chapter 4 - carbs

carbohydrates

made of carbon, hydrogen and oxygen (CHO). It is the key energy providing nutrients. only carb source from animals comes from lactose.

main sources are plant based through the photosynthesis process. the main form of glucose in plants are in starches (like wheat, grain, potato).

Energy Cycles

through photosynthesis, plants combine carbon dioxide, water and the suns energy to form glucose (6 carbon molecule).

when humans metabolize glucose, energy and carbon dioxide are released. the glucose is transformed into a pyruvate (2 carbon molecule). this process is called glycolysis

Types of carbs

simple CHO (sugars, like mono/disaccardies like fruits, milk), and

complex CHO or polysaccharides (10+ carbon molecule)(starch and fibre)

monosaccharides

glucose, galactose, fructose.

Fructose or fruit sugar, the intensely sweet sugar of fruit, is made by rearranging the atoms in glucose molecules. Fructose occurs naturally in fruits, in honey, and as part of table sugar. However, most fructose is consumed in sweet beverages, desserts, and other foods sweetened with high-fructose corn syrup (HFCS) or other added sugars.

glucose and fructose are most common monosaccharides in nature.

galactose, has the same number and kind of atoms as glucose and fructose but in another arrangement. Galactose is one of two single sugars that are bound together to make up the sugar of milk.

Galactose rarely occurs free in nature but is tied up in milk sugar until it is freed during digestion.

Glucose

brain is completely dependent on glucose as its energy sources. spikes blood glucose levels as it metabolizes in intestine

Galactose

differs from glucose only in that hydroxyl group faces in a different direction on the number four carbon

Fructose

same chemical formula as glucose but different structure. found in natural sources like fruits, and honey. Also found in soft drinks, cereals and products with high fructose syrup.

when dissolved in liver, your blood glucose level doesn't spike but it converts it into fat

Disaccharides

pairs of two monosaccharides linked together -

sucrose (glucose +fructose, table sugar),

Maltose (glucose + glucose, breakdown of starches),

Lactose (glucose + galactose, milk sugar).

When you eat disaccharides, though, you must digest them first. Enzymes in your intestinal cells must split the disaccharides into separate monosaccharides so that they can enter the bloodstream.

The blood delivers all products of digestion first to the liver, which possesses enzymes to modify nutrients, making them useful to the body.

Glucose is the monosaccharide used for energy by all the body’s tissues, so the liver releases abundant glucose into the bloodstream for delivery inside the body.

Galactose can be converted into glucose by the liver, adding to the body’s supply.

Fructose, however, is normally used for fuel by the liver or broken down to building blocks for fat or other needed molecules.

Sucrose

glucose + fructose.

sucrase is the enzyme to digest it.

table sugar, also found in sugar beets and sugarcane

Lactose

glucose + galactose - lactase is the enzyme to digest it.

milk sugar, found in dairy products like yogurt and cheese

Maltose

glucose + glucose - maltase is the enzyme to digest it.

common breakdown of plant starches, rarely found in foods. Associated with sweet taste in mouth when chewing bread.

Starch is a plant’s storage form of glucose. starch is useful because it is an insoluble substance that will stay with the seed in the ground and nourish it until it forms shoots with leaves that can catch the sun’s rays.

Glucose, in contrast, is soluble in water and would be washed away by the rains while the seed lay in the soil.

The starch of corn and other plant foods is nutritive for people, too, because they can digest the starch to glucose and extract the sun’s energy stored in its chemical bonds.

Polysaccharides

long chains of monosaccharides that may be branched or not branched.

plant forms - starch and fibre.

human digestive enzymes can break bonds between glucose units in starch but not fibre(ex cellulose).

animal form - glycogen. human digestive system can break down the bonds, found in liver and muscle (meat)

glycogen

Glycogen resembles starch in that it consists of glucose molecules linked together to form chains, but its chains are longer and more highly branched

Unlike starch, which is abundant in grains, potatoes, and other foods from plants, glycogen is nearly undetectable in meats because it breaks down rapidly when the animal is slaughtered.

fibres

they differ from starch in that the sugar units are held together by bonds that human digestive enzymes cannot break.

Most fibers therefore pass through the human body intact, without providing energy for its use.

A little energy arises, however, when certain fibers encounter the colon’s bacterial colonies, which do possess fiber-digesting enzymes (fermentation - a form of breakdown that produces tiny products, mainly fat fragments, which the human colon absorbs.)

DRI for carbs

45-65% of energy from carbs, emphasis on complex and whole grain.

minimums 130g per day.

<25% of energy from added sugars.

food sources - pasta, rice, beans, milk products .

limit added sugars to 10% of total calories.

