Transcript Nutrition Part 2 Powerpoint

Nutrition and Metabolism
Calories
• A Calorie is a unit of energy
– Measures how much heat
could be released by
completely burning a given
amount of material
• The average adult requires
around 2000 Calories a day
– The exact rate at which we
burn calories is called the
metabolic rate
Calories in Food
• Carbohydrates and Proteins
have 4 Calories per gram
• Fats have 9 Calories per gram
– This is why our body uses fat as a
long-term energy storage
material
– This is also why fat tastes
delicious: it’s a very calorie-rich
food!
• Fun fact: alcohol has 7 Calories
per gram!
Metabolism
• Metabolism is a combination of
two processes: anabolism
(building up of materials) and
catabolism (breaking down of
materials)
– Growing new cells and proteins is
anabolism
– Burning glucose for energy is
catabolism
• When not active, you are at your
basal metabolic rate (BMR)
Basal Metabolic Rate
• BMR is affected by:
– Age (decreases with every
decade past 30s)
– Muscle mass (more skeletal
muscle, more calories burned)
– Thyroid activity and iodine
intake (thyroxine increases
BMR)
• Activity above basal levels
contributes substantially to
your overall calorie use
– Exercise burns calories!
Exercise and Metabolism
• Exercise is very healthy to be able to do regularly
– Increases muscle mass, which increases BMR
– Increases use of cholesterol and saturated fats, so they
don’t clog your arteries
– Sweating helps balance your sodium
• Blood cholesterol is measured as HDL and LDL levels,
often called “good cholesterol” and “bad cholesterol”
– HDL (High density lipoproteins) transports lipids like
saturated fats and cholesterol to liver for processing
• Exercise increases HDL levels
– LDL (Low density lipoproteins) transports lipids to fat cells
for storage
Anabolism and Catabolism
• A major example of both anabolism and catabolism is a
process called gluconeogenesis
– The production of blood glucose
• Glycogen is made of glucose, so breaking it down to glucose
is pure catabolism
• Proteins and lipids can be disassembled and reassembled
into glucose through anabolism
– Amino acids release ammonia when this happens
Excess Nutrition
• An excess of nutrients above
what is needed to make more
cells and perform cellular
respiration causes the body to
store extra materials
– Excess glucose stored as
glycogen (glycogenesis)
– Excess glucose and fat also
stored as fat (lipogenesis)
– Protein cannot be stored
Lipid Metabolism
Nutrient Storage
• People have genetic differences
in how they form and store fat
– Some people break down fat
more easily than others (lipolysis)
– Fat is also stored in different
places in the body
• Due to its high calorie density,
storing fat is vital for life
– Pictured is Lizzie Velasquez, who
has a genetic condition where
her body literally cannot form fat
– If she were to stop eating for
more than a few hours she will
die (once her glycogen runs out)
Nutrient Deficiencies
• If insufficient carbohydrates or
lipids are eaten, the body digs
into its reserves
• The body also lowers the
metabolic rate to try and slow the
loss of nutrients
– Prevents starvation
• Insufficient protein poses serious
health risks because protein
cannot be made from fat or sugar,
so protein is taken out of the
muscles
Nutrients and Dieting
• Due to sociocultural forces, being
“thin” is currently conflated with
being “attractive” by many people
– This has led to fats and “carbs”
having a negative connotation since
they may result in fat buildup
• Can often lead to eating disorders
– Please note that having a high
metabolic rate is a better indicator
of health than body weight or BMI
(body mass index)
• Ironically an increasing proportion
of people in the US are also obese
due to high-sugar diets
Hunger Effect
• Hunger is a complex effect in the body mediated by the
hypothalamus, and affected by ghrelin, leptin, cortisol,
glucagon and other hormones, as well as psychological
factors
– “7PM? Well it’s dinnertime then.”
• Diabetics who inject insulin after a meal often report
being very hungry again soon, because their blood
sugar has crashed
– Processed sugars are unhealthy often because they cause
a large insulin release, a blood sugar crash, and a new
feeling of hunger
– The large amount of insulin also ensures that fat cells
absorb a lot of the glucose
Hunger and Stress
• Stress (Sympathetic nervous
system and cortisol) both
block hunger
• Ghrelin is released by the
parasympathetic nervous
system in response to food
stimuli (even thoughts)
– This allows you to eat even
when you’re stressed
– Also, mmm, donuts…
Who’s Hungry?
• Next week: last week of new material!
– Monday: Kidneys
– Wednesday: Reproductive Systems
– Friday: Review day!