Low fat is a term that has many definitions. I'm noding about the fat content in food.
Fat content in food is usually expressed in terms of the percentage of total calories in the item that come from fat. To determine the % of calories from fat (CFF) you need to know both the total calories and grams of fat:
%CFF = 100 * {(grams of fat X 9) / (total calories)}.
The 9 is because all fats have 9 calories per gram.
Recommendations for optimal (or maximal) fat content in the diet vary. Current US recommendations are to eat no more than 30%CFF. This limit translates into 67 grams of fat for small or sedentary individuals who need just 2000 calories per day and 100 g of fat for larger or more active individuals who need 3000 calories per day.
Some diets recommend 20, 15, or 10% calories from fat or less. Recommending a lower limit is controversial because of the risks of nutrient inadequacy or other adverse effects. Some population subgroups, such as growing children, pregnant women, lactating women, and the elderly have higher needs for essential fatty acids and caloric density and should NOT be placed on overly restrictive low fat diets.
SOURCES:
http://www.americanheart.org
www.fatfree.org | 
