NUTRITIONAL BIOCHEMISTRY ARJUN.KAMBHAMPATI.

What is a Calorie?

A calorie is a unit of energy. Technically a calorie is the amount of heat energy required to raise the temperature of 1 gram of water up 1 degree Celsius (1.8 degrees Fahrenheit).

When applied to food, we are actually talking about a kiloCalorie (1000 calories). However the word Calorie (note capitalization) is used in most literature.

The measure of Calories gives us an indication of the potential energy that food possesses. This can easily be calculated with the following formula:

1 gram of Protein = 4 Calories1 gram of Carbohydrate = 4 Calories1 gram of Fat = 9 Calories1 gram of Alcohol = 7 Calories

Therefore Calories can be calculated simply by knowing the amount of these three building blocks in the food.

Calorific or Caloric ValueThis is the number of calories in any given food or drink.

Nutritional value of foods, and the usefulness of fuels is determined by the heat (energy) they produce on heating. The energy released by the combustion of foods or fuels is usually compared in terms of their combustion energy per gram. It is known as calorific value. It is defined as the amount of heat produced in calories (or joules) when one gram of a substance (food or fuel) is completely burnt.

The calorific value is usually expressed in kcal per gram or kilojoules per gram (1 kcal = 4.184 kJ).

For example, when methane burns, 890.3 kJ mol-1 of energy is liberated as

Therefore, calorific value of methane is:

(Molar mass of CH4 =16)

The fuels are graded, and priced on the basis of their calorific values.

Amongst the fuels, hydrogen has the highest calorific value. But, hydrogen is not used as the domestic/industrial fuel because of the following reasons:

Hydrogen has a very low boiling point. So, it needs special cryogenic containers, which are very expensive.

Hydrogen is combustible. It forms an explosive mixture with air. So, it is not safe to store or use hydrogen.

Among the foods, fats and carbohydrates are the principal sources of energy, which have high calorific values. Proteins are also the main constituents of foods. On an average an adult requires 8000 to 12000 kJ of energy per day. This means that the balanced diet of a person must include food-stuffs, which provide enough carbohydrates, fats, proteins, oils, vitamins, etc.

Renewable (Non-depletable) and non-renewable (Depletable)

energy sources

Renewable sources of energy are produced continuously in nature and are non-depletable. Sources like water, sunlight, air, tidal energy, nuclear energy, geothermal power, are not exhaustible.

A non-renewable source of energy gets depleted over a certain period of time, and is not easily replaceable. These include energy sources like, crude oil, coal, natural gas, uranium etc.

At the beginning of the industrial and technological revolution, most renewable sources of energy were not developed for commercial exploitation, because of the comfortable levels of fossilized fuels reserves. Now, due to the looming energy crisis, intense research is on to develop these resources and their applications, in a cost effective manner. Available applications are more expensive than fossil fuels, and hydroelectric power. For example, solar energy is so diffused, (collected over a large area) that a solar power station generating 100 megawatts will occupy 344 x 10m2(84 acres) as compared to 185m2 (0.05 acres) occupied by a thermal power station utilizing coal. Energy from nuclear fusion is still very far from practical exploitation. In nutshell, energy is going to be more expensive in coming years, and hence we should conserve energy.

SPECIFIC DYNAMIC ACTIONn. Abbr. SDAAn increase in the production of heat caused by the ingestion of food, especially proteins.

Thermic effect of food (also commonly known simply as thermic effect when the context is known), or TEF in shorthand, is the increment in energy expenditure above resting metabolic rate due to the cost of processing food for storage and use. It is one of the components of metabolism along with the resting metabolic rate, and the exercise component. Another term commonly used to describe this component of total metabolism is the specific dynamic action (SDA). A common number used to estimate the magnitude of the thermic effect of food is about 10% of the caloric intake of a given time period,

though the effect varies substantially for different food components. Dietary fat is very easy to process and has very little thermic effect, while protein is hard to process and has a much larger thermic effect. Raw celery and grapefruit are often claimed to have negative caloric balance (requiring they take more energy to digest than usable energy received from the food), presumably because the thermic effect is greater than the caloric content, due to the high fiber matrix that must be unraveled to access their carbohydrates; however, there has been no research carried out to test this theory and a significant amount of the thermic effect depends on the insulin sensitivity of the individual, with more insulin sensitive individuals having a significant effect while individuals with increasing resistance have negligible to zero effects.

The thermic effect of food is increased by both aerobic training of sufficient duration and intensity and by anaerobic weight training. However, the increase is marginal, amounting to 7-8 cal per hour. The primary determinants of daily TEF are the quantity and composition of the food ingested.

Basic metabolic rate

Basal metabolic rate (BMR), and the closely related resting metabolic rate (RMR), is the amount of daily energy expended while at rest in a neutrally temperate environment, in the post-absorptive state (meaning that the digestive system is inactive, which requires about twelve hours of fasting in humans). The release of energy in this state is sufficient only for the functioning of the vital organs, the heart, lungs, nervous system, kidneys, liver, intestine, sex organs, muscles, and skin.

