Carbohydrates Flashcards
What are the different types of carbohydrates?
- monosaccharides
- disaccharides
- polysaccharides (starches & glycogen)
- polyols
- resistant starch
- non-starch polysaccharides (fibres)
What is the WHO recommendation for added sugar intake?
<10% of energy (approx 50g)
What are the monosaccharides?
Glucose
Fructose
Galactose
What are the disaccharides?
Lactose (glucose + galactose)
Maltose (glucose + glucose)
Sucrose (glucose + fructose)
What are food sources of oligosaccharides?
- legumes
- garlic and onion
- inulin from chicory root
- breast milk (& infant formula)
What is an example of a polysaccharide?
Starch
What are the 3 types of starch?
- resistant starch (fermentable)
- amylopectin (digestible)
- amylose (digestible)
Why is amylopectin more soluble than amylose?
Amylopectin has branches, whereas amylose is unbranched
What are sugar polyols?
Artificial sweeteners
What happens if we eat excess polyols?
Laxative effect
What foods are natural polyols found in?
- stone fruit
- mushrooms
- avocados
What are FODMAPs?
Fermentable oligosaccharides (inulin), disaccharides (lactose), monosaccharides (fructose), and polyols (sorbitol)
If poorly tolerated can cause GI symptoms eg bloating, pain, constipation, diarrhoea
What are the 3 types of dietary fibre?
- soluble fibre
- insoluble fibre
- resistant starch
What are the benefits of dietary fibre?
- decrease gastric emptying rate
- increase transit time in small intestine
- decrease transit time in large bowel
What is the role of insoluble fibre?
Absorbs water in the bowel to bulk stool
Where is insoluble fibre found?
In plant cell walls e.g.
- cellulose (wheat bran)
- lignin (hard seed coats)
- hemicellulose (whole grains)
What is the role of soluble fibre?
Soluble in H20 so forms a gel in SI and slows nutrient absorption, removes cholesterol from body and slows glucose release
Where is soluble fibre found?
Non-cell wall components e.g.
- pectins (apples, pears, citrus)
- gums
- fructans
Where is resistant starch found?
Unripe bananas
High Maize corn
cooked and chilled pasta and rice and potatoes
Where is resistant starch fermented?
Large intestine
What is the role of gut microbiota?
- regulation and development of gut immunity
- harvesting energy
- protecting against pathogens
- maintaining the structure and function of intestinal epithelium
- imbalance can lead to problems - dysbiosis
What are the 2 main phylum that make up the microbiome?
Firmicutes ~70%
Bacteroides ~20%
What are the short chain fatty acids produced by gut bacteria?
- butarate and propionate - anti-obesogenic, anti-inflammatory, protect against bowel cancer
- acetate - associated with reduced asthma, some benefit for obesity, inflammation
What can change the gut microbiome (positive/negative)?
Positive - probiotics, fruit and nuts, vegetable and polyphenols, cereal fibre
Negative - sugar, high fat high protein. sweeteners, antibiotics
What foods should we increase/decrease for a healthy gut microbiome?
Increase
- prebiotics
- probiotics
- fibre and resistant starch
- omega-3
- polyphenols
Decrease
- animal products
- processed foods
- omega-6
What starts CHO digestion?
Salivary amylase in the mouth
What is the mechanism of action for insulin
Binds to insulin receptor, activates GLUT4 transporter to signal glucose into cells to be stored as glycogen in liver and muscle
What molecule signals the breakdown of glycogen during fasting/between meals?
Glucagon
What are some conditions related to CHO metabolism?
- diabetes
- lactose intolerance
- fructose intolerance (rare enzyme converting deficiency)
- fructose malabsorption
- glycogen storage disease
What is the relationship between fructose and non alcoholic fatty liver disease?
excess fructose in the liver goes through lipogenesis
What is GI?
Glycemic index - the ranking of CHO foods based on their postprandial blood glucose response over 2 hours
How do low GI foods promote satiety?
Glucose stimulates satiety hormones, so a low GI will allow glucose to be present for longer = promoting satiety
What are the ranges for GI?
High >70
Medium 56-69
Low <55
What are examples of high GI foods?
- brown rice
- white bread
- glucose
- watermelon
- potato
What are examples of medium GI foods?
- basmati rice
- sweetcorn (boiled)
- sucrose
- weetbix
What are examples of low GI foods?
- dark chocolate
- fructose
- milk
- legumes
- apples
What are factors that affect GI?
- variety of starch (eg amylopectin higher GI than amylose due to easier breakdown)
- cooking
- processing (eg instant oats vs traditional)
- fibre - slows GER and increases intestinal transit time
What are the different uses for GI?
- diabetes - controlling BGL
- sports nutrition - low GI before, high GI after event
- weight management - satiety
What is GL?
The weighted mean of GI + g of CHO per 100g/food
GL is affected by the amount of CHO in a meal
What are the GL ranges?
High GL >20
Medium 11-19
Low <10
Aim for <10 per food
Aim for <100 whole day (approx 33 per meal)
