Referring to this column.
In my junior high science classes, where I first learned what a “calorie” was, I was taught that a Calorie (uppercase “C”) was equal to a kilocalorie, or a thousand calories (lowercase “c”).
Was this a 70’s thing that went away, or a Colorado thing, or what? Did anyone else learn it this way?
I heard that from someone or other, but I don’t think it was from any reliable source. It’s mentioned in the Wikipedia article for ‘calorie’, which points out how this suggested convention creates ambiguity if a sentence begins with ‘calorie’ or ‘Calorie’.
I helped Cecil out with this one, since he knew I had a strange interest in the history of measurement units.
It is a frequent convention to use the capital C for kilocalorie, but it’s not mandated in most places. The US FDA labeling code doesn’t require it to be lower or upper case, and mixes cases within its publication (Nutrition labeling of food. ), and even the NIST lists it as either case. Special Publication 811
One of the earliest references I found when Cecil sent out his call for research slaves to help him was this: Atwater, W.O. and Woods, Chas D. “The Chemical Composition of American Food Materials”. USDA Bulletin Number 28, 1896, wherein Atwater uses “Calorie” to mean “kilocalories,” and he mixes lower and upper case (such as at the top of Page 9). Atwater, who was a professor at Wesleyan University and later the first director of the USDA Office of Experiment Stations, and is described by several texts as being the “father of modern American nutrition.” Atwater’s research was the basis of a large number of other nutritional texts in the first “scientific nutritional revolution”, and my guess is most other authors followed his examples and assumed everyone knew what a “calorie” with respect to food really meant.
Early usage and sloppy usage notwithstanding, the better convention to support is Calorie for the larger unit and calorie for the smaller. It isn’t perfect (What is, given the degree of ignorance prevalent out there?) but it is preferable unless one is willing to use “kilocalorie.” It’s not so much a matter of clarity as it is an acknowledgment to the reader that the author is educated enough to be aware of the distinction.
I heard it in chemistry and biology classes as recently as 2006. Like the Master said, it’s really not a big deal, since there’s no reason to use small calories in any context whatsoever. You’re certainly never going to see it on a nutrition label, and joules are preferred for scientific uses.
What kind of sentence would start with “calorie”? Maybe “Calories are equal to 1/1000 Calories”, but that can be avoided with “Calories are equal to 1000 calories”, which is a silly sentence anyway.
Calories can be discussed in a variety of contexts. Calories are of interest to many people, each with different interests in the units. Calories can be the focus of scientific research. Calories, by contrast, often are the focus of concerned consumers. Calories, therefore, should have some differentiating identifier besides “Calories.” 
Well played, sir.
At least he uses the modifier nearly, but chemistry is hardly a major science to be ignored, and we are all about calories. Usually in terms of kcal/mol. That will not likely change anytime soon.
I never confuse Calories for calories simply because the context is so different.
ETA: Also a calorie is usually defined as the amount of heat required to raise one gram of water one degree celcius with an initial temperature of 20 ˚C.