There’s nothing better than a really good spin class first thing in the morning—it’s a great sweat and an incredible endorphin boost.

But sometimes it seems like cardio has overtaken every other fitness activity. More and more of my patients are turning into serious aerobic exercise junkies, and I’ve begun to see a pattern of women in their 20s, 30s, and 40s who are spinning, dancing, and running three, four, even five times per week. They all tell me that they feel like they should be in incredible shape—but they’re not.

Despite being so active, these women commonly describe being tired and anxious, having trouble sleeping, and finding it difficult to shed “the last 10 pounds.”

Despite being so active, these women commonly describe being tired and anxious, having trouble sleeping, and finding it difficult to shed “the last 10 pounds.” Many also have hormone imbalances such as PMS, irregular periods, Polycystic Ovarian Syndrome (PCOS), and even infertility.

What’s behind this trend of cardio junkies sweating to exhaustion?

Here are the warning signs that you might be ODing on cardio—and the 3 things all balanced fitness plans need.

First warning sign: cortisol spikes

Take the case of a 33-year-old patient of mine I’ll call Liz.

A successful tech VP, Liz was gaining weight despite spinning five times a week. She was exhausted at the end of the day but when she lay down in bed, her heart would race and she couldn’t fall asleep for another hour or two. Her periods were bouncing around every one to two months—sometimes not coming for over 60 days. She also had sporadic acne she couldn’t figure out but blamed on her hormones.

We tested her cortisol levels throughout the day and showed her that they were high after her evening spin class and still elevated at bedtime. Cortisol, the major stress hormone, should be high in the morning and low by afternoon, staying down through bedtime. When cortisol is high, your blood sugar and blood pressure go up, you store more calories as fat—especially around your abdomen—and your immune system is suppressed. You may also have a hard time sleeping and can experience anxiety or that “wired” feeling at night.

If it’s chronically high, it can increase hormones like testosterone and subsequently estrogen, while simultaneously decreasing hormones like progesterone, causing disruptions in the menstrual cycle and acne.

Second warning sign: high blood sugar

In the morning, Liz was having oatmeal or cereal for breakfast, loading up on carbs when her cortisol was also naturally high. After spin class, she was typically starving because she’d gone there straight after work.

Sometimes she was showering at spinning then heading out for dinner—where she’d usually enjoy a glass of wine or two. Other times she’d stay in at night and have a fruit and greens smoothie—sounds healthy, but without any fat or protein, it was a recipe for weight gain and hormone imbalances.

Unwittingly, she was setting herself up for another common health issue cardio junkies suffer from: high blood sugar. We tested her hemoglobin A1C, which was 5.7. Liz was shocked to find that, despite all the cardio, she was borderline for Metabolic Syndrome, an imbalance in the body’s ability to handle blood sugar.

Third warning sign: menstrual irregularity

Hoping to get pregnant in the next year, Liz knew she had to figure out some of these issues in her body out first. At her day 21 (AKA her luteal phase in the ovulation cycle), her progesterone level was only 0.2, meaning she wasn’t ovulating on time, and her balance of estrogen to progesterone was off for a healthy cycle, leading to her irregular periods and likely her acne.

Much to Liz’s disbelief, I asked her to only spin one day per week, and to replace the other four sessions with two yoga classes, and twice-weekly 20-minute weight training sessions.

Within two months, she had lost her belly fat, her acne went away, she was sleeping again, and her periods hit a normal 31-day stride. Also, her Hemoglobin A1C went down to 5.4, in the normal range.

So, what’s the deal with cardio overload?

The extra time Liz put in on a stationery bike did nothing to build muscle (which increases resting metabolism) or calm her nervous system and relieve stress. She’d been overdoing it—spiking cortisol and depleting her body’s energy, hydration, and mineral balance through so much sweat.

Research shows that cardio is not usually that helpful for weight loss, either. The body becomes “used to” the calorie deficit from long aerobic sessions and stores energy as fat to compensate. In addition, studies show most people eat more after exercise, and overestimate how many calories they burned while working out.

But the answer isn’t starving yourself or hyper-focusing on calories—it’s looking at the kinds of exercise you’re doing and the kinds of foods you’re fueling with. Here’s your three step plan.

1. ReplaceSwap two spin or long-haul cardio classes with weight training sessions. Lifting weights and building muscle increases your basal metabolic rate, which accounts for 60–75 percent of calories burned daily (another 10 percent goes to digesting food while, for, most people, only 10–20 percent goes to physical activity of any kind). Resistance training has been shown to boost basal metabolism and fat burning for 24-plus hours—something cardio doesn’t do.

2. RestoreDoing restorative exercise like yoga isn’t “useless” for weight loss; it both strengthens and lengthens the muscles and connective tissue, while simultaneously reducing stress and, therefore, cortisol (one of the major reasons for weight gain and hormone imbalance).

3. EatDon’t starve, just up your protein, fat, and fiber intake. In particular, axe carbs/sugar/alcohol after a workout. You’re probably undoing that workout in five minutes with a juice or a night out at the bar. The way the body metabolizes a cup of broccoli isn’t the same as how it metabolizes a cup of soda. The veggie, for example, is metabolized slowly—which means that you’re avoiding the insulin spike that leads to sugar being stored as fat.

So it’s not about counting calories, it’s about eating the foods that give you a slow burn, instead of a sugar spike.

Robin Berzin, MD, is the founder and CEO of Parsley Health, an innovative primary care practice with offices in New York, Los Angeles and San Francisco. Dr. Berzin attended medical school at Columbia University. She is a certified yoga instructor and a meditation teacher.

Looking for more ways to keep your cortisol levels in check? Studies show this stress-fighting adaptogen and a yoga nidra practice can both help balance out the hormone.