Convert from Btu to Calorie [nutritional]

Unit Definition (Btu)
The Btu is a unit of heat energy defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. In America the British thermal unit is sometimes called the heat unit. In defining the Btu, it is necessary to specify the temperature of the water; thus there have been several definitions over the years. However, one Btu is equal to about 251.996 (small) calories, or 0.251 996 of the (kilo-)calories counted by dieters. Using the current definition of the calorie (the IT calorie), one Btu equals approximately 778.169 foot pounds, 1.055 056 kilojoules or 0.293 071 watt hour. The symbol BThU has also been used, especially in Britain.

Unit Definition (Calorie [nutritional])
Food energy is the amount of energy in food that is available through digestion. The values for food energy are expressed in kilojoules (kJ) or food Calories (kcal). One food Calorie (1 kcal or 1,000 calories) is the amount of digestively available food energy (heat) that will raise the temperature of one kilogram of water one degree Celsius. Some advocate the convention of the capitalizing the C in these so that one food Calorie is equal to 1000 lowercase calories, but that convention is not generally followed. The large Calorie is sometimes abbreviated kcal, to indicate clearly that is 1000 times as large as the small calorie formerly common in chemistry and physics usage. Consequently, the prefix kilo- is not used with large Calories. Food calories are also more specifically called kilocalories on the basis of the small calorie usage. This term, which makes it clear that large calories are intended, is widely used by professional nutritionists when speaking in terms of calories rather than joules, but the term kilocalorie for the large calorie is less often used by laypersons