NUTRTION AND METABOLISM

The human body requires the periodic supply of a series of basic substances needed for tissues formation, for obtaining the energy that is needed, for performing its physiological activities, and for regulating metabolism. Such substances are present in different proportions in the foods we eat daily, the nutrients. Each type of nutrient has some specific function, but all nutritional principles are essential: depletion of any of them can mean in a health problem.

FUNCTIONS OF NUTRIENTS

The body uses each type of a nutrient in a different way, but generally, it is considered that as a whole, nutrients have three types of functions.

 

STRUCTURAL FUNCTION

They are used for construction and regeneration of tissues and organs. Proteins and some minerals are used this way.

ENERGY FUNCTION

They are used for obtaining the necessary energy for metabolic  chemical reaction that constitute the basis for life, for retaining body heat, for the development of  mechanical action such as muscular contraction, and for many other purposes. Carbohydrates and fats, and secondly, proteins, are used for this purpose.

REGULATORY FUNCTION

They are used as elements that modulate metabolic chemical reactions and the activity of various organs. Several minerals and vitamins are used for this purpose.

 

TYPES OF NUTRIENTS

Carbohydrates                                                Proteins

Fats                                                             Minerals

Vitamins                                                        Water

 

                 Carbohydrates

 

Complex carbohydrates, as natural starches, are found in wholegrain cereals and brown rice.

 

Reviewed by Dr Jeni Worden, GP

                                                        

Carbohydrates are an ideal source of energy for the body. This is because they can be converted more readily into glucose, the form of sugar that's transported and used by the body, than proteins or fats can.

Even so, a diet too high in carbohydrates can upset the delicate balance of your body's blood sugar level, resulting in fluctuations in energy and mood which leave you feeling irritated and tired.

It is better to balance your intake of carbohydrates with protein, a little fat and fiber

There are two types of carbohydrate: complex and simple.

 

Complex carbohydrates

 

Complex carbohydrates are often referred to as starch or starchy foods. They are found naturally in foods and also refined in processed foods.

Complex carbohydrates as natural starches are found in:

 

  • bananas

  • barley

  • beans

  • brown rice

  • chickpeas

  • lentils

  • nuts

  • oats

  • parsnips

  • potatoes

  • root vegetables

  • sweet corn

  • whole grain cereals

  • whole meal breads

  • whole meal cereals

  • whole meal flour

  • whole meal pasta

  • yams.

 

Complex carbohydrates as refined starches are found in:

 

  • biscuits, pastries and cakes

  • pizzas

  • sugary processed breakfast cereals

  • white bread

  • white flour

  • white pasta

  • white rice.

 

 

Simple carbohydrates

 

Simple carbohydrates are also known as sugars. They also exist in either a natural or refined form.

 

Natural sugars are found in fruit and vegetables.

Refined sugars are found in:

 

  • biscuits, cakes and pastries

  • chocolate

  • honey and jams

  • jellies

  • brown and white cane sugar

  • pizzas

  • prepared foods and sauces

  • soft drinks

  • sweets and snack bars.

Simple carbohydrates (sugar) cause tooth decay.

 

The difference between complex and simple carbohydrates

 

All carbohydrates form glucose when digested. Glucose is transported around the body via blood and taken into cells to be converted into energy.

 

The pancreas gland in your abdomen secretes the hormone insulin, which controls the uptake of glucose by your cells.

 

If you have any excess glucose, this is converted into glycogen – which is stored in the liver or in fat around the body.

 

When your body needs more energy, a second hormone called glucagon is secreted by the pancreas. This converts the glycogen back into glucose, which is then released into your bloodstream for your cells to use.

 

This means the body's glucose (sugar) metabolism is a cycle of glucose, insulin and glucagon reactions.

 

  • The slower the release of glucose and hormones, the more stable and sustainable the energy levels of the body.

 

  • The more refined the carbohydrate, the faster the glucose is released into your blood. This can cause peaks and drops in your blood sugar level and less stable energy levels in the body.

 

Complex carbohydrates provide a slower and more sustained release of energy than simple carbohydrates.

In their natural form they contribute to long-term good health, appetite control and sustained energy levels.

 

How much do I need?

 

Current advice is that we should get half our energy needs from carbohydrates, with at least one third of our daily intake of food being starchy carbohydrates.

