Nutrition & Appetite Flashcards
Learning Outcomes
- Understand how macronutrients and micronutrients interact to promote normal metabolism and growth in humans.
- Describe macro-and micro-nutrients.
- Describe essential and non-essential nutrients.
- Describe the absorptive and post-absorptive states.
- Describe the regulation of blood glucose.
- Understand how an imbalance of nutrients can lead to adverse health
outcomes
Why study nutrition?
> The study of how living organisms obtain and utilize nutrients needed to grow and sustain life.From an evolutionary perspective…
* Fitness = survival and reproduction
* Cravings for sugar, fat and salt
* Food rituals - uniquely human
Nutrition
All living organisms need nutrients to survive.
All animals obtain their nutrients by the consumption of other organisms.
Nutrients:
* Include most biomolecules, vitamins, and minerals
* Required for synthesis of new molecules
* Required for energy for maintenance, growth, and repair
* Obtained through food
* Levels regulated during and following meals
One of the challenges in human nutrition is maintaining a balance between food intake, storage, and energy expenditure. Imbalances can have serious health consequences.
Feeding or fasting
Absorptive state (the fed state):
* Time eating, digesting, and absorbing nutrients
: Concentrourons of alucose, trielverides, and
amino acids increase as absorbed from Gl tract
Post-absorptive state (the fasting state):
* Time between meals
* Body relying on stores of nutrients
* Body working to maintain homeostatic levels of nutrients
Nutrients
Any substance in food that is used by the body to promote normal growth, maintenance and repair.
Macronutrients
* Must be consumed in relatively large quantities
* Needed in daily amounts
* Carbohydrates, proteins, lipids,
Micronutrients
* Must be consumed in relatively small quantities
* Vitamins and minerals
Essential
* Must be obtain from the diet
Nonessential
* Provided by biochemical processes of body
* Not required in diet
Water
* Water is considered a nutrient
Carbohydrates
Polysaccharides:
* Dextrose
Stalose
* Glycogen
Disaccharides:
* Sucrose
* Lactose
* Maltose
Monosaccharides:
* Glucose
* Fructose
* Galactose
Carbohydrate metabolism
- Monosaccharides are
absorbed from the small intestine into the blood and then enter hepatocytes.
Fructose and galactose are converted to glucose. - Noncarbohydrates are converted to glucose by gluconeogenesis.
- Glucose molecules are bonded together to form glycogen by glycogenesis.
- Glucose molecules are released from glycogen by glycogenolysis.
Glucagon & insulin work antagonistically to maintain blood glucose levels.
Pancreas
Exocrine function: secretion of digestive enzymes
Endocrine function: secretion of glucagon & insulin
* Pancreatic islets (clusters of cells)
* Alpha cells
= Secrete glose level drop › lucagon act n elis
causing glycogen (storage polysaccharide) and amino acids to be converted to glucose.
* Raises blood glucose levels
* Beta cells
> Secrete insulin
> After meals (high blood glucose) insulin stimulates cells to take up glucose.
> Promotes synthesis of fats, glycogen.
> Lowers blood glucose
Negative feedback & blood sugar regulation
High blood glucose (hyperglycaemia)
> B cells secrete insulin
> insulin stimulates tissue uptake of glucose
and glycogen formation
> fall in blood glucose
Low blood glucose (hypoglycaemia)
> a cells secrete glucagon
* glucagon stimulates glycogenolysis
> rise in blood glucose
Pancreas
Absorptive
State
Absorptive state (the fed state):
* Insulin is the major regulatory hormone released during the absorptive state
* Released from pancreas in response to increased blood glucose levels
* Stimulates:
* Liver and muscle cells - form glycogen from glucose
* Adipose tissue - increases uptake of triglycerides from blood
* Stimulates most cells to increase amino acid uptake
* Causes acelerated protein synthesis
Post-absorptive
State
Post-absorptive state (the fasting state):
* Glucagon is the major regulatory hormone released during the post-absorptive state
* Released in response to decreasing blood glucose levels
* Stimulates:
* Liver to increase breakdown of glycogen to glucose
* Gluconeogenesis from noncarbohydrate sources
* Adipose tissue to break down triglycerides
Diabetes Mellitus - Type 1
Type 1: inability to produce sufficient insulin (insulin-dependent diabetes mellitus; IDDM)
* ~ 10% of diabetics
* previously called juvenile diabetes
* treated by self-monitoring of blood glucose and provision of exogenous
insulin
The pancreas: Regulating blood sugar
Why is regulation of blood glucose so important?
* Low blood glucose levels compromise normal brain function.
* High blood glucose levels damage blood vessels & nerves
* Homeostatic responses ensure appropriate glucose levels despite intermittent fuel supply and variable rates of glucose utilization.
Transport maximum (renal threshold)
- The upper limit of the amount of a substance that can be reabsorbed.
Tubular reabsorption of glucose - I filtrate [glucose] → all glucose reabsorbed
- filtrate [glucose] = transport max → all carrier sites for glucose occupied
- 1 filtrate [glucose] → glucose in urine
Diabetes mellitus → 1 blood [glucose] → 1 filtrate [glucose] > glucose transport max → glucose in urine
Diabetes Mellitus - Type 2
Type 2: reduced responsiveness to insulin (non-insulin dependent diabetes mellitus; NIDDM)
* ~ 90% of diabetics
* risk factors: genes, age and obesity
* treated by changes in diet & exercise
Obesity - What is it?
Having a very high amount of body fat in relation to lean body mass.
