Chapter 8: Water and Minerals
EXCI 204 — Food for Sport · Chapter Study Notes (with formulas & calculations)
Chapter Overview
Scientists propose that life first appeared in Earth’s first seas — a complex mixture of minerals, organic
compounds, and water. As organisms left this environment, they brought a similar internal environment
with them: within our bodies, minerals and water form an “internal sea” that allows the chemistry of
life to function. Inadequate and excessive mineral intakes contribute to high blood pressure, bone
fractures, anemia, and infection risk. Getting enough clean water may be an even greater challenge: by
2025, half the world’s population will live where there isn’t enough safe water, and failing municipal
infrastructure puts some U.S. supplies at risk.
The chapter covers: (8.1) water distribution, balance, functions, dehydration, and needs; (8.2) major vs.
trace minerals, sources, bioavailability, and functions; (8.3) the electrolytes sodium, potassium, and
chloride and hypertension; (8.4) bone minerals — calcium, phosphorus, magnesium, fluoride — and
osteoporosis; (8.5) iron and copper for healthy blood; (8.6) antioxidant minerals — selenium, zinc,
manganese, sulfur, molybdenum; and (8.7) iodine and chromium in energy metabolism. Math in this
chapter: water balance, salt ↔ sodium conversion, % of an intake target, fluoride per kg body weight,
label % DV and sodium descriptors, absorption percentages — each boxed where it appears and
collected at the end.
8.1 Water
Learning objectives: Describe factors that affect water distribution · Explain how water is regulated ·
Describe the functions of water · Discuss factors that increase water needs.
Water is an overlooked but essential nutrient. Lack of water causes deficiency symptoms more rapidly
than any other nutrient, and they can be relieved almost as rapidly by drinking enough water.
Water in the Body ⭐
Water distribution ⭐
Fact Value
Water as % of adult body weight About 60%
Muscle weight that is water About 75%
Bone weight that is water About 25%
Intracellular (inside cells) About two-thirds of body water
Extracellular (blood, lymph, between cells, GI tract, eyes, About one-third
joints, spinal cord)
EXCI 204 · Chapter 8 · Page 1
, KEY DEFINITION
solute — (Described in text) A dissolved substance, such as proteins, sodium, potassium, and other
small molecules, whose concentration drives the distribution of water.
KEY DEFINITION ⭐
osmosis — (Described in text) The diffusion of water in a direction that equalizes the concentration
of dissolved substances on either side of a membrane.
• Cell membranes are not watertight — water moves through them by osmosis toward the side
with the higher concentration of dissolved substances (Figure 8.1a).
• Blood pressure forces water out of capillaries into tissues at the arterial end; lower pressure and
solute differences at the venous end draw water back in by osmosis (Figure 8.1b).
• The body regulates water in compartments by adjusting dissolved particle concentrations and
relying on osmosis.
KEY DEFINITION ⭐
blood pressure — The amount of force exerted by the blood against the walls of arteries.
Water Balance ⭐
Because water cannot be stored, intake and output must balance. Intake: water and beverages (coffee,
tea, milk, juice, soft drinks), solid foods (most fruits and vegetables > 80% water; roast beef ≈ 50%), and
a little metabolic water. Output: urine, feces, evaporation from lungs and skin, sweat.
FORMULA ⭐
Water balance
Water in (drink + food + metabolism) = Water out (urine + feces + evaporation + sweat)
What it means: to keep body water constant, every source of loss must be replaced. If evaporation
and sweat stay constant, drinking more increases urine output proportionately; hotter weather or
more activity increases evaporative and sweat losses.
Figure 8.2 — Daily water balance of a typical woman in a temperate environment ⭐
Water intake mL Water output mL
Drink 2200 Urine 1650
Food 500 Evaporation and sweat 1100
Metabolism 250 Feces 200
Total 2950 mL (12.5 cups) Total 2950 mL (12.5 cups)
EXCI 204 · Chapter 8 · Page 2
, WORKED EXAMPLE — calculated from textbook numbers
Checking and using Figure 8.2
• Intake: 2200 + 500 + 250 = 2950 mL; output: 1650 + 1100 + 200 = 2950 mL → balanced.
