Human Nutrition: Ch 4 - Carbs
COMPLEX CARBOHYDRATES
-many monosaccharides bonded together in a variety of arrangements -includes: oligosaccharides + polysaccharides
SIMPLE CARBOHYDRATES
AKA simple sugars category of carbohydrates consisting of monosaccharides and disaccharides
FIBER IN YOUR DIET
fruits, vegetables, whole grains see table 4.3 and 4.4
DEXTRINS
A partial breakdown product formed during starch digestion; shorter polysaccharide chains of varying lengths
SYMTOMS OF DIABETES
type 1: -fatigue (no energy in cells) and lethargic -frequent urination -unusual weight loss -extreme hunger -ketosis type 2: -frequent urination -fatigue -unusual weight loss -excessive thirst -dehydration -glucose in the blood -high blood sugar -infections -tingling limbs -blurry vision
HEXOSE
-all monosaccharides each contain six carbon atoms -therefore referred to as hexose (meaning six) sugars
OLIGOSACCHARIDES 1) RAFFINOSE 2) STACHYOSE
-carbohydrate made of relatively few (3 to 10) monosaccharides -present in a variety of foods, including dried beans, soybeans, peas, lentils -RAFFINOSE and STACHYOSE are the two most common oligosaccharides -humans lack the enzymes needed to digest these two carbohydrates; they pass undigested into the large intestine where bacteria break them down (prebiotic role / give microflora energy) -cause abdominal discomfort and flatulence for some people (Beano!) -components of cell membranes; involved in cell signaling -also made in the breasts and incorporated into human milk; help infants from disease-causing pathogens
CARBOHYDRATES
-organic compounds made of one or more sugar molecules -produced primarily by plants, yet abundant in a wide variety of foods -provide cells with a vital source of energy and are components for RNA and DNA
COW / GLYCOGEN
Cow in a field >> source of glycogen Cow on a plate >> no longer a source of glycogen because he was killed The slaughtering process triggers a fight/flight response, so cow uses all his glycogen storage, therefore he is now carb free *Fight or flight response occurs when the killing is both blunt or anticipated by the animal
Dietary Fiber / Functional Fiber / Total Fiber
DIETARY FIBER: -fiber that naturally occurs in plants -promotes selective growth of beneficial intestinal bacteria -found in a variety of plant foods, such as whole grains, legumes, vegetables and fruits FUNCTIONAL FIBER: -fiber added to food to provide beneficial physiological effects TOTAL FIBER: -combination of dietary fiber and functional fiber
POLYSACCHARIDES 3) FIBER
FIBER: -non-digestible plant-based polysaccharide -not digested or absorbed in the human small intestine; contains glycosidic bonds that are resistant to digestive enzymes -passes from the small to large intestine relatively intact -microflora break down fiber, producing gas (flatulence) -promotes the selective growth of beneficial intestine bacteria, which in turn help inhibit the growth of pathogenic bacteria (fiber=prebiotic)
LIMIT DEXTRINS // α-DEXTRINASE
LIMIT DEXTRINS: -because salivary and pancreatic amylase only hydrolyze α-1,4 glycosidic bonds, partial breakdown products called limit dextrins form during amylopectin digestion -contains 3 to 4 glucose molecules and an α-1,6 glycosidic bond α-DEXTRINASE: -brush border enzyme that hydrolyzes α-1,6 glycosidic bonds -completes the digestion of amylopectin (result = numerous glucose molecules ready to be transported into the enterocytes)
WHY IS IT CALLED DIABETES MELLITUS?
MELLITUS means sweet those with diabetes have sweet tasting urine (due to the glucose)...back in the day the urine would actually be tasted to diagnosis it
MONOSACCHARIDES // DISACCHARIDES
MONOSACCHARIDES -carbohydrate consisting of a single sugar molecule -made up of carbon, hydrogen, and oxygen atoms (1:2:1) DISACCHARIDES -carbohydrate consisting of two monosaccharides bonded together (2 sugar molecules)
Soluble & Insoluble Dietary Fiber
SOLUBLE -tends to dissolve or absorb water (sponge-like swelling) -slows motility in intestine by water absorption -can be digested by microflora; fermented into short chain fatty acids, which can be absorbed as an energy source -has a prebiotic role INSOLUBLE -cannot absorb water -doesn't get digested by enzymes -doesn't slow motility; it increases/promotes movement in the colon (ex. like steel wool in intestine, grabbing pieces of food material stuck on the intestinal walls) -includes cellulose, hemi-cellulose, peels/seeds of plants, etc.
