Jane,
I think we've lost sight of your original question (sorry!). Let's recap: You are only consuming, on average, close to 1000 cals/day. I suggested you consume more cals. in order to keep your metabolism fired up. You replied that you can't eat any more food, so I then suggested choosing more calorically dense foods and explained that since fat is the richest source of cals in our diet, they would be an easy way to add cals.
From your previous message, it sounds as if you are incorporating some good fats into your diet already. I'm really not sure why you're having difficulty meeting your calorie needs, so here's a tool that may help you evaluate your diet more closely. Below, I've listed each food group and how much you should consume from each one on a daily basis. Try keeping a food record for a few typical days and compare it to the recommended amounts in this chart. That will give you a good idea of what foods you may need more or less of. It's possible that you are filling up on low-calorie bulky foods and, as a result, don't have enough room left for some of the more calorically- dense foods. Shoot for at least the minimums from each group.
Keep in mind that the serving sizes listed are not meant to restrict you, but simply to help you count/evaluate your diet.
Food Group: Grains
Servings Per Day: 5-8
Serving Sizes: 1 slice whole wheat bread, 1 cup dry cereal, 1/2 whole wheat bagel, 1/2 English muffin, small dinner roll or muffin, 1/2 cup cooked cereal, 1/2 cup brown rice, 3 cups popcorn, 1/2 cup whole wheat pasta, 6 soda crackers, 3 graham cracker squares, 1 tortilla
Food Group: Milk
Servings Per Day: 3
Serving Sizes: 1 cup skim or 1% milk, 1 cup low-fat yogurt, 2 slices cheese, 1/3 cup shredded cheese
Food Group: Fruit
Servings Per Day: 3-4
Serving Sizes: 1/2 cup chopped fresh, 1/2 cup canned (light), small piece whole fresh, 1/2 cup berries, 1/2 grapefruit, 16 grapes, 1/4 cup dried, 1/2 cup 100% juice (4 oz.)
Food Group: Vegetables
Servings Per Day: 4-6
Serving Sizes: 1/2 cup cooked, 1/2 cup raw chopped, 6 baby carrots, 1 cup raw leafy, 1/2 cup juice (4 oz.)
Food Group: Meat & Beans
Servings Per Day: 5-6 oz.
Serving Sizes: 1 oz. lean meat, fish, or poultry, 1 oz. cheese, 1/4 cup low-fat cottage cheese, 1/4 cup canned tuna or salmon, 1 egg or 1/4 cup egg substitute, 1/4 cup beans, 1/2 oz. nuts or seeds, 1 Tbsp peanut butter
Note: The serving sizes listed in the Meat & Beans group are all equivalent to 1 oz. meat/fish/poultry.
Let me know how your diet fares and we can take it from there.