Dietary Fibre

suggested intake - WHO >25g per day.

for younger than 50 = males need 38g/d and for females 25g/d.

for older than 50 = males 30g/d and for females 21g/d.

water soluble fibre

food components that readily dissolve in water, become viscous, and often impart gummy or gel-like characteristics to foods.

types - gum, mucilages, etc… sources - oats, bran, rye, seeds, fruits.

benefits - lowers blood cholesterol, slow glucose absorption, slow transit of food through upper digestive tract, holds moisture in stools, softening them and it oppose allergies, reduce inflammation, .

YIeld small fat like molecules after fermentation that the intestine can use for energy. and lower risk of heart disease/diabetes

insoluble fibre

the tough, fibrous structure of fruits, vegetables, and grains; indigestible food components that do not dissolve in water, poorly fermented.

types - cellulose, lignin and some hemicellulose. Sources - brown rice, wheat bran, whole grains, seeds, fruits, vegetables, legumes.

benefits - alleviate constipation, reduced risk for diverticular disease, provides a feeling of fullness, weight management

fiber intakes

14 grams per 1,000 calories, or 25 grams per day for most women and 38 grams for most men. most fiber-rich foods supply a mixture of fibers.

An effective way to add fiber while lowering saturated fat is to substitute plant sources of protein (legumes) for some of the animal sources of protein (meats and cheeses) in the diet.

Another way is to focus on consuming the recommended amounts of fruits, vegetables, legumes, and whole grains each day.

FIbre excess

No Tolerable Upper Intake Level has been established for fiber, but consuming purified fiber added to foods or supplements can be taken to extremes. Binders in some fibers act as chelating agents.

This means that they link chemically with important nutrient minerals (iron, zinc, calcium, and others) and then carry them out of the body.

The mineral iron is mostly absorbed at the beginning of the intestinal tract, and excess insoluble fibers may limit its absorption by speeding foods through the upper part of the digestive tract.

flour types

refined, enriched, fortified and whole grain.

Whole-grain flours retain all edible parts of grain kernels. It could be that whole grains fill up the stomach, slow down digestion, or promote longer-lasting feelings of fullness than refined grains.

The same three daily servings of whole grains also correlate with lower risks of heart disease and type 2 diabetes. Finally, people who make whole grains a habit have lower risks of certain cancers, particularly of the colon. It may be that the fiber, phytochemicals, or nutrients of whole grains improve body tissue health.

refined flour

the husk, germ and bran have been removed, which leads to lower nutrients in flour.

grains and grain products from which the bran, germ, or other edible parts of whole grains have been removed; not a whole grain.

Many refined grains are low in fiber and are enriched with vitamins, as required by U.S. regulations

enriched flour

some or all nutrients lost when the flour was processed have been added back. refers to the addition of nutrients to a refined food product.

A defined by U.S. la , these terms mean that specified levels of thiamin, riboflavi niacin, folate, and iron have been added to refined grains and grain products.

how carbs become glucose in body

mouth (minor digestion by salivary amylase 5%) ->

stomach (mechanical digestion, turns bolus into chyme) ->

small intestine (digestion by pancreatic amylase, starch -> disaccharides) and enzymes on intestinal walls (disaccharides -> monosaccharides), fibre travels unchanged to the colon. absorption of glucose, fructose, and galactose into bloodstream ->

liver (liver converts galactose and fructose to glucose). stored from of glucose is glycogen.

To obtain glucose from newly eaten food, the digestive system must first render the starch and disaccharides from the food into monosaccharides that can be absorbed through the cells lining the small intestine. The largest of the digestible carbohydrate molecules, starch, requires the most extensive breakdown. Disaccharides, in contrast, need be split only once before they can be absorbed

starch digestion into glucose

Digestion of most starch begins in the mouth, where an enzyme in saliva mixes with food and begins to split starch into shorter units. a slightly sweet taste can develop which is the disaccharides maltose being liberated from enzyme, and continues to break it down while it remains in the stomachs upper storage area. the enzyme is deactivated when it reaches the stomach.

in small intestine there is another starch splitting enzyme that breaks them down into disaccharides and small polysaccharides.  The starch of refined white flour, for example, breaks down rapidly to glucose that is absorbed high up in the small intestine.

Other starch, such as that of cooked beans, digests more slowly and releases its glucose later in the digestion process.

The least digestible starch, called resistant starch, is technically a kind of fiber because much of it passes through the small intestine undigested into the colon.

sugar digestion into glucose

Sucrose and lactose from food, along with maltose and small polysaccharides freed from starch, undergo one more split to yield free monosaccharides before they are absorbed.