KETOGENIC DIETS AS THERAPY?
Starting to see research in these areas: -seizures disorders in adults/children -babies born without glucose receptors to the brain -people with other brain related issues (injury, trauma, brain cancer) -Alzheimer's
DIABETES: TYPE 2
TYPICAL AGE OF ONSET: -middle-aged + older adults (adult-onset) -increasing incidence in childhood/adolescence -90 to 95% of all diabetes patients HYPERGLYCEMIA RISK FACTORS -related to obesity and sedentary lifestyle -risk is influenced by genetics (and dramatically increases if accompanied by obesity) -someone who is NOT clinically obese, but is metabolically obese = they have extra fat stored in the liver or abdominal area INSULIN RESISTANCE -insulin receptors have difficulty recognizing/responding to insulin -because insulin can't do its job, the transport of glucose across the cell membrane is impaired and glucose accumulates in the blood -elevated blood glucose levels cause the pancreas to release even more insulin into the blood -pancreas becomes worn out and can no longer produce extra insulin needed to lower blood glucose TREATMENT -can often be managed by diet control, weight loss and exercise -may require glucose-lowering meds -eat carbs with lower glycemic index -in some cases, insulin injections are still needed
GLYCOSIDIC BOND
Type of chemical bond that forms between two monosaccharides -There are different types: facing down is called ALPHA, facing up is called BETA Formed when the hydroxyl group (-OH) from one monosaccharide interacts with a hydrogen group (-H) from another monosaccharide = results in the loss of one molecule of water
DIABETES MELLITUS
a metabolic disorder characterized by elevated levels of glucose in the blood (hyperglycemia) -until the discovery of insulin a little over 100 years ago, people with diabetes just died -now classified by underlying cause (etiology) *type 1 (autoimmune) *type 2 (insulin resistance) *gestational (temporary during pregnancy) *secondary (brought on by other diseases) -in the past, it was classified by age of onset and insulin-dependent or non-insulin dependent
RELEASE OF INSULIN AND GLUCAGON FROM THE PANCREAS
-Islets of Langerhans (endocrine cells in the pancreas) consist of: 1) pancreatic β-cells that produce the hormone INSULIN and release it in response to elevated blood glucose levels 2) pancreatic α-cells that produce the hormone GLUCAGON and release it in response to low blood glucose levels -Both of these hormones play an important role in blood glucose regulation and energy storage
SUGAR ALCOHOLS
-a group of alternative sweeteners that are neither sugar nor alcohols -they are "polyols" meaning that the sugar molecule has multiple alcohol groups attached -common sugar alcohols include: SORBITOL, MANNITOL, XYLITOL are often found in "sugar free" products like gum, breath mints, candies, toothpastes, syrups, etc. *OL= alcohol -naturally occur in plants (mostly fruits) or can be produced industrially by manufacturing sugar molecules to add alcohol groups -have half the sweetness and calories of sucrose (only 2 to 3 kcal/g) and don't promote tooth decay -don't get digested properly in the gut and overconsumption can have a laxative effect, leading to diarrhea and abdominal discomfort -can also stimulate the same type of pleasure response in the brain as regular sugar
GLYCEMIC INDEX (GI)
-a rating system based on a scale of 0 to 100 that can be used to compare the glycemic responses of various foods -foods with with HIGH GI's may raise health concerns: *will make your blood sugar levels spike rapidly *will feel fuller faster, but will feel hungry again faster *constant cycle of eating like this (high spikes) can lead to weight gain *concern about overstressing the pancreas -foods with LOW GI's keep you fuller for longer and don't spike your blood sugar rapidly
MONOSACCHARIDES: 3) GALACTOSE
-a six-carbon monosaccharide found mainly bonded with glucose to form the milk sugar lactose -few foods contain galactose in its free state -the body uses galactose to make certain components of cell membranes, plays a role in cell signaling, and synthesizes lactose (important sugar in breast milk) -majority of galactose is converted into glucose and used for energy
