Nutrition and Sodium Intake Guidelines

Water and the Body Fluids

• Water accounts for about 60% of an adult's body weight.
• Water makes up about 75% of the weight of lean tissue.
• Lean tissue includes body water, total body protein, carbohydrates, non-fat lipids, and minerals.
• Females, elderly, and obese people have a smaller proportion of lean tissue, leading to a lower proportion of their body weight being water.

Functions of Water in the Human Body

• Carries nutrients and waste products
• Maintains structure of large molecules (proteins, glycogen)
• Participates in metabolic reactions
• Serves as a solvent for minerals, vitamins, glucose, and amino acids
• Acts as a lubricant and cushion around joints and inside the eyes
• Aids in regulation of body temperature (e.g., evaporation through sweat)
• Maintains blood volume

Distribution of Body Fluids

• Fluid inside cells is intracellular fluid.
• Fluid outside cells is extracellular fluid.
• Extracellular fluid surrounding each cell is interstitial fluid.
• Extracellular fluid in blood vessels is intravascular fluid.
• Fluid composition differs between interstitial and intravascular fluid.
• Fluid composition remains relatively constant despite continuous loss and replacement of components.
• The body regulates water intake and excretion to maintain balance.

Water Intake

• Thirst and satiety influence water intake based on signals from the mouth, hypothalamus, and nerves.
• Inadequate water intake leads to concentrated blood, a dry mouth, and the hypothalamus triggering drinking behavior.
• Excessive water intake triggers stomach expansion and stretch receptors, signaling the body to stop drinking.

Dehydration

• Dehydration occurs when water loss exceeds replacement.
• An early sign of dehydration is fatigue.
• Other symptoms can range from thirst to weakness, exhaustion, and delirium, progressing rapidly if thirst is not addressed.
• Dehydration results from both inadequate intake and excessive water loss.
• A table details the symptoms of dehydration based on the percentage of body weight lost.

Water Intoxication

• Water intoxication is rare but can occur with excessive water intake or kidney dysfunction reducing urine production.
• Symptoms may include confusion, seizures, and even death.
• Excessive water ingestion (10-20 liters within a few hours) can severely dilute blood sodium, leading to hyponatremia.
• Guidelines recommend limiting fluid intake during periods of heavy sweating to 1-1.5 liters per hour.

Water Sources

• Water itself is the primary dietary source, providing about one-third of total water intake.
• Other beverages and nearly all foods also contain water.
• Many fruits and vegetables contain up to 90% water, and most meats and cheeses contain at least 50% water.
• Metabolic water is created as an end product of condensation reactions.
• Daily water intake from these sources generally averages around 2.5 liters.

Water Losses

• The body must excrete water to remove waste products, with a minimum of 500 milliliters daily.
• Water excreted via urine increases when total intake increases, making the urine more dilute.
• Water is also lost through the lungs as vapor and the skin in sweat; some is also lost in feces.
• Daily water loss averages about 2.5 liters.
• Maintaining this balance requires healthy kidneys and adequate fluid intake.

Water Recommendations

• Water needs vary based on diet, activity, temperature, and humidity, making general requirements difficult to establish.
• A person expending 2000 kcalories per day typically requires 2-3 liters of water.
• Total water intake includes beverages and water in foods.
• Water-only beverages can meet fluid needs without contributing to weight gain.

Health Effects of Water

• Water quality impacts health.
• Hard water, high in calcium and magnesium, may have health benefits for certain conditions.
• Soft water with high sodium can worsen hypertension and heart disease.
• Soft water dissolves contaminant minerals from aging pipes more easily, harming health.

Blood Volume and Blood Pressure

• The kidneys regulate blood volume and blood pressure, managing water and substance retention/excretion via urine.
• Hormones like ADH, renin, angiotensin, and aldosterone control substance levels in the bloodstream.
• ADH, a water-conserving hormone, is activated with low blood volume/pressure or high extracellular fluid concentration, stimulating the kidneys to reabsorb water and trigger thirst, promoting homeostasis.
• Renin activates angiotensin I, which becomes active angiotensin II, contracting blood vessels and raising blood pressure.
• Aldosterone is triggered, promoting sodium retention and therefore water retention.

Dissociation of Salt in Water

• Mineral salts (e.g., NaCl) dissociate into positively and negatively charged ions (e.g., Na+ and Cl-) when dissolved in water.
• These ions, called electrolytes, conduct electricity readily in solution compared to pure water.
• Anion and cation concentrations balance in electrolyte solutions to maintain electrical neutrality.
• Ions entering/leaving cells (e.g., sodium and potassium) are balanced by counterpart ions.

Electrolytes Attract Water

• Electrolytes, due to their charged nature, attract water molecules.
• Water molecules surround ions, enabling dissolution of salts and the movement of fluids throughout the body.

Water Follows Electrolytes

• Electrolytes' location (intracellular vs. extracellular) influences their movement across cell membranes.
• Water, following dissolved electrolytes, moves across membranes in response to differing concentrations to maintain osmotic balance.

Proteins Regulate Flow of Fluids and Ions

• Proteins attract water, affecting fluid movement.
• Leaking proteins from blood vessels can cause edema, or fluid build-up in tissues.
• Cell membrane proteins control ion and substance passage, influencing water and ion movement.
• Water and ions move towards more concentrated solutions, regulating fluid flow.

