There could also be something else your body is hungering for, it's not all about quantity.

Sounds like you haven't found the right ratio of fat to carb to protein that hits your satiety sweet spot. Try more carbs, try less. Try more fiber, try more fat. We're all individuals and our diets need to be tailored to fit our needs and preferences.

I find that, with dinner, if I eat a really healthy protein and veggie dinner, even if it's cooked with liberal amounts of fat, I'm hungry an hour later. If I add something like avocado, I'm fine.

Protein, water, and fiber play an important role in satiety. You also need fat in order to reduce feeling hungry. In your question, you mentioned that you are eating a large amount of protein and have been adding fat. Consider increasing fiber rich vegetables if you're not getting enough now.

NutritionData.com has a handy tool to rank foods based on how "full" they make you feel, called the "fullness factor". You can analyze your diet and substitute foods that rank higher on the fullness factor.

Definitely fat :-)

I can't really imagine that your stomach would be able to digest 50 grams of tallow along with you meal in less than 1 hour. You might want to puree it with your veggies, since some people cant stand lots of liquid fat.

How many/what carbs are you eating? Maybe a varying blood sugar level tricks you into thinking you're hungry short after dinner.

Chicken and Fish are the stereotypical low-fat meats that are considered healthy in the SAD. Since you don't mention what type of fish, I'm guessing some white fish? Overall, I've personally had more success with grass fed beef and salmon as protein sources.

Not to say that chicken and fish are bad but you'll get more omega 3 and saturated fats from grass fed beef and wild caught salmon. Also starchy tubers are helpful, and so is liberal use of grass fed butter and coconut oil, my preference being expeller pressed as the flavor is neutral which means it can go into all of my food.

Also whole eggs are great. Maybe some dairy might be helpful such as heavy cream and cheese. I also like to eat lots of bacon. All that fatty stuff tends to knock out hunger, although I do eat some starchy carbs in the earlier part of the day as well. I also like to add a large serving of green veggies with butter if possible.

It does sound like you are low carb. I like to have both lots of fat and some carb like yams. Straight out of the Robb Wolf recommendations, I find it works great cuz I keep the fat around always and vary the carbs depending on how I feel and what I'm up to.

I think beef and lamb are more satisfying than chicken or fish, so maybe try having other meats a couple of days a week and see if that helps. One reason may be that they are fattier meats.

Last night I had steak, a small sweet potato, salad and some mixed veggies for supper and couldn't quite finish the sweet potato.

As jesuisjuba said, every body is different.

I can make a 4-egg bacon and veggie omelet and I'm starving again in an hour. I can have a cup of extra-fat yogurt with a banana and a fig and I'm still hungry when I finish.

I can slow-fry 6-8 ounces of fatty beef chuck and I may not eat again until the next day.

I don't believe it's totally explained by the amount of protein and fat, either, or the satiation after the beef wouldn't last quite so long. I think it could also be due to the robust texture and chewing required with the beef on the assumption the "harder work" carries forward into digestion. I make my omelets with bacon, bacon fat and butter and my yogurt is 3/4 whole milk with 1/4 heavy cream. I could see the beef lasting 6 hours instead of 2, but 24?

Anyhow, if you haven't already tried how you react to beef give that a try.