14 Energy Values of Foods

Dr. Suman Dua

1. Food Energy

Green leaves make food using sunlight during photosynthesis. The energy stored in food is known as chemical energy and this gets converted into muscular energy when we eat it, (respiration). The human body requires energy for maintaining body temperature, metabolic activities, physical work and growth. Dietary energy intake from food must satisfy these requirements for proper functioning of body for optimal health.

1.2. The Energy Value of Foods

The energy or colorific value of food depends on amount of energy yielding factors in them. Classically the total energy content of a food was determined using a bomb calorimeter. The food was burned in a bomb colorimeter and the amount of energy released was measured. Major energy sources in foods are carbohydrates, fats and protein. In some other foods alcohols, organic acids and polios may be sources of energy.

1.3. The Units of Energy Include

• (i) Calorie– one calorie expresses the quantity of heat needed to raise the temperature of 1 kg (1 lit). Of water 10C (specifically from 14.5 to 15.50C). Kilogram calorie or kilocalorie (kcal) aptly define calorie.
• (ii) The british thermal unit, or btu- is the quantity of heat that is necessary to raise the temperature of 1 lb (weight) of water 0F from 83 to 84 0
• (iii)The standard international unit for expressing food energy is joule, or kilojoules (kj). The kilocalories can be converted to kilojoules; kilocalorie value is multiplied by 4.184.

The energy of a particular food is calculated by its composition of nutrients and allowance made for body losses.

The most energy dense macronutrient is fat. Fat is followed by alcohol, protein and carbohydrate. Vitamins and elements do not have energy value of heat needed to raise the temperature of 1 kg (11) of water 10C.

2. The term ‘energy’ is used as the provider of fuel. The amount of food energy needed to balance energy expenditure of order to maintain body size body composition and desirable physical activity is preferred to as energy requirement.

2.1 Human beings need energy for the following:

2.1.1basal metabolism – Functions essential for life such as cell function and replacement. Synthesis, secretion and metabolism of enzymes and hormones to tram post substances and molecules, as well as maintenance of body temperature, muscular function as well as brain. Basal metabolic rate refers to the amount of energy utilized by the body for basal metabolism in a period of time it is measured when the subject is awake, 10 -12 hrs fasting, 8 hers of physical rest and in supine portion. Basal metabolic rate depends on subjects age, gender, body size and body composition.

2.1.2. Metabolic Response to Food

For ingestion and digestion of food, transport, absorption adaption etc., energy is required which is term as dietary induced thermo genesis.

2.1.3. Physical Activity

The physical activity also determines the energy expenditure and includes the daily activities as well as physical activities done to keep fit for health.

2.1.4. Growth

The energy cost of growth is determined by the energy needed for new tissues as well as energy stored in these tissues. During the first three months of age 35% of total energy requirement is used for growth processes which are 5% and 3% at 12 months and 2nd year respectively. During mid adolescence it is 1 to 2% and almost negligible is late adolescence pregnancy and location extra energy is required during these phases by the mother as the growing focus, placenta as well as maternal tissues, the production and content of milk.

3. Recommendations For Dietary Energy Intake from food must satisfy these requirements for the attainment and maintenance of optional health, physiological function, and well being (WHO 2004). The methods used to assess energy intake are weighed or observed diet records dietary recalls and food frequency questionnaires. Measurement of total energy expenditure (TEE) by double labeled water (DLW) has shown that reported energy intakes are underestimated and underreporting varies from 10% -45% depending on age, gender and body composition.

Requirements of energy should be assessed in terms of energy expenditure rather than energy intake. Energy requirements can be specified by measures of energy expenditures plus the energy needed for growth pregnancy and lactation. An individual is assured to be in steady state, when energy balance is maintained over a prolonged period (WHO 2004).

“Energy balance is achieved when input (or dietary energy intake) is equal to output (or energy expenditure) plus the energy cost of growth in childhood and pregnancy, or the energy cost to produce milk during lactation”. (FAO, 2004).

4. Food Energy Is Of Two Types

4.1. Metabolisable Energy – food energy available for heat production and body gains at nitrogen and energy balance.

4.2. Net metabolisable Energy – food energy available for body functions that require ATP. It is therefore, based on ATP producing capacity of foods rather than total heat producing capacity.

