What I Learned from Watching Sumo as an Obesity Medicine Doctor

I just got back from Japan, where I had the rare privilege of attending day 14 of the Grand Sumo September Tournament. Sumo is super popular right now—both in Japan and abroad. There are two active Yokozunas (sumo grand champion), both competing at a high level. Interest is intense and getting a ticket was no easy feat.

At home, I’m an obesity medicine doctor. I help people who struggle to lose weight. So the irony wasn’t lost on me that here I was, attending a sport that seems to embody the exact opposite.

But the deeper I looked, the more I realized: sumo isn’t just about size. It’s a fascinating window into human metabolism, body composition, and how the body fiercely defends its physiology against long-term changes.

💪 Sumo Bodies Are Built, Not Just Gained

In sumo, mass equals advantage. The heavier and more stable you are, the harder it is for an opponent to push you out of the ring. Wrestlers train to make themselves immovable.

Their diet centers on chankonabe — a giant stew loaded with meat, fish, tofu, and vegetables. A single meal can reach 5,000–7,000 calories, and wrestlers often eat twice a day, totaling close to 10,000 calories daily. Meals are frequently followed by large amounts of beer, which boosts appetite and adds more easy calories, and then a long nap to slow digestion and promote weight gain.

Interestingly, many wrestlers admit they actually dislike eating that much. They describe it as a daily chore — forcing themselves to eat long after they’re full. Just as many people struggle to stop eating when full, these athletes struggle to keep eating past comfort to maintain their weight.

⚖️ The Weight Struggle — Losing It When You Need It Most

Not all wrestlers can easily bulk up. Just like some people struggle to lose weight, others struggle to gain it, no matter how much they eat. Metabolism, appetite signaling, and genetics all play a role.

And when injury interrupts training, that delicate balance collapses fast. Without daily exertion, wrestlers can lose weight rapidly — and not the kind they want to lose.

A good example is former Ōzeki Asanoyama, who tore his ACL. During recovery, he was unable to train and reported losing significant weight. Regaining that weight — especially functional muscle mass — proved far more difficult than expected. He has struggled to climb back into the top ranks.

It’s a striking reminder that the body resists change in both directions — fighting weight loss and weight gain depending on context.

🧠 What MRI Scans Reveal

MRI studies of sumo wrestlers show something remarkable: most of their fat is subcutaneous, stored under the skin, rather than visceral, which wraps around internal organs.

That distinction matters. Visceral fat is the kind that drives insulin resistance, diabetes, and heart disease. Thanks to their intense training and high muscle mass, many active wrestlers maintain surprisingly healthy metabolic profiles — normal glucose tolerance, favorable cholesterol levels, and relatively low inflammation.

One factor may be the hormone adiponectin, produced by fat cells. Active sumo wrestlers tend to have higher adiponectin levels than expected for their size. This hormone improves insulin sensitivity and reduces inflammation, suggesting their fat — while abundant — behaves in a more metabolically protective way.

Matsuzawa Y, Shimomura I, Nakamura T, Keno Y, Tokunaga K. Pathophysiology and pathogenesis of visceral fat obesity. Diabetes Res Clin Pract

❤️ The Hidden Health Costs

Despite those adaptations, sumo wrestling takes an undeniable toll. Years of extreme weight cycling and physical strain contribute to joint damage, sleep apnea, hypertension, and cardiac stress.

Former Yokozuna Terunofuji is a powerful example. He never officially retired, but his career was nearly ended by severe knee injuries, diabetes, and infections that kept him out of multiple tournaments for years. His success despite his health challenges highlights how precarious the balance between performance and health can be.

After retirement, many wrestlers lose weight quickly, like former Ozeki Takakeisho. However, the reduced training after retirement brings with it the many problems of sedentary life, including the buildup of visceral fat.

🌏 Lessons from the Dohyo

Watching sumo reminded me that weight regulation isn’t simple math. The same physiology that frustrates patients trying to lose weight also challenges athletes trying to gain it. The body resists extremes, constantly pushing toward its internal “set point.”

Sumo isn’t a model of healthy living — but it’s a living laboratory of human metabolism. It shows how behavior, hormones, genetics, and training all interact to determine not just how much fat we carry, but where we carry it, and how our bodies adapt to defend equilibrium.

In the end, the dohyo (sumo ring) isn’t just a battleground of strength. It’s a mirror of biology — a reminder that every body, no matter its size, is always fighting to stay balanced.