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

Wheat Seed

Wheat Seed

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

Obesity

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)