Lipids all about lipid metabolism

Lipids: all about lipid metabolism

Although they have been singled out for many years, lipids or dietary fats are essential for good health. These provide the human body with “essential” fatty acids that can not 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 can not manufacture them
  • Lipids are found mainly in vegetable oils, butter, industrial products, etc.
  • Constituents of all cell membranes of the body
  • Deficiency or excess can have serious consequences

Why consume foods that contain fat?

Definition of lipids

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

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

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

Roles of lipids in the body


Unlike proteins and carbohydrates that provide 4 kcal per gram, lipids provide 9 kcal per gram. They participate in the coverage of 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 provide the plasticity and elasticity of the skin because they are important constituents of dermal cells.

Transport of fat-soluble vitamins

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

Synthesis of hormones

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

Lipid balance and exploration of a lipid abnormality

A lipid assessment makes it possible to make an inventory of the lipids present in the blood and to know if they are in excess or not. Levels of LDL cholesterol, HDL cholesterol and triglycerides are the most studied lipid levels. The results of the lipid assessment give a good idea of ​​the cardiovascular risk. Indeed, an excessively high level of total cholesterol or triglycerides is a risk factor for cardiovascular events that must be taken seriously.

Digestion of lipids

Once ingested, the 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 come out in the form of chylomicron. Chylomicrons release lipids into the blood where they circulate related to lipoproteins: HDL, LDL, etc. It is the presence of these lipoproteins that is measured during a blood test in order to detect a possible lipid abnormality.

Fat-rich foods

The main sources of fat are butter, margarine, vegetable oils, fried foods, pastries, and some prepared foods. As they enhance the flavor and texture of foods, they are used extensively for the development of industrial foods.

Here is in detail the lipid content of certain foods:

FoodsServingsQuantities (g)
Donut, cake type, sweet coating


Commercial chocolate biscuits

Regular ground beef

Cream 35%

Ice cream


Chicken nuggets

Cheese type cheddar

Vegetable oil (all varieties)

Egg yolk

Whole milk (3.25% M.G.)


Pecan nuts


Yogurt with whole milk

1 (57 g)

5 g

2 biscuits (20 g)

100 g

15 ml (1 tablespoon)

125 ml (1/2 cup) or 70 g

1 average 60 g

6 (110 g)

50 g

5 ml (1 teaspoon)

1 (17g)

250 ml (1 cup)


125 ml (75 g)

100 g or ¼ of pâté

175 g (3/4 cup)

















The sources of Omega-3 are fatty fish, flaxseed and chia seeds, enriched eggs, rapeseed oil and nuts. Omega-6 fatty acids are found mainly in vegetable oils such as grape seed oil, corn, safflower or sunflower oil.

How to properly use lipids?

Use of lipids

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

For healthy adults, here are the nutrition recommendations for lipid consumption:

Recommended Dietary Allowance (NCA) for Healthy Adult
Total lipids35 to 40% of Total Energy Supply (TEA)
Saturated fatty acids
Palmitic acid, lauric and myristic
Oleic acid (monounsaturated)15 to 20% of the AET
Omega-64% of the AET
Omega-31% of the AET
DHA250 mg / day
EPA + DHA500 mg / day

Food supplements based on lipids

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

Lipids and bodybuilding

In sports and bodybuilding particularly, a good intake of high quality fatty acids is essential. Lipids can indeed 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 may in some cases be a good solution.

Adverse effects of lipids

Lipid deficiency

Inadequate dietary fat intake can lead to growth problems and increased risk of chronic diseases. If the low fat intake is also accompanied by an inadequate intake of carbohydrates and protein and therefore energy, this can lead to malnutrition. Adequate intake of lipids is especially important during childhood and during pregnancy. In addition, a diet that is low in fat but high in carbohydrate may lower HDL cholesterol levels and increase the glycemic and insulin response after food intake.

Excess lipids

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

Interactions with other nutrients

Lipids slow 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 the 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. In contrast, mono and poly unsaturated fatty acids are liquid fats at room temperature, their double bonds makes them unstable and particularly sensitive to oxidation. The lipids may 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 lipid digestion. It was not until the end of the 1920s that the first studies demonstrated the more or less serious consequences of deficiencies in different lipids: reproductive disorders, hormonal disorders, etc. Researchers then begin to understand the essential character of certain fatty acids, which the body is not able to synthesize. However, it will be necessary to wait until 1965 for the metabolism of lipids interest biochemists. For a long time the 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 some fats want us much more good than harm.