Nutritional Importance of Lipids & BMR

By

Dr Khaled Saleh AlgaririJune 2014

Basal Metabolic Rate (BMR)

Basal Metabolic Rate (BMR) is the rate of energy expended by animal (such as human) bodies when at rest.

This is the minimum amount of energy needed by the organism to perform essential functions such as breathing (and associated movements), heartbeat and blood circulation, synthesis of molecules e.g. proteins, maintenance of ion gradients across membranes, etc.. Another way to describe this is energy that is just sufficient for the functioning of the body's tissues and vital organs.

Definition of Metabolic RateMetabolic rate is the energy used by the body

in the performance of its normal functions including both maintaining the body itself (replacing tissues, etc.) and using the body to perform external functions e.g. physical work, sports and daily tasks.

Basal Metabolic Rate (BMR)

What is meant by "at rest" ?BMR is measured:When the subject (e.g. a person) is lying still, i.e.

not making physical movements When the subject (e.g. a person) is quiet, i.e. not

talking or otherwise under mental stressIn a room that is comfortably warm - so that the

body does not need to adjust body temperatureApprox. 12-18 hours after the subject's most

recent meal, so that energy is not being used for digestion and absorption of food (which can require significant energy).

Basal Metabolic Rate (BMR)

BMR can be expressed in units of kJ per square metre of body surface area per hour. This can be written as kJ / m2 / h or kJ m-2 h-

1.

Basal Metabolic Rate (BMR)

Main Factors affecting BMR:1- Age - BMR decreases as ages increases because:   The proportion of lean body mass decreases as age increases The synthesis of molecules such as proteins decreases as age

increases.

2- Gender (male or female) -Males usually have a higher BMR than females (of the same age)

because males tend to have a higher proportion of lean body mass than females of the same age. Conversely, females tend to have a higher proportion of fat cells and fat cells have a lower metabolic rate than lean muscle cells.

3- Pregnancy - BMR increases during pregnancy and lactation due to the high

energy requirement of producing foetal tissues and then breast milk.

Basal Metabolic Rate (BMR)

Other factors that increase BMR:1-lncreased intake of foods -Eating large amounts of food requires the digestive system

to process more material which therefore requires more energy. (However, as food is the source of the body's energy any resulting increase in BMR is likely to be less than the increase in energy intake due to the additional consumption of food.)

2-lncreased secretion of certain hormones -The thyroid hormones triiodothyronine (T3) and

thyroxine (T4) are the main regulators of BMR. BMR increases when the quantity of these hormones in the blood increases. Some other hormones such as testosterone, insulin and human growth hormone (HGH) can also increase the body's metabolic rate.

) Basal Metabolic Rate (BMR)

3-Increased physical exercise -Exercise requires and uses energy. Although

BMR is energy expended at rest, exercise has both short-term effects (during the time of the exercise itself) and long-term effects (after and between exercise sessions). One of the longer term effects of frequent physical exercise is an increase in BMR. This is due to increased overall activity of the heart and vascular system, together with other body systems and tissues.

Basal Metabolic Rate (BMR)

4-Environmental conditions -e.g. extremes of temperature. If/when body

temperature increases above or decreases below its ideal range, mechanisms within the body act to reduce or raise its temperature to preserve health (and ultimately life - as prolonged elevated body temperature can destroy proteins within the body and prolonged depressed temperatures can cause cardiac arrhythmias - which can be fatal in both cases). In general, the higher the body temperature the higher the metabolic rate, hence metabolic rate is higher when a person has a fever.

Basal Metabolic Rate (BMR)

5-Increased stress and anxiety -Stress is sometimes thought of as an unpleasant

combination of overwhelming worry, anxiety, fear and the feelings of constraint and helplessness. Such emotions are associated with physical responses within the body which vary but may include e.g. increased heart rate or blood pressure, difficulty sleeping, nausea, abdominal discomfort, increased sweating, etc.. To the extent that these involve (e.g. increased heart rate), cause (e.g. difficulty sleeping) or are caused by (e.g. nausea, abdominal issues) increased bodily function and so increased use of energy, BMR increases accordingly.

Basal Metabolic Rate (BMR)

Other factors that decrease BMR:1-Malnutrition - If the body is not supplied with sufficient energy and nutrients in the

form of solid food and liquids (water, drinks, soups, etc.) it becomes unable to support the body by performing all necessary functions as effectively as if supplied with those. When the body is not sustaining itself and e.g. replenishing worn-out tissues effectively, it tends to use less energy than when supplied with the dietary resources to do so.

2-Fasting - During fasting the digestive system does not expend energy

processing foodstuffs at each stage of the alimentary canal. The body's energy requirement is therefore adjusted to be lower during fasting than at times of regular eating.

3-Sleep - The body uses less energy during sleep than when awake. The

proportion of time a person spends sleeping can affect his or her BMR.