 

According to the British Nutrition Foundation, the average adult's daily diet meets this target with women getting 47.7 per cent of their daily energy from carbs (203g) and men 48.5 per cent (275g).

 

But not all carbohydrates are equal: refined sugars should make up only 11 per cent of your daily diet. For adults, the average intake of refined sugars is slightly higher than this recommended level, with men the worst offenders at 13.6 per cent.

 

The average child's intake is 16 per cent, with the main culprits being fizzy drinks and confectionery.

 

Do carbohydrates make you fat?

 

Eating too much will lead to weight gain, regardless of what foods you get your energy from. Yet while low carb diets have had much publicity, gram for gram carbohydrates contain less calories than fat, protein and alcohol:

 

  • 1g carbohydrate contains 3.75 calories.

  • 1g protein contains 4 calories.

  • 1g fat contains 9 calories.

  • 1g alcohol contains 7 calories.

 

Sugar and starch are found in both healthy and 'unhealthy' foods, so the type of carbohydrates you eat is important for your wellbeing.

 

  • Many foods high in sugar (cakes, pastries, chocolate) are also high in fat or prepared with fat (chips, roast potatoes, sandwiches).

  • Starchy foods, such as wholegrain bread, pasta etc, are rich in fiber, which is essential for digestive health and helps control appetite so you don't feel hungry.

 

Tips for healthy living

 

  • Your daily diet should be a balance of carbohydrate and protein. As a guide, your plate should contain twice as many carbs as protein.

 

  • Base each of your meals on a complex carbohydrate, such as potato, whole meal bread or brown rice, and include vegetables. Finish the meal with fruit, and this should ensure you get a balance of complex and simple carbohydrates.

 

  • Use high fiber wholegrain cereals as part of your breakfast, and use whole meal bread for your toast.

 

  • For lunch, choose lean protein, such as fish or chicken, with only a small amount of carbohydrate to get you through the afternoon.

 

  • Large carbohydrate meals will make you slow and sleepy so save your big pasta meal for the evening.

 

  • Cut down on the amount of refined white flour products in your diet, such as white bread, pizza and white pasta and rice. The refining process produces simple carbohydrates and many vitamins and minerals are lost.

 

  • Fruit is naturally high in sugar, which means so are fruit juices and smoothies. In liquid form these sugars can damage your teeth. But these drinks count towards your five a day and contain fiber, vitamins and minerals. To avoid tooth decay, it's best to drink them with a meal.

 

Based on a text by Dr Dan Rutherford, GP


Protein

 

Animal proteins contain all the essential amino acids. This type of protein is found in eggs.

                                         

Reviewed by Dr Jeni Worden, GP

Protein is the building block of all life and is essential for the growth of cells and tissue repair.

All proteins are made up of different combinations of 20 compounds called amino acids.

Depending on which amino acids link together, protein molecules form enzymes, hormones, muscles, organs and many other tissues in the body.

 

There are two types of amino acids:

 

  • non-essential amino acids can be made by the body

 

  • essential amino acids cannot be made by the body and must be got from food. There are eight essential amino acids for adults and a further seven that children need.

 

 

Types of protein

 

Animal protein

 

Animal proteins contain all the essential amino acids. This type of protein is found in:

 

  • meat

  • poultry

  • fish

  • eggs

  • dairy products.

 

Oily fish (salmon, sardines, trout, and tuna) is a good source of protein. It has the added advantage of being high in types of fatty acid that provide protection against heart attack and to some extent stroke.

Oily fish contain up to eight times as much omega-3 and omega-6 fatty acids as lean fish (cod, haddock, skate).

 

Plant protein

 

Plant protein contains many amino acids, but no single source contains all of the essential amino acids. This type of protein is found in:

  • legumes (peas, green beans)

  • cereals

  • beans

  • pulses

  • grains

  • nuts

  • seeds

  • soya products

  • vegetable protein foods, such as Quorn or veggie mince.

 

You need to combine different plant proteins to make up the complete range of amino acids needed by your body.

In practice, this is achieved without any special effort, for example by eating baked beans with bread (toast) or using milk on cereal.

 

Plant versus animal proteins

 

In terms of healthy eating, you should aim to eat a diet with a higher proportion of plant proteins than animal ones.

