Carbohydrate Flashcards
Carbohydrate
The term carbohydrates denotes a class of nutrient ranging from simple sugars (e.g glucose) to complex carbohydrates such as starch and indigestible fibre. Carbohydrates are widely distributed in food and their primary role is to provide energy to the body.
Carbohydrate functions
Provide a source of energy to facilitate body metabolism and control body temperature.
- Provide glucose, upon which the brain and the white and red blood cells rely as their sole source of energy.
- Glucose can also be converted to glycogen (glycogenesis) in muscle and liver for storage.
- Work to “spare” protein, when there is sufficient carbohydrate and fat in the diet to meet energy needs, protein is “spared” to be used for its primary role of tissue synthesis.
- Required for proper fat metabolism (when there is too little carbohydrate, products of fatty-acid metabolism called “ketone bodies” accumulate in the blood and might be harmful.
The main ketone bodies
- Acetone
- Acetoacetate
- Hydroxybutric acid
How can carbohydrates be classified?
From simple sugars (monosaccharides, disaccharides) to complex polysaccharides (starch, fibre)
Glucose
Is a monosaccharide and is the most abundant carbohydrate found in nature.
Monosaccharides
The simplest carbohydrates are the monosaccharides glucose, fructose, and galactose. Glucose is the final breakdown product of carbohydrates in the body and the major energy source. Glucose and other monosaccharides are known as “simple sugars”.
Food sources for monosaccharides
Glucose is naturally in fruits and vegetables such as grapes, figs, tomatoes and apples
Fructose is the sweetest of the monosaccharides and can be found in honey and many fruits
Galactose does not occur in nature alone and is found in dairy products (derives from lactose hydrolysis)
Disaccharides
Disaccharides are composed of two monosaccharides. The major disaccharides are lactose, maltose and sucrose.
Food sources for disaccharides
Sucrose: sugar cane, sugar beets, maple sugar, fruits and vegetables
Maltose: malt beverages and cereals, malt liquor (strong lager), beer
Lactose: milk and related dairy products
Polysaccharides
Polysaccharides are composed of more than 10 sugar units linked together in different configurations. The dietary polysaccharides include starch and fibre.
Starch
Storage form of glucose in plants found in grains legumes, and tubers. It is the plant form of storage for polysaccharides and is found in 2 digestible forms (amylose and amylopectin). However, some starches are not digestible and are called “resistant starches”.
Glycogen
It is the animal storage form of glucose. Glycogen is formed in the liver through a process known as “glycogenesis”. It is stored in the muscle and liver for utilization when the body needs energy.
Fibre
It is non-digestible and is not used for energy by the human body. However, it has beneficial effects on the body.
The 3 main roles of fibre
- Promoting gastrointestinal function and motility
- Interfering with absorption of dietary fat and cholesterol
- Slowing the absorption of glucose to regulate insulin secretion
Food sources for starch
Breakfast cereals
Bread
Crackers
Snacks (e.g. pretzels)
Pastas
Rice
Legumes – soybeans, kidney beans, dried peas
Potatoes, corn
Whole unprocessed grains
Fruits and vegetables
Food sources for starch
Breakfast cereals
Bread
Crackers
Snacks (e.g. pretzels)
Pastas
Rice
Legumes – soybeans, kidney beans, dried peas
Potatoes, corn
Whole unprocessed grains
Fruits and vegetables
Food sources for fibre
Whole-grain bread
Whole-grain breakfast cereals
Whole-grain pasta
Potatoes with skin
Unpeeled vegetable
Whole fruits
Whole cooked peas, beans and pulses
Nuts and seeds
Sugar alcohols
In the food industry they are used as sweeteners (chewing gum, oral health products-non cariogenic).
Sugar alcohols are fermented by?
By the microbiota in the large intestine (2 kcals/g).
Sources of sugar alcohols
Plants and industrially produced
Examples of sugar alcohols:
sorbitol, xylitol, mannitol
For adults should .. come from carbohydrate
50 % = 300g
Sugar intake should be
<5% = 30g
Fibre intake should be
30 g per day
“Avaliable or glycaemic» carbohydrate”
That fraction of carbohydrate that can be digested by human enzymes, is absorbed and enters intermediary metabolism.
“Unavaliable or non-glycaemic” carbohydrate
It is digested by the gut microbiota, producing short chain fatty acids which are used as fuel for tissues.
Plant energy store
starch (amylose and amylopectin)
Animal energy store
Glycogen
Carbohydrate metabolism
Carbohydrate is an important energy source for cells. They are broken down into glucose, which is the main furl for cells. The concentration of blood glucose is tightly regulated by homeostatic mechanisms.
If glucose levels exceed the energy needs..
Insulin is secreted and directs excess glucose to be stored as glycogen
When the body need energy…
Glucagon is secreted and stimulates the conversion of glycogen to glucose
Diabetes mellitus
Diabetes mellitus encompasses a group of disorders characterized by high levels of serum (blood) glucose (hyperglycaemia).
Diabetes mellitus encompasses a group of disorders characterized by high levels of serum (blood) glucose (hyperglycaemia) resulting from:
Insulin resistance by cells
Impaired insulin secretion by the pancreas
And/or increased hepatic glucose production
Diabetes is a major cause of
Blindness
Amputations
Renal disease
Premature deaths
Type 1 diabetes mellitus
Insulin-dependent diabetes mellitus (IDDM). Cellular-mediated autoimmune -cell destruction occurs, resulting in absolute insulin deficiency. As a result, glucose cannot be taken up by cells and rises in the blood above normal levels (hyperglycaemia).
Individuals with T1DM are likely to exhibit symptoms such as:
Polydipsia (excessive thirst)
Polyphagia (excessive appetite)
Polyuria (excessive urination)
Weight loss
Dehydration
Electrolyte disturbances
People with T2DM can have defects in:
Secretion of insulin by the pancreas (as in T1DM)
Increased hepatic glucose production
And/or defects in the action of insulin at the cellular level (insulin resistance)
Risk factors for T2DM
Family history of diabetes (parents or siblings)
Obesity (body mass index >27 kg/m^2
Habitual physical inactivity
Previously identified as pre-diabetic
Hypertension 140/90 or greater
HDL cholesterol >35 mg/dl and/or triglyceride level >250 mg/dl
Race/ethnicity
Glycemic index:
“Blood glucose response measured as area under the curve (AUC) in response to a test food consumed by an individual under standard conditions expressed as a percentage of the AUC following consumption of a reference food”