Body Mass Index (BMI):
A measure of a person’s weight in relation to their height.
BMI (kg per m3) = weight / height?
Overweight: BMI >25 kg per m2
Obese:
BMI >30 kg per m?
Obesity - How big is the problem?
- > 600 million people worldwide are obese
- > 2 billion are overweight
- Around 1/3 Australians are obese and another 1/3 are overweight (doubled in the last 20 yrs)
- Mostly reflects excessive caloric intake (relative to energy expenditure)
Fats & Lipids
We can’t survive without fats & lipids in our diet.
* Used for:
* fuel (energy reserve)
* building cell membranes
* to cushion organs, e.g. kidneys, eyes
* provide insulation (hypodermis of skin)
* Stored in adipose tissue
* Fat-soluble vitamins stored in adipose tissue
* Liver can make most fats from protein and carbohydrates
* The fats it cannot make are the “essential fatty acids”
Obesity -
What’s driving it?
- Why do we gorge on high-calorie food?
- Humans evolved to cope with variable food supply.
- Capacity to store energy is a selective advantage.
- Higher incidence of obesity in certain human populations.
- Genes-environment mismatch.
- Obesity is NOT a personal failing!!!
Proteins
- Proteins are needed to replace worn out protein structures.
- Proteins are broken down into amino acids.
- Amino acids are then used for protein synthesis in cells.
- 20 amino acids:
- 8 amino acids are “essential amino acids”,
- other 12 can be synthesized in the body
- Most animal proteins are complete.
- Nearly all plant proteins are incomplete.
- Vegetarian diets need a combination of diferent plants.
Perfect quinoa - Amount needed depends on age - infants and children need more for growth.
- More needed to fight an infection, following an injury, stressful conditions, pregnancy.
Dietary lipids
Protein Metabolism
- Deamination: Amine group removed
from amino acids
* NH, is converted to urea and urea enters blood (urea eliminated by kidney)
* Remaining components oxidized in cellular respiration to generate ATP
from the liver - Amino acids used to form proteins.
- Transamination: Amino acids converted
from one form to another.
Vitamins
- Organic substances.
- Not used as a fuel source but have an essential role in metabolism.
- Coenzymes critical for use of other nutrients
- Act as antioxidants
- Each vitamin has a specific metabolic function.
- Essential vitamins
- Necessary from diet
- Deficiency if intake or absorption is impaired
- At least 13 essential vitamins
- include vitamins A, C, D, E, K, B group, and folic acid
- Nonessential vitamins
- Can be synthesized by the body
- E.g. vitamin D
Vitamin deficiency
- Most vitamins are necessary for normal biological processes
- Sustained absence of a vitamin is detrimental to health
- Deficiencies in Vitamin D (important for calcium absorption and bone metabolism), may result in an increased risk of osteoporosis.
- Deficiencies of Vitamin K (important blood coagulation factor) result in a decrease in blood clotting, leading to a higher risk of bleeding.
lodine
- Needed to produce thyroid hormone
Calcium
- Required for formation and maintenance of skeleton, muscle contraction, blood clotting…
Sodium and potassium
- Maintain resting membrane potential in excitable cells
- Required to generate action potential
Minerals
- Inorganic ions obtained from diet
- Essential role in metabolism and required in daily amounts
All minerals are essential and must be obtained from the diet
Zinc
- Roles in protein synthesis and wound healing
- Required for electron transport chains
- in aemo stin, side ome hormones, neurotransmiters, & amino acids
Iron deficiency
(Anaemia)
- Most common nutritional deficiency
- Iron required in haemoglobin and myoglobin
- Symptoms: fatigue, weakness, pale skin, and sensitivity to cold
- Cause: insuficient dietary intake or iron loss from excessive bleeding
- Obtained from: meat, poultry, fish, dark leafy vegetables, nuts, and whole grains
Iron overload
Hereditary haemochromatosis (HH, “Iron overload disease”)
- Autosomal recessive
- More common in people of Celtic or northern European descent
osticsk for thie discadition of Caucasian populations; approx. I in 200 individuals at
- Characterized by excessive iron absorption
- Can lead to liver disease, arthritis, diabetes, cardiac failure….
*tem menstruationales due to increased iron requirements during pregnancy and blood loss
- “Bronzed diabetes”
- May have been a survival advantage in populations that evolved in iron-poor environments.
- Disadvantageous in environments with high iron food sources.
Learning outcomes
Nutrition and Appetite
*
Understand how macronutrients and micronutrients interact to promote normal metabolism and growth
in humans.
Describe hormonal mechanisms involved in the regulation of appetite.
Three key steps in energy (ATP) production
Step 1: Glycolysis
Energy supply: overview
Summary of ATP generation from glucose
Step 2: Krebs Cycle
Determinants of Food Intake
Step 3: Oxidative Phosphorylation
All effects mediated
by
the hypothalamus
Hypothalamic regulators of appetite:
Stimulants (orexigeneic neuropeptides)
neuropeptide Y (NPY)
orexins
endocannabinoids
Suppressants (anorexigenic neuropeptides)
Melanocortins (POMC)
glucagon-like peptide-1 (GLP-1)
serotonin
Leptin signalling
Leptin deficiency results in severe obesity
But, almost all obese humans have more than enough LEPTIN!
PPARS
- Peroxisome proliferator-activated receptors
- Critical role in fat storage and fat burning
- Could PPARs explain why different people seem to burn fat more easily?
- Could PPARs explain why different types of food (eg, fish) influence fat differently?
The Human Life Cycle
PPARs and Fat Storage
