Flashcards in dietary carbs Deck (19):
Describe how to calculate the number of grams of carbohydrate consumed per day by an individual in energy balance
energy expenditure= 25-35kcal/kg per day. And carb= 4kcal/g so for 70kg man: 30kcal/kg x 70kg= 2,100kcal/day. Then if they consume 50% carbs in their diet: ( 2100kcal/day x 0.5)/ 4kcal/g: 262 grams of carbs in a day
sugars, oligosaccharides, polysaccharides
for sugars, list class and components
Monosaccharides (glucose, galactose, fructose), disaccharides (sucrose, lactose) and polyols (sorbitol, mannitol, xylitol, hydrogenated starch hydrolysates)
for oligosaccharides, list class and components
malto-oligosaccharides (maltodextrins) and other oligos (raffinose, stachyose)
for polysaccharides, list class and components
starch (amylose, amylopectin) and fiber (cellulose, hemicellulose, pectins)
Describe why fructose has unique metabolic properties.
Fructose produces a lower glucose excursion but is cleared by liver where it is a substrate for fat synthesis (de novo lypogenesis) producing higher triglyceride levels and insulin resistance compared to other carbs.
describe fructose metabolism
1. enters cells through a general hexose transporter not regulated by insulin. 2. does not stimulate insulin release. 3.Does not enter glycolysis at fructose 1,6 bisphosphate, because hexokinase is typically completely used to metabolize glucose. It enters glycolysis at a step which effectively bypasses the key regulated step of PFK. For this reason fructose much more readily cleared by the liver, and in the liver readily passes down “glycolysis” to pyruvate. It is a bit like a “super glucose”. This may explain why there may be adverse health effects from fructose like insulin resistance and hypertriglyceridemia.
Describe the concepts of glycemic index and glycemic load
glycemic index: how much does blood sugar ans insulin change with carbohydrate consumption. Low GI means lower change blood sugar and lower insulin change. Glycemic load: glycemic index X amount of food eaten (carb content by weight in %). Glycemic load is correlated with adverse health effects.
List the types of studies that can be used to inform nutritional recommendations
1. animal studies - diet can be controlled but relevance to humans is limitation. can provide most detailed mechanistic info 2. epidemiological- self reporting tools (diet records) correlated with diseases. Weakness in inaccuracies of self report. 3. small randomized controlled trials with surrogate marker endpoints- diet is controlled and changes in endpoints observed. weakness is small N. 4. Large randomized controlled trials with disease specific endpoints- Gold standard!!
describe Large randomized controlled trials with disease specific endpoints
Can show reduction in disease with certain diets. Limitation is that they include other interventions so specific effects of diet alone are not clear. Also diets are not always rigorously controlled
What is lactose
This disaccharide of glucose and galactose is present in milk products
what are sugar alcohols
hydrogenated mono and disaccharides that are incompletely absorbed by GI tract, thus have energy <4kcal/g but can cause diarrhea
short chain polysaccharides are present in beans, onions, asparagus other vegetables and a number of probiotics (yeast containing yogurts). They are incompletely absorbed and as a result can contribute to colonic fermentation. May have beneficial effects on insulin sensitivity and lipid levels, but can cause gas
what is amylopectin
highly branched form of starch. has many “free ends” of the polymer to digest and as a result the digestion and absorption is rapid. This is the predominate form of starch in white bread, potatoes and many pastas. This chemical structure explains the high GI of these foods.
what is amylose
long single chain of glucoses, with only 2 “free ends” that can be subjected to digestion by amylase. Slowly digested and absorbed. Found in basmati rice and bananas
What is resistant starch
ie. corn starch-used as thickening agent. Because of its crystal structure it is slowly absorbed. Used in children with inborn errors of metabolism that predispose them to hypoglycemia due to problems with hepatic glucose production during fasting.
What is fiber
complex carbohydrate that is not digestible by human intestinal enzymes. Increase stool volume and lower serum cholesterol levels. Recommended 15-25g/day
compare soluble vs insoluble fiber
insoluble: does not absorb much water. Examples are bran, whole wheat, and celery. Soluble: absorbs water. Creates greater bulk in GI tract, lower LDL levels, lower post-prandial glucose exercursions more than insoluble. Examples include guar gum, psyllium, beta glucan in beans, oats, barley, apple, fruits.