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Food Constituents

Food is vital for optimal health and wellbeing. This video outlines the role of macronutrients and micronutrients in the diet.
The human body is made of a skeleton, tissues, cells, and fluids, which need to be maintained. We need materials to refill our storages and to replenish the components we lose every day. The mere material we need is water. But after that, carbohydrates, lipids, and proteins are needed in the diets in large amounts for fueling and tissue maintenance. Because of this, we call them macronutrients. Fibre is also considered a macronutrient, although it is not a true nutrient because it passes the gastrointestinal tract unabsorbed and is directly excreted. Humans have daily requirements for macronutrients. Every single day, we need fuel for the 2,100 kilocalories of energy we use.
And we have to provide our body at least with 70 grammes of lipids, 260 grammes of carbohydrates, and 50 grammes of protein. These numbers are only indicative, as our daily intake largely depends on our activity and condition. Carbohydrates are used mainly as fuel. 1 gramme provides about 4 kilocalories to the body. Dietary carbohydrates, such as starch, are broken down by gastrointestinal enzymes into glucose. They’re passed to the bloodstream and then to the tissues where it is metabolised to ATP, a universal, energy molecule in nature. Excessive glucose is stored in the form of glycogen. If blood glucose drops, glycogen refills it. Carbohydrates intake come mainly from vegetable sources. Fruits are rich in carbohydrates, mainly sucrose, glucose, and fructose.
In addition, those parts used for storage in plants, such as potatoes and carrots, are rich in carbohydrates, particularly starch. This is also the case of seeds, legumes, such as peas or beans, or cereal greens. Wheat, for instance, has a 60% of starch by weight. Products processed from rich carbohydrate vegetables, such as flour, sugar, bread, or bakery products, are all good sources of carbohydrates. Lipids are fats whose main function is energy storage. The body fuel reserve of a person is about 100,000 kilocalories and lipids. About 1/3 of the energy spent everyday comes from lipids. A combination of glucose and lipids gives us the energy for regular, daily activities.
Each gramme of lipid releases 9 kilocals of energy, twice the 4 kilocalories provided by protein or glucose. Lipids are stored in the adipose tissue as triglycerides. A molecule of glycerol bind to three fatty acids. When energy is needed, fatty acids are mobilised and subjected to a process called beta oxidation and further transformation into ATP. Dietary fats are classified into fats and oils based on their melting temperature, and this depends on their fatty acid composition. Fats are rich in saturated fatty acids and, therefore, solids at room temperature, while oils are mainly made up of unsaturated fatty acids and liquids at room temperature. Unsaturated fatty acids are considered healthier than saturated ones, and, therefore, oil consumption is preferred than fats.
Protein constitute our machinery, fueled by the energy produced from carbs and lipids. Each tissue and cell builds up its own specialised set of proteins. We have structural proteins, transporters, hormones, antibodies, or enzymes. Dietary proteins are broken down into amino acids by gastrointestinal enzymes. Cells take them from the bloodstream and synthesise their own proteins. When no longer needed, proteins are broken down again into amino acids. Synthesis and breakdown occur continuously. Every day, about 300 grammes of new proteins are synthesised in our body. This is a tremendous energy cost process and about 300 kilocalories are needed only for this purpose.
Many amino acids are recycled for making new proteins, but about 50 grammes of protein a day are lost and need to be taken from the diet. Proteins can be used for energy as well. But unless we are starving, only a 5% of protein intake is used for energy. Dietary proteins are present in animals and plants but especially in those with muscle tissues, such as meat or fish. 0.75 grammes of protein per kilogramme of body weight a day is the intake recommended for adults. Protein quality is a very important nutritional consideration. Essential amino acids must be taken from the diet in appropriate amounts. Different foods contain different combinations of essential amino acids.
For instance, cereals, such as rice, corn, or wheat are per in the amino acid lysine. Protein from animal sources contains the full range of essential amino acids. Vegans and vegetarians can get all the amino acids they need by combining different plant sources of protein, for instance, pulses and cereals. Micronutrients are vitamins and minerals. They’re required in small amounts. They’re essential nutrients because the body can’t make or can’t make in sufficient quantity and, thus, they must come from the diet. They have many functions. Vitamins are frequently involved in metabolic reactions as co-factors. For instance, pyridoxal phosphate, a chemical form of vitamin B6, is involved in the metabolism of amino acids or neurotransmitters. Regarding minerals, calcium is well-known for bone’s help.
Sodium and potassium keep the osmotic pressure of cells and fluids. And iron maintains a haemoglobin function. Some minerals found in traces are used to maintain the appropriate confirmation and activity of particular enzymes. Vitamins are needed in different demands every day four milligrammes per day of niacin or vitamin C to the micrograms of vitamin D. In the case of minerals, sodium, potassium, and chloride are needed in large amounts– grammes per day– while selenium or iodine are needed in micrograms. Micronutrients are present in natural foods, but it is more difficult to find them all simultaneously in the same food.
Although the different vitamins and minerals can be obtained from various sources, in general, vitamin A and D are liposoluble and are found in lipid-rich foods, such as meat or fish. Vitamin C is hydrosoluble and found in citrus fruits. Vitamins B are found in meats and are limited in vegetables. The reason why it is of great importance to control its intake in vegetarian diets, regarding minerals, salt is our main source for sodium and chloride. Salt is used as a carrier for iodine. Calcium intake is preferable taken from dairy products because they facilitate its absorption over other sources, such as broccoli. Dairy also provides phosphorus– red meat iron and zinc and shellfish, copper, and selenium.
The combination of different foods allows us to get them all.