Fluid and Electrolyte Imbalance

• Certain medical conditions (vomiting, diarrhea, severe burns) can lead to significant fluid and electrolyte (e.g., sodium) loss.
• Imbalance requires urgent intervention, potentially leading to serious health consequences.
• Replacing fluids and electrolytes using proper solutions and regular foods is vital for recovery.
• Oral rehydration therapy (ORT) is a simple, effective treatment for dehydration.

Regulation of pH

• Buffers, like bicarbonate and carbonic acid, protect the body by neutralizing acids and bases.
• Carbon dioxide forms carbonic acid in the blood and further dissociates into hydrogen and bicarbonate ions, crucial for pH maintenance.
• The respiratory system regulates carbonic acid levels by controlling breathing rate—increased breathing removes excess carbon dioxide, while slowed breathing allows more to be retained, adjusting pH levels accordingly.

The Minerals—An Overview

• Minerals are inorganic elements that maintain their chemical identities unlike organic compounds like vitamins.
• Minerals are not destroyed by cooking methods or mixing.
• The minerals remain during a food's ash residue.
• Some minerals are readily absorbed, transported, and excreted, similar to water-soluble vitamins.
• Others, like calcium, require carriers for absorption.

The Minerals—An Impact Overview

• Food compounds like phytates and oxalates bind with minerals, reducing their bioavailability.
• Excess of one mineral can affect the absorption of another.
• Interactions between minerals and sodium intake illustrate such interactions.

Minerals in a 60-Kilogram Human Body

• Calcium and phosphorus are the most abundant minerals in the body, exceeding one pound.
• Other major minerals like potassium, sulfur, sodium, chloride, magnesium, and trace minerals are vital for bodily functions, though present in smaller amounts.

Major Minerals: Sodium

• Sodium is the principal extracellular cation, crucial for nerve impulse transmission and muscle contraction.
• It plays a vital role in maintaining acid-base balance.
• Sodium is continually transported to the kidneys, which regulate their blood composition to maintain homeostasis.
• High/low sodium levels can impact fluid balance, leading to health issues.

Sodium Recommendations

• Sodium deficiency is rare, as the body adapts to its loss via sweat and urine.
• High sodium intake correlates with hypertension, exceeding recommended levels.
• Guidelines for people with prehypertension/hypertension recommend lower sodium intake.
• Dietary Approaches to Stop Hypertension (DASH) is a diet specifically formulated to decrease sodium intake.

Sodium Deficiency

• Cases of hyponatremia, arising from excessive sodium loss, present symptoms like headache, confusion, seizures and coma.
• Excessive sweating can result in sodium and water losses.
• Marathon runners can develop hyponatremia.
• Long-term high sodium consumption can damage blood vessels in some individuals and can lead to chronic conditions.

Sodium and Hypertension

• High sodium intake is a significant determinant of high blood pressure, correlated with permanent damage to blood vessels.
• Excessive salt intake can worsen the development of heart conditions, and lowering sodium to no more than 1,500 mg per day can benefit blood pressure.

Sodium and Bone Loss (Osteoporosis)

• High sodium intake increases calcium excretion and correlates to less bone density.
• Potassium helps protect against bone loss.
• DASH diet recommends low sodium and abundant potassium-rich foods and calcium-rich low-fat milk to counter bone loss.

Potassium

• Potassium is a primary intracellular cation, performing various body functions.
• It plays a crucial role in maintaining fluid and electrolyte balance, cell integrity, and nerve/muscle function.
• Fresh foods are major sources of Potassium.
• Dietary potassium intake influences blood pressure.

Potassium Intakes

• Potassium is abundant in cells but lost during processing.
• Fresh foods are the richest potassium sources.
• Daily recommended potassium intake is 4700 mg.
• Avoiding low potassium intake can help maintain appropriate blood pressure levels.

Chloride

• Chloride is an essential extracellular anion, important for maintaining fluid and electrolyte balance.
• Chlorine is found in hydrochloric acid, vital to the digestive system.
• Vomiting can lead to chloride loss, having serious consequences.
• Chloride intake is abundant in processed foods and comparable to sodium recommendations.
• It is not typically deficient in diets.

Calcium

• Calcium is the most abundant mineral in the body, crucial for forming teeth and bones, growth during youth, and maintaining bone strength into older age.
• Calcium plays roles in blood pressure, blood clotting, and cellular functions.
• Regulatory hormones—calcitonin and parathyroid hormone—control calcium levels.
• Inadequate calcium intake over time can result in osteoporosis, characterized by weak, porous, or fragile bones.
• Calcium absorption rate and dietary calcium recommendations differ by age and sex.

Phosphorus

• Phosphorus is the second most abundant mineral, crucial for bone structure, energy processes (DNA/RNA), and cellular functions.
• High intake is not an issue in the modern diet.
• Abundant sources include calcium-rich foods.

Magnesium

• Magnesium primarily resides within bones and plays vital roles like maintaining bone health, crucial energy processes, and immune function, muscle contraction, and blood clotting.
• Most magnesium occurs as a non-food source.
• Adequate intake is crucial and is present in many daily foods.

Sulfate

• Sulfate is the oxidized form of sulfur and is found within amino acids like cysteine and methionine.
• It's a component of structural proteins like those found in skin, hair, and nails .
• It is important for proper protein synthesis.
• No specific, isolated dietary recommendation exists beyond the standard protein requirement.