We have all heard of the benefits of a Mediterranean diet—but it amused me to find out how far back this goes. What did people in antiquity eat?

The Ancient Greeks were not big eaters like the Romans. In fact they mocked the Persians, who were very much into gastronomy, and considered them gluttons. They believed eating was for the delectation of the palate, not for overfilling the stomach.
They ate a great variety of foods, but in small quantities. Most frugal were the Spartans, who on a daily basis subsided on a cup of Melas Zomos (black broth, made with pork, salt, vinegar and blood) and a piece of bread, and for special occasions ate boiled pork, accompanied by pies and wine.
For the rest breakfast, Akratisma, was very light, consisting of barley bread dipped in wine, with a few olives and figs—often accompanied by a drink called kykeon, made with boiled barley flavoured with mint or thyme.
Around midday they partook of the Ariston, another light meal usually of fish such as sardines, anchovies, mullet or eels; pulses such as lentils, peas, and broad beans; bread, eggs, fruits and nuts.
An occasional afternoon snack, the Hesperisma, consisted of bread, olives and dried fruit.
Deipnon, taken in the evening, was the most important meal of the day. That is when meat was eaten, especially by wealthy families; mostly pork and beef, as well as venison, and wild birds such as quail and thrush. This was the time, after dark, when wealthy families also held banquets, Symposia, served by their slaves. The women usually ate apart. The meal would be followed by deserts flavoured with honey, somewhat like a modern baklava.

Ancient Greeks loved all kinds of breads, and also ate snails, which were cooked in Crete since the reign of Minos. They grew vegetables in their gardens, and foraged for foods such as mushrooms, asparagus and nettles. Fruit played a large part in their diet, but they were limited to pomegranates, cherries, pears, apples, figs, plums, and mullberries—there were no bananas, peaches, citrus fruits or potatoes, which were imported later.
Kitchen shelves would be well stocked with spices and herbs: oregano, basil, mint, thyme, coriander, capers and sesame were all used to flavour dishes, together with sea salt and olive oil. Another flavouring was gáros, a sauce or condiment made out of fermented fish, a little like Worcestershire sauce. Food was quite light, since it was mostly baked, meat was roasted on spits, and deserts sweetened with honey—there was no sugar or cocoa. Milk and cheese were also consumed, as well as oxygala, a form of yogurt.
Wine was drunk mostly mixed with water, and was widely traded, like olive oil.

While wealthy Greeks were able to afford elaborate banquets—the aforementioned Symposia—which boasted a wide variety of fine meats, the average person lived very frugally. However, their diet was still quite varied and based on fresh produce, and therefore healthy. As for the Symposia, some were the scenes of learned philosophical and literary discussions, while others were more like rowdy parties with hired performers and other forms of entertainment.