The Dark Side of Getting Too Lean

Everywhere you look these days, there’s a new social media post glorifying razor-sharp abs or detailing the “secrets” to a leaner physique. It’s no wonder so many of us automatically equate less body fat with better health. But as someone who works with patients navigating the complexities of weight and health, I’ve learned that the human body rarely rewards extremes.

In fact, pushing body fat too low can derail the systems that keep you alive and thriving. If you’re chasing an ultra-lean physique, here’s what you need to know.

Hormones go haywire

Body fat isn’t just sitting there filling out your jeans. It’s actively supporting your health, especially your hormones. Women with extremely low body fat often stop ovulating and lose their menstrual cycles altogether—a condition called hypothalamic amenorrhea. It’s the body’s way of saying, “I don’t have enough resources to support a pregnancy.” For men, it’s a different story, but no less disruptive: testosterone levels can plummet, leading to muscle loss, low libido, and chronic fatigue.

Bones pay the price

Fat and bone health are closely connected. Without enough fat, your bones don’t get the support they need to maintain density. The result? Increased risk of fractures and long-term conditions like osteoporosis. I’ve seen this most often in patients who’ve spent years overtraining or under-eating in pursuit of a leaner body.

This might surprise you, but low body fat can weaken your immune system. Fat helps regulate immune function, so when levels drop too low, you’re more vulnerable to infections and slower to recover from illness. It’s one of the reasons I see so many athletes struggling with frequent colds or lingering injuries.

Reclaiming your health

For most people, a healthy body fat range lands somewhere between 18% and 25% for women and 10% and 20% for men. These aren’t rigid rules—they’re guideposts. What really matters is how your body feels and functions. Do you have the energy to get through your day? Are you recovering well from workouts? Is your immune system keeping you healthy?

If the answer is no, take these steps to help replenish your fat stores in a healthy way.

Lean into nutrition

Forget restrictive diets. Instead, focus on whole, nutrient-dense foods that provide healthy fats, fiber, and protein. Avocados, nuts, seeds, olive oil, legumes, and whole grains are great starting points. Food should support your health—not feel like a punishment.

Train smarter, not harder

The most common mistake I see are patients who rely on intense cardio to burn calories without realizing the toll it takes on their bodies. Swap some of that cardio for strength training, yoga, or even a brisk walk. Exercise should build you up, not wear you down.

Ask for help

It’s OK to not have all the answers. A therapist, dietitian, or physician can help you sort through the noise and develop a plan that works for your life. This isn’t just about body fat; it’s about the bigger picture of your own well-being.

Find balance

One of the hardest lessons I’ve learned as a doctor is how deeply tied health is to our mindset. I’ve met patients who are perfectly “healthy” on paper—good lab results, low body fat—yet they’re exhausted, irritable, and unhappy. They’ve bought into the idea that physical perfection equals health, and it’s failing them.

If there’s one thing I could say to them—and to you—it’s this: Health is about resilience. It’s about how well your body can adapt, recover, and keep going. It’s about strength, energy, and joy. When you stop chasing extremes, you start making room for balance, which is the real key to long-term health and happiness, no matter what social media tells you.

• A healthy body is more than what’s on the scale.
• What experts do when it’s time to exercise.
• Learn more about Northwell’s Rehabilitation Network.