 

  • Many animal proteins are high in saturated fat or cooked with a lot of fat (oil, lard, dripping).

 

  • Studies have linked eating a lot of red and processed meat to an increased risk of bowel and stomach cancer.

 

  • Cooking meat, poultry and fish at high temperatures creates chemicals called heterocyclic amines (HAs) and polycyclic aromatic hydrocarbons (PAHs). It's thought HAs and PAHs may increase our risk of cancer, but more research is needed. PAHs are also found in the exhaust fumes and tobacco smoke.

 

  • Plant-based proteins are low in fat and high in fiber, vitamins and minerals.

 

  • Plant proteins contain phytochemicals that contribute towards health and disease prevention. For example, isoflavones found in soya beans have antioxidant  properties, thought to be important in the prevention of cancer  and menopausal symptoms.

 

How much do I need?

 

Current advice says protein only has to make up 10 to 15 per cent of your daily diet to meet your body's needs. That's around 55g for men and 45g for women.

 

Most of us eat more than this, and the British Nutrition Foundation puts the average adult intake at 88g for men and 64g for women.

 

  • Around two thirds of the protein we eat is from animal sources.

 

  • We get a quarter of our protein from cereal products (wheat, bread, oats).

 

  • Nuts and pulses make up most of the final twelfth.

 

How much protein do foods contain?

 

Below are some examples of foods, so you can compare protein content.

 

You can also check nutrition labels to find out how much protein something contains.

 

  • One skinless chicken breast (130g): 41g protein.

  • One small fillet steak (200g): 52g protein.

  • One beef burger or pork sausage: 8g protein.

  • One portion of poached skinless cod fillet (150g): 32g protein.

  • Half a can of tuna: 19g protein.

  • One portion of cheese (50g): 12g protein.

  • One medium egg: 6g protein.

  • 150ml glass of milk: 5g protein.

  • One tablespoon of boiled red lentils (40g): 3g protein.

  • One portion of tofu (125g): 15g protein.

  • One slice medium whole meal bread: 4g protein.

  • One slice medium white bread: 3g protein.

 

Tips for healthy living

 

  • Include oily fish in your diet at least twice a week.

 

  • Try using soya products, such as veggie mince and tofu. They will take up the flavour of the dish if you add them to stews and sauces.

 

  • Snack on seeds and unsalted nuts. Try sunflower, pumpkin or sesame seeds and brazils, cashews, walnuts, hazelnuts or almonds.

 

  • Look at using pulses as an alternative source of protein. They include chickpeas, a wide range of lentils, split peas and a vast range of beans from the black-eyed to the broad, butter and kidney.

 

  • Have one vegetarian meal each week.

 

You don't need to banish meat from your diet altogether.

 

  1. Use lean cuts of meat and poultry.

  2. Trim off any fat, eg the skin on chicken breasts and the rind on bacon.

  3. Choose smaller portions.

  4. Reduce the frequency of meat-based meals.

  5. Pay particular attention to how you cook meat.

 

Temperature is the most important factor in the production of heterocyclic amines (HAs).

 

  • Frying and barbequing produce the largest amounts of HAs when the cooking temperature is increased from 200°C to 250°C.

 

  • Oven roasting and baking use lower temperatures and so produce lower levels of HAs.

 

  • Stewing, boiling and poaching all use temperatures below 100°C and so produce very few HAs.

 

  • Avoid gravy made from dripping because it contains substantial amounts of HAs.

 

  • Microwaving meat for two minutes before cooking reduces the HA content by about 90 per cent.

 

 

  • Cooking meat for a long time (ie well done or very well done) produces more of these chemicals.

 

  • Protein from milk, eggs, tofu and organ meats, such as liver, have very little or no HA content, even when cooked.

 

Based on a text by Dr Dan Rutherford, GP

 Fats

Unsaturated fats contain essential fatty acids that cannot be manufactured by the body.

 

Reviewed by Dr Jeni Worden, GP

 

Some fat is essential in everyone's diet.

 

Fats provide a source of concentrated energy as well as the fat-soluble vitamins A, D, E and K. Fat transports these vital nutrients around the body.

 

We also need fat for hormone metabolism, healthy skin and hair, tissue repair, protecting the internal organs and to prevent excessive loss of body heat.

