Which fats are good for us? Which ones aren't? What foods contain which fats? How much of each should we consume?

It's enough to make you chuck your healthy intentions and dive into a big bowl of Chunky Monkey.

Most of us know we don't want the jiggly stuff gathering around our waistline, but that's the extent of many people's knowledge about this essential food that's often villainized.

“The messages about fat have been very conflicting over the years. It's so much more than just good fat, bad fat,” says Christine Zoumas, senior research dietitian and clinical instructor at the University of California San Diego School of Medicine. “People need to understand that total fat is not evil. Fats can be a normal and healthy part of your diet. But there are fats you need to watch out for and moderate.”

Along with protein and carbohydrates, everyone needs some fat in the diet. Fats are a key source of energy, and they aid in the synthesis of hormones and the absorption of some vitamins.

“People shouldn't be fat phobic. We need to have some fat in order to absorb fat-soluble vitamins (A, D, E and K),” says Joan Rupp, registered dietitian and instructor at San Diego State University's Department of Exercise and Nutrition Science. “If you don't eat any fat, you'll just have a healthy toilet.”

Fat provides essential fatty acids, which are not made by the body and must be obtained from food. They are important for controlling inflammation, blood clotting and brain development. Fat also helps maintain healthy hair and skin.

Lately, many folks have been focused on trans fat, the hydrogenated, artery-clogging stuff that's used in lots of processed foods and bakery goods, and by many fast-food restaurants.

They have been so concerned about tran fat's ability to increase low-density lipoprotein (LDL), or “bad” cholesterol, and decrease high-density lipoprotein (HDL), or “good” cholesterol, that Gov. Arnold Schwarzenegger signed legislation banning it in California restaurants starting in 2010 and from all baked goods by 2011.

But just because food will soon be trans-fat-free, doesn't mean it will be healthy, say nutrition experts.

“You can't replace trans-fatty acids with saturated fats like palm oil and call it a healthy product. But, that's what a lot of food manufacturers are doing,” Zoumas says.

Tropical oils such as palm, palm kernel and coconut oils, which are frequently used in place of the maligned trans fats, are all saturated fats which also raise blood cholesterol levels and increase the risk of coronary heart disease. A healthier option is to substitute unsaturated fats and oils for trans fat.

“That's why it's so important for people to really pay attention to food labels,” Zoumas says, noting that it's important to look not only for foods that are trans-fat-free, but also for those that are low in saturated fat and don't contain tropical oils.

However, no matter how virtuous you are about choosing the right fat, all fat – trans, saturated and unsaturated – has calories. Lots of calories. In fact, fat of any kind provides nine calories per gram, more than twice the number provided by carbohydrates or protein. Consuming too many calories increases the chance of obesity, another risk factor for heart disease and some types of cancer.

“Gram for gram, you get more calories with fats. That's why when you eat a high-fat meal, it's very satisfying and you stay (satiated) longer,” Rupp says. “And, it tastes really good. But, you have to use some moderation.”