Nutrients For The Human Diet Biology Essay


The human body needs food as a source of engery and for the growth and maintence of cells and tissues. The average human requires food from the main food groups to support a healthy diet.

From the food we eat:





Mineral Salts



Each plays a specific role within the body

The food comes in 2 catagories, Micronutirents and Macronutrients. Macronutrients are nutrients required in large amounts for normal growth and development of the body. These are carbohydrates, proteins, fats or lipids, and water. Micronutrients are dietary elements only required in minute amounts for the normal physiological processes within the body. These are vitamins, minerals or chemical elements such as zinc, iron, magesium or iodine.

Every human body works differently and diet needs to be adjusted to suit each individual. Some humans can produce too much or too little hormones that can effect how the food is processed in the body. Organ functions also play a role, chronic kidney failure requires a low protein diet. Athletes need more carbohydrate than a person that holds a sedentry job. The amount of food we take in should be correlated to our lifestyles. It is when a person eats more calories than they are burning, weight gain becomes an issue.


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Carbohydrates are the primary source of energy for the body and one of the main macronutrients. Carbohydrates can be found in a range of foods like whole grains, beans, vegetables and fruit. They come in the form of starch, sugar and fibre. The digestive system breaks down most carbohydrates by converting them into glucose and this is the energy source for the cells within the body.

Glycemic Index

Carbohydrates in dietry terms are classified by the Glycemic Index. Foods that are low GI are digested slowly and maintain glucose in the blood for longer, this results in keeping energy levels balanced and stable making you feel fuller for longer. High GI foods often come in the form of sugary snacks and cause a rollercoster effect on glucose levels. This is why many people have sugar cravings inbetween meals.

Problems with high or low carbohydrate diets

A diet that is high in high GI foods can potentially be damaging to the body and has been linked to a number of different dieseases like type 2 diabeties, high blood pressure, atherosclerosis, heart disease and high cholesterol levels. A diet that is high in refined sugars lacks minerals and vitamins, the body must then use its stores of micronutrients in an attempt to keep the body healthy. High levels of triglycerides and cholesterol are present resulting in obesity due to high fatty acids being stored around the organs. High triglycerides can be a result of insulin resistant. This occurs when too much carbohydrate is being converted by insulin. It is made in the liver from excess sugars that are not being used for energy.

A diet that has little or no carbohydrate can be just as damaging a high content one. The human body is designed to pull most of its energy from carbohydrates. This can result in physical and mental exhaustion. A zero carb diet usually means high protein and fat which can increase the risks of heart disease, cancer, constipation, elevated blood cholesterol levels and vitamin deficiencies. Antioxidants found in fruit and vegetables are thought to reduce the risk of cancer and have anti-aging properties. According to new research by Arizona State Univeristy diets that cause Ketones can lead to inflammation and osteoporosis. Ketone bodies are by products of incomplete fat metabolism which increases blood acidity and ketosis can damage the bodies tissues and blood vessels. Ketosis occurs when the liver runs out of glycogen and starts using fatty acids as energy sources.


Proteins are made up of amino acids held together in trains called piptide bonds. There are 20 different types of amino acids. These are either essential or non-essential. There are 9 essential amino acids that need to be taken from food as the body can't produce these. The non-essential amino acids can either be extracted from food or made in the liver from surplus essential amino acids. The surplus amino acids are removed from the body through the urine as the body can't store them.

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Roles of proteins.

According to the British Nutrition Foundation most (36%) of the protein in the UK comes direct from animal products.

The average UK consumption of proteins is above the recommended levels at 88g for men and 64g for women. The recommended levels are 55.5 g/day for men aged 19-50 years and 45.0 g/d for women aged 19-50 years

Proteins are very important within the body and one of its most important function is to build and replace tissues. Muscles, organds and some hormones are made mostly of protein. They also produce antigens, enzymes and antibodies. They make structural proteins for the hair and nails (keratin) as well as collagen found in tendons. Plasma proteins are needed to clot blood and to make conjugated proteins like haemoglobin.

Children have higher requirements of proteins than adults in terms of unit body mass as they are constantly growing as do pregnant females who need aditional amounts for the growth of the foetus.

Foods High in Biological Value

Food Source

Biological Value (BV)

Whey protein


Soy bean


Human milk




Soy bean milk


Cows milk










Whole wheat


White flour


Proteins are catagorised through their biological value (BV). Foods of a high BV have a range of amino acids required and are mainly found in fish, eggs, meat and cheese. If food has a low BV it doesn't contain enough amino acids or is low in quanity. This is usually from plant proteins.

Vegans and vegetarians are most likely to suffer from protein deficiency illnesses. Many of the amino acids, vitamins and minerals the body require come from meat, dairy and fish proteins. Although they can be found in other sources they are not as plentiful.

Omega-3 fatty acids are found in oily fish and health professionals recommend we eat them twice a week. Omega-3 fatty acids have been shown to slow the progression of artheosclorosis, reduce trigliceride levels, act as an antiinflammatory agent, possibly help with depression and other personality disorders. Vitamin B12 is found in animal proteins as well as fish and dairy. Vitamin B12 deficiancy can lead to anemia and irreversable nerve damage. Dairy products account for upto 70% of calcium intake. Although calcium can be found in non-dariy products it is lacking in quantity. Calcium absorption from spinach is about one-tenth of that from milk. Vegans are at a higher risk than vegetarians from calcium deficency. Iron is found in animal protein and lack of iron can result in fatigue and decrease immune functions.

