Science of Nutrition

Chapter 1: The Science of Nutrition

Fact or Fiction?
 Eliminating all fat from the diet will improve

health.
 Avoiding carbohydrates will lead to weight

loss.

 Protein is the most important nutrient.  As long as you take a vitamin and mineral pill each day

you don’t have to worry about eating healthy.

 Our genes determine our weight.

Superfoods?
Example: WebMd
 Low fat or    

Example: Be Well Buzz:
 Goji Berries







fat-free plain yogurt Eggs Nuts Kiwis Quinoa Beans Salmon Sweet potatoes Berries

 Acai Berries
 Cacao

 Maca Root

http://www.bewellbuzz.com/superfoods/16-superfoods-you-should-know-about-part-1/

Low-Carb Diet
1 slice whole wheat bread: 22 g 1 banana 27 g 1 medium potato 33 g 1 cup cooked pasta 43 g 1 apple 19 g 1 can soda 35 g 20 -

Why study nutrition?
Over the last two decades:
 Percentage of obese adults doubled (33 %)  Percentage of overweight children doubled (16 %)  Percentage of overweight adolescents tripled (16%)

Life Expectancy

Leading Causes of Death in 1997 and 1900

Leading causes of death
Major health problems are largely causes by poor diet

How are genetic traits passed from one generation to another?

The Epigenome
The DNA sequence (genome) does not change and is passed on to the next generation. But: The access to the DNA changes biochemically and can be passed on to the next generation.

DNA Methylation Methyl groups added to certain DNA bases represses gene activity

Histone Modification Molecules attached to histone tails alter DNA activity.

Genes and Nutrition
Genes Lifestyle

Nutrition related diseases

Nutrition

Consequences:
 We have control over our DNA.
 Diet
 Exercise

 Control can be passed on to the next

generations.

Nutrigenomics
How nutrition effects gene expression and

stability.
Food stimulates short-term gene expression.
 Vitamins and minerals can stabilize or

destabilize DNA.
 High

intake of biotin, riboflavin destabilize  High intake of vitamin E, retinol, calcium stabilize  Impaired intake of folate, B6 induces DNA breaks

How genetics effects nutrient utilization.

Systems Biology Approach
How all components of a biologic system interact over time under varying conditions.

 Group of scientist with varying expertise

collaborate.
 Examples: Nutrigenomics, proteomics,

metabolomics

Assess your Risk
High Risk:  More then one first degree relative with certain condition
 Condition occurs before

age 50 – 60 years
 Use family tree to asses your own

risk

Diabetes, obesity, certain cancers, osteoporosis, hyperlipidemia, hypertension

NOVA: Epigenetics
 http://www.pbs.org/wgbh/nova/sciencenow/3411/02.h

tml
 http://www.pbs.org/wgbh/nova/sciencenow/video/341

1/w02-350.html

Nutrition
 The Science of food  Action, interaction and balance of nutrients in

relationship to health and disease
 Process of ingestion, digestion, absorption,

transport, utilization and excretion of food substances

Nutrients
 Nourishing substances  6 classes of nutrients :

Carbohydrates Lipids Protein

Vitamins Minerals Water

Essential Nutrients
 Specific biological function.  Removing from diet leads to decline in biological body

function.
 Adding to diet before permanent damage is done

restores biological body function . Example: Vitamin C, sodium, niacin, fluoride

Nonessential Nutrient
 Body is able to make these in sufficient

amounts when they are needed.

 Humans do not need to consume these.

Example: Cholesterol

Functional Categories
Provide Energy Most carbohydrates Proteins Promote Growth and Development Proteins Lipids Regulate Body Processes Proteins Some lipids

Most lipids

Some vitamins
Some minerals Water

Some vitamins
Some minerals Water

Macronutrients vs. Micronutrients

Carbohydrates
 Energy yield: 4 kcal/g
 Composed mainly from carbon,

hydrogen and oxygen.
 Primary dietary sources are fruits, vegetables and

grains.
 Simple carbohydrates: glucose, fructose, sucrose,  Complex carbohydrates : starch, glycogen, fiber

Lipids
 Energy yield: 9 kcal/g  Composed mainly from carbon,

hydrogen and oxygen
 Triglycerides are the main energy

source and store for the body
 2 basic types of fatty acids:

saturated, unsaturated

Protein
 Energy yield: 4 kcal/g  Composed from carbon,

hydrogen, oxygen and nitrogen.
 Main structural material, enzymes, immune factors.  Formed by amino acids (9 amino acids are essential

nutrients for adults, 10 for infants).

