7. Energy and Food

chapter 8

Energy = the ability to do work

A calorie is the amount of heat (or energy) needed to raise the temperature of one gram

of water by one degree Celsius.

A kilocalorie (kcal) is 1000 calories. A joule is 0.24 calories.

Almost all of the chemical energy contained in any substance is stored in its chemical bonds.

calorie vs

kilocalorie

Bond Energy

• The E required to break a chemical bond or

• The E released when the bond is formed

• C-H ~ 100 kcal/mole; C-C ~ 90kcal /mole;

• O-H~ 110 kcal/mole; C=O~ 170 kcal/mole

• O=O ~118 kcal/mole

An exothermic reaction is a reaction that releases heat as it proceeds .

CH4 + 2O2 CO2 + 2H2O + energy

An endothermic reaction is a reaction that absorbs heat as it proceeds .

exo

endo

Why is this reaction exothermic?

• E required to break the bonds of reactants is 4 x C-H bond E + 2 x (O=O) bond energy = 4 (100) + (2 x118) = 636 kcal

• E liberated when bonds of products are formed = 2 x (C=O) bond Energy +4 x (O-H) bond E ie (2x170) + 4 (110) = 780 kcal

• Thus Energy is released in this reaction: 780-636= 144 kcal/ mole of methane burned

FOOD = FUEL FOR THE HUMAN ENGINE

The Energy Equation

Energy In = Energy Out + Energy Stored

Metabolism is the combination of all chemical reactions that take place in any living organisms.

1 Kilocalorie = 1 nutritional Calorie (Cal)

ENERGY IN: The Macronutrients

The macronutrients of our food are the three major groups that make up the great bulk of our food supply, the chemicals that serve as the only source of energy for the human machine .

Through the elegant, intertwined complex of chemical reactions that constitute human metabolism, the chemical energy of these

compounds becomes transformed into the human energy of our lives .

The Macronutrients

fats and oils

carbohydrates

protein

Energy from Macronutrients

• From fat: 9 Calories per gram

• From protein: 4 Calories per gram

• From carbohydrate: 4 Calories per gram

Why do we get more calories from fat than from carbs or protein?

• Fats contain long hydrocarbon chains in the fatty acid part of the molecule

• More C-H bonds to be oxidized to Water and CO2.

• Recall relatively high bond Energy in C=O and O-H vs. C-C and C-H bonds (methane combustion ).

Calories for Healthy Eating

• Recommended levels from macronutrients

• From carbohydrates (55%): 10% from simple sugars (sucrose, glucose, fructose); 45% from complex carbohydrates (starch)

• From fat (30%): maximum 10% from saturated fat, best from unsaturated

• From Protein (15%)

Some would disagree

• Atkins Diet : advocated as few calories as possible from carbohydrates

• Theory (1972 book) was that sugars and carbohydrates increase insulin levels and facilitate fat storage

• Depriving the body of carbohydrates facilitates fat burning and hence weight loss

Problems with the Atkins diet

• Too much saturated fat -> coronary disease

• Too little fibre, hence poor waste product elimination and risk of kidney disease and colon cancer

• Conclusion: Not a healthy alternative

• Expensive: Permitted foods were Atkins Diet products

Atkins Diet products

North American Problems

• Too much simple sugar

• Too much saturated fat

• Too many calories!!

• Not enough physical activity

• Obesity is a major health issue

Micronutrients

• Food components such as Vitamins and Minerals, which are required in relatively small amounts for good health

• Not significant sources of calories

What is Junk Food?

• Food that supplies a large number of calories but few Vitamins or Minerals (Micronutrients)

• “Empty Calories” –ie. highly refined sugar (Sucrose) –provides calories but no micronutrients

“Empty”Calories from soft drinks

• Classic Coke 42 grams of sugar per 341 mL can x4 Cal/gr= 168 Calories

• Diet Coke: no sugar, artificial sweeteners (aspartame and potassium acesulfame) 0 Calories (on can)

• Carbonated water, caramel flavor, caffeine, phosphoric acid, citric acid, sodium benzoate, 0.1 gr of protein, so not quite 0 Cal.

Enzymes in Digestion

• Enzymes (bio-catalysts) help to break down complex substances into simpler ones which can be absorbed

• Need optimal pH-ie pepsin in the stomach works best at pH near 2

• Suffix “ase” denotes an enzyme

Carbohydrase enzymes

• Amylase in saliva, breaks starch and complex carbohydrates into maltose

• Maltase then breaks the maltose into glucose

• Sucrase, lactase act on sucrose and lactose breaking them down into simpler sugars such as glucose and fructose

Protease enzymes

• Pepsins-secreted in stomach and pancreas to help proteins break down into peptides and eventually into amino acids

Lipases

• Secreted in pancreas and walls of the small intestine

• Digest lipids (fats) and breaks them up into fatty acids and glycerol

Digestion

ENERGY OUT

Exercise

Specific Dynamic Action

Basal Metabolism

Specific dynamic action, SDA, the energy consumed in digesting and metabolizing food and

converting its energy for use in exercise and basal metabolism.

It is the price we pay, in energy, for extracting energy from food .

(~10% of the energy obtained from food)

ie. consume 2500Cal and use 250Cal for SDA

We can sense SDA in operation as we grow warmer and find our heart beating a bit faster

after a meal. The warmth and higher pulse are both signs that our body is working at digesting

the food and using up energy through SDA.