5. Analytical Methods for Food Analysis

Human body is not as efficient as bomb calorimeter. Therefore, nutrient density is calculated known as coefficients of digestibility have been detained by several groups. It has been generally. The at water systemic based on the heats of combustion protein, fat and carbohydrates which are corrected for losses in digestion, absorptions accepted that among human beings energy is utilized in some 97% of carbohydrates, 95% of fats and 92% of proteins in foods. These coefficients are used to adjust the data abstained from bomb calorimeter for use by the people.

5.1.a number of analytical methods for food analysis have been developed since the late nineteenth century. Similarly there are varieties of conversion factors for foods. The common analytical methods used are the Atwater system, extensive general factor system ad at water specific factor system. All of these are based on me (metabolizable energy). The energy values based on at water system (g) dr. O. Atwater in 1988 and modified:

5.1.1. The extensive general factor system has been obtained by making refinements, additions and modifications to the at water general factor system. For the division of total carbohydrate into available carbohydrate and fiber, more factors were needed. Moons saccharine, as an added factor for available carbohydrate was added by south gate and Durnin (1970). Different weights for carbohydrate were obtained by measuring directly or considering the difference. Fiber, is assumed to 70 percent fermentable. The energy generated by fermentation is lost in the form of gas while some of it is incorporated in colonic bacteria and goes into faces. General factors are also used for alcohols, organic acids.

5.1.2 at water specific factor system

Merill and Watt (1955) made a refinement of the Atwater system. According to this there are ranges in heats of combustion and in the coefficients of digestibility of different proteins, fat and total carbohydrate proteins different in amino acid composition, heats of combustion etc. Heat of combustion of protein in rice is more as compared to potatoes, different energy factors should be used for them. Even the milling process affects the digestibility of the different flours also. This system is definitely superior to original Atwater system.

5.1.3. Net metabolizable energy system

All the three systems are based on metabolizable energy (Me). However me values can be modified to account for energy that is lost in heat from different substrates and will not be available for production of ATP. This results in NMe factors. The differences between Me and NMe factors are found in estimating the energy content of proteins, carbohydrates and alcohol.

5.1.4. Hybrid system: different countries use different systems based on countries food composition databases and regulations of food liabilities. There is considerable confusion due to array of conversion factors, analytical methods. The discrepancies arise for carbohydrates, fibres etc. The participates at fibers etc. The participants at FAO technical workshop (2004) reached on consensus that the continued use of me rather than NMe factors is recommended.

6. Energy Expenditure

It is recommended that the requirements of energy should be assessed in terms of energy expenditure rather than in terms of energy intake. Many methods are available to study human energy expenditure, they are:

1) Direct Calorimetry

2) Indirect Calorimetry

3) Heart Rate Monitoring 

4) Doubly Labelled Water

5) Physiological

 Correlates. 6.1 Direct Calorimetry

Measurement of an individual is done in a whole body calorimeter which measures the amount of heat produced by an individual in a whole body calorimeter. Direct calorimeter can be of three typesisothermal, heat sink and connection systems. All the tree approaches can be used in combination, but this approach does not conduct the measurement in natural environment.

6.2. Indirect Calorimetry

The second method measures the heat production indirectly by measuring oxygen consumption, CO2 production and respiratory quotient (Rq), R Q is the ratio of Vco2 to Vo2. Indirect calorimetric can be measured by using total collection system or flexible total collection system. Open or closed circuit system

6.3heart Rate Monitoring

This method is based on the linear relationship between heart rate and energy expenditure. Due to individual variations, age, gender, body size and nutrition, the relationship has to be calibrated for every individual.

6.4Doubly Labelled Water

By this technique others method, can be validated. In this method isotopic forms of water are administered to the individual. The 18O and 2H2O disappearance rates from the body are measured for 7 to 21 days in the samples of blood, urine or saliva. CO2 production can be estimated from the difference in eliminations rates of boyd hydrogen and oxygen. The water flux is reflected by disappearance rate of 2H2O, water flues plus the Vco2 is reflected by 18H2O. This is due to the rapid equilibrium of body water and bicarbonate pools by carbonic anhydrate. Vco2 is calculated by the disappearance rates and then assuming a RQ, energy expenditure is calculated. RQ is calculated from the composition of diet using food quotient (FQ).