Fats & lipids

Fats are a concentrated energy source and has many roles within the body. Lipids are defined by 'good' and 'bad' fats. Good fats or mono and polyunsaturated fats raise HDL cholesterol levels and bad fats, trans and saturated fats raise LDL-cholesterol and lower HDL-cholesterol thought to be one of the leading causes of chronic heart disease as well as contributing to obesity, diabeties and certain cancers.


Found in

Monounsaturated fats

Olive oil, peanut oil, canola oil, nuts & avocadoes.

Should get 10-15% of calories from these types of fats

Polyunsaturated fats

Omega 6 â€" sesame, soy & sunflower oils

Omega 3 â€" Flaxseed, walnuts & oily fish like salmon, tuna, mackeral. Should make up 10% of calories

Saturated fats

Meat, poultry, cheese, palm oil, coconut oil, whole milk & processed foods. Should be limited

Trans fats

Pastries, cookies, fried food, margerine, sweets. Should be avoided as much as possible

The body only needs 30% of its calories from fats and the overconsumption of fats, good and bad can result in obesity.

One of roles of lipids is to transport, absorb and digest fat soluble vitamin A, D, K and E. Removing fats all together or in very low amounts can interfer with the absorbtion of the fat soluble vitamins. Fat soluble vitamins are stored in the liver and fatty tissue and are used much more slowly than water soluble vitamins.

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Physiological Functions



A (retinol) (provitamin A, such as beta carotene)

Vitamin A: liver, fortified milk and dairy products, egg yolk.

Provitamin A: carrots, leafy green vegetables, sweet potatoes, pumpkins, winter squash, apricots, cantaloupe

Helps to form skin and mucous membranes and keep them healthy, thus increasing resistance to infections; essential for night vision; promotes bones and tooth development. Beta carotene is an antioxidant and may protect against cancer.

Mild: night blindness, diarrhea, intestinal infections, impaired vision.

Severe: inflammation of eyes, keratinization of skin and eyes. Blindness in children

Mild: nausea, irritability, blurred vision.

Severe: growth retardation, enlargement of liver and spleen, loss of hair, bone pain, increased pressure in skull, skin changes.


Vitamin D-fortified dairy products, fortified margarine, fish oils, egg yolk

Synthesized by sunlight action on skin. Promotes hardening of bones and teeth, increases the absorption of calcium

Severe: rickets in children; osteomalacia in adults. Mild: nausea, weight loss, irritability.

Severe: mental and physical growth retardation, kidney damage, movement of calcium from bones into soft tissues


Vegetable oil, margarine, butter, shortening, green and leafy vegetables, wheat germ, whole grain products, nuts, egg yolk, liver

Protects vitamins A and C and fatty acids; prevents damage to cell membranes. Antioxidant.

Almost impossible to produce without starvation; possible anemia in low birth-weight infants..

Nontoxic under normal conditions. Severe: nausea, digestive tract disorders


Dark green leafy vegetables, liver; also made by bacteria in the intestine

Helps blood to clot

Excessive bleeding.

Fats have other important roles to play; They provide protective cushioning around the vital organs, assist with insulation, supply the body with essesial fatty acids, store energy and are a source of fuel.


70% of the human body is water and is the main component of cells, blood, lymph, tissue fluid, sweat, synovial fluid, gastric juice, saliva, semen and urine. We get our water from drinks and food and as a biproduct of respiration. We use about 9 litres of water per day. It also prevents constipation by moving food through the intestinal tract. Water is used as a solvent in which many of the bodies solutes are disolved as metabolic processes within the body. Without water the human body would die within a few days as every cell and organ needs water to function properly. Dehydration is a potentially life threatening

Dehydration can be caused by losing too much fluids from vomiting, diarrhea, diabetes and fevers or it can be caused by not drinking enough fluids because of nausea, loss of appetite or sore throats. Dehydration is common in sick children and the elderly who refuse to drink while ill. The majority of dehydration cases can be resolved through taking in more fluids or elecrolyte solutions and only sever cases need medical attention. Untreated severe dehydration may result in seizures, permanent brain damage, or death.

Water soluble vitamins are different from fat soluble vitamins as the body cannot store excess supplies, instead they are secreted out through the urine. As they cannot be stored the body needs a continuous supply. These vitamins are the B-complex group and vitamin C. Smoking and alcohol consumption can decrease the amount of vitamins the body absorbs.


Micronutrients are the minerals and vitamins the body requires but only in very small quantities. They are still essential for many different functions within the body such as growth and development. Even though they are only required in small amounts micronutrients are widespread affecting approximately a third of the worlds population. Deficiencies are most common in developing countries where malnurishment is still a problem. The most common deficiencies are iron, vitamin A and iodine. These have negative impacts on children and their physical growth and mental functions. It can lead to poor growth, low immunity and mental retardation. The World Health Organisation state 'their lack represents a major threat to the health and development of populations the world over, particularly children and pregnant women in low-income countries'.