MONOSACCHARIDES: 1) GLUCOSE
-a six-carbon monosaccharide produced by photosynthesis; most abundant monosaccharide in the body -primary function is to provide cells with a source of energy (ATP) -pure glucose isn't typically found in foods
MONOSACCHARIDES: 2) FRUCTOSE
-a six-carbon, naturally occuring monosaccharide (sometimes called levulose) -found primarily in fruits, vegetables, and honey -converted into glucose and used for energy
HIGH FRUCTOSE CORN SYRUP
-a widely used sweetener found in a variety of foods and beverages (a syrup that blends readily with liquids) -corn is a cheaper resource than cane sugar, which is expensive to harvest PROCESS: -corn is a starch (G-G-G-G) -glucose molecules are isolated and around half of them are converted to fructose via technology, resulting in: G-G-F-F (sweeter) -HFCS tastes like sucrose (glucose + fructose) because it has a very similar chemical makeup -the ratio of fructose to glucose in HFCS can be considerably higher (55/45) than it is in sucrose (50/50)
ENERGY STORAGE // INSULIN
-after a meal, more glucose may be available then needed; the body will store the excess energy contained in glucose for later use 1) GLYCOGENESIS: insulin promotes conversion of glucose to GLYCOGEN -occurs mainly in liver and skeletal muscle cells -glycogen can't be infinitely stored because it's bulky, and once the limit is reached... 2) insulin promotes uptake of excess glucose by adipose tissue -glucose is converted to fatty acids (type of lipid) -endless capacity to store body fat -conversion of glucose into a fatty acid is irreversible *insulin also stimulates protein synthesis in muscle cells
GLUCONEOGENESIS
-after liver glycogen is depleted, body must find an alternate source of glucose -fatty acids cannot be converted to glucose -when glycogen stores are no longer available, the body uses a process called GLUCONEOGENESIS; it is the synthesis of glucose from non-carbohydrate sources (amino acids from muscle proteins) -insulin inhibits gluconeogenesis (not surprisingly) -the breakdown of muscle protein to provide glucose can have damaging effects, especially if it involves the cardiovascular/respiratory systems (failure will cause death over time) -this is another SHORT TERM SOLUTION
HOW ARE CARBS DIGESTED, ABSORBED AND CIRCULATED IN THE BODY?
-because carbs are structurally diverse, the steps involved in the digestive process vary -ultimate goal: to break down large, complex molecules (such as starches) into small, absorbable monosaccharides -this process requires a series of enzymes -glucose/fructose/galactose can be absorbed (in the monosaccharide form) -disaccharides must be converted to monosaccharides to be absorbed
GLUCAGON // GLUCOGENOLYSIS
-blood glucose levels fall several hours after eating -unless glucose is replenished by food (carbs), the body will begin to break down liver glycogen to maintain adequate levels; the hormone GLUCAGON provides the signal for this to occur -adequate glucose levels need to be maintained to avoid HYPOGLYCEMIA, which causes nausea, dizziness, anxiety, etc. -GLUCOGENOLYSIS kicks in (the breakdown of liver and muscle glycogen into glucose) *liver glycogen can supply glucose for 24 hours before being depleted; a SHORT TERM SOLUTION *glucose released during glucogenolysis is used only by the muscle cells and not made available to other tissues *muscle glycogen does not play a role in blood glucose regulation
POLYSACCHARIDES
-complex carbohydrate made of many monosaccharides (more than 10) -most polysaccharides are made of hundreds of monosaccharides bonded together three most common: 1) STARCH 2) GLYCOGEN 3) DIETARY FIBER
DISACCHARIDES 3) SUCROSE
-disaccharide consisting of glucose + fructose -found primarily in fruits and vegetables, especially abundant in sugar cane and sugar beets -pure crystallized sucrose is refined table sugar -converted into glucose and used for energy
DISACCHARIDES 1) LACTOSE
