Nutrition: Nutrients and Dietary Reference Intakes

Nutrition Overview

• Nutrients from food are needed to maintain normal bodily functions.
• Energy is provided by three classes of nutrients.
• Macronutrients, such as proteins, fats, and carbohydrates, are needed in larger amounts than other dietary nutrients.

Dietary Reference Intakes (DRI)

• DRIs are quantitative estimates of nutrient intakes used for planning and assessing diets for healthy people.
• The amounts of nutrients estimated are required to prevent deficiencies and maintain optimal health and growth.

Estimated Average Requirement (EAR)

• EAR is a nutrient intake value that meets the requirement of one half of the healthy individuals in a group.

Recommended Dietary Allowance (RDA)

• RDA is the average daily dietary intake level sufficient to meet the nutrient requirement of nearly all (97 to 98 percent) healthy individuals in a group.

Adequate Intake (AI)

• AI is a value based on observed or experimentally determined approximations of nutrient intake by a group or groups of healthy people.
• AI is used when an RDA cannot be determined.

Tolerable Upper Intake Level (UL)

• UL is the highest level of daily nutrient intake likely to pose no risk of adverse health effects to almost all individuals in the general population.
• The risk of adverse effects increases as intake increases above the UL.

Energy Requirement in Humans

• The Estimated Energy Requirement (EER) is the average dietary intake predicted to maintain an energy balance in a healthy adult.
• The EER calculation is determined by age, gender, and height.
• Genetics, body composition, metabolism, and lifestyle affect EER.
• Sedentary adults need 30kcal/kg/day.
• Moderately active adults need 35kcal/kg/day.
• Very active adults need 40kcal/kg/day.
• Food labels list EER as either 2000 or 2500 kcal/day.

Energy Content of Food

• The energy content of food is calculated from the heat released by the total combustion of food in a calorimeter.
• It is expressed in kcal or cal.
• 1 cal = 4.2 Joules
• Carbohydrates contain 4 kcal/g.
• Protein contains 4 kcal/g.
• Fat contains 9 kcal/g.
• Alcohol contains 7 kcal/g.

Use of Food Energy in the Body

• Energy from metabolism is used in three ways.
• The total calories expended is known as Total Energy Expenditure (TTE).
• The absorptive state occurs during and right after eating a meal within a 4 hour period.
• The postabsorptive state is when the GI tract is empty, and energy comes from the breakdown of body reserves, to maintain blood glucose levels.

Resting Metabolic Rate (RMR)

• RMR measures of energy expended by an individual in a resting state in the postabsorptive state.

Basal Metabolic Rate (BMR)

• BMR is determined under stricter conditions where a hospital stay is required.
• BMR is calculated as 0.9kcal/kg/h for females and 1kcal/kg/h for males.

Connection between RMR and BMR

• RMR is 10% higher than BMR.

Physical Activity

• Muscular activity provides the greatest variations in total energy expenditure (TEE).
• Sedentary people require about 30-50% more calories than the RMR.
• Highly active people require about 100% more calories than the RMR.

Thermal Effect of Food

• Heat production by the body increases as much as 30% above the resting level during digestion and absorption of food.
• It is the caloric cost of digesting and processing food.
• Thermic effect (thermogenesis) may account for 5-10% of TEE.

Acceptable Macronutrient Distribution Range (AMDR)

• AMDR is the range of intake for a particular energy source associated with reduced risk of chronic disease while providing essential nutrients.
• Consuming excess AMDR may increase risk of chronic diseases and/or insufficient intake of essential nutrients.
• Acceptable ranges for macronutrients:
  • Fat: 20-35% of energy, including 5-10% from ω-6 polyunsaturated fatty acids and 0.6-1.2% from ω-3 polyunsaturated fatty acids.
  • Carbohydrate: 45-65% of energy, no less than 130 g/day, and no more than 25% of total calories from added sugars.
  • Fiber: 38 g for men and 25 g for women.
  • Protein: 10-35% of energy.
  • Approximately 10% of the total fat can come from longer-chain ω-3 or ω-6 fatty acids.

Dietary Fats

• The incidence of certain chronic diseases is influenced by the kinds and amounts of nutrients consumed.
• Dietary fats strongly influence the incidence of coronary heart disease (CHD).
• There is weaker evidence linking dietary fat and the risk for cancer or obesity.

