Factors that affect an individual’s daily caloric intake

Age:

• Calorie needs peak at about age 25 and then decline by about 2 percent every 10 years.
• The aging body replaces muscle with fat, which burns fewer calories than muscle does and therefore limits the amount of calories that should be consumed in a day.

Gender:

• Males have less body fat and about 10 to 20 percent more muscle than a female of the same size and age.
  

  
  
• Because muscle burns more calories than fat does, a male’s calorie needs are generally about 5 to 10 percent higher than a female’s.

Metabolism:

• The speed of a person’s metabolism, a.k.a Basal Metabolic Rate (BMR), determines how fast and how many calories they can burn in a day.  
• If you have a fast metabolism, you need more calories in your diet.  
• If you have a slow metabolism, you need less calories in your diet.

Genes:

• The metabolic rate that you inherit from your family in part determines the number of calories that your body needs to function
• Inherited metabolic diseases, specifically those that affect your thyroid, can cause you to burn calories very quickly or very slowly. .

Lean Body Mass:

• If you have a greater proportion of muscle to fat, your metabolism is higher, allowing your body to burn calories faster.
• If you have more body fat and less muscle, your metabolism is lower, and therefore your body burns calories slower.
  
  Body Size:
  Your body size greatly affects the number of calories you need.  The bigger your body, the more calories your body needs to sustain itself. It takes more energy for a person with a bigger body to function than a person with a small body, so therefore their caloric intake should be greater.
  

  
  

Activity level:

• When you’re active, you burn more calories.
• And if you burn (or expend) more calories than you eat, you lose weight.
• The kind of exercise you choose, and how long and how intensely you do it, determines exactly how many calories you burn.
• People who are active and work out on a daily basis need more energy and therefore should consume more calories.

SOURCES/LINKS: http://www.dummies.com/how-to/content/what-factors-affect-your-calorie-needs.html