Please enable JavaScript.
Coggle requires JavaScript to display documents.
Macronutrients Metabolism - More on Protein ((((Protein intakes vary…
Macronutrients Metabolism - More on Protein
Lecture outline
Describe major nutrients and their properties
Discuss digestion and absorption of these nutrients
Understand energy metabolism of these nutrients
Macronutrients
Proteins
Carbohydrates
Fats
Used to calculate the available energy of foods
Developed by Wilbur Atwater in the 19th C century and are debated
Based on the heats of combustion for different foods
Essential to know available energy of foods for developing dietary guidelines
Energy measured using Atwater factors**
What are some examples of foods that fit into these categories?
Protein
Major sources: meat, poultry, fish, eggs, beans and pulses, eggs and dairy
Proteins build muscle and repair cells
Provide structure for cellular membranes
Promote movement of muscle fibres
Are composed of amino acids essential and non essential
Amino acids are the building blocks of proteins
Essential amino acids cannot be synthesized by the body
9 essential amino acids: valine, isoleucine, leucine, lysine, phenylalanine, methionine, tryptophan, threonine, histidine
The body’s requirement is not simply for protein, but for the amino acids which make up proteins, in the correct proportions to replace the body proteins.
Protein Metabolism
Meeting Protein demands through fed and fasted states
At night demands are met from tissue protein: during daytime food meets the demand and replaces tissue lossess
Regulation of body Protein
1st concept: The diurnal cycle of gains and losses:
an influence on the metabolic demand
2nd concept: Adaptation of the metabolic demand to
varying protein intakes.
Protein intakes vary markedly between individuals and population groups because of dietary type and lifestyle
Lifestyle influences: energy expenditure and requirements, food and therefor protein intake
Dietary type and protein intake: Variation in dietary composition
Protein quality evaluation
6.1 Prediction of protein quality: using the protein digestibility corrected amino acid score (PDCAAS) approach
6.1.1 Protein digestibility
6.1.2 Biological value
6.1.3 Amino acid score
6.2 Current concerns about the protein digestibility corrected amino acid score (PDCAAS) approach
determination of protein requirements for human nutrition - Several meeting at FAO to determine requirements of protein
PDCAAS (Protein Digestibility Corrected Amino Acid Score) uses crude faecal digestibility values in measuring the oro-faecal nitrogen balance which includes contributions from intestinal secretions and colonic bacteria, thus underestimating the protein available for absorption
DIAAS (Digestible Indispensable Amino Acid Score) measures the oroileal nitrogen balance by calculating the ileal digestibility of individual amino acids. (THINK PIGS)
superior conceptually to faecal digestibility
Inadequate data for wide population adaptation
Data used not representative of human diet especially in developing countries
Assement of the impact of this method is not yet compeleted
Protein synthesis dipeptide amino acid Peptide bond forms between the amino group of one amino acid & carboxy group of another; process produces a molecule of water process requires energy
Protein synthesis occurs as a result of series of signals
:specific DNA sequences transcribed in the nucleus to make specific messenger RNA (mRNA) mRNA goes to ribosomes on the endoplasmic reticulum in the cell cytosol
where it indicates sequence of amino acids to join together process called translation
Some modifications of amino acids occur after linked into proteins, e.g. linking 2 sulphur molecules on cysteine or methionine post translational modification
Meat Vs plant based protein
Nutrients more readily available and easily absorbed in meat based protein
Plant based proteins rarely contain a full set of essential amino acids so combining them is often recommended
Bioavailability of proteins in pulses increase through sprouting/germination
Carbohydrates
Major sources: grains, breads, flours, fruits, vegetables, sugars
Primary source of energy for the body
Comprised of glucose and other sugars
requirements
Varies depending on energy expenditure
5g/kg of body weight for low energy expenditure, up to 12g/kg of
body weight for very high energy expenditure