It’s about both calorie intake as well as portion size as one goes with the other.
The smaller the portion and the less junk the less calories you are going to consume, but that shouldn’t be rocket science.
Also, people say they need bigger portions because they eat bigger portions, and therefore their body is used to them. So anything smaller seems like not enough. But if you modify your eating habits then your body will also adjust.
I remember the first time I went to the states we ate at some diner in the morning and had a breakfast which consisted of two bacon, two eggs, two sausages, two pancakes and hash browns. 
. At the beginning of the week I struggled to eat it all but by the end I was happily munching through it.
Also the amount of eating between meals is something we need to look at. We seem to be obsessed with the need for snacking. The kids should have a couple of snack times, even at school, and as babies we build snacks into their routine and don’t leave the house without them. Then this follows into adulthood.
While it’s perfectly ok to eat snacks between meals we don’t need to snack on the level that we seem to.
And then we also need to keep an eye on what’s in the food. Salt for instance will make you retain fluid which in turn makes you gain weight, but other than that it has its own detrimental impact on the body, the heart etc. I am currently fluid restricted for medical reasons and have been told to keep an eye on my salt intake, and the results have been eye watering. E.g. one stock cube contains a 3rd of your daily salt allowance.
The consultant essentially said anything that isn’t fresh is going to contain more salt, and while not everyone might want to enter down the home made chicken stock route, there are other changes you can make to balance out.
Equally sugar is empty calories and low fat meals contain loads of it.
And we need to get past this need to not discuss food lest it upset someone with food issues. Truth is that it’s this amount of avoidance which leads to the obesity epidemic, because people are led to believe it’s something which shouldn’t be discussed for fear of what it might trigger.
Yet we happily discuss someone’s drinking with them, when alcohol could equally be based on wanting to deal with other things iyswim.