 

There are two main types of fat: saturated and unsaturated.

 

      Saturated fat

 

         Excessive amounts of fat are found in saturated animal fats and trans-fatty acids. These types of fat            raise cholesterol levels and increase your risk of many chronic diseases, such as heart disease, stroke and    certain cancers.

 

Saturated fats are solid at room temperature and are found mainly in the following animal and dairy products:

 

  • meat

  • butter

  • cream

  • cheese

  • eggs

  • lard

  • full fat milk

  • suet and dripping

  • full fat yoghurt.

 

Saturated fats are also found in hard margarines that are formed by the 'hydrogenation' of vegetable oils.

 

Hydrogenation increases the shelf-life of food, but it also creates trans fats (trans-fatty acids) that are harmful for health.

 

Hydrogenated margarine or butter is often used for making cakes, biscuits and pastry.

 

       Unsaturated fat

 

          Unsaturated fats are generally liquid at room temperature.

They come from vegetable sources and are also found in oily fish and in soft margarines labeled 'high in polyunsaturates'.

 

Unsaturated fats contain essential fatty acids that cannot be manufactured by the body. This means you need to get them from food.

 

Good sources of unsaturated fats include:

 

  • avocados (one quarter of an avocado contains 5g of unsaturated fat)

  • unsalted nuts (cashew, brazil, pecan, walnut)

  • seeds (pumpkin, sunflower, sesame).

 

Omega-3 and omega-6 essential fatty acids play an important role in the functions of the body that promote health and wellbeing.

 

In particular, studies have shown that omega-3 fatty acids protect against heart disease. Oily fish is the best source of omega-3:

 

  • salmon

  • tuna

  • trout

  • sardines

  • mackerel

  • pilchards

  • herring.

 

Current advice is to eat oily fish two to three times a week. While oily fish is the best source of essential fatty acids, other omega-rich foods are:

 

  • corn oil

  • flaxseed oil

  • nut oil

  • safflower oil

  • sunflower oil

  • virgin olive oil.

 

 

    Tips for healthy living

 

We tend to eat a lot of fat, so aim to include some essential fatty acids in your daily diet and reduce your intake of saturated fats.

 

Below are a few ways to improve your diet.

 

Swap saturated fat for unsaturated

 

  • Cook with vegetable oil instead of lard, butter or margarine, and use sparingly. Sesame seed oil is a good choice for stir-frying.

  • Pour warmed virgin olive oil on bread instead of butter or margarine.

  • Replace the meat in your Sunday roast with salmon or trout.

  • Dress your salads with virgin or nut oils instead of mayonnaise.

  • Instead of reaching for crisps or chocolate, try one of these: pumpkin seeds, sunflower seeds, unsalted nuts or raw vegetables.

 

Get the most from your food

 

  • Check food labels for fat content before you put something in your trolley. It can be surprising how much (and how little) fat some foods contain. Knowing what food contains means you can find a healthier, tasty alternative.

  • Poach or lightly grill your oily fish to maintain the essential fatty acid content.

  • Purchase and store your vegetable oils in dark frosted glass bottles. Light and heat can easily destroy the oils' nutrients.

 

Make healthier choices

 

  • Choose lean meat or poultry and remove the excess fat before cooking. This means the skin on chicken breasts, the rind on bacon and the crackling on pork.

  • Avoid margarine that contains hydrogenated oil. This will be stated on the packaging, so check your favorite brand. Margarines made without hydrogenated oil include Clover, Biona and Olivio.

  • Choose your dairy products carefully. You won't compromise your calcium intake by opting for lower-fat yoghurts and skimmed or semi-skimmed milk.

  • Keep frying and roasting to a minimum. Better choices are to bake, grill, steam or stir-fry.

  • Make biscuits, cakes and pastry an occasional treat. They are high in saturated fats and are likely to contain hydrogenated vegetable oil.

 

Based on a text by Dr Dan Rutherford, GP

 

 

Minerals

Reviewed by Dr Jeni Worden, GP

Vitamins and minerals are essential for the maintenance of good health and the prevention of a number of diseases.

 

        Types of minerals

 

Minerals can be classified according to the amount your body needs.