• Share of intake from beverages: 2200 ÷ 2950 × 100 ≈ 75% (food ≈ 17%, metabolism ≈ 8%).
• Share of output as urine: 1650 ÷ 2950 × 100 ≈ 56% — the majority, as the text states.
• Cups: 2950 mL ÷ 12.5 cups ≈ 236 mL per cup.
Routes of water loss ⭐
Route Typical amount Notes
Urine 1–2 L (4–8 cups)/day Usually the largest loss; varies with
water intake and the waste to be
excreted
Feces < 1 cup/day About 9 L (38 cups) of fluid enters the
GI tract daily (drinks + secretions), but >
95% is absorbed; severe diarrhea can
cause large losses
Evaporation (skin and ≈ 1 L (4 cups)/day inactive, Increases with activity, temperature,
lungs) temperate climate body size, and low humidity
Sweat 2–3 L (8–12 cups)/day light work More with intensity, heat, humidity;
at 84°F (29°C); 2–4 L (8–16 cups) clothing that lets sweat evaporate
per hour strenuous exercise in keeps you cooler and reduces sweat
heat
WORKED EXAMPLE — calculated from textbook numbers
Calculated from the textbook’s numbers
• GI fluid absorbed: > 95% of 9 L → > 8.55 L reabsorbed, leaving < 0.45 L (and normally under a
cup) in feces.
• Strenuous exercise in heat: 2–4 L per hour → a 2-hour session could lose 4–8 L — more than
the whole daily intake of Figure 8.2.
Regulating water intake — thirst. Thirst arises from a dry mouth (less water for saliva) and brain signals
when the thirst center senses decreased blood volume and increased solute concentration (Figure 8.3).
Thirst is powerful but often lags behind the need for water, so it can’t be relied on alone.
KEY DEFINITION
thirst — (Described in text) The sensation, caused by a dry mouth and signals from the brain, that
motivates fluid intake.
EXCI 204 · Chapter 8 · Page 3
, Regulating water loss — the kidneys. Kidneys act like a filter: water and small molecules leave the
blood; blood cells and large molecules stay. Some water is reabsorbed, the rest excreted. Wastes in
urine: urea (protein breakdown), ketones (incomplete fat breakdown), sodium and other minerals.
KEY DEFINITION ⭐
antidiuretic hormone (ADH) — (Described in text) A hormone secreted by the pituitary gland that
signals the kidneys to reabsorb water, reducing the amount lost in the urine.
ADH and the kidneys ⭐
Step Regulating urinary water losses (Figure 8.4)
1 Not enough water → blood volume ↓, solute concentration ↑
2 The pituitary gland secretes ADH
3 ADH signals the kidneys to reabsorb more water into the blood
4 Less water lost in urine → body water conserved
Opposite case After guzzling water, solute concentration is low → ADH ↓ → less reabsorption →
more urine
Alcohol Inhibits ADH release → more urine even when solute concentration is high →
possible dehydration
• The kidneys’ ability to concentrate urine is limited, so a minimum water loss is needed to excrete
wastes — more wastes, more water.
The Functions of Water ⭐
Functions of water
Function Details
Solvent / medium for Glucose, amino acids, minerals, proteins dissolve in water; metabolic
metabolism reactions take place in water
Participant in reactions Joins small molecules or breaks large ones; some reactions help
maintain acid-base balance
Transport Primary constituent of blood — delivers oxygen and nutrients,
carries wastes to lungs and kidneys
Lubrication and protection Tears (eyes), synovial fluid (joints), saliva (chewing, swallowing,
taste); resists compression → cushions joints; amniotic fluid
protects the fetus
Body temperature regulation Holds heat and changes temperature slowly; skin blood vessels
dilate to release heat; evaporation of sweat cools skin and blood
(Figure 8.5)
EXCI 204 · Chapter 8 · Page 4
EXCI 204 — Food for Sport · Chapter Study Notes (with formulas & calculations)
Chapter Overview
Scientists propose that life first appeared in Earth’s first seas — a complex mixture of minerals, organic
compounds, and water. As organisms left this environment, they brought a similar internal environment
with them: within our bodies, minerals and water form an “internal sea” that allows the chemistry of
life to function. Inadequate and excessive mineral intakes contribute to high blood pressure, bone
fractures, anemia, and infection risk. Getting enough clean water may be an even greater challenge: by
2025, half the world’s population will live where there isn’t enough safe water, and failing municipal
infrastructure puts some U.S. supplies at risk.
