The food that we eat is the source of the nutrients that our body needs. These consist of macronutrients, which include proteins, lipids (fats) and carbohydrates, and micronutrients, consisting of minerals and vitamins. The perfect food, i.e. one that contains all the macro and micronutrients, does not exist, and consequently each particular food is a mixture of certain macro and micronutrients. So, what’s in beef? The nutrients in beef are: proteins, lipids, B group vitamins, and minerals such as iron, zinc and selenium...
Proteins are nutrients that are essential for the construction and maintenance of the body. They are not stored to any great extent in the body, unlike lipids, and are not especially energy-giving (1 g of protein supplies 4 kcal). The muscles make up the only reserve of proteins. In certain cases of deficiency, they can be used as a ‘fuel’, but their main function is as the ‘building bricks’ of our organs.
Proteins have many functions. They play a part in growth, reproduction, nutrition, the immune system (the body’s system of defence), and in the make-up of muscles and skin. They can also play a role in hormones, and are omnipresent in intercellular communication.
Amino acids, the basic constituents of proteins
In nature, there are millions of different proteins, but they are all made up of the same basic building blocks strung together: amino acids.
There are only 20 different amino acids, but it is by varying their number and the sequence in which they are linked together that our body produces the thousands of different proteins that it is made from. However, among these 20 amino acids there are eight that cannot be produced in our bodies, and which must be supplied by food. They are called essential amino acids.
If just one of the essential amino acids is lacking, the body cannot properly assimilate the others. This is why a protein is said to be of high quality if it contains the right balance of all the essential amino acids.
Two types of protein
The proteins in our food are either of animal origin or of plant origin.
Animal proteins: these are the proteins found in meat, eggs, fish and seafood, and dairy products. What’s special about these proteins is that they supply large quantities of all the essential amino acids the body needs.
Plant proteins: these are supplied by cereals (pasta, rice, bread, flour, etc), pulses, and tubers (potatoes). Unlike animal proteins, they lack one or more essential amino acids.
As these proteins complement one another like the pieces of a jigsaw puzzle, it is necessary to eat proteins from both sources.
Lipids (i.e. fats) are present in all natural or processed foods.
They are of great nutritional and organoleptic value... Although lipids are often considered merely as a source of energy, ( 1 g of lipids = 9 kilocalories), they also have other important functions. Located in the subcutaneous tissue, they play a major role in human body heat regulation. Lipids supply and/or transport fat-soluble vitamins such as vitamins A and D, found in butter and cream, or vitamin E, found in vegetable oils.
The composition of lipids
Lipids are substances that are insoluble in water. They are basically made up of triglycerides (a molecule of glycerol + 3 fatty acids). There are three different types of fatty acids: saturated, monounsaturated and polyunsaturated. Their physical and nutritional properties vary from one structure to another.
Essential fatty acids
Lipids are also practically the only source of essential fatty acids, thus named because the body cannot synthesise them by itself. There are only two essential fatty acids:
- linoleic acid (omega 6)
- alpha-linolenic acid (omega 3)
Omega 6 fatty acids play a part in most physiological functions. They have a structural function within cell membranes, and they are the source of prostaglandins, which play an active biological role in the regulation of cell metabolism.
Omega 3 fatty acids play a more specific role in vision and in the brain.
Since the body cannot synthesise these two essential fatty acids, they must be provided by food in order to satisfy the body’s needs.
Sources of lipids
Just as for proteins, there are two types of lipid:
- animal lipids,
- plant lipids.
Within both these types of lipid, we can distinguish between so-called ‘concealed’ and ‘visible’ lipids. Concealed lipids are part of the make-up of foods and are not usually visible to the naked eye. Lipids that are visible to the naked eye are usually fats or oils that are added for cooking, spreading, seasoning, etc.
Meat and fat: how are they linked?
The lipid content of meat varies considerably, depending on the species and the cut. For instance, most cuts of beef contain less than 6% of fat. The fat content of veal varies from 2 to 15%. Lamb, a meat for more special occasions, contains between 9 and 25% of lipids.
Meat provides the three types of fatty acid in varying proportions. For instance, in most cuts of beef, half the fatty acids are of the unsaturated kind. The lipids in a roast joint of beef are divided up as follows (1):
- 45% saturated fatty acids
- 51% monounsaturated fatty acids
- 4% polyunsaturated fatty acids
Just as there are lean (white) fish and fatty (oily) fish, in the same way there are cuts of meat that are lean and others which are fattier. It is therefore important to choose your cut according to how you intend to cook it.
The average cholesterol content of beef is modest, and similar to that of fish (2): less than 80 mg / 100 g. It should also not be forgotten that cholesterol is one of the constituents of cell membranes, and that it is a precursor of bile acids and steroid hormones.
