Researchers at Pennsylvania State University are providing some clues to help you achieve permanent weight loss. They are looking at the effects of your food choices and how they affect your ability to lose weight. (The influence of food portion size and energy density on energy intake: implications for weight management. Am J Clin Nutr. 2005 Jul;82(1 Suppl):236S-241S.)

The researchers were interested in finding out what determined how much food people eat at each meal. You might think that people would tend to eat until they were no longer hungry and then stop. Or that they would eat a certain number of calories and their body would sense they had enough and they would stop.

But what they found was somewhat surprising. They found that people tend to eat a meal based on how big it is.

In other words, the participants in the study were used to eating food of a certain size. Whether half a plate, a full plate, a small bowl or a large bowl, they found that people tend to eat the same size meal. It is as though they do not feel it is a full meal unless it is a certain size portion.

The problem of meal size and weight loss is that some foods are much denser than others. For example, fatty meats and rich sauces are much denser than fresh fruits and vegetables.

So when you eat a full plate of fatty meats with sauces and potatoes with gravy you are getting very calorically dense food. It is very easy when eating this kind of food to get excess calories. Even a small number of extra calories will store as fat, and over the years your weight will creep up.

As hard as it may be to believe, if you eat an extra 100 calories per day you will gain nine pounds per year. And it takes very little of this calorically dense food to amount to 100 calories.

The most common solution is to try to cut down on the amount of food at each meal. But as the researchers showed, it is difficult to cut down on meal size. When you eat a smaller meal you do not feel satisfied.

Now, it is true that portions of foods in our modern society have become bloated beyond all reason. A generation ago eight ounces of soda was considered a full serving; now you see people drinking 64 ounce cups.

It used to be that a dinner salad was a portion; now you see restaurants serving a 2000 or 3000 calorie platter of salad heaped with meat, bread, cheese and ladles of salad dressing. This is more food than your body needs for an entire day.

If you are living in this society and are overweight you are suffering from these oversized portions to some degree.

It is not easy to adjust to normal size portions when you have grown used to the large portions. As the research shows, you will not be satisfied until you have eaten your usual volume of food.

If you are used to eating a whole plate of food, you will want to eat a whole plate whether the food is light or heavy. If you are used to eating two bowls of food, you will want to eat two bowls full whether the food is low calorie or high calorie.

But what you can do is change the composition of what you eat. When you eat one of the very dense foods, like fatty meats and rich sauces for instance, you are not generally satisfied with a small amount.

Your body only needs about 600-700 calories for each meal; this is a normal meal size in a lean, healthy adult.

But a small portion of meat and gravy will probably not seem like a meal to you. It is not very likely that you are going to be satisfied with that. You might have to double the portion to feel satisfied.

But a meal with less dense foods, like grains, soups and vegetables, will be a lot of food. There are not too many calories in a bowl of soup and a heap of lettuce, and add some grains and you will have plenty of food. Even with some lean meat you will still get more to eat.

Soup in particular can be very helpful when you are trying to slim down. If it is prepared properly soup can provide a very tasty, nutritious, low-density food. It can help you feel you had a meal and not leave you feeling hungry or deprived.

So when you add in the less calorically dense foods, which are mainly foods like fruits, vegetables, grains and rice, you get a lot more to eat, plain and simple. And it is always easier to stick with your weight loss efforts if you feel you are getting enough to eat.

If you are overweight this is the place to start. Substitute less dense foods for the heavier foods you may be used to. And finally get on the road to permanent weight loss.