-disaccharide consisting of glucose + galactose (joined together through a beta glycosidic bond) -converted into glucose and used for energy -produced by the mammary glands; the most abundant carbohydrate in milk (one doesn't have to drink milk to produce lactose in the body)
DISACCHARIDES 2) MALTOSE
-disaccharide consisting of glucose + glucose -formed during starch digestion; not found in many foods -converted into glucose and used for energy
LACTOSE INTOLERANCE III *not on test
-especially common among certain ethnic groups (more than half of Asian Americans, Native Americans and African Americans; only 12% of people of Northern European descent are LI) -certain diseases, medications, and surgery that damage the intestinal mucosa can also increase the risk of LI (usually temporary; lactase production returns once the underlying condition is no longer present) -in most cases, LI does not pose serious health threats -products such as lactose-free milk and over-the-counter enzyme lactase enzyme tablets make it easier to enjoy dairy products and consume sufficient calcium -lactose-reduced dairy products contain all of the nutrients found in regular milk products, with the exception of lactose -if lactose-reduce alternatives aren't available, it is important for individuals to consume alternate sources of calcium, such as fortified soy products, fish with edible bones, fortified orange juice, and calcium-rich vegetables (Swiss chard and rhubarb); may also need calcium supplements
WHOLE GRAIN FLOUR WHITE/REFINED PROCESSED FLOUR ENRICHED FLOUR
-fiber is NOT found in refined grains -it is found in whole grains with all three components of the grain intact 1) bran (fiber) 2) germ (vitamins/minerals) 3) endosperm (starch) WHOLE GRAIN FLOUR -contains bran/germ/endosperm WHITE/REFINED/PROCESSED FLOUR -just contains the endosperm -tastes better, but has micronutrient deficiencies -illegal to produce now ENRICHED FLOUR -contains just the endosperm, but also... -is enriched with vitamins and minerals that were stripped out (by law) -no more vitamin deficiencies, but fiber is not required to be added back
NATURALLY OCCURRING SUGARS vs ADDED SUGARS
-foods like fruits, vegetables and milk contain naturally occurring sugars -many processed foods contain added sugar or syrups -although added sugars are chemically identical to naturally occurring sugars, foods with naturally occurring sugars are usually nutrient dense (ex. oranges contain sucrose, many vitamins/minerals and fiber) -in contrast, foods with large amounts of added sugars (soft drinks, cakes, candy) often have little nutritional value beyond the calories they contain -honey is believed to be a healthier alternative to refined white sugar, but natural sweeteners also have limited nutritional value other than energy
GLUCOSE TRANSPORTERS
-glucose enters cells via facilitated diffusion, mediated by carrier proteins known as glucose transporters 1) in response to a rise in blood glucose, the pancreas releases more insulin in the blood 2) insulin binds to a membrane-bound insulin receptor 3) the binding of insulin to its receptor signals glucose transporters to move from the cytoplasm to the cell membrane 4) glucose is allowed to enter the cell
BENEFITS OF FIBER
-helps with diarrhea (soluble) or constipation (insoluble) -prebiotic role (soluble) -lowers cholesterol *soluble fiber: short chain fatty acid production sends signal to liver to make less cholesterol -probiotic role in lowering cholesterol -soluble fiber in digestion can bind to bile in the gut *liver uses cholesterol as ingredient in bile *soluble fiber binds to bile and takes it out in the feces *liver now has to pull in cholesterol from the blood to make new bile, decreasing cholesterol levels -lower rate of heart disease -lower obesity rates/better weight control because it makes you feel full (soluble fiber is bulky so it slows motility and promotes satiety) -blood sugar control in diabetes -lower rates of colon cancer *insoluble fiber pushes things out of the colon and into the feces (ex. carcinogens may have less contact time against the wall of the colon)
KETOSIS