(1) source: Centre d’Information des Viandes (Meat Information Centre): tests carried out by specialised laboratories
(2) source: Ciqual 1995
Minerals: iron, zinc and selenium
There are many minerals that are essential to life and that are found in the body. These minerals may have a specific role, but can also complement each other. They play a part in various processes such as growth, maintenance, regulation and various equilibria...
Two types of mineral
> Mineral salts, more commonly known as minerals, which are found in large quantities in the body. They are: calcium, phosphorus, sodium, potassium and magnesium.
> Trace elements, which are only found in very small quantities in the body. These are: iron, iodine, zinc, selenium, fluorine, copper and chromium.
All these mineral salts and trace elements are provided by a varied diet, which thus covers all our needs. However, high-risk situations can arise, and in this case, it is necessary to be more vigilant with regard to the supply of certain minerals, such as calcium or iron.
So, what should you do? Rush off to the pharmacy? Actually, it’s probably better to pop down to your local market. The minerals and trace elements in food are more effective because they are supplied within the naturally nutritional context of food and are thus non-toxic, unlike some commercially available chemical cocktails…
Iron is a trace element that mainly goes to make up haemoglobin, the pigment that colours our blood cells red, and which transports and exchanges oxygen and carbon dioxide with the outside environment. It is also a constituent of a large number of enzymes (small molecules which catalyse and speed up the chemical reactions that are vital to the working of the cell).
Due to its role as a constituent of enzymes, iron is involved in fundamental functions, such as brain development, physical ability and resistance to infection. It therefore has considerable biological importance.
To all intents and purposes, the metabolism of iron takes place in a closed circuit, since the body recycles part of the iron contained in the red blood cells. However, there are physiological situations where there is an increased need for iron.
This is especially true during menstruation, and growth (childhood, pregnancy and breastfeeding). A lack of iron can lead to a deficiency which can eventually end up as the final stage in anaemia. The symptoms are great physical and mental fatigue, shortness of breath, palpitations and a pale complexion.
Two kinds of iron
There are two kinds of iron in food, and they have a completely different bioavailability, or absorption, i.e. the ability to cross the gut wall and get into the blood: haeminic iron and non-haeminic iron.
|absorption from 15 to 25%|
|Non haeminic iron|| fruit and vegetables|
|absorption from 2 to 5%|
So, it is not enough for iron to be present in food; it must also be absorbed during digestion. Only a small fraction of the iron present in food is actually absorbed.
In addition, when several different kinds of food are eaten at the same time (as during meals), factors found in certain foods interfere with the absorption of non-haeminic iron found in fruit and vegetables. For instance, eating meat with vegetables during the same meal helps to increase the absorption of the iron contained in the vegetables.
Factors such as tannins (e.g. in tea or coffee) or phytates inhibit, i.e. reduce, the absorption of non-haeminic iron, whereas others, such as vitamin C, some amino acids and haeminic iron, increase the absorption of non-haeminic iron.
Where can this all-important iron be found?
The foods that are richest in haeminic iron are: offal (blood sausage, liver, kidneys, heart, etc), red meat (beef, lamb), seafood (mussels, oysters, prawns) and some fish (tuna, sardines).
Source: Ciqual 1995 and CIV
The essential nature of this trace element was only proved in the 1960s. Zinc is essential for growth and plays an important role in the body’s immune defence system against infection. It plays a part at different stages in the synthesis of proteins, facilitates the action of numerous enzymes and takes part in the metabolism of energy nutrients. It also plays a role in the development of brain functions.
Zinc is especially important for certain populations such as:
- children, since they are in a period of rapid growth,
- pregnant women and nursing mothers, since they have greater needs due to their physiological situation,
- vegetarians, since their diet is poor in zinc,
- older people, since they have a reduced immune response.
In which foods is zinc found?
The main dietary sources of zinc are meat products, dairy products, eggs and pulses. The zinc supplied by meat is especially assimilable. Moreover, in order to make sure that zinc is assimilated, it is better if the iron/zinc ratio remains below 2. This is the case for beef, since the iron/zinc ratio in meat lies between 0.3 and 0.7 (source ISA).
Does zinc deficiency exist?
Zinc deficiency can lead to a serious disruption of the immune system.
Several specific cases where there may be a risk of zinc deficiency are known:
- During pregnancy: zinc deficiency is associated with a risk of premature birth, and with the more serious condition spina bifida, which is an extremely serious malformation of the nervous system during the growth of the foetus.
- For sportsmen and women: in the event of zinc deficiency, people who do sports are observed to have diminished stamina, since zinc plays a role in carbohydrate metabolism, not only before and during exercise, but above all afterwards, when the reserves of glycogen are replenished.
- In the event of restrictive diets such as vegetarian diets.
Zinc is thus a trace element which is essential for the proper working of the body, especially for people in exceptional physiological states (growth, pregnancy, pathologies) and for people who do sports. Including meat regularly in the diet helps to cover the body’s zinc requirements.