The chapter covers: (8.1) water distribution, balance, functions, dehydration, and needs; (8.2) major vs.
trace minerals, sources, bioavailability, and functions; (8.3) the electrolytes sodium, potassium, and
chloride and hypertension; (8.4) bone minerals — calcium, phosphorus, magnesium, fluoride — and
osteoporosis; (8.5) iron and copper for healthy blood; (8.6) antioxidant minerals — selenium, zinc,
manganese, sulfur, molybdenum; and (8.7) iodine and chromium in energy metabolism. Math in this
chapter: water balance, salt ↔ sodium conversion, % of an intake target, fluoride per kg body weight,
label % DV and sodium descriptors, absorption percentages — each boxed where it appears and
collected at the end.
8.1 Water
Learning objectives: Describe factors that affect water distribution · Explain how water is regulated ·
Describe the functions of water · Discuss factors that increase water needs.
Water is an overlooked but essential nutrient. Lack of water causes deficiency symptoms more rapidly
than any other nutrient, and they can be relieved almost as rapidly by drinking enough water.
Water in the Body ⭐
Water distribution ⭐
Fact Value
Water as % of adult body weight About 60%
Muscle weight that is water About 75%
Bone weight that is water About 25%
Intracellular (inside cells) About two-thirds of body water
Extracellular (blood, lymph, between cells, GI tract, eyes, About one-third
joints, spinal cord)
EXCI 204 · Chapter 8 · Page 1
, KEY DEFINITION
solute — (Described in text) A dissolved substance, such as proteins, sodium, potassium, and other
small molecules, whose concentration drives the distribution of water.
KEY DEFINITION ⭐
osmosis — (Described in text) The diffusion of water in a direction that equalizes the concentration
of dissolved substances on either side of a membrane.
• Cell membranes are not watertight — water moves through them by osmosis toward the side
with the higher concentration of dissolved substances (Figure 8.1a).
• Blood pressure forces water out of capillaries into tissues at the arterial end; lower pressure and
solute differences at the venous end draw water back in by osmosis (Figure 8.1b).
• The body regulates water in compartments by adjusting dissolved particle concentrations and
relying on osmosis.
KEY DEFINITION ⭐
blood pressure — The amount of force exerted by the blood against the walls of arteries.
Water Balance ⭐
Because water cannot be stored, intake and output must balance. Intake: water and beverages (coffee,
tea, milk, juice, soft drinks), solid foods (most fruits and vegetables > 80% water; roast beef ≈ 50%), and
a little metabolic water. Output: urine, feces, evaporation from lungs and skin, sweat.
FORMULA ⭐
Water balance
Water in (drink + food + metabolism) = Water out (urine + feces + evaporation + sweat)
What it means: to keep body water constant, every source of loss must be replaced. If evaporation
and sweat stay constant, drinking more increases urine output proportionately; hotter weather or
more activity increases evaporative and sweat losses.
Figure 8.2 — Daily water balance of a typical woman in a temperate environment ⭐
Water intake mL Water output mL
Drink 2200 Urine 1650
Food 500 Evaporation and sweat 1100
Metabolism 250 Feces 200
Total 2950 mL (12.5 cups) Total 2950 mL (12.5 cups)
EXCI 204 · Chapter 8 · Page 2
, WORKED EXAMPLE — calculated from textbook numbers
Checking and using Figure 8.2
• Intake: 2200 + 500 + 250 = 2950 mL; output: 1650 + 1100 + 200 = 2950 mL → balanced.