Plasma Lipids and Coronary Heart Disease

• Plasma cholesterol may arise from diet or from endogenous biosynthesis.
• Elevated levels of cholesterol increase risk for CHD.
• CHD and LDL-Cholesterol has a stronger relationship, and have proportional relationships.
• HDL-C and CHD have inversely proportional relationship.
• Elevated plasma lipids with smoking, obesity, sedentary lifestyle, and insulin resistance increase CHD.
• Lowering plasma cholesterol by diet or drugs decreases LDL-C, increases HDL-C, and decreases the risk of CHD.

Dietary Fats and Plasma Lipids

• TAGs are the quantitatively most important class of lipids.
• The structural features of fats include the absence, presence, number, and configuration of the double bonds.
• Consumption of saturated fats is positively associated with high levels of total plasma cholesterol and increased risk of CHD.
• Limit saturated fats intake to less than 10%.

Mediterranean vs. Western vs. low fat diet

• Monosaturated FAs lower both total plasma cholesterol and LDL-C but maintain or increase HDL-C.
• Mediterranean diets rich in olive oil (monosaturated FA oleic acid) and fish oil (PUFA) show low incidence of CHD.
• The fat percentage is 38% in both Mediterranean and western diets.
• The fat percentage is 20% in the low fat diet.

Polyunsaturated Fats

• TAG primarily FA with more than one double bond.
• Consuming Omega-6 and PUFAs lowers plasma LDL-C.
• Sources of PUFA include nuts, avocados, olives, soybeans, and various vegetable-based oils.
• Long chain Omega-3 PUFAs lower blood pressure, reduce risk of cardiovascular mortality, and decrease arrhythmia.
• Fish oil contains long chain omega-3 Fas.
• consume two fatty fish, salmon, anchovies twice per week.

Trans Fatty Acids

• Trans fatty acids are chemically altered FAs.
• Trans fatty acids behave like saturated fatty acids by elevating LDL-C and increase risk for CHD.
• They form during the hydrogenation of liquid vegetable oils.
• Trans Fatty Acids are a major component of many commercial baked goods.

Dietary Cholesterol and Alcohol

• Only animal products contain cholesterol.
• The effect of dietary cholesterol on plasma cholesterol is less important than the amount and types of fatty acids consumed.
• Red wine may provide cardioprotective benefits due to phenolic compounds that inhibit lipoprotein oxidation.
• These antioxidants are also present in raisins and grape juice.

Effects of Different Types of Fat

• Trans fatty acids increase risk of coronary heart disease by increasing LDL and decreasing HDL..
• Saturated fatty acids increase LDL levels and may lead to an increased risk of prostate and colon cancer.
• Monounsaturated fatty acids lowers LDL and maintains/ increase HDL decreasing the risk of coronary heart disease.
• Polyunsaturated fatty acids (-6) lowers LDL and and increases HDL but also provides arachidonic acid, which is an important precursor of prostaglandins and leukotrienes decreasing the risk of coronary heart disease.
• Polyunsaturated fatty acids (-3) affect LDL slightly increases HDL by suppressing cardiac arrhythmias, reducing serum triacylglycerols and decrease tendency for thrombosis while also lowering lower blood pressure and reducing risk of coronary heart disease and risk of sudden cardiac death.

Dietary Carbohydrate

• Carbohydrates are the major source of energy.
• Some studies link increased carbohydrate consumption with obesity.
• Obesity is related to inactive lifestyle and consumption of excess calories.

Classification of Carbohydrates

• Simple and complex sugars are the two classes of carbohydrates.
• Glucose and fructose are the principal monosaccharides found in food.
  • Glucose sources are fruits, sweet corn, corn syrup, and honey.
  • Fructose sources are honey and fruits.

High-Fructose Corn Syrup

• It is a corn syrup processed to convert glucose into fructose and mixed with pure corn syrup (100% glucose).
• It is a common substitute for sucrose in beverages.
• Its composition and metabolism are similar to sucrose, but is ingested as a mixture of monosaccharides.

Disaccharides

• Sucrose = Glucose + Fructose
• Lactose = Glucose + Galactose
• Maltose = Glucose + Glucose
• Sucrose is table sugar abundant in molasses and maple syrup.
• Lactose is found in milk.
• Maltose is found in beer and malt and is a product of enzymic digestion of polysaccharides.
• Fructose is 1.7X sweeter than sucrose.