 

                Major minerals

 

Are those we need more than 100mg of a day.

 

  • Calcium.

  • Magnesium.

  • Phosphorus.

  • Potassium.

  • Sodium.

  • Chloride.

 

            Minor minerals

 

Are those we need less than 100mg of a day.

 

  • Chromium.

  • Copper.

  • Iodine.

  • Iron.

  • Fluoride.

  • Manganese.

  • Selenium.

  • Zinc.

 

The minor minerals are not less important than the major ones – all are needed for good health. Instead, deficiency depends on the natural availability of the mineral: if the mineral is found in lots of foods, it's unlikely your intake will be low.

  • Chromium, copper, iodine, manganese and phosphorus are found in a wide variety of foods, so deficiency is rare.

  • Sodium (salt) is the one mineral that we need to reduce in our diet.

 

.

Calcium

 

This mineral is essential for strong bones and teeth. It also plays an active role in the body's immune system.

A lack of calcium in the diet is a contributing factor to osteoporosis, a condition that causes brittle bones in adults.

High levels of calcium are found in dairy products such as milk and yoghurt. On average 250ml (half a pint) of cows' milk or 150g yoghurt contains 300mg of calcium.

Some dairy products are high in fat, so you should meet your body's calcium needs by eating a diet containing a balance of dairy and non-dairy foods.

 

Non-dairy food sources of calcium include:

 

  • almonds, brazil nuts, hazelnuts

  • broccoli, curly kale, okra, spinach, watercress

  • dried apricot and figs

  • mackerel, oysters, pilchards, salmon, sardines

  • pulses, sesame seeds

  • tofu

  • calcium-enriched soya cheeses and milks.

 

The RDA for an adult is around 800mg.

 

 Iron

 

Your body needs iron for healthy blood and muscles. It plays an essential role in the production of the body's white blood cells and in the activities of the immune system.

Lack of iron causes anemia and symptoms such as tiredness and irritablilty. Women lose iron when they menstruate, and one in four British women doesn’t get enough iron.

There are two types of iron in food:

 

  • haem iron found in meat and offal (essentially the iron from blood and muscle)

  •  

  • non-haem iron derived from some plants, grains and nuts.

 

Vegetable sources of iron also contain salts (oxalates and phytates) that affect how well the body can absorb the iron. This means you need to eat a lot more to get the iron that your body requires.

 

Oily fish and egg yolks are quite rich in iron, but also contain substances that affect your body's ability to absorb the iron.

 

The body can absorb:

 

  • 20 to 40 per cent of the iron found in meat.

  • 5 to 20 per cent of the iron found in vegetable sources.

 

How much iron the body can absorb also depends upon the presence of vitamin C and folic acid, which improve your body's uptake of this mineral.

 

Sources of iron include:

 

  • apricots, blackcurrants, figs, prunes, raisins

  • beans (including baked beans), lentils

  • broccoli, curly kale, peas, savoy cabbage, spinach, watercress

  • eggs

  • lean red meat, poultry or game, liver, kidney

  • liquorice

  • mackerel, oysters, sardines, tuna

  • nuts

  • wholegrain cereals and whole meal bread.

 

The RDA for an adult is 14mg.

 

 Magnesium

 

Magnesium helps to regulate potassium and sodium levels within the body, which are involved in the control of blood pressure.

 

It's also used in the release of energy, for building strong bones, teeth and muscles, and regulating body temperature.

 

Magnesium helps the body absorb and breakdown various other vitamins and minerals – for example calcium and vitamin C.

 

Magnesium is found in lots of foods, and the following are good sources:

 

  • apricots, bananas, figs, prunes, raisins

  • brown rice, granary bread, whole meal bread, whole-wheat pasta, nuts, pulses

  • courgettes, green leafy vegetables, okra, parsnips, peas, sweet corn

  • lean meat

  • milk, yoghurt.

The RDA for an adult is 300mg. You should be able to get this amount from your daily diet.

 

Zinc

 

Zinc is an antioxidant and important for the maintenance of a healthy immune system.

 

It's found in water, meat and cereal products so deficiency is rare.

 

A lack of zinc may be associated with skin problems, slow healing of wounds and low sexual libido.

 

Good sources include:

 

  • brown rice and wholegrain breads.