• Share of intake from beverages: 2200 ÷ 2950 × 100 ≈ 75% (food ≈ 17%, metabolism ≈ 8%).
• Share of output as urine: 1650 ÷ 2950 × 100 ≈ 56% — the majority, as the text states.
• Cups: 2950 mL ÷ 12.5 cups ≈ 236 mL per cup.
Routes of water loss ⭐
Route Typical amount Notes
Urine 1–2 L (4–8 cups)/day Usually the largest loss; varies with
water intake and the waste to be
excreted
Feces < 1 cup/day About 9 L (38 cups) of fluid enters the
GI tract daily (drinks + secretions), but >
95% is absorbed; severe diarrhea can
cause large losses
Evaporation (skin and ≈ 1 L (4 cups)/day inactive, Increases with activity, temperature,
lungs) temperate climate body size, and low humidity
Sweat 2–3 L (8–12 cups)/day light work More with intensity, heat, humidity;
at 84°F (29°C); 2–4 L (8–16 cups) clothing that lets sweat evaporate
per hour strenuous exercise in keeps you cooler and reduces sweat
heat
WORKED EXAMPLE — calculated from textbook numbers
Calculated from the textbook’s numbers
• GI fluid absorbed: > 95% of 9 L → > 8.55 L reabsorbed, leaving < 0.45 L (and normally under a
cup) in feces.
• Strenuous exercise in heat: 2–4 L per hour → a 2-hour session could lose 4–8 L — more than
the whole daily intake of Figure 8.2.
Regulating water intake — thirst. Thirst arises from a dry mouth (less water for saliva) and brain signals
when the thirst center senses decreased blood volume and increased solute concentration (Figure 8.3).
Thirst is powerful but often lags behind the need for water, so it can’t be relied on alone.
KEY DEFINITION
thirst — (Described in text) The sensation, caused by a dry mouth and signals from the brain, that
motivates fluid intake.
EXCI 204 · Chapter 8 · Page 3
, Regulating water loss — the kidneys. Kidneys act like a filter: water and small molecules leave the
blood; blood cells and large molecules stay. Some water is reabsorbed, the rest excreted. Wastes in
urine: urea (protein breakdown), ketones (incomplete fat breakdown), sodium and other minerals.
KEY DEFINITION ⭐
antidiuretic hormone (ADH) — (Described in text) A hormone secreted by the pituitary gland that
signals the kidneys to reabsorb water, reducing the amount lost in the urine.
ADH and the kidneys ⭐
Step Regulating urinary water losses (Figure 8.4)
1 Not enough water → blood volume ↓, solute concentration ↑
2 The pituitary gland secretes ADH
3 ADH signals the kidneys to reabsorb more water into the blood
4 Less water lost in urine → body water conserved
Opposite case After guzzling water, solute concentration is low → ADH ↓ → less reabsorption →
more urine
Alcohol Inhibits ADH release → more urine even when solute concentration is high →
possible dehydration
• The kidneys’ ability to concentrate urine is limited, so a minimum water loss is needed to excrete
wastes — more wastes, more water.
The Functions of Water ⭐
Functions of water
Function Details
Solvent / medium for Glucose, amino acids, minerals, proteins dissolve in water; metabolic
metabolism reactions take place in water
Participant in reactions Joins small molecules or breaks large ones; some reactions help
maintain acid-base balance
Transport Primary constituent of blood — delivers oxygen and nutrients,
carries wastes to lungs and kidneys
Lubrication and protection Tears (eyes), synovial fluid (joints), saliva (chewing, swallowing,
taste); resists compression → cushions joints; amniotic fluid
protects the fetus
Body temperature regulation Holds heat and changes temperature slowly; skin blood vessels
dilate to release heat; evaporation of sweat cools skin and blood
(Figure 8.5)
EXCI 204 · Chapter 8 · Page 4
