Transcript The Macronutrients

Macronutrients
Carbohydrates
• Carbohydrates are an energy source made by plants during
photosynthesis.
• This plant energy provides human energy when eaten.
The functions of carbohydrates
Carbohydrates are needed for:
• Providing energy
• Acting as a ‘protein sparer’
• Dietary fibre (a carbohydrate) produce soft, bulky faeces that help the
body to get rid of waste products when going to the toilet
If the diet is low in carbohydrate, then protein is used as an energy source.
Carbohydrate should stop the use of protein as an energy source so that the
protein can continue its primary function for growth and repair.
Carbohydrates exist in many forms. They can be divided into three groups:
• Sugars
• Starches
• Dietary Fibre
Sugars are the simplest form of carbohydrates
Complex carbohydrates are starches and fibre
Sources of carbohydrate
1.Sugars
• Monosaccharides (single/simple sugars)
Glucose (fruit, onions, potatoes)
Fructose (fruit, honey)
Galactose (milk)
• Disaccharides (double sugars)
Lactose = glucose + galactose (milk, yoghurt, cream, cheese)
Maltose = glucose + glucose (cereals like barley, used to make
breakfast cereals, biscuits, beer, malty hot drinks)
Sucrose = glucose + fructose (sugar beet or sugar cane –
granulated, caster, demerara, treacle, icing, golden
syrup)
Free sugars and fruit sugars
Another way to classify sugars is according to where it is found in food
- Free sugars: Sugars that are added to food or found outside the cell
structure. Free sugars are processed sugars, such as:
Granulated, Caster, Demerara, Icing sugar, Treacle, Golden syrup
They include the sugar found in honey and unsweetened fruit juices.
- Fruit sugars: naturally found inside fruit and vegetable cells. Sometimes
called natural sugars
Hidden sugars are found in foods you would not expect to contain sugar i.e.
salad dressings, sauces, soups, bread.
Normally highly processed foods – look carefully at food labels to identify
hidden sugars
• A diet high in free sugars can lead to tooth decay and obesity.
• Sugar provides energy but contains no other nutrients.
2. Starches
Starches are complex carbohydrates also known as POLYSACCHARIDES.
Polysaccharides are long chains of one type of monosaccharide joined together.
They are thus big molecules and most are insoluble in water.
The most important starches are:
a. Starch
-
Starch is the energy reserve of plants. It can be recognised under microscope
by its shape that is granular with a size and shape distinctive to each plant.
-
Nutritionally starch is important because it provides the body with a slow
release form of energy from the carbohydrate which the starch provides. Unlike
the monosaccharides however, starchy foods can provide other essential
nutrients to the diet, including protein, fat, the B-group of vitamins, vitamin C in
the case of potatoes, potassium, copper, calcium, selenium, magnesium,
manganese, iron and non-starch polysaccharide.
-
Sources: cereals (wheat, rice, oats, barley, maize/corn, biscuits, pastries, cake,
bread, breakfast cereal), starchy vegetables (potato, yam, sweet potato,
parsnip, pumpkin, butternut squash, peas, beans, lentils), seeds, quinoa
b. Pectin
Complex mixture of polysaccharides found in many fruits and
some root vegetables i.e. apples, the peel of citrus fruits,
apricots, plums and some root vegetables i.e.
Main importance: Gelling agent for jam making
Pectin is broken down in fruit as fruit ripens – jam will not gel well
if made from over ripe fruit.
pH affects gel strengths i.e. lemon juice lowers this setting.
(It is actually classified as a soluble NSP (Non-Starch Polysaccharide) as it forms a gel in water)
c. Glycogen
Small amount are stored in the muscles and liver and when
required, the human body (and other animals) converts it to
glucose which provide energy.
3. Dietary Fibre (NSP – Non-Starch Polysaccharides)
-
A non-starch polysaccharide found in the cell walls of vegetables, fruits,
pulses and cereal grains.
- It acts as a bulking agent absorbing the end-products of digestion to allow
waste products to be removed from the body
- They have the ability to hold water and thus aid peristalsis.
- Heating may soften the cellulose, but it does not gelatinise as starch does,
thus remaining undigested in the digestive system, aiding peristalsis.
Function:
- Allowing the digestive system to remain healthy and function properly
- Leaving us feeling fuller for longer and thus therefore help with weight
control
- Prevent some bowel diseases i.e. constipation, diverticulitis, bowel cancer
- Providing soluble fibre (pectin) which can help to reduce cholesterol levels
Sources of dietary fibre (NSP)
Two types of dietary fibre: soluble and insoluble
Soluble
Insoluble
Oats
Wholegrain foods (wholegrain bread,
Nuts
breakfast cereal, pasta)
Legumes (peas, beans, lentils)
Brown rice
Fruit (prunes, apples, pears, plums,
Wheat bran
part of citrus peel)
Fruit and vegetable peel and skins
Vegetables (flesh of potato, sweet
Nuts and seeds
potato, carrot)
Excess and Deficiency
1. Sugars and Starches
Excess: Convert into fat and stored in the body if not used for energy and lead
to weight gain (obesity)
Tooth decay
Deficiency: Lack of energy
Tiredness/fatigue
Weight loss
2. Dietary fibre
Excess: A diet rich in in cereals can reduce the body’s ability to absorb iron and
calcium . The cereal can bind with the minerals making them less likely
to be absorbed in the intestines.
Deficiency: Can contribute towards constipation which could lead to an increase
in bowel cancer
DRVs for sugars and starches
• High intakes of free sugars have been linked to tooth decay and
obesity.
• Free sugars need to be reduced in the diet and should be restricted
to providing 5% of daily energy (calorie) requirements. This is about
30g of sugar a day for those aged 11 and over.
• All population groups exceed this recommendation.
• Teenagers’ intakes are the highest of all groups – they
consume 50% more sugar on average than is currently
recommended.
DRVs for fibre
• SACN (Scientific Advisory Committee on Nutrition)
recommends a Dietary Reference Value (DRV) for dietary
fibre of 30g for adults.
• Children should eat less because of their small body size.
• Very young children should avoid too many fibre rich foods
as being full up with fibre can make it difficult for them to
meet their other nutritional needs.