-ketone synthesis is not without consequences -KETOSIS is a condition that occurs when ketone production exceeds the rate of ketone use, resulting in the accumulation of ketones in the blood -happens when energy intake is very low or when the diet provides insufficient amounts of carbs -causes complications like loss of appetite and the possibility of diabetic ketoacidosis (if you have other underlying health issues)
LACTOSE INTOLERANCE *not on test
-most babies produce enough lactase to digest the high amounts of lactose found in milk -however, some people produce very little or none of this enzyme, so they have difficulty digesting lactose -when people with lactose intolerance consume lactose containing foods, much of the lactose enters the large intestine undigested -bacteria in the large intestine break down (ferment) the lactose, producing several by-products, including gas
PRE-DIABETIC // INSULIN RESISTANCE
-obesity/sedentary lifestyle both are associated with insulin resistance (most obese people are pre-diabetic and genetically linked to cross over from PD to Type 2) -initial insulin resistance doesn't automatically lead to diagnosis of type 2 -hyperinsulinemia can occur: glucose can still get into the cell, but an increased insulin level will be detected (sign for pre-diabetic) -if bad habits aren't corrected, insulin resistance gets worse over time -pancreas gives up and stops sending out insulin, now you can't get glucose into the cells and you're diagnosed with Type 2
CARB-RELATED HEALTH ISSUES: LACTOSE INTOLERANCE
-occurs when the brush border LACTASE ENZYME is declining or isn't produced at all -sometimes may be a result of damage to the brush border, may happen with age, theory that humans don't need lactose after weening off mother's breast milk (good thesis topic) -in order to receive a real diagnosis, one is given a LACTOSE INTOLERANCE TEST *patient given a huge load of lactose *over time, blood glucose levels are measured (they should theoretically go up) -if your blood glucose levels stay the same, you are lactose intolerant -need to obtain calcium from other sources (supplements or diet) or take Lactaid enzyme when you eat dairy
MONOSACCHARIDE ABSORPTION
-once disaccharide and starch digestion is complete, the resulting monosaccharides are readably absorbed from the small intestine into the blood -glucose and galactose are absorbed across the lumenal membrane of the enterocytes (via ACTIVE TRANSPORT) -fructose is absorbed into the capillaries through FACILITATED DIFFUSION -after crossing the basolateral membrane, monosaccharides then circulate in the blood directly to the liver via the hepatic portal system
POLYSACCHARIDES 2) GLYCOGEN
-polysaccharide consisting of a highly branched arrangement of glucose molecules (big, bulky branches) -found primarily in liver and skeletal muscle -serves as a form of energy storage in animals; can be broken down quickly when energy is needed (fight/flight response)
POLYSACCHARIDES 1) STARCH -Amylose -Amylopectin
-polysaccharide that includes grains (corn, rice, wheat), products made from them (pasta and bread), legumes (such as lentils and split peas), potatoes, and winter (hard) squashes Two Forms 1) AMYLOSE -type of starch consisting of a linear (unbranched) chain of glucose molecules -contains only α-1,4 glycosidic bonds 2) AMYLOPECTIN -type of starch consisting of a highly branched arrangement of glucose molecules -contains both α-1,4 and α-1,6 glycosidic bonds
STARCH DIGESTION: AMYLOPECTIN
-salivary glands release SALIVARY α-AMYLASE, which hydrolyzes α-1,4 glycosidic bonds in amylopectin, forming DEXTRINS -in the stomach, acidity of gastric juice deactivates the enzymatic activity of salivary α-amylase (dextrins pass unchanged into small intestine) -pancreas releases PANCREATIC α-AMYLASE into small intestine; it hydrolyzes the α-1,4 glycosidic bonds in amylopectin -dextrins are broken down into maltose and LIMIT DEXTRINS -maltose is hydrolyzed by MALTASE (a brush border enzyme) forming two free glucose molecules -the α-1,6 glycosidic bonds in limit dextrins are hydrolyzed by α-DEXTRINASE (a brush border enzyme), forming free glucose -now in a form that can be digested by the body
STARCH DIGESTION: AMYLOSE
