Ok, i am the adult who was your son as a toddler. Based on how my parents dealt with it this is my advice to you;
Keep offering dinner/lunch, but always have something on the plate that you know he does like and eats.
Dont put any pressure on him at meals. Set the plate down and begin a conversation about something else, like peppa pig or something to distract him- you eat as normal, try not to watch him eating/not eating.
Offer him smaller meals, (perhaps more often) they can seem less daunting to a child wary of food.
Involve him in preparation- where possible. Make it a fun activity for him. Even if its just him stirring a sauce. Get him involved and talk about how good a job he is doing and how much you will love his food.
Relax. I know, i know how hard this is to do- you are worried about him getting enough, but as long as he is eating something then he will be fine. I speak as a totally healthy adult who ate only cereal and chips until i was around 13. I still dont eat any fruit and very very little veg and have a very bland diet. I have never been ill other than a cold or a tummy bug. My food refusal has lasted for life due to how it was dealt with by those around me as a child. Please dont make the same mistake with your son.
Relax, keep offering, know that he will be fine.