This can be the most confusing part about eating Paleo. Take a look at modern diets; they all revolve around counting calories, points, macros, checking to see if you are in Ketosis, and tracking every single thing you put in your mouth.
The first thing I realized when I started eating Paleo was that is was so liberating! There's no counting involved, no tracking calories, and no strict meal plan. You eat what you want, within the realms of approved foods, and you eat it whenever you want. For starters, this can actually be confusing.
Melissa Hartwig, author of the amazing new book, It Starts With Food, and founder of the Whole30 program, has a VERY good section on portion sizes that I will reference for this. Generally, you should eat 3 meals a day. This works well from a hormonal and social perceptive, as well it gives your body a good 4-5 hour break between meals allowing glucagon time to do its job and mobilize energy. It also keeps leptin levels normalized.
You build your plate around your protein source, whatever that may be for that meal (meat, seafood, or eggs). Protein is essential at every meal to help stabilize blood levels and to keep you from overeating at your other meals. Protein satiates! Your portion size of protein should be “palm-size”. So, look at the palm of your hand and use that as a guide. The thickest part of your protein source should be the same size as the palm of your hand. For deli meat, stack them to be approximately the thickness of your palm. You should eat 1-2 palm size servings at each meal. Go by your size and activity level. If your small eat one palm. If your big or very active, then eat two.
For WHOLE eggs, a good meal-size portion is the number of eggs you can hold in one hand. This is usually between 3-5 eggs. And you are eating the WHOLE egg. Throw out all that garbage you have heard about not eating the egg yolk. That is half the protein! There is no way you are going to get enough protein if you are just eating egg whites.
Fill the rest of your plate with vegetables. Yea, that's it. I like to include at least two vegetables with each meal for diversity and I have a huge cupboard of spices to add to them. Some vegetables are nutrient-dense and some are carbohydrate-dense. Vegetables like butternut squash, pumpkin, sweet potato, beets, acorn squash, and parsnips are carbohydrate-dense…which isn't a bad thing! Just eat them appropriately to your body. If you are active, then you need to make sure you are eating some of these to support your activity.
Next is fruit. Hartwigg goes onto add that we should start with eating one to two servings of fruit a day. And a serving size is the size of your fist. You can eat fruit with your meals or after your meals. My family enjoys fruit as a dessert. I usually whip up some coconut milk to make a dipping cream for our fruit.
Lastly, the portion size of healthy fats is critical to each meal. You can eat one or more fat sources per meal. If you are coming from a traditional diet, then “healthy fats” is an oxymoron. I assure you though, fats are crucial to your body. Here is a short list of healthy fats that Hartwigg gives in her book:
All oils: (olive oil, coconut oil, etc.) one to two thumb-size portions (this is about a TB or two)
All butters: (coconut butter, nut butter, clarified butter, and ghee) one to two thumb-size portions
Olives: one to two open (heaping) handfuls
Coconut (meat/flakes): one to two (heaping) handfuls
Nuts and seeds: up to one closed handful
Avocado: half to one avocado
Coconut Milk: between 1/4 – 1/2 of a (14 oz.) can
If your little, not that active, and need to lose weight, then Hartwigg suggest to choose a fat from the lower end of the specified quantities (It Starts With Food, pages 188-195)
I hope this answers some questions you may have and I hope it also liberates you the way it did me. You should feel satiated after you eat. It should carry you 4-5 hours till the next meal. Eating a portion of protein, vegetables, fruit, and healthy oils at each meal (3x a day) ensures that you are getting the proper nutrition that your body needs.