Merchant ships, whaling ships, or navy ships, I imagine many sailors expended a large number of calories a day. What was their diet? What would the average sailor look like? How “fit” were they?
I've written about victualling before a few times:
And this answer has some depictions of common sailors in it that may be of interest:
https://www.reddit.com/r/AskHistorians/comments/2pdr6j/how_did_the_sailor_suit_develop/
The tl;dr is that the basic foodstuff for men in the Royal Navy during the period I study was bread, either as soft loaves when in port or hardtack while at sea. The men were entitled to a pound of it a day, in either form.
The next item in a seaman's diet was meat, salted, and the sailors were entitled to four pounds of beef and two of pork per week, served out in some sort of a rota, as well as a "banyan" day where they each got a pound of flour to make into puddings, usually with the fat that was skimmed off the meat. Most likely they spread their meat rations out so no one was eating two pounds of beef in a day, but our sources on this are fairly sparse.
The other aspects of the seaman's diet were peas (2 pints a week), oats (3 pints a week), butter (6 oz per week) and cheese (12 ounces per week).
And now we have to talk about alcohol. Sailors drank a lot. The beer ration for sailors in home waters was a gallon per person per day (the beer was likely around 4% although there's some dispute on this). Beer stows very large, though, and for overseas expeditions sailors would drink wine or brandy in the Mediterranean, arrack in the Far East, other spirits including aquavit and vodka in the Baltic, and rum in the Caribbean. The basic rule of thumb was that a half-pint of spirits would equal a gallon of beer, and the sailors' rum ration was served twice (a quarter pint each time, mixed with 3 parts water) under supervision.