Many functions of this trace element remain to be discovered. Nonetheless, it is possible today to set out a certain number of its characteristic properties.
Selenium plays several important roles in protecting the body. It acts as an antioxidant: it plays an essential role in the action of an enzyme (glutathion peroxidase) which protects cell membranes against free radicals. It is thus a trace element with beneficial effects, protecting us from the ageing of tissue and from cardiovascular disease.
In which foods is selenium found?
Generally, the foods which are richest in proteins are also the richest in selenium, i.e. meat and seafood. Liver and kidneys, which are the organs where selenium is stored, are especially rich in this element. Dairy products and eggs also provide a certain amount of selenium, unlike fruit and vegetables.
In addition, some studies show that the bioavailability of selenium in food from plants is poorer than in food from animals.
Vitamins are substances that are essential to life. They belong to the micronutrients. They are thus non-energy giving substances that enable macronutrients, i.e. proteins, lipids and carbohydrates, to be used and transformed.
Only small quantities are needed to obtain the desired effect. The body does not synthesise them in sufficient quantities to meet its own needs, and they must therefore be provided by food.
They are absolutely essential because if the body is deprived of them, this may lead to the development of disorders. Indeed, the outward signs of vitamin deficiency have been known for centuries.
What is the function of vitamins?
They take part in numerous biochemical reactions in every cell in the body. Without vitamins, the body would not be able to make use of the building and energy-giving substances supplied by food. The ways in which these micronutrients work are very complex, and some are only poorly understood.
What different kinds of vitamins are there?
Vitamins are classified into two groups:
- the water-soluble vitamins, which include B group vitamins as well as vitamin C,
- the fat-soluble vitamins, vitamins A, D, E and K.
Functions and sources of vitamins:
|Vitamin A||It protects the eyesight and facilitates night sight; it plays a part in preserving the skin and in the immune system; it is found in liver, egg yolk, whole milk, green vegetables and carrots.|
|B group vitamins||Vitamins B1, B2, PP, B5 and B6 ensure the smooth running of the brain and muscles; vitamins B9 (folic acid) and B12 play a part in the production of new cells; B group vitamins are found in liver, egg yolk, meat and fish.|
|Vitamin C||Acts as an antioxidant, protects against infection, facilitates the absorption of iron; it is found in fruit, especially citrus fruit, and in vegetables.|
|Vitamin D||Fixes calcium; has the distinctive characteristic of being activated by exposure to sunlight; found in liver, egg yolk, butter, fat cheeses, whole milk, oily fish (herring, mackerel, sardines, salmon).|
|Vitamin E||Protects the cells and plays an important anti-ageing role; found in whole milk, butter, eggs, and plant-based oils and margarines. |
|Vitamin K||Necessary for the clotting of blood; produced by bacteria in the intestine; it is found in liver, eggs, meat and green vegetables (broccoli, spinach and lettuce).|
Deficiency or minor deficiency?
Genuine vitamin deficiency diseases are no longer found in industrialized countries where, in general, the diet is sufficiently varied. However, some people do suffer from minor deficiencies. The people concerned are those who have an insufficient supply of vitamins, as well as population groups who have an increased need for vitamins, either in the short or long term, and whose eating habits may not allow them to satisfy their needs. These individuals are classified as being a ‘high-risk group’.
The main causes of these risks, and the groups of people concerned, are as follows:
1] bad eating habits, such as skipping meals, frequent eating of fatty foods, snacking, and, more generally, not eating enough or having an unbalanced diet.
The people concerned are mainly:
- adolescents: they have considerable needs, but often do not eat enough or have an unbalanced diet;
older people, who often suffer from digestion problems, or who have an unbalanced and unvaried diet;
- any person on a low calorie or unbalanced diet;
- excessive drinkers: poor eating habits and poor assimilation can lead to a deficiency in several vitamins, especially those of the B group.
2] increased need for vitamins, either in the short or long term, for:
- pregnant women and nursing mothers: they have a greater need for vitamins, but their eating habits are rarely adapted accordingly;
- women using oral contraceptives: oestrogen-progestogen combinations lead to an increased need for certain vitamins, in particular vitamin B6 ;
- smokers, for whom studies have shown that consumption of vitamin C by the cells is greater than for non-smokers. Consequently, smokers need more vitamin C.
3] loss of part of the vitamins in food due to the food having been stored too long, poorly prepared, cooked badly, or kept hot too long.
4] post-operative or chronic digestion problems. This can lead to a genuine deficiency since, even if vitamins are supplied in sufficient quantity, they are only slightly absorbed, or not at all.
These minor deficiencies are hard to spot. This is because the symptoms associated with them are not specific:
- lack of appetite,
- lack of concentration,
- insomnia, etc.
Moreover, many months can go by before the characteristic symptoms of vitamin deficiency appear.
The nutritional qualities of various cuts of meat