Nutrition II

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Nutrition II

• Carbohydrates
• Lipids
• Proteins
• Vitamins and minerals

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Disaccharides
All are C6H12O6 All are energetically
equivalent NOT physiologically equivalent
Sucrose (table sugar)
a
Require specific enzymes to digest Without
which these, sugars can make you sick
intolerance
a
Maltose
b
Lactose (milk sugar)

• Starlings, catbirds, robins are sucrose
  intolerant
• 80 90 of the human population is lactose
  intolerant
• 10 of native Greenlanders are sucrose
  intolerant

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Typical intestinal lactase expression in mammals
birth
100
maximal Lactase expression
50
weaning
5 expression
0
Normally lactase expression drops prior to
weaning This helps mom end nursing period
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Physiological ecology of humans lactose
tolerance and geography
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Lactase Persistence

• 1 locus, 2 alleles
• LACR lactase restriction, LACP lactase
  persistence
• LACP is newer allele and is dominant
• Present in African pastoralist societies
• Tuareg, Beja, Bedouins
• North/Central Europeans
• Why lactase persistence in these societies?
• Plentiful milk supply
• No tradition of processing milk to yogurt and
  cheese
• Most of protein and carbohydrate comes from milk

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Lactase Persistence

• These arguments dont work for N. Europeans
• Calcium hypotheses
• Ca absorption is facilitated by
• Vitamin D (important in production of Ca
  transporter)
• Galactose transport
• Digesting lactose could be a way of making up for
  Vit D deficiency.

Does culture shape physiology or does physiology
shape culture??
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Feeding lactose to a marine mammal pup can kill
it!
Dont feed me cows milk!
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Comparative milk composition
Protein 1 (humans) - 15 (rabbits) Fat 1
(donkey) - 50 (marine mammals) Lactose 0
(marine mammals) - 7 (primates)
Cow milk Protein 3.2 Fat 3.4 Lactose 4.6
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What do we get from food?
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The skinny on sweeteners
Coke was once sweetened with sucrose (from
imported sugar cane) Now it is sweetened with
high fructose corn syrup WHY? 1) Its cheap
you can make it from cornstarch! 2)
Palatibility sucrose gt fructose gt glucose
Amylase maltase
isomerase
Starch
Glucose
Fructose
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Starch is the most common source of energy for
humans were functionally granivores
rice
potatoes
wheat
However, were not very good at digesting it!
manioc
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Polysaccharides
1-6 a bonds
1-4 a bonds
Higher ratio more branching, more open
structure Lower ratio tightly packed, resists
digestion
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Cooking loosens the structure of starch
Experiment with digestive enzymes in a test tube
Think also rice, beans, potatoes, grains
Cooking causes structure of starch to open up
allows access of soluble digestive enzymes.
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Glycogen MoleculeA LARGE STORAGE POLYSACCHARIDE
How animals (including us) store glucose
Lots of branches (1-6 bonds)
Easy for enzymes to access and break down
Stored in LIVER (lots) muscle (a little)
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Liver stores and metabolizes
Portal vein
Hepatic vein
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Blood glucose is tightly regulated
Too much is toxic Too little starves CNS
Blood Glucose Level
90 dg/ml (5 mM)
meal
1
2
0
Time (hrs after eating)
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BGL regulated by insulin and glucagon

• Insulin
• - cells
• Islets of Langerhans
• Pancreas
• Liver
• Fat cells
• Muscle
• Others
• Takes up glucose
• from blood
• Storage in general

Secreted into blood by Acts on Function

• Glucagon
• - cells
• Islets of Langerhans
• Pancreas
• Liver
• Releases glucose into
• blood

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Hepatic control of glucose
Portal ?
From gut, to liver
Hepatic ?
From liver, to body
In the dog, Liver absorbs glucose after a meal
and releases it in fasted state
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Hepatic control of glucose
Why is there no glucose absorption in sheep?
What can you infer about the digestive system of
a quokka?
Would you expect foregut fermenters to ever
exhibit elevated blood glucose?
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Making ATP from carbs
Glucose can make ATP either with (36) or without
(2) oxygen
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Lipids
Big, heterogenous class of compounds Defined as
at least partially hydrophobic Includes
triglycerides, fatty acids, phospholipids,
cholesterol
Two ways to identify where bonds are (always
spaced 3 C apart) n and D designation
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Fatty acid nomenclature
D-Designation
Carbon numbering starts from carboxylic acid end
Changes as you add carbons to the carboxyl end
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First double bonds always inserted at 9th C
n designation good if you want to keep track of
FAs origin
D designation good if you want to keep track of
how FA has been metabolized
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Essential fatty acids
Essential cannot be synthesized, must come from
diet!
Linoleic acid (2 double bonds, a.k.a. Omega 6)
182n6
183n3
Linolenic acid (3 double bonds, a.k.a Omega 3)
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Lipids also include cholesterol and steroids

• Plants dont make cholesterol
• Animals do
• Humans make 10mg/kg/day
• Important precursor
• Vitamin D
• Cortisol corticosterone
• Testosterone, estrogen, etc.
• Cholesterol stabilizes membranes
• Makes packed membranes more fluid
• Makes fluid membranes more stable

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Waxes
long hydrocarbon chains with an ester bond in the
middle
(etc) C - C - C - C - C - O - C - C - C - C -
C - C (etc)
Great for waterproofing Hard to digest!
Need Wax ester hydrolase (few animals have it)
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Wax DigestionHoneyguides
Use wax as a primary source of nutrition and
energy possesses wax ester hydrolase
Honeybadger
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Making ATP from fatty acids
1) Like glucose, fatty acids are broken down to
acetyl-CoA
Triglycerides

• Unlike glucose, fatty acids cannot be burned
  anerobically

• Fat burning activity is sustainable exercise
  80 maximal output

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When supply exceeds demand
Triglycerides
Glucose (6C)
Fatty acids (16C)
Glycolysis
Pyruvate
When glucose supply exceeds ATP demand (and
glycogen stores are full) Krebs cycle stops
Triglycerides are synthesized
mitochondrion
Acetyl CoA
CO2
Aerobic metabolism
CO2
ATP
O2
NADH2 FADH2
CO2
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How is fat stored?

• Fat is stored in Adipose Tissues, in specialized
  cells termed adipocytes, located subcutaneously
• It provides a long term supply of energy in case
  of fasting, pregnancy, or other situations of
  increased energetic demand
• The energy stored in fat can be increased nearly
  indefinitely, unlike carbohydrate (stored as
  glycogen in liver and muscles only)

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Energy storage
Glycogen
Fat
Time to Recruit Can it be burned Anaerobically
? Where stored? Energy density Other?
Fast Slow
Yes No
Muscle Adipose Liver Tissue
Low High 4.1 kcal/g 9.6 kcal/g
Cant be synth. Can be synth. From fat from
Carbs