The advantage of DLW method is that, it is noninvasive and can be measured is free living states. However the technique is costly because of isotope and the equipment.

6.5. Physiological Correlates Include

(I) Activity recall using questionnaire, interview and time and motion studies

(ii) Monitors can be complied to unmeasured the degree and intercity of movements.

Energy requirements for the different groups can be estimated for different age groups. The FAO/WHO/UNU (1985) expert consultation used the BMR factors for estimating the energy requirements. In 1989, the Indian council of medical research adopted this method in 1989 to extant energy requirements of Indian man and women. The method is based on the time allotted to activities that are performed habitually and the energy cost of those activities and it also combines two or more factors such as some of energy spent in activities like sleeping, resting or household activities or leisure activities. The time allotted to each activities and its energy cost in used to calculate the energy spent. The total energy expenditure is measured as a product of predicted. Basal metabolic rate and physical activity level. The ICMR has developed a set of equations for computing BMR of Indian adults. Table 1&2, give the list of equations for predicting BMR, proposed by FAO/WHO/UNU and energy requirements for Indians at different ages, respectively.

7. Nutrition and Chronic Diseases

Nutrition and diet play an important role in the etiology of chronic diseases. Nutrition related no communicable chronic diseases have become more common in the low- and middle-income countries. Rapid changes in diet and lifestyles due to urbanization and economic development have significantly impacted the health and nutritional status of developing countries and countries in transition. Increased consumption of energy-rich diets, high in fat, saturated fat, and low in unrefined carbohydrates, along with decrease in physical activity have become common. Epidemiological research suggests that a relationship exists between chronic noninfectious disease and diets that include excessive amount of energy, fat, and refined sugars but are low in complex carbohydrates. Evidence also suggests that chronic disease risks begins early in life and continues into old age, (1). Thus prevention through interventions of diet and physical activity can be a important steps in reducing the progression of existing chronic diseases as well as decreasing mortality and the disease burden caused from such diseases.

7.1. Excessive Weight Gain and Obesity

Optimal nutrition plays an important role in the prevention of obesity. Although the causes of obesity are multifactorial, social and environmental factors that either increase energy intake or decrease physical activity will create additional load on the normal mechanism of appetite control and metabolic regulation.

7.1.1 Dietary Factors

Factors linked to overweight and obesity include nutrients (high intake of energy, fat, low intake of fiber, type of carbohydrate), eating behaviors (excessive snacking/eating frequency, fast foods, eating out), and environmental (obesogenic or obesity promoting).

7.1.2 Nutrients

Nutrition transition towards higher intake of energy, fat, refined sugars, saturated fat and reduced intake of fruits, vegetables, complex carbohydrates, and dietary fiber,’ coupled with reduced physical activity, both at work and leisure time activities, is quite evident. India is in the phase of a rapid demographic transition with rapid urbanization and huge shifts in populations from rural to urban areas. Traditional diets rich in complex carbohydrates are being replaced by diets high in sugar, fat, and animal products. Increased intake of high energy foods: food rich in energy are often high in fat, highly processed, low in dietary fiber, and micronutrients and the increased consumption of these foods have shown to promote weight gain. Evidence from long-term randomized trials and epidemiological studies linking fat intake to weight gain or obesity is weak and inconsistent.3 -5 short-term studies of ad libitum total intakes, with manipulations of fat and carbohydrate proportions have observed an increase in the total energy intake and body weight on higher percent fat diets and the reverse on lower percent fat diets, suggesting that the physiological and behavioral consequence of high-fat diet is a slow weight gain through the “passive overeating” of total energy.() satiety, palatability, and energy density are some of the mechanism suggested to be responsible for the passive overeating of total energy through high-fat diets. Trials of ad libitum high- fat versus low-fat diets suggested that a 10% reduction in fat content results in about 3 kg reduction in body weight.’ results from a large longitudinal study of women observed that overall, percent of calories from fat had only a weak association with weight gain, while percentage of calories from animal, saturated, and trans fat has stronger associations. Overweight women with either overweight parents or with normal weight parents appeared to be more susceptible to weight gain due to dietary fat composition, suggesting that the association may not be genetic. Trans fat intake was shown to be more predictive than total fat of changes in waist circumference9 but more research is needed to determine the mechanism.