Introduction to Human Nutrition
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Transcript of Introduction to Human Nutrition
Introduction to Human Nutrition
the science of foods and the nutrients they contain
DIET: THE FOOD ONE CONSUMES
The food choices you make daily have a cumulative impact on your health. Poor food choices lead to chronic disease.
What is Food?
• Food contain nutrients and are derived from plant or animal sources
• Nutrients are used by the body to provide energy and to support growth, maintenance and repair of body tissues
Functional Foods
• Functional foods contain substances that provide health benefits beyond those of their nutrients
• May be a natural functional food or as a result of additives– Tomatoes – contain lycopene– Orange juice with calcium
THE 6 CLASSES OF NUTRIENTS
1. Carbohydrates2. Lipids (fats)3. Proteins4. Vitamins5. Minerals6. Water
Body Composition
Classification of Nutrients
– Organic or inorganic– Essential or nonessential– Macronutrient or micronutrient– Energy yielding or not
Essential Nutrients
• Nutrients the body either cannot make or cannot make enough of to meet its needs
• Must be obtained from foods• Examples:
• Vitamins• Calcium, iron, and other minerals• Some of the amino acids
Nonessentail Nutrients
• Body can make from other nutrients ingested• Examples:
• Cholesterol• Some amino acids
Classifying Nutrients by Composition
• Organic nutrients - contain carbon• Carbohydrates• Lipids• Proteins• Vitamins
• Inorganic nutrients - do not contain carbon• Minerals• Water
Quantity Needed
• Macronutrients: need in relatively large amounts– Carbohydrates, lipids, proteins
• Micronutrients: need in relatively small amounts– All other nutrients
3 Energy Yielding Nutrients
– Carbohydrates– Fats (lipids)– Proteins
• Where does the energy come from?
A little more on energy
• Measure energy in kilocalories in U.S.– What most think of as a “calorie” is really a
kilocalorie– Kcal = amount of energy needed to raise the
temperature of 1 kg of water by 10C• Measure energy in kilojoules (kJ) in most
other countries
Energy-Yielding Nutrients
Carbohydrates
– C H O– 4 kcal/gram– Body’s primary source of energy
• Use as glucose– Brain’s only source of energy– Stores are limited ~12-24 hours (in liver and
muscle)
Carbohydrates
• Energy Metabolism– Glucose is the fuel used by cells to
make ATP• Neurons and RBCs rely almost entirely
upon glucose • Excess glucose is converted to glycogen
or fat and stored
Carbohydrates
• Dietary sources– Starch (complex carbohydrates) in grains and
vegetables– Sugars in fruits, sugarcane, sugar beets,
honey and milk– Insoluble fiber: cellulose in vegetables;
provides roughage– Soluble fiber: pectin in apples and citrus fruits;
reduces blood cholesterol levels
Carbohydrates
• Dietary requirements– Minimum 100 g/day to maintain adequate
blood glucose levels– Recommended minimum 130 g/day – Recommended intake: 45–65% of total calorie
intake; mostly complex carbohydrates
Carbohydrates
• Dietary Fiber– water-insoluble fiber adds bulk to fecal
matter facilitating its passage through and elimination from the digestive system
– water-soluble fiber may absorb dietary cholesterol, reducing its absorption by the digestion tract
Lipids
– C H O (P)– 9 kcal/gram– Body’s alternate source of energy
• Use fat along with glucose as an energy source most of the time
– Stores are unlimited
Lipids
• Dietary sources– Triglycerides
• Saturated fats in meat, dairy foods, and tropical oils
• Unsaturated fats in seeds, nuts, olive oil, and most vegetable oils
– Cholesterol in egg yolk, meats, organ meats, shellfish, and milk products
Lipids
• Essential fatty acids– Linoleic and linolenic acid, found in most
vegetable oils– Must be ingested
Lipids
• Essential uses of lipids in the body– Help absorb fat-soluble vitamins– Major fuel of hepatocytes and skeletal muscle– Phospholipids are essential in myelin sheaths
and all cell membranes
Lipids
• Functions of fatty deposits (adipose tissue)– Protective cushions around body organs– Insulating layer beneath the skin– Concentrated source of energy
Lipids
• Regulatory functions of prostaglandins– Smooth muscle contraction– Control of blood pressure– Inflammation
• Functions of cholesterol– Stabilizes membranes– Precursor of bile salts and steroid hormones
Lipids
• Dietary requirements suggested by the American Heart Association– Fats should represent 30% or less of total
caloric intake– Saturated fats should be limited to 10% or
less of total fat intake– Daily cholesterol intake should be no more
than 300 mg
Pathways of Lipid Metabolism
Atherosclerosis
normal diseased
• Cholesterol: <175 mg/dl• Triglycerides: blood fats, 30-175
mg/dl• HDL: Good cholesterol, > 35 mg/dl• LDL: Bad Cholesterol, <130 mg/dl• Chol/HDL ratio: < 4.5 indicates heart
disease
Your Cholesterol Level
Protein
– C H O N – 4 kcal/gram– Body’s least desirable source of energy
• WHY? – Protein is used for energy only when there isn’t
any carbohydrate available as an energy source.
