The Major Human Dietary Macro and Micro Nutrients
The definition of a macronutrient, according to The Oxford Dictionary of Biology (2008), is “a type of food required in large amounts in the diet”, since the word is made from the term macro (meaning large or required in large quantities) and nutrient (a substance needed for growth, metabolising or other vital functions). They consist of the carbohydrates, proteins and fats. They are particularly important in the maintenance of the brain and heart, hence why the body will cannibalise itself to support these areas in times of starvation.
Carbohydrates are a vast source of energy in humans and, according to the United States Department of Agriculture (2013), are 45-65% of the daily calorie intake. This means they are the body’s main source of energy and so are required for the central nervous system, kidneys, brain and muscles to function correctly. Carbohydrates can be stored in the muscles and liver to be metabolised at a later date.
The structure of carbohydrates comprises of the elements carbon, hydrogen and oxygen. Monosaccharides are soluble and sweet. They have the general formula (CH2O)n and are monomers named according to the number of carbon atoms such as: triose (C3) (e.g. glyceraldehyde), pentose (C5) (e.g. ribose, deoxyribose) or hexose (C6) (e.g. glucose, fructose, galactose). Disaccharides are also soluble and sweet. They have the general formula Cn(H2O)n-1 and so are formed by two hexose units joining (for example sucrose = glucose + fructose or maltose = glucose + glucose or lactose = glucose + galactose). There are also insoluble polysaccharides. Glucose exists as two structural isomers α and β glucose, which form different polymers: starch (amylose and amylopectin), glycogen and cellulose.
Starch is the main dietary carbohydrate. They take a long time to digest, causing slow release energy. This means it is only required it small amounts however, relatively regularly. It can be obtained from root plants (for example yams, potato tubers), grass seeds (e.g. cereals large enough to be harvested) and fruit (within the sugar fructose). It is an efficient storage polysaccharide because glucose can be hydrolysed easily and they have no osmotic effect in cells because they are insoluble.
Sugar is refined starch. Naturally, it occurs in ripe fruits and honey, however in the modern environment today it is easily obtained by the majority of people. This can have negative consequences, for example in the study by Yudkin et al. (1980), where 14 healthy participants altered their diets to consume 260g sugar daily for 3 weeks, resulting in 10/14 having lowered fasted blood concentrations of high density lipoprotein cholesterol, which is an indication of coronary risk, making coronary arterial disease or heart attacks more likely.
Cellulose is the structural material of plants, since the alternating β glucose (isomers) allow cross linking between long chains, forming relatively strong microfibrils. Thus, it is found in fruits, vegetables and whole grain products. It provides energy but it also provide bulk to slow digestion, allowing the body to get more nutrients from the rest of the food that is uptaken, and exercising the digestive system. The negative consequences of a lack of cellulose have been observed in both sailors of the past and astronauts, solely reliant on dehydrated foods. It can cause constipation, haemorrhoids and can increase the likelihood of getting certain types of cancer (e.g. colon). Also, high fibre in the diet can be particularly beneficial, resulting in decreased risk of heart disease, obesity and lower cholesterol. Humans are unable to produce cellulase; the enzyme required to break down cellulose and so we are unable to digest it. However, they can get it indirectly by predating herbivores. Herbivores themselves do reflux to get 60% efficiency at digesting cellulose but it comes at the cost of continuous feeding, reducing time available for them to sleep.
To conclude, carbohydrates are of utmost importance for the energy required for survival. This was as important 13,000 years ago where Northern groups of Homo sapiens planted species which are high in starch, such as wheat and rye, as it is today, when were understand what nutrients we need and why we need them at a more scientific and in depth level.
Proteins are needed for growth, development and maintenance. According to the United States Department of Agriculture (2013), they are 10-35% of the daily calorie intake (however this does depend on the activity level of the individual). It is found in meat, poultry, fish, meat substitutes, nuts and starchy foods. Protein is required regularly but not every day, as can be imagined, it would have been very difficult for hunter gathers to be able to hunt prey and they would certainly have not been able to do this on a daily basis. However, its necessity is shown by the way that if there is a protein deficiency when a person is young, they are likely to have permanently stunted growth and brain development.
Protein also has a role in haemoglobin production, causing anaemia if it is absent in individuals. Tolentino and Friedman (2007) describe anaemia as being the condition where there is a reduction of haemoglobin content in the blood, resulting in the individual feeling tired and weak, due to decreased oxygen-carrying capacity. This is so important because red blood cells are broken down every few weeks and so the degrading cells need to be replaced. The World Health Organisation (2001) provides different definition of anaemia, depending on sex and age, for example, adults males Hb < 13 g/dL and non-pregnant females Hb < 12g/dL. Thus the amount of protein intake per day is dependent on the size and age of the individual requiring it.
Another reason why protein is important is it maintain muscle cell, for example the actin and myosin required for movement. A muscle cell is composed of many longitudinal myofibrils, which are combinations of actin and myosin filaments, which themselves are made from fibrous protein. Furthermore, the actin filaments in skeletal and cardiac muscles contain troponin and tropomyosin to control calcium activation and calcium sensitivity. Thus, the requirements for these structural proteins are far more complex than just for those specific muscle filaments.
