more good than harm.

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