We all know that exercise is supposed to be good for us, but only about 20 percent of people move regularly. Those of us who exercise may be drawn into popular workout trends, like CrossFit or hopping on the elliptical for 60 minutes, but in my research, I've learned that overly aggressive high-intensity interval training (HIIT) or chronic cardio may not be the smartest way to look and feel our best.


Overexercising releases two key hormones.

Overexercising releases two key hormones: CRH and cortisol, both related to the stress response. CRH increases the permeability (or leakiness) of the intestinal wall as well as the permeability of the lungs, skin, and blood-brain barrier. Cortisol levels rise with rigorous exercise, such as running, which may cause too much wear and tear and accelerate aging. High cortisol also alters tight junctions between cells such that small harmful substances may pass through the barrier. Additionally, high cortisol reduces gut motility, blocks digestion, blunts blood flow to the gut, and lessens mucus production, an important immune function. For people with dysregulation of the control system for CRH and cortisol, the hypothalamic-pituitary-adrenal axis, you may need to back off your workouts in order to fully heal, as part of a comprehensive functional medicine protocol. Even elite athletes get help from several workarounds, such as by supplementing with probiotics, omega-3s, and vitamin C; however, moderation may be your best bet.


Sometimes weight loss is counterintuitive.

Personally, I love to run. But at age 35, I discovered that my serum cortisol was three times what it should be in the morning. Intense exercise raises cortisol even further, which was causing several downstream problems for me: weight gain, short telomeres, blood sugar problems, knee pain, leaky gut, fatigue, and I was stuck in a pattern of revving my body too much with my workouts. When I backed down on running mileage each week and added more adaptive exercise like yoga, Pilates, gyrotonics, and barre class, my HPA healed and I got a better response to exercise. I lost weight. My joints were happier. My telomeres were better.


How much exercise is too much?

On the flip side, inactivity and sitting too much are not good for you either. In particular, sitting too much increases your risk of diabetes and heart disease, plus it makes your hip flexors tight, which can contribute to low back pain and stiffness. Just like Icarus's mandate not to fly too high or too low, there's a middle ground that provides the greatest longevity benefits. When you don't exercise enough, it can harm your immune system, reduce your stress resilience, and dysregulate your circadian rhythm. When you exercise too much—too long, too intensely, too frequently, and without sufficient recovery—you may cause problems to your stress-response system, leading to immune problems, injury, and a leaky gut.

In summary, like many things when it comes to health, exercise has a U-shaped association, meaning that moderate amounts are optimal but low or high levels can be harmful. The general recommendation I subscribe to is to exercise 20 to 30 minutes per day four times per week.

What kind of exercise is ideal? I call it targeted exercise—burst training and adaptive workouts, like Pilates, barre, or yoga. These will stabilize cortisol levels, help with weight loss, and keep your muscles toned.


  1. Move less but more Often
  2. Get enough sleep
  3. Burst Training

Written by Dr Sara Gottfried MD for MBG.


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