Carbohydrates Flashcards
give a brief summary of carbs
Carbohydrates are an essential nutrient for the body as they are the most readily available source of energy and can be accessed rapidly when needed. They are the body’s preferred energy source and the only available fuel source for the brain. We consume a variety of carbohydrates through our diet: they are classified according to their different chemical structures and properties.
Daily recommended carb intake?
Carbohydrates are required in relatively large amounts on a daily basis and should make up around 50% of total energy intake (food.gov.uk/BDA/NICE.org). Complex carbohydrates should form the largest part of the diet as they contain substances helpful to health such as fibre (discussed in more detail later).
what do carbs do?
They are the primary and prefered energy substrate, especially during high intensity exercise.
They are the only fuel used by the central nervous system, under normal circumstances.
They act as a ‘metabolic primer’ meaning that they promote fat burning. Glucose must be present in order for us to burn fat stores.
They have a ‘protein sparing’ role. Using carbohydrates as an energy source ensures that proteins are not used as fuel, allowing them to be saved for their primary functions of growth and repair.
They provide a source of fibre.
Classification of carbohydrates
All carbohydrates are made up of three basic elements: carbon, hydrogen and oxygen (hence carbohydrates are often abbreviated to CHO).
what are simple carbs?
Simple carbohydrates are naturally occurring sugars found in fruit, honey and milk. Refined and artificial sugars such as table sugar and corn syrup are also classed as simple. There are two types of simple sugars - monosaccharides and disaccharides
Monosaccharides
Single molecules and are the basic sugars that make up all types of carbohydrate.
Examples include: Glucose (table sugar, honey, soft drinks, confectionary)
Fructose (fruit sugar)
Galactose (found in dairy products and sugar beets)
what are complex carbs?
Complex carbohydrates also known as polysaccharides are made up of longer chains of simple sugars. The three most important complex carbohydrates are. Glyogen, Found in animals. This is the stored form of glucose. Starch, Found in seeds, corn and grains, this type of complex carbohydrate should make the greatest contribution to the body’s glucose supply. Fibre, Found in the cell walls of plants and commonly referred to as ‘roughage’.
the two classifications of fibre
Soluble fibre - dissolves in water to form a gel and prolongs stomach emptying.
Insoluble fibre - does not dissolve in water and adds bulk to the diet. It passes through the gastrointestinal tract relatively intact, speeding up the movement of food and waste through the gut
benefits of fibre
Benefits of soluble fibre: Attaches to fat to help lower LDL cholesterol.
Regulates blood sugar levels: glucose is absorbed and released more slowly.
Benefits of insoluble fibre: Prevents constipation. Help people to feel fuller for longer assisting with weight loss.
sources of fibre
Sources of soluble fibre: Oats, oat bran and barley. Pulses, beans, peas and lentils.
Sources of insoluble fibre: Fruit and vegetables Whole wheat products such as bread, rice, Bran, nuts and seeds.
how much and where is glycogen stored?
the body stores 80% in the muscles, 20%in the liver.
The body can store 375 - 475g of glycogen, the equivalent of 1500-2000 kcals.
regulating blood sugar levels
For the brain and body cells to function there must always be a certain level of glucose circulating in the blood stream so not all of it is converted and stored as glycogen or used immediately in energy production. If blood glucose levels fall below normal a person can become dizzy, confused or weak, and if it continues to drop it can lead to a coma in severe cases. Blood glucose levels are closely controlled by two hormones, insulin and glucagon released by the pancreas
recommended glucose levels
Blood glucose levels are measured in mmol/L. The National Institute for Health and Clinical Excellence (NICE) recommends a normal glucose level range of 4-5.9mmol/L, with levels up to 7.8mmol/L considered normal in the two hours following a meal.
Insulin and Glucagon
Insulin: Stimulates the uptake of blood glucose into our liver and muscles.Glucagon: Stimulates the breakdown of glycogen into glucose
High blood glucose
When a person eats, blood glucose rises.
High blood glucose stimulates the pancreas to release insulin.
Insulin stimulates the uptake of glucose into cells ans storage as glyogen in the liver and muscles.
Insulin also stimulates theconversion of excess glucose into fat for storage.
Later, low blood glucose stimulates the pancreas to release glucagon into the bloodsteam.
Glucagon stimulates liver cells to break down glycogen and release glucose into the blood.
effect of carbs on blood sugar
Low GI foods help stabalise blood sugar levels.
The higher the GI the greater effect on blood glucose levels.
Low GI; <55
Medium GI; 55-69
High GI; >70
Limitations of GI
GI can be influenced by a foods fibre content, the amount of fat and protein it contains and also how itis processed. Quite often we don’t just eat carbohydrate on its own, there will also be a mix of protein and fat and this can reduce the effect that it has on our blood glucose levels and lower the insulin response of the body. GI looks at a specific potion size of food, 50g, which isnt necessarily an accurate reflection of how much we would eat.
Glycaemic Load
Glycaemic load may be more practical in application than glycaemic index. Glycaemic load provides an indication of not only how quickly a food affects blood glucose, but also what effect a particular portion size of food will have.
Glycaemic load = grams of carbohydrate x glycaemic index/100
