This is a question I am frequently asked. Thanks to the cardio-marathon mindset of the 80s (which we all lived through), most women are convinced they need to exercise for over an hour, seven days a week, to "get fit." Believe it or not, that couldn't be farther from the truth.
First and foremost, your nutrition is more important than your exercise habits when it comes to fat loss and longevity. If you run for an hour each day but still have a Danish for breakfast every morning and chips every night, you could be shortening your life span and increasing your waist size. To set the foundation for fat loss and fitness, stick with whole, natural foods, such as fruits, vegetables, nuts, fish, and protein.
For your exercise sessions, focus on quality and intensity, not quantity. By exercising three days per week for only 45 minutes per session (or less!), you can strengthen your entire body. Try multi-muscle resistance exercises for strength, and burn fat with short-burst interval training. Follow that up with stretches for tight muscle groups only, and you'll be finished your training session before you know it.
Spend the remaining four days of the week staying active and keeping your butt off the couch. Keep your body and mind busy with activities you love, such as walking with your dog, doing yoga, playing sports, jogging or running errands by bike or on foot.