Food energy is chemical energy that animals derive from their food and molecular oxygen through the process of cellular respiration. Humans and other animals need a minimum intake of food energy to sustain their metabolism and to drive their muscles.
Organisms derive food energy from carbohydrates, fats and proteins as well as from organic acids, polyols, and ethanol present in the diet. Some diet components that provide little or no food energy, such as water, minerals, vitamins, cholesterol, and fiber, may still be necessary to health and survival for other reasons.
Using the International System of Units, researchers measure energy in joules (J) or in its multiples; the kilojoule (kJ) is most often used for food-related quantities. An older metric system unit of energy, still widely used in food-related contexts, is the "food calorie" or kilocalorie (kcal or Cal), equal to 4.184 kilojoules.
<>Fats and ethanol have the greatest amount of food energy per mass, 37 and 29 kJ/g (8.8 and 6.9 kcal/g), respectively. Proteins and most carbohydrates have about 17 kJ/g (4.1 kcal/g).
Conventional food energy is based on heats of combustion in a bomb calorimeter and corrections that take into consideration the efficiency of digestion and absorption and the production of urine.
Overnutrition, a type of malnutrition, is emerging with rates of obesity and related chronic diseases associated with urbanisation, aging populations, technological development and globalisation of food supplies and industry. Billions of dollars are spent annually by the food industry to promote the consumption of highly refined, high-calorie foods with little or no nutritional value.
At least 35 million overweight children are living in developing countries and 8 million in developed countries. Children are increasingly exposed to high-fat, high-sugar, high-salt, energy-dense, micronutrient-poor foods which tend to be cheaper than healthy foods. General imbalance in energy intake compared to physical activity levels is driving the obesity epidemic. In industrialised countries, child obesity risk is associated with lower household income, women with less education, and single parent households.
Obesity is increasingly prevalent among adolescent girls and women, as access to a greater quantity of inexpensive, tasty, and convenient foods increases.
Taxation on high-calorie, low-nutrition foods can play a significant role in reducing the consumption of such products. Population-wide weight-control campaigns that raise awareness among medical staff, policy-makers and the public at large can also help to reduce obesity. Particularly important is the promotion of health literacy. Additional measures include restrictions on the marketing of unhealthy foods and sugary drinks to children, and controls on the use of misleading health and nutrition claims; mandatory front-of-pack food labelling helps consumers to identify healthier options.