After having being treated to a huge banquet by their hosts, the two visitors remember being told that all the animals they brought with them, in the ship that founded the settlement, died.
None of the local animals can be safely eaten by humans.
One man feels quite unwell when he realises the only possible source of meat on this planet. The author does not state the source of the meat but leaves it for the reader to work out the only possible option.
I'm guessing Disqualified by Charles L Fontenay It's only a couple of pages long so I've copied the entire story from Project Gutenberg:-
After the morning inspection tour, Tardo, the Solar Council's Planetary Aid agent, and his companion, Peo, were taken to the castle which stood on a hill overlooking the area.
Tardo and Peo were entertained royally at luncheon by Saranta, their host, who appeared to be the wealthy overlord of this portion of the planet. The meal was delicious—tender, inch-thick steaks served with delicate wine sauce and half a dozen of the planet's exotic vegetables, topped off by a cool fruit dessert.
"My recommendation will be of considerable importance to you," said Tardo as they ate. "If it is favorable, there is certain technical aid aboard ship which will be made available to you at once. Of course, you will not receive advanced equipment from the Solar Council until there is a more thorough investigation."
"I'm afraid our culture is too simple and agrarian to win your approval," said Saranta modestly.
"That isn't a major consideration. The Council understands the difficulties that have faced colonies in other star systems. There are certain fundamental requirements, of course: no abnormal religious practices, no slavery ... well, you understand what I mean."
"We really feel that we have done well since we ... our ancestors, that is ... colonized our world a thousand years ago," said Saranta, toying with a wineglass. A smiling servant filled the glasses of Tardo and Peo. "You see, there was no fuel for the ship to explore other planets in the system, and the ship just rusted away. Since we are some distance from the solar system, yours is the first ship that has landed here since colonization."
"You seem to have been lucky, though," said Peo. He was navigator of the Council ship, and had asked to accompany Tardo on the brief inspection trip. "You could have landed on a barren planet."
"Well, no, the colonizers knew it was liveable, from the first exploration expedition," said Saranta. "There were difficulties, of course. Luxuriant vegetation, but no animal life, so we had no animals to domesticate. Pulling a plow is hard work for a man."
"But you were able to solve this situation in a humanitarian way?" asked Tardo, peering at him keenly. "That is to say, you didn't resort to slavery?"
Saranta smiled and spread his hands slightly.
"Does this look like a slave society to you?" he countered. "The colonists were anxious to co-operate to make the planet liveable. No one objected to work."
"It's true we've seen no slaves, that we know about," said Tardo. "But two days is a short time for inspection. I must draw most of my conclusions from the attitudes of you and the others who are our hosts. How about the servants here?"
"They are paid," answered Saranta, and added ruefully: "There are those of us who think they are paid too well. They have a union, you know." Tardo laughed.
"A carry-over from Earth, no doubt," he commented. "An unusual one, too, for a culture without technology."
When the meal was over, the two men from the ship were conducted on a tour of the area. It was a neat agricultural community, with broad fields, well-constructed buildings and, a short distance from Saranta's castle-like home, a village in which artisans and craftsmen plied their peaceful trades.
Peo tried to notice what he thought Tardo would look for on such a short inspection. The Council agent, he knew, had had intensive training and many years of experience. It was hard for Peo to judge what factors Tardo would consider significant—probably very minor ones that the average man would not notice, he thought.
Tardo had seemed most intent on the question of slavery, and Peo looked for signs of it. He could see none. The people of the planet had had time to conceal some things, of course. But the people they saw in the village wore a proud air of independence no slave could assume.
Saranta apologized for their having to walk, explaining that there was no other means of transportation on the planet.
"And, without transportation, you can understand why we have not been able to develop a technology," he added. "We hope transport will be included in the first assistance you will give us."
Tardo asked about the fields.
"I see there is no one working them," he said. "Is that done by the villagers?"
"Our labor supply is transient," answered Saranta after a moment's hesitation. "The laborers who will work our fields—for a wage, of course—are probably in the next town or the one beyond it now."
Alpha Persei was sinking in the western sky when Tardo and Peo took their leave of Saranta and made their way down the road toward their planetary landing craft.
"It looks like a good world to me," said Peo. "If tomorrow's inspection is as satisfactory, I suppose you will recommend the beginning of technical aid?"
"There will be no inspection tour tomorrow, and I shall recommend against aid at this time," replied Tardo. "I've seen enough."
"Why?" asked Peo, surprised.
"There are two classes of people on this planet, and we've seen only one," said Tardo. "Those we have seen are freemen. The others are no better than animals. We give no aid that helps men tighten their hold over their fellows."
"If you haven't seen them, how do you know there is another class?" demanded Peo. "There is no evidence of any such situation."
"The evidence is well hidden. But if you think your stomach can take it now, I'll tell you. If you remember your history, colonizing ships 1000 years ago had no space to carry animals along. They had to depend on native animal life of the planet, and this planet had none."
"Saranta said that. But I don't see ..."
"Those were delicious steaks, weren't they?" remarked Tardo quietly.
"Courtship Rite" by Donald Kingsbury as per Book where humans on another planets are cannibals
Geta is a harsh planet settled by humanity centuries before the novel begins.
Geta is much drier than Earth. Terraforming was never, or very minimally, initiated on the planet's biosphere, leaving it very inhospitable to the descendants of the original settlers, who have become mythic, God-like creatures to its denizens.
Apparently the only Earth-life on Geta are humans, bees, and the "Eight Sacred Plants", including wheat, soybeans, barley, and potatoes. Native, "profane" life includes plants, a wide variety of sea-creatures and "insects", but no large land-animals. Each has a different biochemistry, so each is largely toxic to the other. As a result, food is a commodity that is very precious on Geta, and in most places the only source of meat is humans themselves. Cannibalism has insinuated itself into the very fabric of social and religious life.
I have to mention Arthur C. Clarke's Food of the Gods.
It's written in the form of Congressional Testimony, concerning a competitor's line of Ambrosia Plus line of foods.
