Download Topic D.1 Human Nutrition

HUMAN NUTRITION
Option D.1
U: Essential nutrients cannot be synthesized by the body,
therefore they have to be included in the diet.
Nutrients = a substance used for growth & metabolism
Essential nutrients = body cannot synthesize on its own (in adequate amounts) and must be
obtained in food
E.g. some amino acids, some unsaturated fatty acids, some minerals, calcium, vitamins, water
Non-essential nutrients = still needed everyday but they can be made in the body or another
nutrient can be used for same purpose
E.g. glucose, starch (lipids can be used in cell resp instead of carbs)
Conditionally essential = some bodies can synthesize, some can’t
E.g. vitamin K – in adults, produced by metabolism of symbiotic bacteria in intestines;
in babies, have not built up colonies of such bacteria yet; in ppl with digestive disorders, colonies
may be disrupted
App: production of ascorbic acid by some mammals, but
not others which need a dietary supply
Vitamin C = ascorbic acid
Non-essential in most plants & animals; Essential in some animals
Needed for synthesis of collagen = protein used as connective & support tissues in skin,
ligaments, bone, blood vessels (makes skin firm and elastic)
Inability to synthesize vitamin C due to mutations in GLO gene that codes for enzyme that
catalyzes final rxn in making ascorbic acid
Most mammals can make vit C: dogs, cats, elephants, sheep, pig, horse, squirrel, rabbit, mouse,
lemur
Most primates cannot: humans, chimps, apes
Lost ability: ray-finned fish (cod, salmon, herring)
Vitamin C deficiency can lead to scurvy (general weakness, anemia, gum disease, and skin
hemorrhages)
Phylogenetic tree showing mammals’ ability to synthesize vitamin C
(capable = black; incapable = gray)
Synthesis of ascorbic acid from glucose
Glucose vs Ascorbic acid
U: Some fatty acids and some amino acids are essential.
Fatty Acids
Essential fatty acids:
α-linolenic acid (omega-3 fatty acid)
Found in fish, flaxseeds, walnuts
linoleic acid (omega-6 fatty acid)
Found in nuts, sunflower seeds, veg
oil, some whole grains
Needed for healthy brain and eye
development, energy, cell membranes
(omega-3 is anti-inflammatory, may
play role in preventing diabetes &
cancer)
Non-essential fatty acids: all others
Amino Acids
Essential Amino Acids: Histidine,
Isoleucine, Leucine, Lysine,
Methionine, Phenylalanine,
Tryptophan, Valine
Conditionally essential: arginine
(required in baby’s diet); threonine (can
be made if phenylalanine is present)
Non-essential amino acids: all others;
can be made if enough essential aa’s
are present
Difference between omega-3 & omega-6 fatty acids
U: Lack of essential amino acids affects production of proteins.
Protein deficiency malnutrition = shortage of 1 or
more essential amino acids needed to make proteins
Aka “Kwashiorkor” (from the Ga language of coastal
Ghana, translated as "the sickness the baby gets when
the new baby comes“)
Causes lack of blood plasma proteins, resulting in
edema (swelling due to fluid retention in tissues)
Symptoms of protein deficiency: edema in abdomen,
stunted mental and physical growth & development in
children, serious weight loss (wasting) in adults
U: Dietary minerals are essential chemical elements.
Minerals are needed in relatively small quantities (mg and μg)
2 main groups of minerals:
Electrolytes: sodium, potassium, chloride, calcium, magnesium and phosphorous
Trace minerals: chromium, cobalt, copper, iodine, iron, manganese, molybdenum, selenium, zinc
Deficiency results in disease:
e.g. Iodine Deficiency Disorder (IDD) = lack of iodine, needed to synthesize thyroxin, hormone made by
thyroid gland that stimulates metabolism & ensures enough energy released in body
If pregnant, IDD can cause permanent brain damage in baby
If child, IDD can cause impaired metal development & intelligence (affects tens of millions worldwide)
If adult, IDD causes thyroid to enlarge = goiter; decreased metabolism
Prevention is easy  add iodine to salt! (very cheap & easy)
Iodine naturally found in bread, milk, seafood
Goiter
Iodized vs non-iodized salt
U: Vitamins are chemically diverse carbon compounds that
cannot be synthesized by the body.