Polysaccharides and Fiber

• Complex carbohydrates that do not possess a sweet taste include starches.
• Common sources include wheat and other grains, potatoes, dried peas, beans and vegetables
• Dietary fiber is non-digestible, non-starch carbohydrate and lignin
• It is fermented by bacteria to short chain fatty acids in large intestine

Types of Fibers

• Soluble fibers attract water and turn to gel during digestion which slows digestion.
  • Soluble fibers are found in oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables
  • Soluble fiber is fermented by bacteria to short chain fatty acids in the large intestine.
• Insoluble fiber is found in foods such as wheat bran, vegetables, and whole grains.
  • Insoluble fibers add bulk to the stool helping food pass more quickly through the stomach and intestines

Benefits of Fiber

• Absorbs water up to 10-15x of its weight in order to increase bowel movenent/prevent constipation
• Lowers LDL-C levels by increasing fecal bile acid excretion
• Provides fullness/ reduces calorie intake Dietary Carbohydrates and Blood Glucose
• Glycemic Response (GR) refers to the changes in blood glucose (rapid vs slow rise) after consuming a carbohydrate-containing food.
• The Glycemic Index (GI) is a relative ranking of carbohydrates in foods according to how they affect blood glucose levels.
• GI is defined as area under blood glucose curve after a meal consisting of the same amount of carbohydrate either as glucose or white bread.
• Foods with low GI create sense of satiety over a longer period of time and may be helpful in limiting caloric intake
• The RDA for carbohydrates is 130g/day.
• Adults should consume 45-65% of their calories from carbohydrates and less than 25% of total energy should come from sugar.
• Absence of carbohydrates leads to ketone body production and degradation of body protein so that amino acid skeletons can be submitted to gluconeogenesis.

Dietary Proteins

• Protein in food provides essential amino acids.
  • The Quality of protein is a measure of its ability to provide essential amino acids.
• Protein Digestibility Corrected Amino Acid Score (PDCAAS) is based on the profile of essential amino acids after correcting for the digestibility of the protein
• Protein from animal sources have high quality while proteins from plant sources may be combined to obtain all essential amino acids.
  • Wheat + Lys
  • Kidney beans➔ methionine
• Nitrogen balance occurs when the amount of nitrogen consumed equals to amount of nitrogen excreted in the urine

Nitrogen Balance

• Positive Nitrogen Balance: intake > loss promotes tissue growth, pregnancy, recovery from illness
• Negative Nitrogen Balance: intake < loss from inadequate protein intake due to lack of essential amino acids from physiological stresses such as trauma, burns, surgery.

Humans Protein Requirement

• The RDA for protein is 0.8g/kg of body weight for adults equating to ~56 g of protein for 70 kg individual
• Exercising people need 1 g/kg
• Pregnant/lactating women need an additional 30g/day
• Infants need 2g/kg/day
• There is no physiological advantage to consume protein beyond the RDA with over consumption leading over consumption will lead to fatty acid synthesis via acetyl CoA
• If low carb diet is being followed (<130g/day), gluconeogenesis will speed up

Protein Malnutrition

• Protein-energy malnutrition (PEM) is the most commonly seen condition in low-income countries.
• Certain conditions decrease appetite or alter how nutrients are digested or absorbed, such as in hospitalized patients.
• PEM is also seen in children or the elderly and symptoms include a low immune system.
• Kwashiokor and Marasmus

Marasmus vs Kwashiorkor

• In Kwashiorkor, protein deprivation is substantially greater than the reduction in total calories.
• It's observed in developing countries in children after 1 year when their diet consist predominantly of carbohydrates.
• Signs of Kwashiorkor include stunted growth, skin lesions, depigmented hair, anorexia, enlarged fatty liver, edema, and decreased serum albumin.
• In Marasmus, calorie deprivation is greater than reduction in protein.
• It's observed in developing countries in children younger than 1 year when breast milk is supplemented with native cereals that are usually deficient in both protein and calories.
• Signs of Marasmus include arrested growth, extreme muscle loss, loss of fat, weakness, and anemia and those with Marasmus don't show edema.
• Characteristics of Kwashiorkor:
  • 60%> Weight for age (% expected) is usually between 60-80%.
  • Has Edema
  • Poor Appetite
  • Irritable when picked up and apathetic when left alone
• Characteristics of Marasmus:
  • weight for age is <60%.
  • markedly decreased weight for height.
  • Appears alert and irritable