This split is accomplished by digestive enzymes attached to the cells of the lining of the small intestine. The conversion of a bite of bread to nutrients for the body is completed when monosaccharides cross these cells and are washed away in a rush of circulating blood that carries them to the waiting liver.

The absorbed carbohydrates (glucose, galactose, and fructose) travel in the bloodstream to the liver, which can convert fructose and galactose to glucose. The circulatory system transports the glucose and other products to the cells. Liver and muscle cells store circulating glucose as glycogen; all cells split glucose for energy.

splitting glucose

First, glucose is broken in half, releasing some energy. Then two pathways open to these glucose halves.

They can be put back together to make glucose again, or they can be broken into smaller molecules.

If they are broken further, they cannot be reassembled to form glucose. The smaller molecules can also take different pathways. They can continue along the breakdown pathway to yield still more energy and eventually break down completely to just carbon dioxide and water. Or they can be formed into building blocks of protein or be hitched together into units of body fat.

Cell enzymes split the bonds between the carbon atoms in glucose, liberating the energy stored there for the cell’s use. Once they are broken down further into 2-carbon fragments, however, they cannot rejoin to make glucose.

protein sparing action

When the body faces a severe carbohydrate deficit, it has two problems.

Having no glucose, it must turn to protein to make some (the body has this ability), diverting protein from its own critical functions, such as maintaining immune defenses.

When body protein is used, it is taken from blood, organ, or muscle proteins; no surplus of protein is stored specifically for such emergencies.

Protein is indispensable to body functions, and carbohydrate should be kept available precisely to prevent the use of protein for energy.

All digestable CHO becomes glucose in the body is used for

energy (directly, from glycogen stores) and Glycoproteins (CHO attached to proteins, ex - mucus, cell membranes)

Postprandial CHO metabolism

blood glucose rises after eating CHO.

Amount of increase reflects - 1. amount of CHO consumed,

2. rate of digestion and

3. rate of entry into the bloodstream, and rate of uptake by cells.

fibre doesnt release glucose which will not cause a strong spike / reduces the risk of glucose into the blood stream

Blood Glucose

under homeostasis so its highly regulated, the normal fasting blood glucose level is 4-6 mmol/L.

when blood glucose is low, the pancreas releases glucagon (hormone). breakdown of liver glycogen -> glucose -> blood -> tissues for energy.

Glucose is produced from protein (gluconeogenesis). If this occurs for a long time, then the result is muscle wasting.

abnormally high, you might become confused or have difficulty breathing. Should your glucose supplies ever fall too low, you would feel dizzy and weak.

excess blood glucose

Chronically elevated blood glucose associated with diabetes alters metabolism in virtually every cell of the body.

Some cells convert excess glucose to toxic alcohols, causing the cells to swell. Other cells respond by attaching excess glucose to protein molecules in abnormal ways; these altered proteins cannot function, causing many problems.

Chronic inflammation of body tissues accompanies uncontrolled diabetes and may contribute to eye, kidney, heart, and other associated problems.

The structures of the blood vessels and nerves become damaged, leading to loss of circulation and nerve function

the body has two safeguards to prevent crazy blood glucose

1. Siphoning off excess blood glucose into the liver and muscles for storage as glycogen and into the adipose tissue for storage as body fat.

2. 2. Replenishing diminished blood glucose from liver glycogen stores.  The hormone insulin stimulates glucose storage as glycogen, while the hormone glucagon helps to release glucose from its glycogen nest.

insulin

insulin regulates blood glucose by - Facilitating blood glucose uptake by the muscles and adipose tissue. and Stimulating glycogen synthesis in the liver.

tissue glycogen stores

The muscles hoard two-thirds of the body’s total glycogen to ensure that glucose, a critical fuel for physical activity. the brain stores a tiny fraction of the total as an emergency reserve to fuel the brain for an hour or two in severe glucose deprivation.

The liver stores the remainder and is generous with its glycogen, releasing glucose into the bloodstream for the brain or other tissues when the supply runs low. Without carbohydrate from food to replenish it, the glycogen stores in the liver can be depleted in less than a day

release of glucose from glycogen

When blood glucose starts to fall too low, the hormone glucagon floods the bloodstream and triggers the breakdown of liver glycogen to single glucose molecules.

Enzymes in liver cells respond to glucagon by attacking a multitude of glycogen ends simultaneously to release a surge of glucose into the blood for use by all the body’s cells.

Thus, the highly branched structure of glycogen uniquely suits the purpose of releasing glucose on demand.

