Research

source:
low-fat diet: whay fat-free in't trouble-free
http://www.webmd.com/diet/low-fat-diet

low-fat food, good or bad?

http://blog.foodnetwork.com/healthyeats/2011/03/31/low-fat-foods-good-or-bad/

my topic: Low-fat food is always a healthy choice?

what I hope to learn from this source:
I want to know the meaning of 'low-fat' and the reason why we need fat.

notes:

There are "fat-free," "low-fat," "light," and "reduced-fat" products available.
Here's what those terms mean:

• "Fat-free" foods must have less than 0.5 gram of fat per serving.
• "Low-fat" foods must have 3 grams of fat or less per serving.
• "Reduced-fat" foods must have at least 25% less fat than regular versions of those foods.
• "Light" foods must have either 1/3 fewer calories or 50% less fat.

Why do we need fat?
Fat isn’t bad — we actually need it to survive. Fat helps protect and cushion our critical organs, helps keeps nerves functions, keeps us warm and is a valuable energy source. It also helps transport vitamins A, D, E and K through our body and helps our immune system properly function.
About 20 to 30 years ago, the recommendation to go low-fat took America by storm. The creation and sale of low-fat products became the hottest fad. To this day, folks still can’t shake the low-fat state of mind.

Keeping the amount of fat in your diet down to about 30% is still important. But what's also important is that you're eating the healthier fats, sometimes called "good” fats.

"Good" fats include both monounsaturated and polyunsaturated fats.

• Monounsaturated fats (like canola and olive oils) are those that have been found to lower the "bad cholesterol" in the bloodstream and raise the amount of HDL "good cholesterol." HDL appears to actually clear the "bad" types of cholesterol from the blood.
• Polyunsaturated fats found in fatty fish such as tuna and salmon help lower cholesterol.

Those don't include saturated fats, which are found in animal products (beef, pork, butter, and other full-fat dairy products), or artificial  trans fats, found in hydrogenated and partially hydrogenated oils.

Choose lean cuts of meat and fish, and low-fat dairy products, and eliminate trans fats from your diet as much as possible.

final thoughts:
'Low-fat' foods have a little of fat, but these make us put other ingredients that are like sweeteners or eat much. Also, we have to eat the fats. If we want to eat less fat, our nerves functions and energy sources suffer greatly.