I have just completed three weeks of strict Paleo, although I did have a glass or two of wine during that time. But no grain, dairy, legumes, sugar or processed food. Prior to this I had been a big cereal in the morning, sandwich for lunch person. At first on this new diet I was getting stomach aches soon after lunch and late afternoon feelings of desperate hunger. I'm feeling a little better now, no stomach ache or only something minor. But when will I start to feel less food insecure in the afternoon? I eat two scrambled eggs cooked in coconut oil with chopped veggies and sausage for breakfast, chicken breast and apple for lunch, two handfuls of pecans in the late afternoon, meat, cooked vegetables and a salad for dinner. I am a very, very slender woman age 54 and I work out every morning at the gym. Despite being generally slim, I have a fair amount of belly fat which is why I started this in the first place. I don't think it has improved any with the Paleo diet, so far at least. I want to stay on it, though. I love a challenge, and this just makes sense. What prompts my question is that I read this site a lot to try to figure out my tummy unhappiness and everyone says to eliminate this and that until I don't feel like there is anything left and I'm hungry to begin with. I drink a lot of water.
Stop working out everyday.
Hold off on the apples and nuts.
Eat less chicken and more butter, coconut milk, heavy cream, grassfed beef and pastured pork.
See what happens.
What if your tummy's upset because you've eliminated a bunch of foods.... but haven't been replacing them with the an appropriate amount of calories?
If you're getting hungry all the time and agonizing about "not being allowed to eat"... then EAT SOMETHING. =)
Fiber-heavy foods sit in the stomach differently than protein does. Fat fuels us differently than sugar does. The changeover can be really disorienting.
There's no rule saying you can't have an omelet in the afternoon. Or slices of roast beef, or hard-boiled eggs in the fridge to snack on when you get the "am I ever going to eat again" munchies. Throw together some "emergency protein" to get you through the hard parts.
This is not a starvation diet. =) You are allowed to eat when you're hungry. During the first stages, when the carb cravings are driving you batty, snacking on some fatty protein really, really helps you feel satisfied. And, it re-trains your mind to think of different "default" foods.
If you're worried that something in your diet might be causing the tummy distress, by all means eliminate the nuts, or nightshades, or whatever... but eat something you know is neutral in its place.
Robb Wolf's Food Matrix is awesome.
It can really help stimulate ideas of what to eat.
From most of Robb Wolf's stuff, stomach fat is usually a sign of insulin resistance.
Also, you seem -- at three weeks -- to be where most people feel the "sticky" spot is. That is, your body is really starting to change metabolic pathways for energy consumption. I'd really give it a month AT LEAST before starting to expect big change. Don't rush into cutting out tons of foods, just try to stay conscious of what you're eating and how it makes you feel. Try spacing your meals out so that you can isolate the effects of each one and how they effect your body. See if there are any patterns in different food types. You seem to be approaching this with a great attitude, which is fantastic!
Other things that are a bit more general would be getting plenty of good sleep and making sure your fitness isn't bumping your cortisol levels. I'm a big fan of the "lots of slow movement with occasional intense effort" fitness plan. It has been working great for me. Food may be a big part of health, but lifestyle changes can work wonders, too.
Overall, I'd say stick with it. Mix up the meals with some recipes from paleo sites if things get boring. I bet you'll see some improvements. Keep us posted!
Food insecurity in the afternoon is probably a sign you needed a little more at lunch. I agree with the others to add some fat in with the chicken. While the other suggestions are great, some aren't comfortable or aren't in a place that allows the addition of butter, coconut milk and other forms of fat. I suggest throwing a piece or two of bacon in there. Maybe a hard boiled egg. Perhaps some guacamole.
Also, I'm not a huge fan of the apple in your daily diet at lunch. I find that a heavy does of fructose without a nice fat "offset" can give me an upset stomach.
Figuring out how to lose the belly fat is a different question. You don't give much information about your workouts (frequency, type, etc) so I cannot offer much insight. Make sure you get plenty of sleep. Many who workout in the morning (like myself) skip this important step and might keep a small extra layer.