Basal Metabolic Rate (BMR)

Measurement of Basal Metabolic Rate (BMR)

1-Direct calorimetry The heat released from the body of a person who is resting, e.g. lying still on a comfortable surface or mattress, while breathing normally is used to increase the temperature of circulating water.The resulting increase in the temperature of the water is proportional to the BMR of the person.

Basal Metabolic Rate (BMR)

LIPIDS2-Indirect calorimetry

While a person rests lying still on a comfortable surface or mattress, a respirometer is used to measure his or her oxygen consumption. His or her BMR is then calculated from the volume of oxygen he or she used according to:

BMR (in kJ/m2/h) = [volume of oxygen gas used (in dm3)] x 18

This formula applies because it has been found that the average human adult typically releases 18 kJ of energy (heat energy) per 1x dm3 of oxygen used by the body.

Average BMR: 70 C/hr or 1680 C/day

Why are lipids important from a nutritional perspective ?

 

• Blood free fatty acids-if elevated concentration then greater risk of type II diabetes.

•Blood triglycerides – if elevated concentration then greater risk of heart disease.

•Blood cholesterol- if elevated concentration then greater risk of heart disease

LIPIDS

Fatty acids can be Saturated or Unsaturated, Monounsaturated, or polyunsaturated & Trans-fatty acids

LIPIDS

LIPIDS

Animal fats are high in saturated fatty acidsVegetable fats are high in unsaturated and

polyunsaturated fatty acidsTrans fatty acids are manufactured fats created

during a process called hydrogenation, which is aimed at stabilizing polyunsaturated oils to prevent them from becoming rancid and to keep them solid at room temperature. They may be particularly dangerous for the heart and may pose a risk for certain cancers. Hydrogenated fats are used in stick margarine, fast foods, commercial baked goods (donuts, cookies, crackers), processed foods, and fried foods.

LIPIDSSaturation Saturated fatty acid – carbon chains filled with hydrogen atoms (no C=C double bonds)

1. Saturated fat – triglyceride containing 3 saturated fatty acids, such as animal fats (butter, lard) .

2. Appear solid at room temperature

Unsaturated fatty acid – carbon chains lack some hydrogens (>1 C=C double bond)

1. Monounsaturated fat – triglyceride containing fatty acids with 1 double bond; i.e. canola & olive oil

2. Polyunsaturated fat- triglycerides containing a high % of fatty acids

with >2 double bonds; i.e. corn,

safflower, soybean, sunflower oils and fish; 3. Appear liquid at room temperature

LIPIDS

Oleic acid – 18-carbon, monounsaturated

Linoleic acid – 18-carbon, polyunsaturated

LIPIDS Essential fatty acids – 2 polyunsaturated fatty acids that must be provided in diet

1. Linoleic & Arachidonoic– omega-6 fatty acids and Linolenic – omega-3 fatty acid

2. Founds in plant oils, nuts, seeds, whole grains and fish

3. Play a role in normal growth & development and may prevent heart disease, hypertension, arthritis & cancer

Eicosapentaenoic and Docoahexaenoic acids

CHOLESTROLCholesteryl esters are composed of a single fatty acid

esterfied to cholesterol, in which the polar component is an alcohol.

Cholesterol is a major component of all cell membranes. It is required for synthesis of sex hormones, bile acids,

steroid hormones and vitamin D. Dietary cholesterol is found only in foods derived from

animals (meat, fish, poultry, eggs and dairy products); it is not present in plants.

LIPIDS

Sources of dietary cholesterolRichest All offal, pat?, egg yolk, fish roes, mayonnaise

and shell fish.

Moderate Fat on meat, duck, goose, cold cuts, whole milks, cream, ice cream, cheese, butter and most commercially made cakes, biscuits and pastries.

Poor All fish and fish canned in vegetable oil, very lean meats, poultry without skin, skimmed milk, low fat yoghurt and cottage cheese.

Cholesterol free All vegetables, and vegetable oils, fruit (including avocados and olives), nuts, rice, egg white and sugar.

Eating lipids-it’s a good news/bad news story

  Saturated fats (12, 14 and 16 carbon fatty acids are the really bad ones in terms of raising concentrations of bad cholesterol)

Eating lipids-it’s a good news/bad news story

  Trans fats-lower good cholesterol and raise bad cholesterol in the blood plasma

Eating lipids-it’s a good news/bad news story

Replacing saturated fats with monounsaturated fats lower concentrations of blood plasma triglycerides, cholesterol and bad cholesterol

 

Eating lipids-it’s a good news/bad news story

Replacing saturated fats with polyunsaturated fats lower concentrations of blood plasma triglycerides, cholesterol and bad cholesterol

Copyright 2005 Wadsworth Group, a division of Thomson LearningCopyright 2005 Wadsworth Group, a division of Thomson Learning

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