Water Balance and Minerals
Week 30
Water: more vital to life than food
• involved in almost every body function
• is not stored--excreted daily
• largest single constituent of the human body, averaging 60% of total body weight
• although most people can survive 6 weeks or longer without food, death occurs in a matter of days
without water
• occupies essentially every space within and
between body cells and is involved in virtually every body function
Basic Principles
• Body water compartments
• Intracellular
• Extracellular
• Intravascular
• Interstitial
• Membranes separate water compartments
• Particles in solution
• Homeostasis
Functions of Water in the Body
Water
• Under normal conditions, water intake equals water output to maintain water balance
• In most healthy people, thirst is a reliable indicator of need
• The body’s need for water is influenced by many variables
• A general guideline is to consume 1.0 mL of fluid per calorie consumed, with a minimum of 1500 mL/day to meet metabolic needs
Water: an essential nutrient
• Water is an essential nutrient because the body cannot produce as much water as it needs
• On average, adults lose approximately 1450 to 2800 mL of water daily
Insensible water loss--immeasurable
• Insensible water losses from the skin and expirations account for approximately half of the total water lost daily
• Extreme environmental temperatures (very hot or very cold), high altitude, low humidity, and strenuous
exercise increase insensible losses
• Water evaporation from the skin is also increased by prolonged exposure to heated or recirculated air such as during long airplane flights
Sensible water loss--measurable
• Sensible water losses from urine and feces make up the remaining water loss
• Because the body needs to excrete a minimum of
500 mL of urine daily to rid itself of metabolic wastes, the minimum daily total fluid output is approximately 1500 mL
• To maintain water balance, intake should approximate output
Sources and average amounts of daily water loss
Source of Water Average Amount Loss Lost (mL/d)
• Perspiration 450 to 900
• Exhalations 350
• Urine 500 to 1400
• Feces 150
• Total 1450 to 2800
Electrolytes
• Small, inorganic substances
• When they dissociate they carry a charge
• Cation
• Na+, K+, Ca++, Mg++
• Anion
• Cl-, HCO3-, PO4-, so4—
• Balanced
• Measured in milliequivalents
Plasma Proteins
• Albumin
• Globulin
• Large molecules
Small Organic Compounds
• Dissolved in water
• Usually small concentrations
• Do not ordinarily influence water movement in the body
Membranes
• Capillary membranes
• Cell membranes
Movement of Water in the Body
• Osmosis
• Diffusion
• Facilitated diffusion
• Filtration
• Active transport
• Pinocytosis
Hormonal Control
• Antidiuretic hormone
• AKA vasopressin
• Aldosterone
Minerals
• Minerals are inorganic substances that cannot be broken down and rearranged in the body
• 117 known elements
• 25 essential to life and perform a variety of metabolic functions
• 7 major and 18 minor minerals
Mineral Metabolism
• Digestion
• Absorbed as ions
• Do not require mechanical or chemical digestion
• Absorption
• Transport
• Tissue Uptake
Functions of Minerals
• Structure
• Fluid balance
• Acid---base balance
• Nerve cell transmission and muscle contraction
• Vitamin, enzyme, and hormone activity
Mineral toxicities
• are not likely to occur from diet alone
• are most often related to
• excessive use of mineral supplements
• environmental exposure
• alterations in metabolism
Mineral balance
• Depending on the mineral involved, the body can maintain mineral balance by
• altering the rate of absorption
• altering the rate of excretion
• releasing minerals from storage when needed
• The absorption of many minerals is influenced by mineral-mineral interactions
• Too much of one mineral may promote a deficiency of another mineral
Sodium
• One of the most plentiful minerals in the body
• Function
• Maintain water balance
• Muscle action
• Nutrient absorption
• Deficiency: rare
Sodium and the American diet
• As much as 75% of sodium consumed in the average American diet is from processed food
• Americans are urged to reduce their intake of sodium because of its potential role in the
development of hypertension
Sodium
National Academy of Science’s Institute of Medicine
Healthy Adult 1500-2400mg Less if >50 or have HTN
Average Adult Male: 3300mg/d
Descriptors of Sodium Content
• If the label says . . . 1 serving contains . . .
• Sodium free <5 mg
• Very low sodium <35 mg
• Low sodium <140 mg
• Reduced or less sodium 25% less sodium
• Light in sodium 50% less sodium
• Salt free <5 mg
• Unsalted or no added saltNo salt added during processing
Calcium
• Many American adults consume less than optimal amounts of calcium, placing them at risk of
osteoporosis and possibly hypertension
• Milk and yogurt are the richest sources of calcium, and their vitamin D and lactose content promote its
absorption
• The National Academy of Science recommends
American adults consume 1000-1200 mg of calcium daily
Calcium Deficiency and Toxicity
• Rickets
• Related to inadequate vitamin D
• Tetany
• Osteoporosis
• Toxicity unlikely from food sources
• Kidney stones
• Decreased absorption of other minerals
Calcium Supplements
• TUMS is made of calcium carbonate--it is 40% elemental calcium and is generally the least inexpensive calcium supplement
• Calcium carbonate supplements can cause constipation-- encourage an adequate fluid intake and a high fiber diet as needed
• Calcium citrate is less likely to cause constipation than calcium carbonate
• Calcium from supplements is absorbed best in doses of 500 mg or less--tablets should be spread out over the day
Phosphorus
• Functions
• Bone and tooth formation
• Energy Metabolism
• Acid-base balance
• Sources
• Found in all plant and animal cells
• Deficiency and toxicity: rare
Potassium
• Functions
• Water balance
• Metabolic reactions
• Muscle action
• Insulin release
• Blood pressure
• AI =4.7g/day for all adults
• Deficiency and Toxicity
• Sources
Chloride
• Major extracellular anion
• One of the elements in HCl
• Acid-base balance
• Deficiency and toxicity
Magnesium
• Mostly in bone
• A cofactor for more than 300 enzymes
• Magnesium intake is 80% of recommended
• Large doses of supplemental magnesium may cause diarrhea, nausea, cramping
• Food sources
Sulfur
• Essential part of protein structure: hair, skin and nails, necessary for collagen formation
• Supplied by protein foods
• Deficiency and toxicity unseen
Iron
• Essential but toxic in excess
• 70% of body’s iron is in hemoglobin
• Necessary for glucose metabolism, antibody production, drug detoxification, conversion of beta carotene to vitamin A
• Deficiency and toxicity
• Food sources
Iodine
• Component of T4 (thyroxine)
• Deficiency
• Goiter
• Cretinism
Hypothyroidism
• Hyperthyroidism
• Toxicity
• Food sources
• Food sources dependent on iodine in the soil
• Major reliable source: iodized salt
Fluoride
• Binds with calcium
• Strengthens tooth enamel
Zinc
• Functions
• Enzyme constituent
• Immune system
• Prohormone
• Deficiency and Toxicity
• Food sources
Encourage healthy beverage choices:
• Replace soft drinks with calorie-free versions such as diet soda or sparkling water
• Use bottled water, if the taste of tap water is objectionable
• Refrigeration usually improves the taste of tap water
• Drink a glass of water before each meal, especially if weight control is a concern
• Eat enough fruits and vegetables