Vitamins
 Wide variety of chemical structure  Enable many chemical reactions  13 Vitamins divided into two groups: Fat soluble and

water soluble
 Can be destroyed during cooking

Minerals
 Simple inorganic substances (Na, Ca, K)  Two groups:  Major minerals: needed in g amounts daily (Na, Ca)  Trace minerals: needed in amounts less than 100 mg daily (Fe, Zn)
 Not destroyed by cooking, can leak out into cooking

water

Water (H2O)
 Macronutrient needed in largest quantity

 Solvent, lubricant, transport medium  Helps regulate body temperature

Phytochemicals, Zoochemicals
 Physiological active compounds from plants and meat  Not considered essential nutrients
 Significant health benefit  Phytochemicals linked to reduced risk of cancer, cardiovascular disease  Research needed  Zoochemicals omega-3 fatty acid, probiotics

Energy sources
 Carbohydrates: 4 kcal/g  Protein: 4 kcal/g  Fat: 9 kcal/g  Alcohol (not essential): 7 kcal/g

Energy Uses
 Build new compounds  Perform muscular movements  Promote nerve transmissions  Maintain ion balance in the cell

Calorie
 The term calorie expresses the amount of energy  Defined as the amount of energy to heat 1 gram of

water by 1 degree Celsius
 Food energy is expressed as Kilocalorie
1 kcal =1000 x cal 1 kcal = 4.18 kJ

 In every day usage the term calorie is used for kcal

Energy
 Measured using a bomb calorimeter
 Estimated by multiplying amount of energy yielding

nutrients by their physiological fuel values

Nutritional Health Status
 Desirable Nutritional Status  Enough nutrients to support normal function and to build and maintain surplus stores
 Undernutrition  Intake does not meet nutrition needs surplus stores used tissue concentrations↓ metabolic processes slow down  Subclinical Clinical  Overnutrition Consumption of more nutrients than body needs.

Assessing Nutritional Status
Factors Background Nutritional Method Medical history Family medical history

Anthropometric assessment: Height, weight, skinfold thickness, arm muscle circumference
Biochemical assessment: compounds in blood, urine, feces Clinical assessment: Blood pressure, skin condition, fatigue Dietary assessment: Food history, food frequency, 24hour recall

Environmental assessment: education and economical background

Example: Iron

Limitations
 Signs of malnutrition often not specific  Diarrhea, fatigue, skin condition

 Long time for signs or symptoms to develop
 Time span between development of

malnutrition and clinical evidence
 Saturated fat, calcium

Steps for Sound Scientific Research
 Observation  Hypothesis

 Experiments  Results and interpretation  Accept or reject hypothesis
 Publication and evaluation  Theory or new observation

Scientific Research
Observation
Hypothesis Research experiments

Cod-liver oil cures rickets. Why?
Missing dietary component: Vitamin A Destroying Vitamin A in cod-liver oil. Accept or reject? Follow-up studies found that codliver oil contains vitamin D.

Follow-up experiments

Accept or reject?

Epidemiology
 Scientific observation of population  Cohort studies  Migrant studies  Case-control studies
 Using statistics  Long or short term

 Basis for many laboratory experiments

Experimental Research
Two types of studies:  Laboratory animal experiment  Human experiment
At least two groups of subjects  Experimental group  Control group

Laboratory Animal Experiment
 Animal model used when experiments are too invasive

or dangerous for human subjects
 Animal model needs to mimic human  Animal experiment have to be approved by an ethical

review board of their university

Human Experiments
 Approval from research review board at university or

company
 Valid experimental protocol
 Expected to produce important knowledge

 Fair and ethical treatment of study participants
 Assesses risks and benefits of potential treatment

 Case - Control Study

 Single -Blind Study
 Double - Blind Study

Case-Control Study
 Compares individuals with a certain condition (case)

to individuals without the condition or (control group)
 Both groups matched for characteristics not being

studied
 Age, race, gender

 Limitation  No claim of cause and effect ⇨ Controlled experiment

Single/Double Blind Study
 Participants are randomly assigned to two groups  Experimental group (treated)  Control group (untreated, placebo)

 Single-blind: Participants don’t know group

assignment
 Double-blind: Participants and scientists don’t know

group assignment (reduces bias)

Peer Review
 Final results are submitted to scientific journals  Critically reviewed by other scientists familiar with the

research area to maximize objectiveness and reliability
 American Journal of Clinical Nutrition, Journal of

Nutrition, Journal of the American Dietetic Association, New England Journal of Medicine

Evaluating Nutrition Claims
 Apply basic principles of nutrition  Claims  Only advantages  New ‘secret’ scientific breakthrough  ‘curing’ disease  Too good to be true  Extreme bias against science
 Examine credentials (Organization, research,

publication source)

Nutrition-Related Products
Be wary of:  Products promising dramatic effect or a quick fix  Simplistic conclusions  Recommendations drawn from one study  Recommendation connected to a sale  Survey conclusions without peer review  Lists of ‘good’ and ‘bad’ foods

Supplements and Nutrition-related Products
 Vitamin-, mineral-, protein- and

herbal supplements are not regulated by FDA as drugs; are classified as food (DSHEA 1994)
 Manufacturer does not have to proof

supplement is safe. FDA has to proof supplement is unsafe to prevent sale
 ‘Evidence’ for function often very

vague (FTC)