For starters, they can keep you slim, happy, and disease free

Full disclosure: I'm a vehemently pro muscle. It keeps your metabolism revved, takes up less space than fat, protects your joints, and allows you to lift heavy objects without the help of a guy.

Full disclosure number two: I almost never weight train. Like most women, I typically choose cardio (my go-to workout is Bikram yoga) over strength training, not because I'm afraid of bulking up, but I'm a sweat addict and hate figuring out the correct weights, reps, muscle groups to target, and so on. But I should. I really really should, for the reasons listed above, as well as the surprising muscle-related facts that follow.

Muscle is Like Scaffolding for Your Entire Body


Without muscle, your bones, joints, and ligaments are considerably more vulnerable to age–related decline and injury, according to Dr. Kenneth Hansraj, an orthopedic and spinal surgeon based in New York City. Building core strength in particular protects your spine, which is key to a healthy musculoskeletal system. In fact, a healthy, straight spine is pretty much the definition of youth and anti-aging, Dr. Hansraj says.

Muscle Equals Fewer Marshmallows


Did I lose you at marshmallows? Stay with me. Muscle is much denser than fat. So if, for example, one pound of muscle is about the size of an apple, one pound of fat is the equivalent size-wise of a pound of marshmallows, according to Dr. Hansraj.

Still confused? Imagine how many marshmallows you would have to pile on a food scale to have it progress to one pound. Probably a lot. at least one full-sized bag. Now imagine the space five of those bags would take up (five pounds of fat) as opposed the amount of space five apples would take up (five pounds of muscle). It's a lot less space-and a lot less marshmallows. For an even easier and entirely fruit-focused analogy, a pound of fat is about the size of a grapefruit, and a pound of muscle is about the size of a tangerine.

Muscle Lets You Eat an Oreo Guilt-Free


Muscle is metabolically active tissue, which means it demands more fuel for support. While protein is the primary source of fuel (hence the body builder obsession with the stuff), this also means that more of the total calories you eat are burned as fuel rather than stored as fat. How many more? About 50 for every pound of muscle you add, according to Hansraj. That's about the calories in a single Oreo cookie, two Hershey kisses, or half a glass of Merlot. It's not a ton, but it does mean that if you watch your overall calorie intake, you can have little treats here and there totally and completely guilt-free.

Muscle Keeps You Sane


While the jury is still out on whether it provides a bigger mood boost than cardio, if you weight train at a high enough intensity, you can experience an effect similar to the runner's high, when your body releases natural pain-relieving opioids, says Richard Hammer, associate clinical professor of pathology and anatomical sciences at the University of Missouri School of Medicine. And according to Dr. Hansraj, weight-training leads to an improved androgenic hormone profile (in essence, a better balance between male and female hormones, which leads to a more stable mood).

Muscle Lowers Your Risk of Two Major Health Threats


According to a study published in the Journal of Strength and Conditioning Research, people who lift weights are 37 percent less likely to have metabolic syndrome-a cluster of risk factors linked to heart disease (the No. 1 killer of women in the U.S.) and diabetes (type 2 diabetes currently affects 26 million Americans and is the fastest growing disease in the in the country, according to the CDC).

How? Muscle helps your body process blood glucose more efficiently, according to Dr. Hammer, which helps lower risk of developing type 2 diabetes. It's also associated with a smaller waist circumference (less marshmallows!), which is an indicator of lower LDL (bad) cholesterol, which in turn equals a healthier heart.

Light Weights Get the Job Done


Not comfortable slinging super heavy weights? You can still reap the many benefits of building muscle. A recent study published in The Journal of Applied Physiology found that participants still experienced strength gains when lifting lighter weights as long as they worked their muscles to fatigue.

This is good news, since the 20-plus pounders tend to reside in the serious weight training part of the gym, which can be intimidating, eye roll inducing, or just too grunt-filled to be a fun place for ladies who lift.