1

Essential Nutrients

•Necessary for normal function

•Must obtain from an exogenous source

•Inadequate intake leads to deficiency*

There are 6 classes of Nutrients

Water

Lipids (fat)

Proteins

Carbohydrates

Minerals

Vitamins

The Nutrients

Whitney & Rolfes. Understanding Nutrition. 2011

2

The Science of Nutrition

Foundation in several other sciences

Biology, biochemistry, physiology

Tremendous growth

Sequencing of human genome

Nutritional genomics

Conducting Research

• Use of scientific method

– Systematic process for conducting research

• Research studies

– Controls

• Randomization

– Sample size

– Placebos

– Double-blind experiments

3

The Scientific Method

Conducting Research

• Epidemiological studies

– Cross-sectional studies

– Case-control studies

– Cohort studies

• Experimental studies

– Laboratory-based animal studies

– Laboratory-base in vitro studies

– Clinical trials

4

The Scientific Process

• Identification

• Establish need

• Understand mechanisms of actions

• Identify role in health & disease

• Toxicity

How much of each nutrient do we need?

Needs (requirements) are determined scientifically

using evidence-base approach

5

Dietary Reference Intakes (DRI) A set of standards that define the amounts of energy, nutrients,

other dietary components and physical activity that best support health.

DRI consists of

Estimated Average Requirements (EAR)

Recommended Dietary Allowances (RDA)

Adequate Intakes (AI)

Tolerable Upper Intake Levels (UL)

(Reading: Understanding Nutrition)

Danger of

toxicity

Marginal

Tolerable

Upper Intake

Level Safety

Safety

Inta

ke

RDA or AI

RDA Estimated

Average

Requirement

Marginal

Danger Danger

of

deficiency

Inaccurate

view

Accurate

view Understanding Nutrition, 2011

(UL)

(EAR)

6

If a person’s usual intake falls above the RDA,

the intake is probably adequate because the

RDA covers the needs of almost all people.

High Intake

probably

adequate

RDA

A usual intake that falls between the

RDA and the EAR is more difficult to

assess; the intake may be adequate, but

the chances are greater or equal that it

is inadequate.

Intake possibly

inadequate

EAR

Usu

al in

tak

e o

f n

utr

ien

t X

(u

nit

s/d

ay)

Intake

probably

inadequate

If the usual intake falls below the

EAR, it is probably inadequate.

Low Understanding Nutrition, 2011

7

Methods to determine requirements

2 Approaches

- Epidemiological

- Experimental

a) Depletion / repletion

b) Balance study (e.g. nitrogen)

c) Factorial approach (e.g. energy)

d) Isotopic study

Epidemiological data provides

approximate (ball-park) values

on requirements

8

Important concepts on nutrient requirements

When intake is established by epidemiological or experimental approaches, a

scatter plot is obtained.

Usually, this is normally distributed. 50% of the population takes in more than

the mean while the remaining 50% of the population takes in less than the mean.

The range of intake is described as BIOLOGICAL VARIATION – generally

estimated to be 15% (i.e. one standard deviation)

Assuming the intake is the physiological need, then 50% of the population will

have needs above the mean intake.

To ensure the majority of the population is free from

deficiency, a level of intake higher than the mean should be

recommended.

Mean + 2SD will statistically cover the needs of

97.5% of the population.

There may be 2.5% of the population whose requirements

are higher than mean+2SD. If these individuals just

consume that particular nutrient at the level of RDA – they

may run into a risk of not having enough.

9

Understanding Nutrition, 2011

Does subject C meet his need for nutrient X ?

10

Energy requirement versus nutrient requirement

Energy requirement is set at the mean of the

population

Requirements for other essential nutrients are set

using statistical approaches and therefore include

a margin of safety.

Characteristics of

Recommended Daily Allowance (RDA)

•For healthy individuals

•Include a generous margin of safety

•Apply to average daily intakes

•Does not cover therapeutic needs

•Does not allow for losses of nutrients due to cooking,

storage or processing