Dietary Macronutrients and their Roles. I. Carbohydrates

Which nutrients must the diet supply?

Essential amino acids

Essential fatty acids

Minerals

Vitamins and water

Essential amino acids

histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine

Essential Fatty Acids

Linoleic acid (n-6)

α-Linolenic acid (n-3)

Arachidonic acid

Minerals

Calcium · Iron · Zinc

Iodine · Magnesium

Phosphorus · Sodium

Potassium · Selenium

Vitamins

13 vitamins:

fat-soluble A, D, E, K

water-soluble B group, C

Water: 2-3 litres a day

why is there no essential Carbohydrate?

there is no essential carbohydrate, because the body can make glucose from amino acids and glycerol.

Classification of dietary carbohydrates

SUGARS

OLIGOSACCHARIDES

POLYSACCHARIDES

Sugars

monosaccharides (Glucose, fructose, glactose) and disaccharidesm (sucrose, lactose, maltose) and Sugar alcohols (polyols) (sorbitol)

Oligosaccharides

α-Glucans — digestible, Non-α-glucans (NDO) → act as prebiotics

Polysaccharides

Starch (amylose + amylopectin), Non-starch polysaccharides (cellulose, pectins, gums

→ the dietary fibre fraction_

corn syrup

Thick, sweet syrup, made from cornstarch.

high fructose corn syrup

A sweetener made by processing corn syrup to increase the level of fructose. It is used extensively as a sweetener in processed foods and soft drinks.

Sugar alcohols (polyols)

sorbitol, mannitol, xylitol (gum) absorbs more slowly than sugar, not calorie free.

Replace sucrose in sugar-free

products; about 2.4 kcal/g.

and cause diarrhoea.

Free sugars

all monosaccharides and disaccharides added to food by the manufacturer, cook, or consumer, plus sugars naturally present in honey, syrups, and fruit juices

Oligosaccharides

α-Glucans — digestible

Non-α-glucans — not digestible

α-Glucans

Linked by α-1,4 and α-1,6 bonds (easily catablised)

Maltodextrins from corn or wheat starch.

Non α-glucans

Raffinose, stachyose, and inulin.

Found in peas, beans, and lentils.

Reach the colon intact and act as PREBIOTICS

Starch — resistant and modified

It behaves like fibre: little effect on blood

glucose, about 2 kcal/g, a good prebiotic

modified starch

a starch that has been chemically or physically modified to create unique functional characteristics

Dietary Fiber

nondigestible carbohydrates and lignin that are intact in plants

Cellulose

long straight chains

insoluble — adds bulk

Hemicellulose

xylose and arabinose

partly soluble

Pectin

galacturonic acid

soluble—forms gels

plant based gelatine

Plant gums

e.g. gum arabic

soluble — thickener

Why fiber matters?

Improves Digestion: Insoluble fiber adds bulk to your stool and helps food pass smoothly through your gut to prevent constipation.

Feeds Gut Bacteria: Soluble fiber acts as food for the good bacteria in your large intestine, supporting a healthy microbiome and reducing gut inflammation.

Lowers Cholesterol: Soluble fiber binds to cholesterol in your digestive tract, helping your body get rid of it and lowering your risk of heart disease.

GLYCEMIC CARBOHYDRATE

• Sugars — mono- and disaccharides

• Maltodextrins and other α-glucans

• Digestible starch

digested and absorbed in the small intestine

NON-GLYCAEMIC CARBOHYDRATE

• Non-digestible oligosaccharides

• Non-starch polysaccharides (fibre)

• Resistant starch

passes undigested into the large intestine

Glycemic Index (GI)

a ranking of foods according to their potential for raising blood glucose relative to a standard food such as glucose

Glycemic Load (GL)

Similar to glycemic index but takes into account the amount of food (carbohydrate) eaten.

Glycemic load = GI × the amount of carbohydrate actually eaten.

The protein-sparing action of carbohydrate

consuming enough carbohydrate so that protein is not used to make glucose

lactose intolerance

impaired ability to digest lactose due to reduced amounts of the enzyme lactase.

Diagnosis: lactose tolerance test (blood glucose fails to rise) or hydrogen breath test.

Lactase Persistence

continuation of lactase production beyond early childhood that allows a person to digest milk and dairy products

Lactose non-persistence

Develops during adulthood when lactase activity declines.