Nutritional Value of Carbohydrates Flashcards
Dentition and gut structures define humans as
omnivores
What diet is thought to be optimal and why?
caveman diets of hunter gatherers 30,000ya - healthy hominid skeletons from this time
Dietary needs vary characteristically by
local populations, most notably lactose intolerance
Carbohydrate is a _______ source of energy
rapid (glucose); cheapest and most abundant fuel
The cheapest, most abundant fuel in the body is
carbohydrates
Fibre has been recommended for how many years?
50 years
Fibre protects against
diverticulosis and haemorrhoids (softer stools); less likely protects against cancer as suggested in the 70s (ugandan’s w/high fibre/fast transit times/no gut cancers)
Low glycaemic index diets are justified by
avoiding the high peak glucose levels that can lead to insulin resistance
GLUT-4
glucose receptor in muscle and fat
Adrenaline affects glycogen by
activating adenylyl cyclase to generate cAMP; stimulates metabolism of glycogen to glucose-1-phosphate for release via glucose-6-phosphate
What is the role of the pentose phosphate pathway?
a fed-state pathway; oxidation of glucose produces NADPH that drives fat and cholesterol synthesis and powers protective pathways against oxidative damage and foreign chemical toxicity
When there is enough glucose in the diet, what is the fate of pyruvate?
Stored as fat
Dextrose =
glucose
What is the releasing signal for insulin from the pancreas?
blood glucose enters (GLUT-2) and is converted to glucose-6-phosphate
Insulin stimulates
uptake of glucose into cells and storage as glycogen in liver and muscles, and excess glucose into fat for storage
Falling blood glucose signals release of what from the pancreas?
glucagon
Glucagon stimulates
breakdown of glycogen in liver (via cAMP) to G1P then G6P for release to glycolysis, blood glucose via liver, and the pentose phosphate pathway
What type of factor is insulin?
growth factor (IGFs) and metabolic factor
Glycogen
storage form of glucose; synthesis requires glucose-6-phosphate generated from dietary glucose or gluconeogenesis
What is the significance of ‘hitting the wall’ during a marathon?
switching over from glycogen stores to fat metabolism
What are the benefits of storing glucose as glycogen?
rapidly mobilized; chemically inert; low osmotic effect (don’t retain water)
Glucagon and adrenaline stimulate what enzyme?
glycogen phosphorylase (glycogen –> G1P)
Why can’t we digest cellulose?
we have no enzymes that can break down B1-4 linked D-glucose
What are free sugars?
mono and disaccharides: glucose, galactose, maltose, lactose, sucrose
Free sugars cause
rapid rise in blood sugar, stimulate insulin release
Free sugars are linked to
diabetes, coronary disease, ageing
What are short chain carbohydrates?
oligosaccharides, fructosaccharides and inulin
How are short chain carbohydrates metabolised?
may be unabsorbed and fermented by gut bacteria particularly in large bowel (eg inulin from beans causing flatulence); may selectiely promote beneficial gut bacteria
What are starches?
branched polymers of glucose
How are starches digested?
some resistant starches are slowly digested; most starch (eg potato) is rapidly digested and absorbed giving a response much like free sugars
What are non-starch polysaccharides?
cellulose or molecules with sugars other than glucose (cell wall, structural material of plants, dietary fibre)
How are non-starch polysaccharides digested?
largely undigested by human enzymes but may be fermented by bacteria in large bowel
What are the benefits of the Palaeolithic diet over the current American diet?
high protein; lower fat content with less saturated fat (animal material) and more polyunsaturated fat (plant material); high fibre; less sodium; more calcium; more ascorbic acid
Why are whole-grain products better than refined grain products?
whole-grain products contain the bran (nutrients and fibre), endosperm (starch and proteins), germ (vitamins and minerals), and husk; refined products contain only the endosperm
Beriberi is caused by
deficiency in thiamin (polished rice)
What is the most important component of grains?
thiamin (in bran); lost in refining wheat and grain products
What are the effects of fibre on digestion?
slows down clearance from stomach and speeds up passage through the gut (peristalsis is more efficient with high fibre)
What is the glycaemic index?
ranking of carbohydrates based on their immediate effect on blood glucose - carbohydrates that break down quickly have high GI indexes and have a fast, high blood glucose response (eg cooked potatoes is the same weight as free glucose)
What is the significance of a low GI?
smaller rise in blood glucose levels after meals which can help in weight loss and prevent insulin resistance
