Carbohydrate Metabolism & Nutrition - Week 4 Part 2

Gluconeogenesis

The conversion of non-carbohydrate sources, such as amino acid carbon skeletons, lactate, and pyruvate, into glucose.

Ketone Bodies

An alternative fuel source produced by the partial breakdown of fats when blood glucose is limited.

Minimum Carbohydrate Requirement

The body needs about 50-100g of carbohydrates per day to spare protein and prevent ketosis.

Glucose

The major monosaccharide in the body that circulates as blood sugar and serves as a main energy source.

Fructose

An intensely sweet monosaccharide found in fruit, honey, and processed foods with a different structure than glucose.

Galactose

A monosaccharide that occurs naturally as a single sugar in only a few foods and is barely sweet.

Maltose

A disaccharide composed of glucose and glucose, produced when starch is broken down (e.g., barley fermentation).

Lactose

A disaccharide composed of glucose and galactose, representing the main carbohydrate in milk.

Causes of Lactose Intolerance

Insufficient lactase enzyme, declining lactase with age, genetics, villi damage, reduced exposure, and bacterial fermentation of undigested lactose.

Sucrose

A disaccharide composed of glucose and fructose, commonly known as table sugar, found in fruits, vegetables, honey, and syrups.

Glycogen

A polysaccharide of hundreds of glucose units in highly branched chains, serving as the storage form of glucose in animal liver and muscles.

Starches

Polysaccharides of hundreds of glucose units (branched or unbranched) serving as the storage form of glucose in plants.

Amylopectin vs Amylose

Amylopectin is branched and broken down quickly (higher GI); amylose is a long chain/resistant starch digested more slowly.

What is dietary fibre?

Plant food components that escape small intestine digestion and contribute little energy while supporting gut health.

What type of substances does dietary fibre consist of?

A group of substances with similar characteristics.

Why can't dietary fibre be digested by the body?

The bonds between monosaccharides cannot be broken down by digestive enzymes.

What is the energy contribution of most dietary fibre?

Most dietary fibre contributes little or no energy.

In which types of foods is dietary fibre present?

Dietary fibre is present in all plant-derived foods, including vegetables, fruit, legumes, and grains.

What is the Glycaemic Index (GI)?

The blood glucose response of a food compared to a standard, influenced by starch structure, fibre, processing, and macronutrients.

What does a lower Glycaemic Index (GI) indicate about blood glucose release?

Lower GI foods release blood glucose more slowly, therefore stimulating a lower insulin release from the pancreas.

What factors influence the Glycaemic Index (GI) of a food?

Starch structure, fibre content, food processing, physical structure, and the presence of other macronutrients, especially fat.

What are the potential benefits of substituting low GI foods for high GI foods?

It offers potential benefits, especially in the management of diabetes.

Does Glycaemic Index (GI) always correlate with nutritional value?

No, GI does not always correlate with nutritional value.

What is more important than the Glycaemic Index (GI) of individual foods?

The Glycaemic load of a meal.

How does portion size influence Glycaemic load?

Portion size influences glycaemic load.

Where is most glucose absorbed in the body?

Most absorption occurs in the small intestine, although a very small amount is absorbed through the lining of the mouth.

Carbohydrate Absorption Site & Rate

Mostly absorbed in the small intestine via villi; glucose/galactose use active transport, while fructose uses facilitated diffusion. -

Fate of Monosaccharides in the Liver

Travel via the portal vein to the liver, where galactose and fructose are converted to glucose or glycogen.

Fermentation of Fibre in Large Intestine

Bacteria ferment undigested dietary fibre into water, gas, and short-chain fatty acids used for energy.

Carbohydrate Overfeeding Effects

Increases carbohydrate oxidation, reduces glycogen synthesis, and increases de novo lipogenesis (fat production). -

Australian Dietary Guidelines (2013) - Guideline 2

Enjoy a wide variety of nutritious foods from the five food groups every day, including vegetables, fruit, and wholegrain cereals.

Australian Dietary Guidelines (2013) - Guideline 3

Limit intake of foods containing saturated fat, added salt, added sugars, and alcohol.

What is the Acceptable Macronutrient Distribution Range (AMDR) for carbohydrates?

45% to 65% of total energy

What percentage of energy from carbohydrates is considered low energy density and/or low glycaemic index food sources?

65% of energy

What percentage of energy from carbohydrates is predominantly from low energy density and/or low glycaemic index foods?

45% of energy

Australian Health Survey (2011-2012) - Sugar Sources

Leading sources of total sugars included fruit products, soft drinks, dairy milk, juices, sugar/honey, and cakes. -

Australian Health Survey - Fibre Intake

Mean fibre intake for Australians was 20-25g/day, generally falling below adequate intake (AI) and suggested dietary target (SDT) levels.

How do monosaccharides enter the bloodstream?

They cross the wall of the intestinal villi.

What mechanism do glucose and galactose use to cross the lining of the small intestine?

Active transport.

What is the saturation limit for glucose absorption per hour?

About 60g.

Why is the rate of glucose absorption important during exercise?

It affects the provision of carbohydrates.

What survey provides data on Australian health from 2011-2012?

Australian Health Survey

What was the average carbohydrate intake per person per day in Australia according to the 2011-2012 survey?

229 grams

What percentage of total energy intake did carbohydrates contribute to in Australia?

45%

What is the significance of the distribution of carbohydrate intakes in the Australian population?

It provides insight but is not a useful way of looking at intake.

What food group contributed the most to total sugars in Australia?

Fruit products and dishes (15.6%)

What percentage of total sugars in Australia came from soft drinks and flavored mineral waters?

9.7%

What was the mean fiber intake for Australians according to the 2011-2012 survey?

20-25 grams per day

How does the mean fiber intake of Australians compare to the Adequate Intake (AI) recommendations?

It is generally below the AI.

What does the fiber intake data suggest about the Australian population?

There is room for improvement in fiber intake.

Simple Carbohydrates

Monosaccharides and disaccharides that are quickly digested and absorbed, providing rapid energy.

Complex Carbohydrates

Polysaccharides such as starches and dietary fiber that consist of long chains of sugar molecules and take longer to digest.

Health Impact of Simple vs. Complex Carbs

Complex carbs provide sustained energy and fiber for gut health, whereas excessive simple carbs (especially refined sugars) can cause rapid blood glucose spikes.