Food is vital for optimal health and wellbeing. The human body requires adequate amounts of macronutrients and micronutrients for energy, growth and maintenance.

What are macronutrients?

Macronutrients are the nutrients we need in larger quantities for energy and tissue maintenance. They include carbohydrates, fats and proteins. Fiber is also considered a macronutrient, although it is not a true nutrient, because it passes the gastrointestinal tract unabsorbed, and it is directly excreted.

  • Carbohydrates: Carbohydrates are a group of important nutrients in the diet as a source of energy. 1g provides about 4 Kcal to the body. They contain the elements carbon, hydrogen and oxygen and are produced in plants by the process of photosynthesis. Carbodhyrate intake comes mainly from vegetable sources.
  • Lipids: Fats and oils, also known as lipids, are broken down in the body by a process of oxidation to release energy. Fat is a more concentrated source of energy than carbohydrates. 1g of fat contains 9kcal. Dietary fats are classified into fats and oils based on their fatty acid compsition.
  • Proteins: Protein is a key component of the structure of the body necessary for growth and maintenance. Although not its primary role, protein can serve as a source of energy when insufficient carbohydrate and fats are available to meet the bodies needs. Dietary proteins are present in animals and plants products such as meat, fish, eggs, bread, nuts and vegetables.

What are micronutrients?

Micronutrients are mostly vitamins and minerals, and are equally important as macronutrients but consumed in very small amounts. They are essential nutrients, because the body can’t make them or can’t make them in sufficient quantity, and thus, they must come from the diet.
  • Vitamins
Vitamins are complex organic substances that are needed in very small amounts for many of the essential processes carried out in the body. Some are involved as co-factors in metabolic reactions; some are antioxidants and one is a pro-hormone. Vitamins have been traditionally grouped into two categories: the fat soluble and water soluble vitamins. Fat soluble vitamins include: Vitamin A, Vitamin D, Vitamin E and Vitamin K. Water soluble vitamins include the Vitamin B complex and Vitamin C.
  • Minerals
Minerals are inorganic substances required by the body for a variety of functions. This includes: the formation of bones and teeth; as essential constituents of body fluids and tissues; components of enzyme systems; and nerve function. Some minerals are needed in large amounts, grams per day, (e.g. Calcium, Magnesium, Phophorus, Potassium, Sodium and Chloride), whilst others are needed in smaller amounts, micrograms per day, also known as trace minerals (e.g. Flourine, Iodine, Iron, Selenium Zinc and Copper).

Micronutrients are present in natural foods, but it is more difficult to find them all simultaneously in the same food. Eating a varied diet will help ensure an adequate supply of most micronutrients for healthy people.

What we would like you to do

Please share your thoughts in the comments section below:

  • Do you think you eat enough macronutrients and micronutrients? Why / Why not?
  • Do you think you could improve your diet? If so, what would help you improve it?
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Introduction to Food Science

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