Intro to Nutrition - Energy

Food energy is the amount of energy in food that is available through digestion. This availability happens through a set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products.

Like other forms of energy, food energy is expressed in calories or joules. Many countries, and we at the Spanimax Institute use the food calorie (Calorie) which is equal to 1 kilocalorie (kcal).

The kilojoule is the unit officially recommended by the World Health Organization and other international organs. But the Calorie is still the most common unit in use. 1 joule (J) is the amount of mechanical energy required to displace a mass of 1 kg through a distance of 1 m with an acceleration of 1 m per second (1 J = 1 kg × 1 m2 × 1 sec-2). The conversion factors between joules and calories are: 1 kcal = 4.184 kJ, or conversely, 1 kJ = 0.239 kcal.

In the context of food energy the term calorie generally refers to the kilogram calorie. However, the term kilocalorie (kcal), referring to one thousand gram calories, is also in widespread use especially by professional nutritionists (when speaking in terms of calories rather than joules). To avoid confusion, the prefix kilo- is not used with the kilogram calorie.

The kilogram calorie, large calorie, food calorie, Calorie (capital C) or just calorie (lowercase c) is the amount of energy required to raise the temperature of one kilogram of water by one degree Celsius. And this is the Calorie we will be referring to when we mention the term.

Human energy requirements are estimated from measures of energy expenditure plus the additional energy needs for growth, pregnancy and lactation. Recommendations for dietary energy intake from food must satisfy these requirements for the attainment and maintenance of optimal health, physiological function and well-being.

An adequate, healthy diet must satisfy human needs for energy and all essential nutrients. Furthermore, dietary energy needs and recommendations cannot be considered in isolation of other nutrients in the diet, as the lack of one will influence the others.

Sources of dietary energy: Energy for the metabolic and physiological functions of humans is derived from the chemical energy bound in food and its macronutrient constituents, i.e. carbohydrates, fats, proteins and ethanol, which act as substrates or fuels. After food is ingested, its chemical energy is released and converted into thermic, mechanical and other forms of energy.

It should be noted that fats and carbohydrates are the main sources of dietary energy, although proteins also provide important amounts of energy, especially when total dietary energy intake is limited.

Ethanol is not considered part of a food system, but its contribution to total energy intake cannot be overlooked, particularly among populations that regularly consume alcoholic beverages.

Energy density: The amount of calories in food account for their energy density. Some macronutrients are very energy dense in relation to the amount. Fats and oils are an example with 9 calories per gram.
 Carbohydrates on the other hand contain only 4 calories per gram, something that would suggest that you can eat more of them. So when eating for energy we must remember that eating fat means automatically that we can eat less. The problem arises when we eat simple carbohydrates in high amounts, because the carbs will rise your insulin levels which in return store the fat for later use. So it is very important to remember this when choosing the preferred energy macronutrient in each meal. It is either complex low GI carbs combined with moderate a fat intake, or a high fat meal with a minimum of carbs like the ones found in vegetables. Protein with its thermogenesis can be safely ingested with either fat or carbs, and should be a part of every meal.

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