For years, we’ve all been told that “cardio” is the golden key to weight loss. Cardio workouts include running, brisk walking, spinning, and aerobics—any vigorous exercise in which your heart rate stays up for extended periods without a break.

But is cardio good for weight loss? For most of us, as we age, the answer is a great big it depends. Too much cardio can affect your health, metabolism, and your weight because of the way it induces oxidative stress.

Oxidative stress is a normal response to exercise in which your body produces free radicals: molecules that are missing an electron. Each free radical seeks to replace its missing electron by pulling it from another molecule. That molecule now has its own unpaired electron, so now it’s a free radical, and therefore it, too, seeks to pull an electron from another molecule …and on it goes. Pretty soon, you get a whole bunch of free radicals—and a lot of dysfunctional molecules that can’t operate properly because they’re each missing an electron.

A free radical’s favorite pastime process is wreaking havoc in your cells, which is why oxidative stress causes your body to age. Over time, the damage created by oxidative stress increases your risk of heart disease, cancer, type 2 diabetes, and autoimmune diseases.

Free radicals are not inherently bad. Ironically, the more free radicals you have, the more your body is triggered to produce and use antioxidants—biochemicals that combat oxidative stress to make your cells healthy and strong. That’s why moderate exercise is actually considered an antioxidant: when you exercise in the right amounts, the stress you cause is the kind that ultimately makes you stronger.

But if you undergo more oxidative stress than your body can handle—more oxidative stress than your antioxidants can combat—then free radicals can overwhelm your cells and you have problems. Big problems, like chronic disease, premature aging, and weight gain.

Now, that being said, some people are blessed to be athletes. You’ve seen them—finishing their marathon looking like Greek gods. If you are one of those people, you can and probably should do more intense exercise than most.

How do YOU find the amount of cardio that’s best for YOUR body? The Metabolism Plan will let you know EXACTLY how much cardio you can do to boost your metabolism, keep your hormones and endocrine system happy and get you to your optimal weight.


Your friend in health,

Lyn-Genet Recitas


Nutritionist and NYTimes best-selling author of The Plan, The Plan Cookbook and The Metabolism Plan.

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