Arriving at her Kakaako gym in sneakers, a sunny yellow top and fashionably torn jeans and toting an overstuffed bag, fitness consultant Lee-Ann Watanabe was the picture of a healthy, multitasking professional on the go. Which she is, except for the healthy part.

Watanabe, 38, suffers from ulcerative colitis, a form of inflammatory bowel disease, an autoimmune disorder that causes inflammation of the lining of the intestine. Although you’d never guess it from a casual glance, she has been in pain every waking moment for almost four years.

“My immune system is attacking my colon,” Watanabe said of the little-known disease. “I have intense cramps and diarrhea. It’s like stomach flu with waves of pain and running to the bathroom, where I lose a lot of blood.”

But Watanabe, who lives in Makiki with her husband, hasn’t let it stop her from leading a full and active life as an athlete and self-employed personal fitness trainer. She works out regularly and trains her clients at the Art of Fitness, where she rents space. She refuses to give in to the disease.

“My friends tell me I’m the sickest healthiest person they know,” she said, with a little laugh that didn’t banish the sadness in her big brown eyes.

Born and raised on the Windward side of Oahu, Watanabe wasn’t interested in exercise until she met her husband, Lekeli Watanabe, a marketing equipment manager for PepsiCo., when the two of them were students at the University of Hawaii at Manoa.

“I was a couch potato until I met my husband,” she said. “I had to start exercising to keep up with him.”

Watanabe was 27 and had just finished running her first marathon when the symptoms of ulcerative colitis first struck.

According to the Crohns and Colitis Foundation website, as many as 700,000 Americans are believed to have ulcerative colitis. While there is no known cause, there is a genetic link: Watanabe’s grandfather had colitis, she said.

After her diagnosis, Watanabe kept competing in races for a decade. “My strength is cycling,” she said. “For smaller triathlon races here on Oahu, within my age group, I’ve always tried to place 1st, 2nd or 3rd.”

Because she isn’t as strong in running and swimming, her priority has been to beat her previous race times in those events.

Unfortunately, vigorous exercise — especially running — makes her symptoms worse. And her disease, she believes, has progressed. The challenge she faces is to exercise enough to relieve mental and emotional stress without over-taxing her body and triggering more severe symptoms, known as flares.

She hasn’t competed since the 2014 Na Wahine Triathlon. Since then, flares have held her back.

“I need exercise because [otherwise] this colitis would drive me insane,” she said. “Now, instead of racing, it’s more about maintaining my exercise routine as a mental release.”

Watanabe loved to run outdoors and swim in the ocean, but now, because she needs constant access to a bathroom, all her workouts take place indoors. “I usually would have to stop three or four times in a five-hour race,” she said. “Now, I have to run to the bathroom every 10 minutes.”

Her cardio routine includes riding a stationary bike, using the StairMaster and Jacobs Ladder machines and running and walking on a treadmill. “I have to accept I’m only able to do 2-3 miles, max, and with frequent interruptions,” she said.

She supplements the cardio with weightlifting and other strengthening exercises, such as lunges.

“I finally learned a lesson,” Watanabe said. “I spent more than 10 years fighting it. When my body said rest, I wouldn’t.”

Now her routine includes relaxing with a heating pad on her belly to soothe the pain.

Although the symptoms can overlap, colitis should not be confused with irritable bowel syndrome, which is a separate and benign condition, said Watanabe’s doctor, Scott Kuwada, a gastroenterologist at The Queen’s Medical Center. Inflammatory bowel disease is chronic, or ongoing, he said.

Inflammatory bowel disease is also uncommon, Kuwada said, but it’s on the increase in the United States. One reason may be that “we’re too clean,” he explained, citing a “sterile hypothesis” that the lack of exposure to bacteria in richer, developed countries harms immune systems.

“Lee-Ann is a high-performance athlete, and you could, at her level of exercise, stress the body pretty good,” Kuwada acknowledged. However, he added, “Exercise doesn’t negatively affect the immune system, and there’s no evidence that it will make the disease worse. Exercise, overall, is good for your health.”

Rather than try and hide her distress (“which is impossible, anyway”), Watanabe has been frank and open about the disease. Her clients have proved loyal and understanding. “I get jealous that my clients can do things I can’t do, ” she said with a laugh, “but it excites me when they’re able to reach their goals.”

Watanabe’s advice to others: Stay as active and positive as you can.

“Don’t get me wrong…I have my pity parties now and then,” she admitted. “But if you throw in the towel, I think it progresses a disease. If you can, try to keep your life as normal as possible, with some sort of routine.”

And now that she’s learned to fight the disease but not her body, Watanabe’s routine includes rest.