5.2 Carbohydrates (nutrition) Flashcards
Why is glucose so important for the brain?
- It is the primary energy substrate in the brain and the body needs to meet the continuous high metabolic demand in a situation of varying plasma glucose level.
- Blood brain barrier only allows glucose to cross, not other pathogens or solutes in the blood
How might carbohydrates have an impact on decision making?
- Research has linked carbohydrates to mood and decision making
- People who had a high-carbohydrate meal were more likely to implement social punishment when playing the ‘ultimatum game’ than those who ate high- protein breakfasts.
- Scientists speculate this may be caused by dopamine levels, which are higher after eating carbohydrates.
How does fibre differ from starch?
Bonds between glucose molecules in fibre cannot be broken by human enzymes. It passes through the body and therefore contributes little or no energy
What is cellulose?
- Polysaccharide consisting of linear chains of several hundred to many thousand glucose units
- Important structural component of the cell wall of green plants
- Straight chain polymer and hydrogen bonds between each of the chains gives it structural rigidity
Who can breakdown cellulose?
Ruminant animals can breakdown cellulose with the aid of cellulase producing bacteria
Starch breakdown
Starch breakdown vs fibre
Starch breakdown vs fibre
Starch breakdown vs fibre
How does the digestion of amylose compare to amylopectin?
- Different rate of digestion for carbohydrates
- Unbranched amylose chains more slowly digested that branched chains (amylopectin)
- In branched form, enzymes have more places to attack and can release glucose into the bloodstream more quickly
- Amylose to amylopectin ratio predict GI of food
What are the two categories of fibre and where are they found?
- All plant foods, vegetables, fruit, legumes and grains, contain a mixture of fibres.
- Insoluble fibre
- Soluble fibre.
- There is usually much more insoluble fibre in plant foods than soluble fibre.
What is resistant starch?
Acts in a similar way to fibre. Doesn’t get digested and ends up as food for bacteria in the large intestine
How does soluble vs insolbule fibre affect digestion?
How are glucose, galactose and fructose absorbed in digestion?
- Glucose and galactose traverse intestinal cells by active transport which requires energy
- Fructose absorbed by facilitated diffusion (requires specific carrier) which slows its entry to the blood stream
- Fructose and galactose are converted to glucose in the liver, extra step delays blood glucose rise
How does lactase activity change in people?
- Only a small percent (~30%) retain enough lactase to digest and absorb lactose in adult life
- Lactase activity declines with age or damaged intestinal villi
- Symptoms include bloating, abdominal discomfort and diarrhoea
How can lactose intolerance be managed?
- increasing consumption of milk products gradually
- mixing dairy with other foods
- spreading dairy intake throughout the day
- use of acidophilus milk, yoghurt or lactose-free products
- use of enzymes.
What are FODMAPs?
- Large group of short chain carbohydrates and sugar alcohols that are found in all sorts of foods and drinks
- These sugars can be poorly absorbed in the small intestine and fermented by bacteria to produce gas
What can a diet high in FODMAPs cause?
- For some people, a diet high in FODMAPs can cause a range of abdominal symptoms such as bloating, excess wind, distension, abdominal pain, constipation or diarrhoea.
- Following a low FODMAP diet can help manage these abdominal symptoms - 75% of people with IBS experience relief from their symptoms with a low FODMAP diet
What is protein sparing action?
Having adequate carbohydrate in the diet to prevent the breakdown of protein for energy
What are these known as?
Ketone bodies
What are ketone bodies?
Metabolic products that are produced during excessive breakdown of fatty acids
What causes ketosis?
During prolonged starvation, very low carb diets and uncontrolled diabetes, ketones accumulate in the blood causing ketosis
How does ketoacidosis come about?
Very high levels of blood ketones can disturb the body’s normal acid base balance leading to ketoacidosis, a life threatening condition
What is the pathway for maintaining blood glucose homeostasis?
What happens in type 1 diabetes?
- The pancreas is faulty and insulin is not produced, usually childhood onset.
- It was fatal in the past now controlled with insulin injections.
- The cause is unknown.
What is type 2 diabetes?
- Large amounts of insulin secreted but the insulin receptor on the body’s cells are faulty and cells fail to respond to take up glucose as they should
- Generally adult onset with fat gain, also some genetic component (insulin resistance)
How is this curve interpreted?
What factors affect the glycaemic response?
Which sugars and starch have higher GI?
What might be the health effects of eating a low GI diet?
Improvements in
- BOdy weight
- Blood lipids
- Blood glucose control for type 2 diabetes
Why is the usefulness of GI being debated?
- Relatively few foods have been tested
- Responses to food vary widely between individuals
- Not always indicated on nutritional labels and is not intuitively apparent.
- Cooking method and how it’s eaten (ie. mixed meal, standard serve vs 50g CHO portion) can effect the glycaemic response
What is the range of values for classifying food as high low or medium GI?
What are the health effects of added sugars?
- Excessive sugar intake can contribute to the development of nutrient deficiencies and dental caries.
- Sugars ferment in the mouth, and can produce an acid that erodes tooth enamel causing tooth decay.
- Not all sugars need to be avoided; only concentrated sources (e.g. soft drink, lollies, etc.)
What are the three groups of alternative sweeteners?
- Artificial sweeteners. Also known as ‘non nutritive sweeteners’ because they provide no energy and no carbohydrate such as aspartame, sucralose
- Herbal products - Stevia. A herbal product that provides no energy or carbohydrates
- Sugar alcohols. ‘Nutritive sweeteners’ because they still provide kilojoules. They will evoke a blood sugar response. Eg isomalt, mannitol, sorbitol
How does a high fibre diet benefit heart disease?
How does high fibre diet benefit gastrointestinal health?
How does a high fibre diet lower risk of cancer?
How does a high fibre diet lower risk of diabetes?
How does high fibre diet improve weight management?
What are the drawbacks of a high fibre diet?
What is the reccomended dietary intake of carbohydrate?
What is the reccomended dietary intake of fibre?