Vitamins = organic compounds; all essential; needed in small amounts
Functions: co-enzymes, anti-oxidants, hormones
Origin of word: “vital amine” (first vitamins discovered contained amino group)
2 categories of vitamins:
Water soluble: not stored in body; have to be constantly consumed; excess lost in urine
Fat soluble: can be stored in body
Note: Antioxidants inhibit oxidation of other molecules. Oxidation can produce free radicals,
leading to chain reactions that may damage cells. Some vitamins (like C) stop this from
happening.
Water-soluble vitamins
•
C (ascorbic acid)
•
B1 (thiamin)
•
B2 (riboflavin)
•
Fat-soluble vitamins
•
A
•
E
B3 (niacin)
•
K
•
B5 (pantothenic acid)
•
•
B6 (pyridoxine)
D (conditionally essential – skin
makes it if sufficient sunlight)
•
B7 (biotin)
•
B9 (folic acid)
•
B12 (cobalamin)
Why do we need vitamins?
U: Malnutrition may be caused by a deficiency, imbalance or
excess of nutrients in the diet.
Malnutrition = poor diet
Can occur when:
1.
Low protein & low calories
2.
Unbalanced, missing some essential nutrients
3.
Excess fats & refined carbs
Often associated with poverty
starvation = diet lacking enough protein and carbs
obesity = excess body fat (in developing countries & lower socio-economic classes of developed
nations)
U: Appetite is controlled by a center in the hypothalamus.
Hypothalamus = gland in brain
~Controls body temp, hunger, appetite & thirst
Contains appetite control center – makes us feel
satiated (satisfied when we’ve eaten enough)
When appetite control center receives these
hormones, it reduces desire to eat:
1.
Small intestine secretes PYY3-36 when it
contains food
2.
Pancreas secretes insulin when blood glucose
is high
3.
Adipose tissue (fat) secretes leptin when
stored fat increases
Overeating can lead to diabetes and obesity.
U: Overweight individuals are more likely to suffer
hypertension and type II diabetes.
Correlation between excess weight gain & hypertension (high blood pressure)
Weight gain can cause:
•
Increase in release of hormones that can raise bp
•
Higher cardiac output which can raise bp
•
Abdominal obesity can increase vascular resistance which can raise bp
•
Arteries to become stiffer and narrower which can raise bp
Excess salt intake can cause:
•
Raise in salt concentration of blood, reducing kidney’s ability to remove water, putting extra
strain on blood vessels leading to kidneys, raising bp
Diabetes mellitus
•
Type I = auto-immune destruction of insulin-secreting cells in pancreas
•
Type II = decreased responsiveness of body cells to insulin due to “burn-out”
Epidemiology = study of rates and distribution of a disease (increased fatty acids linked to type II diabetes)
Risk factors:
•
Diets rich in fat & low in fiber
•
Obesity due to overeating & lack of exercise
•
Genetic factors which affect fat metabolism (huge variation between ethnic groups)
Symptoms:
•
High blood glucose
•
Glucose in urine
•
Dehydration & thirst due to excess urination
Diabetes can lead to:
•
Atherosclerosis = narrowing of arteries by fatty deposits)
•
Hypertension
•
Coronary heart disease (CHD) = narrowing of coronary arteries; increased risk of heart attack)
[also link between these cardio problems & blood lipid concentrations: high LDL (bad cholesterol) & low HDL (good chol)]
U: Starvation can lead to breakdown of body
tissue.
Starvation  severe lack of essential &
non-essential nutrients
If you’re not getting nutrients in your diet,
your body will take it from itself!
1.
First, body gets energy from glycogen
stores (in liver & muscle)
2.
If no glucose available, body breaks
down muscle (protein) to get amino
acids, which are sent to liver and
converted to glucose  loss of muscle
mass
Marasmus = wasting away of fat, muscle
& other tissue due to total lack of nutrition
App: Breakdown of heart muscle due to anorexia.
anorexia = “reduced appetite”
Anorexia Nervosa = psychiatric illness involving voluntary starvation & loss of body mass
Carb & fat intake too small, so body breaks down it’s own protein for energy!
Protein loss results in:
•
Muscle loss (skeletal & cardiac)
•
Thinning of hair
•
Dry, easily bruised skin
•
Growth of soft, fine, white body hair (lanugo) – for insulation
•
Decreased blood pressure, slow heart rate, poor circulation  due to lack of electrolytes (Ca+2,
K+, Na+) needed for contraction
•
Infertility (no ovulation/menstrual cycle)
•
Loss of antibodies
NOS: Falsifying of theories w/ 1 theory being superseded by
another: Scurvy was thought to be specific to humans, b/c attempts
to induce symptoms in lab rats & mice were entirely unsuccessful.