  • cheese

  • crab, lobster, mussels, oysters, sardines

  • duck, goose, kidney, lean red meat, turkey, venison.

 

The RDA for an adult is 15mg.

 

 Selenium

 

We need small but regular amounts of this nutrient for a healthy liver. It's also one of the body's antioxidants.

 

Selenium is found in soil, so the amount found in foods is dependent upon the farming methods used. Over-cultivation of the land results in a depletion of its selenium levels, and a reduction in the selenium content of the crop.

 

A diet that includes a combination of meat, fish and nuts will ensure an adequate intake of selenium. Good sources include:

 

  • Brazil nuts, cashew nuts

  • cheese, eggs, milk

  • chicken, lean meat, liver

  • garlic, onion

  • green vegetables

  • mackerel, salmon, tuna

  • sunflower seeds

  • whole wheat bread.

 

 Potassium

 

Together with sodium, this mineral is active in the regulation of the body's water levels. Potassium is also important in the transmission of nerve impulses, heart rhythm and muscle function.

 

It is found in most foods except oils, fats and sugars, but can be lost if food is overcooked.

 

Most fruit and vegetables contain potassium, with bananas, strawberries, fresh orange juice, apricots, prunes, potatoes and green leafy vegetables providing the best sources.

 

Other sources include almonds, barley, brown rice, chick peas, corn, garlic, ginger, kidney beans and tofu.

The Food Standards Agency (FSA) says adults need 3500mg potassium a day. You should be able to get this amount from a healthy, well balanced diet.

 

Based on a text by Dr Dan Rutherford, GP

 

 

 

Vitamins

 

Water-soluble vitamins are found in fruit and vegetables.

Reviewed by Dr Jeni Worden, GP

 

Vitamins are essential substances that cannot be manufactured by the body. We need small amounts of vitamins for growth and development. Without vitamins the body cannot survive.

 

The term vitamin is derived from the phrase vital amine. There are two types.

 

  • Fat-soluble vitamins (A, D, E and K) are usually found in meat and meat products, animal fat and vegetable oils, dairy products and fish. They are transported around the body in fat, and your body stores any excess in the liver and fatty tissues. This means you don't need to get them from food sources every day.

 

  • Water-soluble vitamins (B, C, and folic acid) are found in meat, fish, fruit, vegetables and wholegrains. They are transported around the body in water. This means your body can't store them because you pass the excess through urine. You need to eat foods containing these vitamins every day. Water-soluble vitamins can be destroyed by cooking – so steam and grill rather than boil.

 

 

                                Water

Get into the routine of drinking water with your breakfast and other meals.

Reviewed by Dr Jeni Worden, GP                                                                    

Water is perhaps the most important component of complex living organisms.

 

It forms the basic medium in which life processes take place – from intricate biochemical reactions inside cells to the removal of waste products from the body.

 

Even the smallest degree of water loss can impair physical and mental function.

 

More than feeling thirsty

 

Thirst is a poor measure of dehydration and many drinks are themselves dehydrating, eg alcohol and caffeine-containing drinks.

 

You become dehydrated long before you feel thirsty so it's a good idea to drink water often.

 

Still water should be your first choice, but other options are fruit teas or herbal blends, decaffeinated coffee and water flavored with fresh fruit juice.

 

Although the body also gets water from foods, such as fruit and vegetables, the average adult requires around two liters of water a day. This equates to six to eight glasses, and you'll need more when you do any physical activity and in hot weather.

 

Illness and fever also increase your water requirement, and water replacement is an essential part of much medical treatment.

 

Do I need to drink more?

 

If your urine is dark in color, this is your body's signal that you need to increase your fluid levels.

 

How to top-up your water levels

 

  • Start the day with a mug of freshly boiled water and a slice of lemon. In summer add a fresh sprig of mint and fresh lemon slices to a jug of cold water.

  • Replace some of your tea and coffee at work with plain water or one of the many herbal or fruit teas.

  • Keep a bottle of water at your desk or close by if you are relaxing at home.

  • Get into the routine of drinking water with your breakfast and other meals.

  • Drink water before you go to bed.

  • Eat fruit and vegetables, which have a high water content.

 

Based on a text by Dr Dan Rutherford, GP

 

 






 

 

 



 

Basics of nutrition