If I got a dime for every time I heard the above, I would be a millionaire by now. I feel like a broken record. I can't tell you how many times I have had to convince women that they will see quicker results using heavier weights. Scientific studies are proving that heavier weights with lower repetitions is what you need for the lean and sculpted look. We have been trained to believe that lighter weights are for muscle tone and heavy weights are for the beefy body building look.
New York times came out with a great article that links to a few studies proving a higher percentage of fat loss when females participated in using heavier weights. Using 70-80% of your 1 rep max keeping the reps under 8 proved to be more effective than lighter weights at 40-50% with higher reps. Using heavier weights will increase your strength, your caloric burn, thus increasing your overall metabolism. You will literally be turning your body in to a fat burning machine with the lean muscle you are putting on your body, while the fat will decrease around it, for the toned look everyone wants. If you want the bulky look, you need to be eating lots of calories and performing medium weights. with high repetitions so you can have the bloated muscle that will not be as strong.
Here is the article that came out today from the New York Times.
This is exactly why I wrote this article "The Need to Train Like a Man, Especially If you are a Woman" 5 years ago.