We use this energy for physical activity as well as for basic functions like respiration, digestion, circulation, and temperature regulation.

The energy used for these involuntary bodily functions is known as resting energy expenditure. 

Energy from food is measured in kilocalories, or the amount of energy or heat required to raise the temperature of 1 kilogram of water by 1° degree Celsius. 

The term Calorie is often substituted for kilocalorie. Calories affect body weight directly:

  • If we  consume more calories than we burn, our bodies will convert the extra calories (energy) to fat and  store it throughout the body.
  • If we burn more calories than we consume, our bodies will draw on stored energy, or fat, to perform the basic functions and to fuel physical activities.


Calories come from four sources
  •  FAT.

The majority of calories should come from carbohydrates, protein, and fat. (Alcohol doesn’t provide any nutrients & is therefore considered non nutritive.)

Generally, nutrition experts recommend that most people get 50% to 55 % of their total calories from carbohydrates, 12 to 15% percent from protein, & no more than 35 % percent from fat, with an emphasis on limiting saturated fat to no more than 10% percent of total calories

Similarly, the United  States Department of Agriculture’s  Dietary Guidelines recommend ranges  of 45 to 65% percent of calories from carbohydrates, and 20 to 35% percent of calories from fat, with the remaining 20 to 35% percent comes  from proteins.

  • This allows for flexibility based on individual or cultural preferences, and for some health conditions.


 “Not all sources of calories are created equal”

Fat supplies are more than two times the calories per gram that carbohydrates & proteins do, so fats and foods that are high in fat are said to be calorie dense. But these foods may also be dense in nutrients.

Alcohol also supplies a significant amount of calories per gram than carbohydrates and protein. 

  • CARBOHYDRATES:  4 calories per gram 
  • PROTEIN:  4 calories per gram
  •  FAT:           9 calories per gram 
  • ALCOHOL: 7 calories per gram 

*(Note: There are 28 grams in an ounce.)


Nutrition needs are discussed in the context of a 2,000-calorie day.  This amount was chosen because it is the basis for the Nutrition Facts label that appears on all packaged food as mandated by federal law, and because it represents the  average caloric needs for males and females between the ages of two and sixty.

The actual number of calories an individual requires depends on a number of factors:

  •  WEIGHT:  In the same way that heavier vehicles use more fuel than lighter ones, heavier people require more calories than lighter individuals to maintain their weight.
  • AGE AND LIFE CYCLE:  People who are growing rapidly, especially infants and adolescents, as well as pregnant and nursing women, have greater caloric needs. As we age, our metabolism often slows down and we require fewer calories. 
  • ACTIVITY LEVEL:  Inactive people require fewer calories than people who move frequently. Physically demanding jobs, strenuous exercise, and even f idgeting translate into more calories expended. 
  • GENDER: Men typically have leaner body mass or more muscle mass than women, and thus have higher basal metabolic rates than women do because muscle burns more calories than fat.

EFSA🇪🇺 sets average requirements for energy intake

  • EFSA has set average requirements (ARs) for energy intake for adults, infants and children, pregnant & breastfeeding women.
  • This AVERAGE REQUIREMENTS (ARs) provides a good estimate of the energy needs of European population & that will help policymakers to develop & monitor nutrition programmes to promote public health including the establishment of food-based dietary guidelines.

EFSA’s scientific advice on energy requirements is laid down in the latest of a series of scientific opinions on the average energy requirements of the specified age & the sex groups were calculated to take account of the different levels of physical activity, that are based on an assumed healthy body mass index of 22kg/m2.

Example, the Panel below has set the following ARs, based on a moderately active lifestyle:

Professional Cooking CHART2

Scientific Opinion on Dietary Reference Values for energy


Professional Cooking CHARTU.S. Department of Agriculture Center for Nutrition Policy and Promotion



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