-salivary glands release SALIVARY α-AMYLASE, which hydrolyzes α-1,4 glycosidic bonds in amylose, forming DEXTRINS -in the stomach, acidity of gastric juice deactivates the enzymatic activity of salivary α-amylase (dextrins pass unchanged into small intestine) -pancreas releases PANCREATIC α-AMYLASE into small intestine; it further hydrolyzes the α-1,4 glycosidic -dextrins are broken down into MALTOSE -maltose is hydrolyzed by MALTASE (a brush border enzyme) forming two free glucose molecules -now in a form that can be digested by the body
LACTOSE INTOLERANCE II *not on test
-symptoms can occur within 30-60 mins and include: *abdominal cramping *bloating *flatulence *diarrhea -severity of symptoms depends on how much lactose is consumed and how little lactase the person produces -most people with lactose intolerance can consume small amounts of dairy products without experiencing discomfort -some dairy products such as yogurt and cheese are easier to tolerate because the bacteria used to make these dairy products convert some of the lactose to lactic acid
DISACCHARIDES DIGESTION - DISACCARIDASES (MALTOSE//SUCROSE//LACTOSE)
-takes place entirely in the small intestine -enterocytes provide brush border enzymes needed for disaccharide digestion (referred to as DISACCHARIDASES) -each disaccharide requires a specific disaccharidase ex) lactase hydrolyzes lactose into glucose and galactose ex) sucrase hydrolyzes sucrose into glucose and fructose ex) maltase hydrolyzes maltose into 2 glucose molecules -once disaccharides have been digested into their component monosaccharides, they can be transported into the enterocytes
GLYCEMIC RESPONSE
-the change in blood glucose following the ingestion of a specific food -rise in blood glucose can be detected after we eat carb-rich foods; however, not all carbs have the same effect on blood glucose levels -some foods cause blood glucose levels to rise quickly/remain elevated, while others elicit a more gradual increase
KETONES // KETOGENSIS
-to minimize the loss of muscle, the body reduces its demand of/dependency on glucose by using an alternative energy source called KETONES -ketones are organic compounds used as an energy source during starvation, fasting, low-carb diets or uncontrolled diabetes *released into the blood and used for energy by the brain, heart, skeletal muscle and kidneys -KETOGENESIS *production of ketones *formed when fatty acids are broken down in a relative absence of glucose *occurs in the liver; stimulated by glucagon -idea behind Atkins diet (LCHF): if you don't have insulin, you won't have fat production because fatty acids are broken down in the absence of glucose
DIABETES: TYPE 1
TYPICAL AGE OF ONSET: -childhood and adolescence (juvenile-onset) -can sometimes develop in adults -5 to 10% of all diabetes patients HYPERGLYCEMIA AUTOIMMUNE DISORDER -disease destroys the insulin-producing B-cells of the pancreas -results in little or no insulin production -there is no insulin to bind to receptors, so glucose stays outside the cells TREATMENT -insulin delivered via daily injections -insulin pump -lower end of daily carb intake (45-65%, so stay near 45%) -eating foods with low glycemic index, which makes blood sugar easier to maintain
DISACCHARIDES
SUCROSE / MALTOSE / LACTOSE -in all disaccharides, at least one of the monosaccharides in the pair is GLUCOSE -a condensation reaction chemically joins monosaccharides together by a glycosidic bond
Why is HFCS unhealthy?
THEORIES 1) fructose tastes incredibly sweet and triggers pleasure chemicals in that brain that make you want more and more 2) fructose doesn't get metabolized the same way that glucose does -can be more easily stored as fat / leads to unwanted weight gain -can be easier to over consume HFCS than fructose from a fruit source (the fiber makes you feel full faster) 3) HFCS is structurally the same as sucrose...so isn't sucrose just as bad? -most corn is genetically modified (underlying GMO issues) 4) yet few studies have demonstrated metabolic differences in response to HFCS and sucrose ingestion *the relationship between HFCS and obesity is likely due to excess consumption of energy-dense foods and beverages and not solely HFCS