BMR decreases with age and with the loss of lean body mass. Increasing muscle mass increases BMR. Aerobic fitness level, a product of cardiovascular exercise, while previously thought to have effect on BMR, has been shown in the 1990s not to correlate with BMR, when fat-free body mass was adjusted for. New research[citation needed] has however come to light which suggests anaerobic exercise does increase resting energy consumption (see "Aerobic vs. anaerobic exercise"). Illness, previously consumed food and beverages, environmental temperature, and stress levels can affect one's overall energy expenditure as well as one's BMR.

BMR is measured under very restrictive circumstances when a person is awake. An accurate BMR measurement requires that the person's sympathetic nervous system not be stimulated, a condition which requires complete rest. A more common and closely related measurement, used under less strict conditions, is resting metabolic rate (RMR).[1]

BMR and RMR are measured by gas analysis through either direct or indirect calorimetry, though a rough estimation can be acquired through an equation using age, sex, height, and weight. Studies of energy metabolism using both methods provide convincing evidence for the validity of the respiratory quotient (R.Q.), which measures the inherent composition and utilization of carbohydrates, fats and proteins as they are converted to energy substrate units that can be used by the body as energy. Studies conducted by Spennewyn in 1990 found strong correlations between lean mass and metabolism based on indirect calorimetry measurements. Spennewyn discovered that lean tissue in men and women required approximately 16 calories per pound per day. Thus, once a lean mass was known it could be multiplied by 16 to reveal daily caloric needs based on the activity level of the individual. This method has been used in many health club environments to determine daily caloric needs.

Nutrition and dietary considerations;;;;;;;___

Basal metabolism is usually by far the largest component of total caloric expenditure. However, the Harris-Benedict equations are only approximate and variation in BMR (reflecting varying body composition), in physical activity levels, and in energy expended in thermogenesis make it difficult to estimate the dietary consumption any particular individual needs in order to maintain body weight.

Physiology::::____ Both basal metabolic rate and resting metabolic rate are usually expressed in terms of daily rates of energy expenditure. The early work of the scientists J. Arthur Harris and Francis G. Benedict showed that approximate values could be derived using body surface area (computed from height and weight), age, and sex, along with the oxygen and carbon dioxide measures taken from calorimetry. Studies also showed that by eliminating the sex differences that occur with the accumulation of adipose tissue by expressing metabolic rate per unit of "fat-free" or lean body weight, the values between sexes for basal metabolism are essentially the same[citation needed]. Exercise physiology textbooks have tables to show the conversion of height and body surface area as they relate to weight and basal metabolic values.

The primary organ responsible for regulating metabolism is the hypothalamus. The hypothalamus is located on the brain stem and forms the floor and part of the lateral walls of the third ventricle of the cerebrum. The chief functions of the hypothalamus are:

1. control and integration of activities of the autonomic nervous system (ANS)

o The ANS regulates contraction of smooth muscle and cardiac muscle, along with secretions of many endocrine organs such as the thyroid gland (associated with many metabolic disorders).

o Through the ANS, the hypothalamus is the main regulator of visceral activities, such as heart rate, movement of food through the gastrointestinal tract, and contraction of the urinary bladder.

2. production and regulation of feelings of rage and aggression 3. regulation of body temperature 4. regulation of food intake, through two centers:

o The feeding center or hunger center is responsible for the sensations that cause us to seek food. When sufficient food or substrates have been received and leptin is high, then the satiety center is stimulated and sends impulses that inhibit the feeding center. When insufficient food is present in the stomach and ghrelin levels are high, receptors in the hypothalamus initiate the sense of hunger.

o The thirst center operates similarly when certain cells in the hypothalamus are stimulated by the rising osmotic pressure of the extracellular fluid. If thirst is satisfied, osmotic pressure decreases.

All of these functions taken together form a survival mechanism that causes us to sustain the body processes that BMR and RMR measure

basal metabolic rate, or BMR, is the minimum calorific requirement needed to sustain life in a resting individual. It can be looked at as being the amount of energy (measured in calories) expended by the body to remain in bed asleep all day!

BMR can be responsible for burning up to 70% of the total calories expended, but this figure varies due to different factors (see below). Calories are burned by bodily processes such as respiration, the pumping of blood around the body and maintenance of body temperature. Obviously the body will burn more calories on top of those burned due to BMR.

BMR is the largest factor in determining overall metabolic rate and how many calories you need to maintain, lose or gain weight. BMR is determined by a combination of genetic and environmental factors, as follows:

Genetics. Some people are born with faster metabolisms; some with slower metabolisms.

Gender. Men have a greater muscle mass and a lower body fat percentage. This means they have a higher basal metabolic rate.