1907 – Holst & Frolisch
•
Caused scurvy in guinea pigs by feeding
them nothing but rabbit pellets (whole
grains)
•
Then cured scurvy by feeding them
cabbage & lemon juice
•
Their animal model allowed for study of
factors leading to scurvy & its prevention
Pigeons were also studied, but found they
make their own vitamin C, so can’t develop
scurvy
Feed your guinea pig fruits & veggies
& guinea pig pellets!
Guinea pigs are one of the
few mammals who cannot
make their own vitamin C.
Neither can humans!
App: Cause and treatment of phenylketonuria (PKU)
PKU = recessive genetic disease
Caused by mutations of gene coding for enzyme that converts phenylalanine to tyrosine
Results in excess phe and deficient tyr.
Consequences of high phe:
•
Reduced growth of head & brain (mental retardation of young children; severe learning
disabilities, hyperactivity & seizures in older children)
•
Lack of skin & hair pigment
Babies with PKU unaffected at birth because mom’s metabolism kept phe & tyr normal
Early diagnosis & treatment is possible: test 24 hours after birth
Treatment: eating diet low in phe for rest of your life!
Foods containing phe: meat, fish, nuts, cheese, peas, beans
Food labels must say “contains phenylalanine”
App: Lack of vitamin D or calcium can affect bone mineralization
and cause rickets or osteomalacia.
Vitamin D needed for calcium absorption from food in intestines
Rickets = skeletal deformity
Osteomalacia = softening of bones
Vitamin D can be synthesized in skin if sunlight available
No vitamin D required in diet if spend enough time outside, skin uncovered
Children, pregnant women, elderly recommended to eat 10 μg per day to supplement
Found naturally in: oily fishes (herring, mackerel, sardines, tuna), eggs, liver
Artificially fortified with vit D: margarine, milk
Melanin in skin intercepts & absorbs UV light
~Dark skin give good protection against skin cancer, but reduce vit D synthesis
~Indigenous human populations balance the risk of skin cancer & vit D deficiency
App: Cholesterol in blood as an indicator of the risk of
coronary heart disease.
Cholesterol is necessary part of plasma membrane, but it’s gotten a bad rap!
Correlation between high cholesterol in blood and increased risk of CHD.
Not certain if lowering dietary cholesterol will actually lower risk of CHD.
Reasons for uncertainty:
•
A lot of research involves total cholesterol, but only LDL is associated with CHD.
•
Reducing dietary cholesterol often has very small effect on blood cholesterol levels, so little effect on CHD
rates.
•
Liver can synthesize cholesterol so diet is not the only source
•
Genetics is more important than diet
•
Drugs can be more effective at reducing cholesterol than reductions in diet
•
Positive correlation between dietary intake of sat fats and intake of cholesterol, so possible that sat fats
cause increased risk of CHD in ppl with high cholesterol intake
Skill: Determination of the energy content of food
by combustion.
Calorie = the energy needed to raise the temperature of 1
gram of water 1 °C
Calorimetry = determination of energy content
Calorimeter = instrument used to measure calories
Specific heat capacity of water: takes 4.186 J of heat
energy to raise temp of 1 g of water by 1 ⁰C
NOTE:
1ml of water has mass of 1g
1 cal = 4.186 J
1000 cal = 1 Kcal = 1 Cal
Activity
https://www.youtube.com/watch?v=Ak7PN8tn4cU
Using the experimental results below, estimate the energy content of the nut
per gram.
Sample data:
Mass of nut = 0.60 g
Volume of water = 25 ml
Initial water temp = 20 ⁰C
Final water temp = 65 ⁰C
Skill: Use of databases of nutritional content of foods and software
to calculate intakes of essential nutrients from a daily diet.
Balanced diet = essential and non-essential
nutrients in correct balance
Fresh fruit and veggies should make up
largest part of diet
Followed by carbs, proteins, then dairy
Fats and sugars should make up smallest part
SuperTracker – free software available from
USDA to track your food intake and compare
it with database of recommended intake
https://www.supertracker.usda.gov/