by Gaia Domenici, Nutrition & Health Coach
The word ʻmacronutrientsʼ refers to the components of food that the body can break down to produce energy.
These are proteins, fats and carbohydrates (including dietary fibre and alcohol).
From a bio-chemical perspective, macronutrients are large molecules (forming the structure of the food)
which, when eaten, are metabolised to be: burned as fuel; used as the building blocks of muscles
and tissues in the body; stored for future usage.
Protein
As its Greek root ʻproteiosʼ (ʻprimaryʼ, ʻholding the first placeʼ) suggests, protein is the
fundamental macronutrient of the human body:
– it is vital to develop and maintain all of the cells in the body, from muscles to bones and organ tissues;
– it is an essential component of several body functions (e.g. proteins can act as hormones and enzymes and they form the structure to transport fats, vitamins, minerals and oxygen around the body);
– it forms the structure of the antibodies in our immune system;
– it regulates the fluid volume of the body;
– it helps maintain the bodyʼs pH balance;
– it creates a feeling of satiety;
– it can be converted into energy, under certain circumstances.
Although there are different types of protein, each of them presenting a different profile and
therefore a different quality.
Natural sources of protein are eggs, meat and poultry, fish, dairy, legumes, algae and, in small amounts, grains, nuts and seeds.
Interestingly, fruit and vegetables also contain some protein. Each gram of protein produces around 4 kcal of energy.
Molecular Structure of Protein
Protein can be thought of as a long chain of simpler amino acids, namely, molecules containing:
carbon, hydrogen, oxygen and nitrogen.
These molecules occur in about 20 different combinations and can be arranged in different sequences and lengths to create longer and complex chains called ʻpolypeptidesʼ. More than half of such combinations, however, can be manufactured by the human body, whereas 9 of them need to be introduced by the body through the diet.
From this distinction originates the classification as ʻessentialʼ (Phenylanine, Valine, Threonine, Tryptophan, Isoleucine,
Methionine, Leucine, Lysine, Histidine) or ʻnon essentialʼ (Aspartic acid, Asparagine, Glutamic acid, Alanine, Serine, Glycine, Tyrosine, Cysteine, Arginine, Glutamine, Proline, Taurine) amino acids.
Based on this distinction, protein can be further classified as ʻcompleteʼ or ʻincompleteʼ, depending on their amino-acidic profile (complete proteins containing all of the essential amino acids at the required amounts for protein synthesis; incomplete proteins lacking one or more essential amino acids). For this reason, when following a vegetarian diet, it is crucial to vary and combine protein sources as often as possible.
Fats
Similarly to protein, lipids (commonly called ʻfatsʼ) are an essential component of several body functions. Indeed, not only do they constantly supply energy to the body, they also:
– insulate the body,
– are crucial to the production and maintenance of red and white blood cells,
– are critical in hormone production and regulation.
Moreover, fats carry fat-soluble vitamins (A, D, E, K) around the body.
With the exception of the so-called ʻessential fatty acidsʼ (omega-6 linoleic acid and omega-3 alpha-linolenic acid), lipids can be manufactured by the body.
Natural sources of lipids are lard, butter, ghee, oil, meat, fish, coconut, avocado, olive, nuts and seeds. Traces of fats can also be found in: grains, legumes (especially soybean), fruit and vegetables.
Each gram of fat produces around 9 kcal of energy.
Molecular Structure of Fats
Lipids can be classified as ʻsimple lipidsʼ or ʻcompound lipidsʼ.
Simple lipids, in turn, can be divided into simple ʻfatty acidsʼ (namely single molecules, formed by chains of carbon molecules), or ʻtriglyceridesʼ (namely compound molecules containing three fatty acids attached to a single glycerol molecule, representing both the most common form of fat in the diet and the main storage form of fat in the human body).
Compound lipids, instead, can be further classified as ʻphospholipids and glycolipidsʼ or ʻlipoproteinsʼ (a combination of lipids and proteins). The former group forms essential components of cell membranes, whereas the latter is essential in transporting lipids around the body (blood cholesterol being the most popular example of such group).
Fatty acids in food sources can be further classified as: saturated, monounsaturated, polyunsaturated, depending on their chemical makeup. In short, the more hydrogen molecules a fatty acid carries, the more stable it is (saturated fats being located at the highest spectrum); the more free carbon molecules a fatty acid carries, the less stable it is (polyunsaturated fats representing the lowest spectrum).
Triglycerides present a similar molecular structure to that of carbohydrates (carbon, hydrogen, oxygen). However they have more carbon and hydrogen than oxygen molecules. For this reason, in order to produce energy from fatty acids, lipid need to be oxidised. This process requires more time and is not always ideal –– for instance when the body utilises the lactic-acid energy system (e.g. during hypertrophy training or a 400m run). Nonetheless, fats can be used as an excellent fuel source during low to moderate exercise (e.g. during a brisk walk) or during high intensity anaerobic
training, when phosphocreatine is the primary source of ATP (e.g. powerlifting or sprinting).
Carbohydrates
Carbohydrates are non essential macronutrients, meaning that the human body does not need them to survive. In fact, through a metabolic pathway known as ʻgluconeogenesisʼ, glucose molecules are manufactured in the liver from carbon substrates found in amino acids and lipids. However, carbohydrates are also the most accessible source of energy to the human body, hence its preferred one.
Carbohydrates can be classified in several ways, depending on their molecular structure and length. The most common classification is: sugar, starches, fibre.
Carbohydrates can be found in a vast array of foods: fruit, vegetables, potatoes, rice, pasta, bread, grains, legumes and, in small amount, nuts, seeds and dairy. Interestingly, eggs and meat (especially organs) also contain some trace. Each gram of carbohydrates produces around 4 kcal in energy.
Molecular Structure of Carbohydrates
Carbohydrates can be thought of as long and complex chains of simpler glucose molecules (made out of carbon, hydrogen, oxygen).
Now it becomes easy to understand why carbohydrates are the bodyʼs preferred source of energy. Indeed, if it is true that the body does not need carbohydrates, it is also true that it needs glucose to run vital brain functions, as well as one of the muscle-skeletal energy systems. Therefore, as it would take longer for the body to manufacture glucose from amino acids and lipids, than to simply break down longer glucose molecules into simpler ones, the body normally prefers utilising carbohydrates to produce energy quickly.
However, not all carbohydrates can be broken down by the body to produce energy: both soluble and insoluble fibre, along with resistant starch, present a molecular structure that our enzymes are unable to break down.
Insoluble fibre (roughage) passes through our GI tract and its only function is to create stool volume. Soluble fibre and resistant starch, instead, are fermented by gut bacteria and dissolved in water, forming a gel in the colon.
Research has shown that soluble fibre can be associated with diabetes management –– as it appears to lower blood glucose –– and, potentially, with reducing the risk of heart disease, as its regular consumption is linked with lower blood cholesterol.
Both soluble fibre and resistant starch are often referred to as ʻprebioticsʼ, namely, the food of ʻprobioticsʼ (the gut bacteria).
Popular sources of soluble fibre are: oats, barley, legumes, citrus fruit. Resistant starch is mainly found in: legumes, cooked and cooled starches and grains, firm bananas, whole grains.
For more help managing your diet and fitness, book a free 30 minute Explorative Session with Gaia. Just email gaia@fitnosophy.com