Additionally humans are unable to make all 20 essential amino acids required for protein synthesis to enable the individual in question to survive in an adequate manner. Out of these 20, only 11 can be obtained from glucose. In particular, those amino acids which contain sulphur are particularly difficult to acquire and so humans are reliant on their diet to get these. For example, lysine, required for: the absorption of calcium from the intestinal tract, the promotion of bone growth, and the formation of collagen and methionine, required for: helping the liver process lipids, increases the liver’s production of lecithin and regulates the formation of ammonia (Haas and Levin, 2006).
Animals are an ideal source of protein because they have similar muscles, blood systems and proteins (for example haemoglobin, actin and myosin) to humans. However, it is possible to obtain all the required proteins from plants, they are just a less ideal source, since they container fewer essential amino acids and a greater proportion of structural proteins.
A useful example of this is that, as Murphy (2007) said, the Mesoamericans established the Milpa system. A Milpa is a field where a farmer would plant a trinity of crops (Phaesolus beans, maize and squash) to provide a good diversity of essential nutrients, an adequate number of calories and a form of sustainable agriculture. This is because, maize is rich in carbohydrates, methionine and oils but deficient in the essential amino acids lysine and tryophan, which are required to make proteins and the vitamin niacin (which is important to help the digestive system, skin and nerves to function a well as converting food to energy). On the other hand, beans are deficient in cyesine and methonone but they are protein-rich with much lysine and trpsophan. Furthermore, squash is rich in carbohydrates, protein and many vitamins. Also, the likelihood of getting diseases affecting all three different types of crops at once was highly unlikely, thus making them useful crops to choose because of this reliability and this added resistance to environmental conditions. It could be said that they ate some other crops (e.g. tomatoes), domestic (e.g. chickens) and wild (e.g. insects) animals, but these were only eaten as a supplement or for special occasions.
The main types of lipids are described as either oils or fats, depending on their melting points. They are immiscible with water but soluble in some organic solvents. The products of lipid hydrolysis are fatty acids and glycerol. Fats are an efficient calorie store and so are a good source of energy e.g. a weeks’ worth of energy, since they have a high yield of energy per gram.
The energy obtained from fats is not necessary for immediate energy and so is stored, for example, as glycogen in the muscles livers of animals. However, humans crave them, due to them having a strong odour and flavour. This is one of the driving causes of obesity in the modern world, for example a study by Drewnowski et al. (1992) showed how when given a choice of foods, obese women were more likely to choose fatty foods. This occurs since fats are far more available today than they would have been in the era of hunter gatherers or in the cattle herders of the Masais and also the activity levels required to gain such fat by hunting animal has been severely decreased. Thus, rather than fat being stored subcutaneously (stored in adipose tissue which are located below the skin), it would be stored viscerally (around the organs) and ectopically (in the ‘wrong’ place, such as the muscles, heart and arteriole walls). This can lead to more server medical issues, such as otheroscleosis (artery hardening), since if it is stored in the arteriole walls forming plaques (fat deposits). When fibre also becomes attached, fibrous plaques are fashioned, which are difficult to move and so are able to grow. Thus, the blood pressure would slowly increase, causing an increased heart rate. Furthermore, if there is a sudden blockage in the coronary artery, a heart attack would be caused. This is particularly likely because animal fats are consumed relatively frequently, which are solid and mostly saturated (due to the fatty acids), whereas plant fats (e.g. in oily fish, sunflower, soybean, olive, avocadoes or fat-rich fruits) are unsaturated and so lower cholesterol, thus meaning they lower cholesterol and do not form plaques.
Fats are also useful for insulation Thus, if there is a deficiency in humans, they are more likely to get infections (for example, if the case of hunter gathers who did not wear clothes to keep them warm and lived in a harsh environment), leading to decreased likelihood of survival. However, it is also applicable to animals; for example, it could decrease the likelihood of being able to survive through a period of hibernation.
Glycogen, however, is a shorter term storage, useful for periods of interrupted nutrition. This is because it is bulky and contains water (while fat is anhydrous), thus it can not be stored efficiently. Instead, enough is stored for one day (20 miles) of activity and is replenished overnight. After this store has been used up, fat is metabolised relatively slowly, causing a feeling of lethargy, known as ‘hitting the wall’. This is why athletes do artificial loading, consuming large amounts of carbohydrates before racing, to increase their glycogen stores, for example as observed in the study by Rapoport (2010).
A micronutrient is defined as being “a chemical element or substance required in trace amounts for the normal growth and development of living organisms” (The Oxford Dictionary of Biology, 2008). These include vitamins (which are organic compounds), for example, vitamins A, D, C and E, and minerals (that are inorganic substances) such as salt, iron, potassium and calcium.