Hypoglycaemia

low blood glucose, can be fatal because the brain runs on glucose

Hyperglycaemia

high blood glucose, extreme thirst and frequent urination

Ketosis

need minimum 130g CHO/day to prevent ketosis and spare protein. Usually consume 200-400G CHO/d.

liver glycogen lasts 4-6 hours depending on CHO intake, exercise etc.

If liver glycogen is depleted, then ketosis occurs. Ketone bodies can accumulate in the blood, causing ketosis.

When they reach high levels, they can disturb the normal acid-base balance, a life-threatening situation. People eating diets that produce ketosis may develop deficiencies of vitamins and minerals, loss of bone minerals, elevated blood cholesterol, impaired mood, and other adverse outcomes

Ketone bodies provide a fuel alternative to glucose for brain and nerve cells when glucose is lacking, such as in starvation or very-low carbohydrate diets. Not all brain tissues can use ketones, however—some rely exclusively on glucose, so the body must still sacrifice some protein to provide it

Diabetes type 1

early/mid life <10% of cases. Hyperglycaemia due to little or no insulin produced by the pancreas. It is an autoimmune response.

if left untreated, glucose wasting(urine) and weight loss.

Treatment - insulin is injected to match food intake and physical activity. has to be injected because if taken orally, the peptides will be broken down.

the type of diabetes in which the pancreas produces no or very little insulin; often diagnosed in childhood. glucose concentration builds up in the blood, while body tissues are simultaneously starving for glucose.

diabetes type 2

usually children and teens >90%. hyperglycaemia due to insulin resistance (associated with being overweight).

Pancreas produced lots of insulin but cells respond poorly. Chronic hyperglycaemia increases risk of cardiovascular disease, kidney disease, blindness, amputations. if you change diet and lifestyle, can cure type 2.

The insulin-resistant muscle and adipose tissues no longer respond to insulin by increasing their uptake of glucose from the blood. As blood glucose climbs higher, the pancreas compensates by producing larger and larger amounts of insulin. Blood insulin may rise abnormally high—but to no avail.

Eventually, the overtaxed cells of the pancreas begin to fail and reduce their insulin output, while blood glucose spins further out of control. if levels are higher than 126mg/dl or 6.5% it is diabetes,

risk factors for Type 2 Diabetes

family history, sedentary lifestyle, overweight, genes - indigenous, african, American etc

warning signs of type 2 diabetes

excessive urine and thirst, glucose in urine, weight loss, nausea, weakness, cravings for food (esp sweets), drowsiness, vision disturbances, frequent infetions (skin, gums, urinary tract), slow healing of cuts, pain in legs, feet or fingers,

Managing Type 2

increasing diet and physical activity as 10% weight loss is beneficial. Oral agents to stimulate insulin production and insulin injections can help

Glycemic effect of food

extent to which foods elevate blood glucose compared to a glucose solution or white bread.

Low number (considered best) - legumes, peas.

high number - white bread, juice.

high index causes a blood sugar spike and then crash. a low index is digested and released slowly for sustained energy.

factors to consider for the glycemic effect

1. consider the type of food and the

2. 2. cooking method. if you cook something its index goes up. fat lowers glycemic index

limits of the glycemic index

does not consider the amount of carb, only type.

combining different high and low GI foods change the GO for the overall meal (glycemic load).

Some nutrient dense foods have higher GI's then less nutritious foods. ex - oatmal has higher GI than chocolate because choc has more fat

lactose intolerance

insufficient lactase enzyme activity to digest lactose -> glucose + galactose (lactase),

usually in people of non european background. symptoms - nausea, pain, diarrhea, and gas. more osmotic particles draws on water and bacterial fermentation in intestine.

how to manage lactose intolerance

small amounts of milk, aged cheeses and yogurt, lactaid pills

milk allergy

immune response to protein in milk. need non dairy sources of calcium. issues with the supplements is that the body doesn't focus on the nutrients from food.

sugar in moderation

added sugars

sugars and syrups added to foods during processing. ex - brown sugar, corn syrup , fructose etc

natural sugars

naturally occurring in foods and have not been added ex - honey

sugar alcohols

members of chemical alcohol family. ex - sorbitol, mannitol, xylitol, isonalt, maltitol, lactitol. not readily used by mouth bacteria.

all have 3-5 calorie but poorly absorbed. sugarlike compounds in the chemical family alcohol derived from fruits or manufactured from sugar dextrose or other carbohydrates; sugar alcohols are absorbed more slowly than sugars, are metabolized differently, and do not elevate the risk of dental caries

artificial sweeteners

acceptiable intake is estimated amount of sweetener that can be consumed daily over a persons lifetime.

200x sweeter than sucrose. aspartame - has been noted to increase cancer