CORTONA, Italy, Sept 5 (Reuters) - Six-time Olympic champion Milo of Kroton trained by carrying a calf on his back until it turned 4 years old. Then he ate it.

A massive wrestler from southern Italy, Milo was said to eat 18 kg (40 lb) of meat and bread washed down with eight litres (8.4 quarts) of wine in one sitting -- 2,500 years ago.

Milo was probably devouring Chianinas, the oldest and biggest bovine breed in the world, and now making a comeback as health-conscious consumers turn to leaner meat that can still compete on taste with fatter breeds.

New York restaurants compete to serve expensive, fat-rich beef, while the Japanese pamper their Wagyu cows with massages and beer to vein the meat with as much fat as possible.

But in Tuscany, where Fiorentina-style steaks are two to four fingers thick and can weigh 1.5 kg (3.3 lb), the lean Chianina rules the grill for top-end foodies.

"Nothing tastes as good as a Chianina steak," said Duccio Masetti, 39, holding a carved T-bone in front of him with two hands as juice dribbled down his chin.

Masetti was one of thousands who thronged the Tuscan town of Cortona for its annual mid-August Chianina fair, where 2,200 steaks were cooked on a huge grill. The livestock breed takes its name from the Chiana valley, which the town dominates.

Chianina beef costs 30 euros a kg ($18.60 a lb), more than the 20 euros a kg for Italian prime beef, but a fraction of the price for Wagyu, which can sell for 750 euros a kg ($460 a lb).

'I CAN EAT A KILO'

Masetti, who has driven two hours from his native Pistoia to attend the Cortona fair every year for the past five years, also travelled to Kobe, Japan, last year to taste Wagyu beef. He said he found it cloying after a few bites.

"The Wagyu is great, but after a while my stomach said 'No more!' It's like eating marzipan. Chianina is light. I can eat a kilo of it," Masetti said.

Chianina bulls stand 1.8 metres tall at the shoulder and weigh 1.5 tonnes. They have short, smooth white coats and short horns.

Used in ritual sacrifices by the Romans, Chianinas have also been used to pull heavy loads over the past 1,000 years -- and almost vanished when tractors replaced them in the 1950s.

But the 1990s mad-cow disease scare sent sales of Chianina soaring as health-conscious consumers sought meat from Chianinas, which did not have a single case of the disease.

"The consumer nowadays is looking more and more for quality and health guarantees," said Stefania Veltroni of the Arezzo province Chianina consortium.

In the last 10 years, the number of farms producing Chianinas has increased 18 percent to 1,347, with a 31 percent boost in the number of Chianinas butchered to 42,000 a year.

Chianinas have an unsurpassed capacity for lean meat production, according to breeders as well as Italian and Australian authorities.

The meat has little waste but still retains a marbling of fat in the muscle, resulting in meat with more protein, less fat and less cholesterol than other beef.

In the United States, they have been cross-bred with Angus to make Chiangus cattle. In Australia and Canada, Chianinas are appreciated for their ability to thrive in harsh weather and terrain.

BLAIR AND MCCARTNEY

The Chianina label is protected under a European Union designation of regional quality as "Vitellone Bianco dell'Appennino Centrale", just like Parma ham.

Under the rules of the breed's consortium in Italy, the calf must be naturally nursed by the mother and then fed on preservative-free grass.

"That's a far cry from the 'meat machines' that are pumped full with growth hormones so they can be butchered at 12 months and cost less than Chianina, which needs 18-20 months to mature," said Stefano Falorni, 60, an eighth-generation butcher.

His 300-year-old shop in Greve near Florence is famed for its Chianina and has become a compulsory stop for foodies from Italy and beyond. Clients include former British prime minister Tony Blair, who likes a roast of a whole fillet, and the pop musician Paul McCartney.