Drowsiness after a large meal comes from the diversion of blood from the brain to the

digestive system. The body is working hard to process all the fuel that’s just been brought in

and - first things first - digestion takes momentary precedence over mental alertness.

After a great dinner!

Basal metabolism accounts for all the work that goes on inside our bodies just

to keep us alive.

It is the energy expended as our heart pumps, as our lungs expand and contract, and as the liver, kidneys and other major

organs work to maintain life .

In a healthy adult the energy spent through

Basal Metabolism amounts to approximately 1 Calorie / hour / kg of body weight

Basal metabolism increases with any bodily stress, desirable (eg. pregnancy or lactation) or

not (eg. illness).

Measured at rest, but awake, after a 12 hour fast

Calorie needs for inactive male

• For 70 kg (154lb) man; need 24 x 70= 1680 Cal per day for basal metabolism

• But also need additional amount for SDA which is about 10% more. Thus ~ 1900 Cal/day total

Resting metabolism represents the combination of basal metabolism and SDA.

Most of the energy coming directly from the food weeat is spent on SDA and BM. The energy we usefor exercise comes largely from stored energy.

If the only metabolic energy available to us, orour predecessors, were the energy from the

macronutrients of a recent meal - none of uswould be alive today.

Our vital organs would run out of energy betweenmeals, even as we sleep, if our body could not store

the excess fuel of each meal and then use thatstored fuel to provide a continuous supply of energy

between meals, as required.

Energy Availability & Storage

• Instant: blood sugar (Glucose) lasts ca. 30 minutes

• Short term Liver and muscles store glycogen (about 2500 Calories) max 6-8 hours.

• Long term: fat is stored in adipose tissue-can last up to 35 days

Hitting the Wall

• Marathon runners use ~ 15Cal/minute

• After 2.5 hours, use 150x 15=2250 Cal

• Glycogen tank is empty!!

• Need to consume short term E : glucose etc.

• Fat metabolism is slow and thus of no use as a short term E source

Energy Stored = Fat! (Adipose Tissue)

Adipose tissue stores chemical energy at ~3500 Cal / lb (~7700 Cal / kg)

Water content of adipose tissue

• Why only 7.7 Cal/gram stored in adipose tissue if fat provides 9 Cal/gram?

• A: ~ 15% of adipose tissue is water

• Thus : 9- (.15x9) = 9- 1.35 =7.65 Cal/gram

But if we don’t ‘exercise’ enough then:

Energy In X SDA + BM + Energy Stored

and the energy/fat remains stored!

The evolution of man

• Sedentary lifestyle needs fewer calories

Daily Energy Needs According to Physical Activity

Very light Men Women

Light MenWomen

Moderate Men Women

Heavy MenWomen

To estimate your energy needs , multiply your estimated BMR (10x your weight in lbs.) by the factor listed in the table that best represents your general level of daily activity.

Very Light : mostly sitting and standing activities

Light : mostly walking activities

Moderate : cycling, tennis, dancing

Heavy : heavy manual digging, climbing, basketball, soccer

1.3

1.3

1.61.5

1.71.6

2.11.9

Activity Level Factor

Typical 175 pounder

• Caloric requirement is 10x 175 x1.3 if inactive, ie 2275 Calories per day.

• If you play for the Ottawa Senators, 175 x 10 x 2.1= 3675 Calories per day

• Females: a bit lower ca 1900 Cal/day• Q: Do women have more efficient

metabolisms? A: yes! Women have less muscle and more fat (on the average).

How many soft drinks per day?

• Recall max. 10% of Cal. from simple sugars, so 10% of 2275 =227.5 Cal/

• Recall one can of regular Coke contains over 160 Cal

• So, the answer is…………………..1 .

Calories from Alcohol

• 7 Calories per gram• Thus in a 341mL can of normal beer (5 %),

assuming its density is 1 gram per mL• Calories = .05 x 341 x 7 = 119.35• A glass of wine or a shot (1.5 oz of liquor)

have about the same caloric content• No nutrients, depresses CNS and is toxic to

liver

Recommended levels of alcohol

• Max. 2 drinks per day (male adult)

• Max. 1 per day (adult female)

• 0 per day if pregnant or lactating!

• 0 per day if on certain medications

• Moderation is KEY!!

Approximate Rates of Energy Expenditure for a 70kg (154lb) Person

Very light Sitting, reading, watching TV, writing, driving Light Slow walking, washing, shop-

ping,light sports such as golf Moderate Fast walking, heavy gardening,

moderate sports such as bicycling, tennis, dancing

Heavy Vigorous work, sports such as swimming, running,

basketball and football

1.0-2.5

2.5-5.0

5.0-7.5

7.5-12.0

60-150

150-300

300-450

450-720

Level Examples Per Minute Per Hour

Calories Expended

Bicycling, 15 mph Bicycling, 5mph Chopping wood Driving an automobile Eating Gardening, weeding Listening to lecture Pick and shovel work Running 5 mph Skiing, cross country Swimming, pleasure Tennis, (recreational/competitive) Walking 3-5 mphWalking up stairs

1257.52.81.55.61.76.7109-1767/115.610-18

Activity Energy (Cal/min)

Energy used in a Variety of Activities

DEMO: Energy from snack foods

• Potato is mostly carbohydrate-ie 4 Cal/gram

• But , if it is deep fried in fat, add 9 Cal per gram of fat

• Burning potato chip: fat burns off

• Black residue is just Carbon

• Salt NaCl adds yellow colour to flame