Proteins
• Enzymes • Structural proteins (shape and
form of cells and tissues)• Hormones• Immunoglobulins (antibodies)
Essential Amino Acids
• Tryptophan• Methionine• Valine• Threonine
• Phenylalanine• Leucine• Isoleucine• Lysine• Arginine• Histidine
(infants)
Proteins
• Dietary sources– Eggs, milk, fish, and most meats contain
complete proteins – Legumes, nuts, and cereals contain
incomplete proteins (lack some essential amino acids)
– Legumes and cereals together contain all essential amino acids
Proteins
• Uses– Structural materials: keratin, collagen, elastin,
muscle proteins– Most functional molecules: enzymes, some
hormones
Proteins
• Use of amino acids in the body1. All-or-none rule
• All amino acids needed must be present for protein synthesis to occur
2. Adequacy of caloric intake• Protein will be used as fuel if there is insufficient
carbohydrate or fat available
Proteins
3. Nitrogen balance• State where the rate of protein synthesis equals
the rate of breakdown and loss• Positive if synthesis exceeds breakdown (normal
in children and tissue repair)• Negative if breakdown exceeds synthesis (e.g.,
stress, burns, infection, or injury)
Proteins
4. Hormonal controls• Anabolic hormones (GH, sex hormones)
accelerate protein synthesis
• Vegetarian diet may result in protein deficiency
• Need essential amino acids– beans lysine & isoleucine– corn tryptophan & methionine
Transamination
Energy-Yielding Non-nutrient
• Alcohol – 7 kcal/gram
• Non-nutrient because it interferes with growth, maintenance and repair of the body– Alcohol’s metabolites are harmful
Energy Density
• Measure of the kcal per gram of food• Fat has the highest energy density of the 3
energy-yielding nutrients.• Foods with a high energy density provide
more kcal per gram than low density foods.
Energy Density
Vitamins• Essential• Organic, micronutrient• Not energy-yielding• Fairly easily destroyed/damaged• Can be water-soluble or fat-soluble
Vitamins
Organic compounds needed by the body in small, but essential amounts
Cannot be synthesized by the body in sufficient amounts
Function in a variety of ways in metabolic reactions
Thirteen known vitamins
Water-Soluble Vitamins
Pantothenic acidBiotinB12 (cyanocobalamin)
Folic acid
C (ascorbic acid)
B1 (thiamin)
B2 (riboflavin)
Niacin
B6 (pyridoxine)
Water-Insoluble Vitamins
A (retinol)DEK
Minerals• Essential• Inorganic, micronutrient• Not energy-yielding• Indestructible
Minerals
• Essential inorganic elements• Involved in a variety of
metabolic processes• Major minerals versus trace
minerals
Major Minerals
CalciumPhosphorusMagnesiumSodiumPotassiumChlorine
Trace Minerals
IronIodineFluorideZincCopper
ManganeseCobaltSeleniumChromium
The Science of Nutrition
• One of the newest sciences– New branch is nutritional genomics
• Study of the interaction of nutrients with DNA/genes and how those genes impact health
• Like all sciences, nutrition is based on scientific research
Dietary Recommendations
Dietary Reference Intakes (DRI)1. EAR - Estimated Average Requirements2. RDA – Recommended Dietary Allowances3. AI – Adequate Intake4. UL – Tolerable Upper Intake Levels
All based on nutritional research.
Improving your Health
• Goal is to reduce the number of risk factors that are in your control – Risk factor = something that statistically increases
the incidence of a disease• Risk factors may not be the cause of the disease………
Improving Health
• Risk factors in your control:– Smoking– Alcohol intake– Over-consumption of calories– Physical inactivity– Poor quality diet
Improving Health
• Risk factors you cannot control:– Age– Gender– Genetics (family history)– Ethnicity
Nutritional Deficiencies
• Overt vs. covert deficiency– Overt – outward signs of the deficiency
– Covert or sub-clinical– deficiency may be detected by lab tests, but not outward signs of the deficiency
Nutritional Deficiencies
• Primary vs. secondary deficiency– Primary – inadequate intake of the nutrient
– Secondary – body doesn’t absorb adequate amounts, excretes too much….
• Body “mishandles” the nutrient
– Diet history helps distinguish between these
• Approximately 24 million people in the US have diabetes (10%)
• Another 16 million have a condition now known as prediabetes
Diabetes Epidemic
Blood Sugar LevelsHomeostasis via Negative Feedback
Diabetes Mellitus
Type I Diabetes hyposecretion of insulin
insulin dependantjuvenile onset
Type II Diabeteslate onset (adult)
insensitivity of cells to insulinmanage by exercise & diet
• sugar in blood and urine• urinate too often and produce too
much urine• Too thirsty• Too hungry
Symptoms (Type I):
• Arteriosclerosis• Cardiovascular problems
- Heart disease- Stroke- High blood pressure
• Gangrene• Blindness• Kidney damage
Complications
• Insulin replacement• Pancreas transplant• Pancreatic cell transplant• Fetal pancreatic islet cell transplant
Treatment:
2010: U.S. spends $170 Billion Annually
Per Person:• Individuals with diabetes:
$13,243/year• Individuals without diabetes:
$2,560/year
Cost $$$$
Obesity may be gene related • Leptin
- leptin levels appetite - loss of body fat leptin levels and appetite
and wt gain
Here are the top 5 obese countries:
• United States (34% of adults were overweight in 2008)
• Mexico (30% in 2006) • New Zealand (27% in 2007) • Australia (25% in 2007) • United Kingdom (25% in 2008)
Lowest: Japan & Korea 3.2%
Obesity
Genetically Modified FoodsCons
• Introducing allergens and toxins to food• Accidental cross pollination • Antibiotic resistance• Creation of "super" weeds and other
environmental risks
Genetically Modified FoodsPros
• Increased pest and disease resistance• Grow food in harsh climate • Increased food supply (more food/acre)• More nutritional value• Make drugs
Ring spot virus
Artificial Sweeteners
• Reduced calories• Reduce tooth decay• Diabetes• Lower cost
Artificial Sweeteners
• Acesulfame potassium (Sunett, Sweet One)
• Aspartame (Equal, NutraSweet)• Neotame• Saccharin (SugarTwin, Sweet'N
Low)• Sucralose (Splenda)