Age. BMR reduces with age. After 20 years, it drops about 2 per cent, per decade. Weight. The heavier your weight, the higher your BMR. Example: the metabolic

rate of obese women is 25 percent higher than the metabolic rate of thin women. Body Surface Area. This is a reflection of your height and weight. The greater

your Body Surface Area factor, the higher your BMR. Tall, thin people have higher BMRs. If you compare a tall person with a short person of equal weight, then if they both follow a diet calorie-controlled to maintain the weight of the taller person, the shorter person may gain up to 15 pounds in a year.

Body Fat Percentage. The lower your body fat percentage, the higher your BMR. The lower body fat percentage in the male body is one reason why men generally have a 10-15% faster BMR than women.

Diet. Starvation or serious abrupt calorie-reduction can dramatically reduce BMR by up to 30 percent. Restrictive low-calorie weight loss diets may cause your BMR to drop as much as 20%.

Body Temperature/Health. For every increase of 0.5C in internal temperature of the body, the BMR increases by about 7 percent. The chemical reactions in the body actually occur more quickly at higher temperatures. So a patient with a fever of 42C (about 4C above normal) would have an increase of about 50 percent in BMR.

External temperature. Temperature outside the body also affects basal metabolic rate. Exposure to cold temperature causes an increase in the BMR, so as to create the extra heat needed to maintain the body's internal temperature. A short exposure to hot temperature has little effect on the body's metabolism as it is compensated mainly by increased heat loss. But prolonged exposure to heat can raise BMR.

Glands. Thyroxin (produced by the thyroid gland) is a key BMR-regulator which speeds up the metabolic activity of the body. The more thyroxin produced, the higher the BMR. If too much thyroxin is produced (a condition known as thyrotoxicosis) BMR can actually double. If too little thyroxin is produced (myxoedema) BMR may shrink to 30-40 percent of normal. Like thyroxin, adrenaline also increases the BMR but to a lesser extent.

Exercise. Physical exercise not only influences body weight by burning calories, it also helps raise your BMR by building extra lean tissue. (Lean tissue is more metabolically demanding than fat tissue.) So you burn more calories even when sleeping.

Short Term Factors Affecting BMR Illnesses such as a fever, high levels of stress hormones in the body and either an increase or decrease in the environmental temperature will result in an increase in BMR. Fasting, starving or malnutrition all result in a lowering of BMR. This lowering of BMR can be one side effect of following a diet and nothing else. Solely dieting , i.e. reducing the amount of calories the body takes on, will not be as affective as dieting and increased exercise. The negative effect of dieting on BMR can be offset with a positive effect from increased exercise.

respiratory quotient :=(or RQ or respiratory coefficient), is a unitless number used in calculations of basal metabolic rate (BMR) when estimated from carbon dioxide production. Such measurements, like measurements of oxygen uptake, are forms of indirect calorimetry. It is measured using Ganong's Respirometer.

Caluculation: The respiratory quotient (RQ) is calculated from the ratio:

RQ = CO2 eliminated / O2 consumed

where the term "eliminated" refers to carbon dioxide (CO2) removed ("eliminated") from the body.

In this calculation, the CO2 and O2 must be given in the same units, and in quantities proportional to the number of molecules. Acceptable inputs would be either moles, or else volumes of gas at standard temperature and pressure (time units may be included, but they cancel out since they must be the same in numerator and denominator).

Many metabolized substances are compounds containing only the elements carbon, hydrogen, and oxygen. Examples include fatty acids, glycerol, carbohydrates, deamination products, and ethanol. For complete oxidation of such compounds, the chemical equation is

CxHyOz + (x + y/4 - z/2) O2 ---> x CO2 + (y/2) H2O

and thus metabolism of this compound gives an RQ of x/(x + y/4 - z/2).

The range of respiratory coefficients for organisms in metabolic balance usually ranges from 1.0 (representing the value expected for pure carbohydrate oxidation) to ~0.7 (the value expected for pure fat oxidation). See BMR for a discussion of how these numbers are derived. A mixed diet of fat and carbohydrate results in an average value between these numbers. An RQ may rise above 1.0 for an organism burning carbohydrate to produce or "lay down" fat (for example, a bear preparing for hibernation).

RQ value corresponds to a caloric value for each liter (L) of CO2 produced. If O2 consumption numbers are available, they are usually used directly, since they are more direct and reliable estimates of energy production.

RQ as measured includes a contribution from the energy produced from protein. However, due to the complexity of the various ways in which different amino acids can be metabolized, no single RQ can be assigned to the oxidation of protein in the diet.

Respiratory Quotients of Some Substances:

Name of the substance Respiratory QuotientCarbohydrates 1Triolein (Fat) 0.7Oleic Acid (Fat) 0.71Tripalmitin (Fat) 0.7Proteins 0.8 - 0.9Malic acid 1.33Tartaric acid 1.6Oxalic acid 4.0