Vitamin A is required for vision, helps cellular differentiation and is needed for embryo and foetus development. Deficiency of vitamin A in the developed world is rare but till can occur. Symptoms include dry eyes, night blindness, diarrhoea, and skin problems.
Vitamin A originates from carotenoids, the yellow/orange pigment which is cleaved to form retinol. It can be found, in the form of retinyl palmitate, in coloured food (especially vegetables), including the salmonid fish, which have pink flesh due to the carotene in the algae they feed on.
Hunter gatherers were able to obtain vitamin A in the form of liver. However, since they were unaware of the quantities of the vitamin were required, hypervitaminosis A was possible. A potential example of this is the study of Walker et al. (1982), who considered the Homo erectus remains of a possible hypervitaminosis A-induced death.
Vitamin D is a calciforal, thus meaning that it carries calcium. It is also a sterol, which is a naturally occurring unsaturated steroid alcohol, such as those in waxy solids. The body is able to synthesise it, however, it requires sunlight. This explains the evolutionary advantage of chimps having fur, since it protects their pale skin from the harmful UV rays within sunlight while also allowing enough sunlight through the fibres for vitamin D production. It also explains why early human had dark skin due to melanin. This is because it acted as a shield to protect the humans from the sun, which was especially important since they resided in Africa, on the equator. Thus, when the migrations from Africa occurred 70,000 years ago, this explained why lighter skin developed because the sunlight had a reduced intensity, thus the shielded skin stopped too much light getting through, resulting in vitamin D deficiency. An absence of vitamin D in the diet causes various bone diseases, such as rickets (irreversibly bowed and deformed legs) and osteoomalacia (bones have reduced calcium and so are more weak and brittle), which would have reduced the life expectancy and the ‘use’, in terms of ability to gather food, of early humans.
Regardless of its earlier prevalence, this deficiency is still an issue in modern times, because of children who spend most of their time in doors and so are not subjected to sunlight. Also, this applies to women who wear veils in countries such as Saudi Arabia (for example, due to religion or cultural norms). However, they are still able to get vitamin D into their body through their diet, since it can be obtained from fish (in particular, oily fish), eggs and meat (especially the liver).
Oxygen often forms radicals (such as O- and O3) which react with nucleic acids and proteins, breaking them down. Among other problems that this causes, it oxidises the keratin in skin, which causes wrinkles. However, vitamin E acts as an antioxidant, repairing the keratin and delaying the onset of wrinkles (for example, if it is used regularly as part of a cream, from plant oils). Other than wrinkles, there are additional consequences of vitamin E deficiency including anaemia and haemolysis (failure to clot the blood). As well as plant oils (e.g. soya, corn and olive oil), it can also be obtained from nuts, seeds and wheat germ. Thus, it was rich in the diets of early humans, since they were reliant on a steady supply of gathered nuts and seeds, however these food sources are not as important today, leading to a greater likelihood of deficiencies.
Vitamin E is also used to help the formation of red blood cells, as well as widening the blood vessels to ensure he blood does not clot inside them.
In addition, Vitamin C (absorbic acid) is an antioxidant (requiring vitamin E too), as well as being needed to form collagen and improve iron absorption. In particular, the prevalence of scurvy in sailors in the 1580s was identified due to the lacking diet which consisted of salted beef and tack (biscuits) (Crandon et al., 1940). The disease caused collagen break down, resulting in muscle and joint pain, tiredness, red dots on the skin and bleeding and swelling gums. However, this was soon rectified when juice was brought on board at every port. It could also have been prevented by the consumption of citrus fruits, vegetables and fresh meat, since in salted meat, the vitamins are removed by the preservation. For example, by eating foods fresh as the hunter gatherers did, since they did not have the technology or the understanding to be able to preserve such foods in this manner, until the Kebaram culture 23,000 years ago, who salted fish, smoked and dried meat.
Iron is found in meat (liver), coloured vegetables, beans, nuts and fruit. Deficiency can lead to anaemia, since it helps make red blood cells to carry oxygen around the body, which would have led to death if the individual had been a hunter gatherer. It originally became an issue with the development of agriculture. Thus, its deficiency is a problem in the modern world because of people (for example those who live in Asia) who are reliant on rice as a staple part of their diet, due to poverty. This rice contains very little iron and can cause anaemia, if this is not rectified. It can also be deficient in pregnant women resulting in a low birth rate and anaemic, undersized, cognitively impaired children.
Calcium is vital for bone development, regulating muscle contraction and ensuring the blood clots naturally. Lacking amounts causes repercussions (such as rickets and osteoporosis) in later life, which would have caused any hunter gatherers to die, since they wold no longer be able to help with food acquisition and would just be a waste of resources. This is also likely to be a problem when the current generation grow old, since in the modern day there is a general trend to have a poor diet which is low in fish, milk and some vegetables (which are the main sources of calcium), as shown by the study of Greer et al. (2006).
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Tolentino, K. and Friedman, J. (2007), ‘An Update on Anaemia in Less Developed Countries’, The American Journal of Tropical Medicine and Hygiene, Volume 77 (issue 1), pages 44-51.
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