Though some studies have shown the traditional Greek diet as one of the healthiest on the planet, and especially so the Cretan diet, one will notice many Greek men with paunches and incipient double chins or fat cheeks even before the age of 30, many pudgy children, and many really fat women, from the age of 40 and upward (though younger as well). Reasons for this are complex.
Looking at the traditional diet first, it is obvious that a large quantity of oil is eaten in Greek food (despite its much touted low cholesterol content), as well as a large quantity of bread (to mop up the copious amounts of oil), and that potatoes, rice or noodles are eaten along with bread, too.
Older Greeks will also eat the fat from fattier meats, sometimes fried up as a delicacy. Traditionally, men got a lot of exercise working in the fields and gardens, and with their animals, and many still do (at least in villages, though most Greeks now live in cities and live a more sedentary life).
Village women in some places also got/get exercise with the tending of chickens, with garden work, and with hauling water, etc. But most village women in the old days also tended to bear several children, and to spend many hours cooking and cleaning - tiring and arduous work, but different from work that requires a lot of walking, climbing, hauling and lifting. Greeks are also fond of pastry and sweets, fried potatoes and fried vegetables. Perhaps the greater fashion consciousness (and desire to be slim and attractive to men) among modern Greek urban women, has been one of the big factors in focus on getting more physical exercise (with gyms springing up everywhere), with consciousness of health issues also increasing, (though not much on the subject of tobacco smoking). Over 51% of Greeks still smoke.
The Greek or Mediterranean diet would be healthy if one followed it: yogurt, fresh fish, meat and vegetables and readily available and inexpensive extra virgin olive oil.
Unfortunately culture in Greece is changing and becoming just another European or Westernized country where money talks louder than ethics (ethos) with advertisements for alcohol, cigarettes, faster and faster cars and usurious bank and credit cards schemes and of course weight loss clinics! And no hot sauces!