For Lisset Felipe, privation is a standard facet of Cuban life, a struggle shared by nearly all, whether they’re enduring blackouts or hunting for toilet paper. But this year has been different, in an even more fundamental way, she said. She has not bought a single onion this year, nor a green pepper, both staples of the Cuban diet. Garlic, she said, is a rarity, while avocado, a treat she enjoyed once in a while, is all but absent from her table. “It’s a disaster,” said Ms. Felipe, 42, who sells air-conditioners for the government. “We never lived luxuriously, but the comfort we once had doesn’t exist anymore.”The changes in Cuba in recent years have often hinted at a new era of possibilities: a slowly opening economy, warming relations with the United States after decades of isolation, a flood of tourists meant to lift the fortunes of Cubans long marooned on the outskirts of modern prosperity. But the record arrival of nearly 3.5 million visitors to Cuba last year has caused a surging demand for food, causing ripple effects that are upsetting the very promise of Fidel Castro’s Cuba.Tourists are quite literally eating Cuba’s lunch. Thanks in part to the United States embargo, but also to poor planning by the island’s government, goods that Cubans have long relied on are going to well-heeled tourists and the hundreds of private restaurants that cater to them, leading to soaring prices and empty shelves. Without supplies to match the increased appetite, some foods have become so expensive that even basic staples are becoming unaffordable for regular Cubans.