It's not unusual for little ones to be up-and-down when it comes to food. You don't want to start any food wars, because you can't win a food war if the mouth isn't your own.
But this is what you must keep in mind: your baby has a good brain. He's sensible. If he is hungry, he WILL eat.
Is his temperature normal? Is his energy level normal? Is his attitude normal? Does he LOOK healthy? Then stay cool about this. He's just not hungry or interested in eating right now. Don't worry in front of him. Provide him with nutritious food at mealtime and snack time, and let him take as little or as much as he desires. He will not starve! (There have been a number of studies done on this, if that helps.)
Right now my youngest grandchild (almost ten months) is eating as if there is no tomorrow. Food is his favorite hobby; now that he has six teeth he finds it more fun than ever. That will not last, and his parents will worry just as you're doing.
You can always talk to your doctor if you're still worried or if you just need more reassurance.