Category Glass and Energy

HUMAN VARIATION IN ENERGY DYNAMICS

1.1 Energy Consumption

Compared to most other mammals, humans are able to survive and flourish eating a remarkably wide range of foods. Human diets range from completely vegetarian (as observed in many populations of South Asia) to ones based almost entirely on meat and animal foods (for example, traditional Eskimo/ Inuit populations of the Arctic). Thus, over the course of our evolutionary history, humans have developed a high degree of dietary plasticity. This ability to utilize a diverse array of plant and animal resources for food is one of the features that allowed humans to spread and colonize ecosystems all over the world.

Table IV presents information on the percentage of energy derived from plant and animal foods for subsistence-level (that is, food producing) and industrial human...

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DETERMINANTS OF DAILY ENERGY NEEDS

A person’s daily energy requirements are determined by several different factors. The major components of an individual’s energy budget are associated with resting or basal metabolism, activity, growth, and reproduction. Basal metabolic rate (BMR) represents the minimum amount of energy necessary to keep a person alive. Basal metabolism is measured under controlled conditions while a subject is lying in a relaxed and fasted state.

In addition to basal requirements, energy is expended to perform various types of work, such as daily activities and exercise, digestion and trans­port of food, and regulating body temperature...

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Proteins

Proteins, in addition to providing an energy source, are also critical for the growth and replacement of living tissues. They are composed of nitrogen – containing compounds known as amino acids. Of the 20 different amino acids required by the body, 9 (leucine, isoleucine, valine, lysine, threonine, methionine, phenylalanine, tryptophan, and histi­dine) are known as essential because they cannot be synthesized by the body and thus must be derived from food. Two others, cystine and tyrosine, are synthesized in the body from methionine and phenylalanine, respectively. The remaining amino acids are called nonessential because they can be produced by the body and need not be derived from the diet.

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Fats

Fats provide the largest store of potential energy for biological work in the body. They are divided into three main groups: simple, compound, and derived. The simple, or neutral fats, consist primarily of triglycerides. A triglyceride consists of two compo­nent molecules: glycerol and fatty acid. Fatty acid molecules, in turn, are divided into two broad groups: saturated and unsaturated. These categories reflect the chemical bonding pattern between the carbon atoms of the fatty acid molecule. Saturated fatty acids have no double bonds between carbons, thus allowing for the maximum number of hydrogen atoms to be bound to the carbon (that is, the carbons are saturated with hydrogen atoms)...

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Carbohydrates

The largest source of dietary energy for most humans is carbohydrates (~45 to 50% of calories in the typical American diet). The three types of carbohy­drates are monosaccharides, disaccharides, and polysaccharides. Monosaccharides, or simple sugars, include glucose, the body’s primary metabolic fuel; fructose (fruit sugar); and galactose. Disaccharides, as the name implies, are sugars formed by a combination of two monosaccharides. Sucrose (glu­cose and fructose), the most common disaccharide, is found in sugar, honey, and maple syrup. Lactose, the sugar found in milk, is composed of glucose and galactose. Maltose (glucose and glucose), the least common of the disaccharides, is found in malt products and germinating cereals...

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SOURCES OF FOOD ENERGY

The main chemical sources of energy in our foods are carbohydrates, protein, and fats. Collectively these three energy sources are known as macronutrients. Vitamins and minerals (micronutrients) are required in much smaller amounts and are important for regulating many aspects of biological function.

Carbohydrates and proteins have similar energy contents; each provides ~ 4 kilocalories of metabolic energy per gram. In contrast, fat is more calorically dense; each gram provides about 9 to 10 kilocalories. Alcohol, although not a required nutrient, also can be used as an energy source, contributing ~7kcal/g. Regardless of the source, excess dietary energy can be stored by the body as glycogen (a carbohydrate) or as fat...

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CALORIMETRY

The study of energy relies on the principle of calorimetry, the measurement of heat transfer. In food and nutrition, energy is most often measured in kilocalories (kcal). One kilocalorie is the amount of heat required to raise the temperature of 1 kilogram (or 1 liter) of water, 1°C. Thus, a food item containing 150kcal (two pieces of bread, for example) contains enough stored chemical energy to increase the temperature of 150 liters of water by 1°C. Another common unit for measuring energy is the joule or the kilojoule [1 kilojoule (kJ) = 1000 joules]. The conversion between calories and joules is 1kcal is equal to 4.184 kilojoules.

Techniques for measuring energy expenditure involve either measuring heat loss directly (direct calorimetry) or measuring a proxy of heat loss such as oxyge...

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Human Energetics

WILLIAM R. LEONARD

Northwestern University Evanston, Illinois, United States

1. Introduction

2. Calorimetry

3. Sources of Food Energy

4. Determinants of Daily Energy Needs

5. Human Variation in Energy Dynamics

Glossary

aerobic respiration (metabolism) Energy producing reac­tions that require oxygen (O2).

basal metabolic rate (BMR) The minimum level of energy required to sustain basic biological function of the body.

body mass index (BMI) A weight-for-height index used to assess physical nutritional health, calculated as weight(kg)/height(meters)2.

calorimetry The measurement of heat transfer.

kilocalorie (kcal) The amount of heat required to raise the temperature of 1 kilogram (or 1 liter) of water by 1°C...

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