What if you or your child had a chronic illness that seriously limited or threatened life and modern medicine had no effective or acceptable treatments for it? An ailment like severe food allergies, rheumatoid arthritis, attention deficit hyperactivity disorder or intractable epilepsy?

Would you be willing or desperate or brave enough to step outside the realm of established medicine and seek help from an unconventional therapist, even someone with no medical or scientific training? What if you heard about others in a similar situation who had tried a purported remedy that appeared to work, or the method seemed to make biological sense?

In her new book, “The Other Side of Impossible,” Susannah Meadows, a Brooklyn-based former senior writer for Newsweek, has compiled compelling stories about people who faced and ultimately surmounted daunting medical challenges. The book focuses on several families, including her own, who felt they had no choice but to wade into the world of unproven therapies.

The families’ ventures into a realm that some would call quackery were typically inspired by love, desperation and hope and were fueled by irrepressible grit and determination to find solutions to debilitating health problems that defied the best that conventional medicine could offer.

Although I’ve always been a person who, when told something couldn’t be done, forged ahead to prove that it could, their stories left me in awe of their persistence against formidable odds. As one mother replied when asked how she persevered through a five-year search for a way to control her daughter’s relentless seizures: “You can’t not try. She’s not better yet.”

In her analysis of the disparate yet related cases, Ms. Meadows highlights at least three important influences on well-being that have yet to receive their just due in understanding what might cause or aggravate certain intractable medical disorders.

One is a characteristic called “leaky gut,” essentially tiny holes in the intestinal walls that allow proteins to reach the bloodstream where they can trigger a vicious immune attack on healthy tissues. Another is an imbalance of microbes in the gut and how communication between the brain and the gut can adversely affect behavior and emotional stability. A third is the still underappreciated interaction of mind and body, especially the effect that anxiety and fear can have on the body’s response to otherwise harmless substances.

There is perhaps a fourth factor, Ms. Meadows said in an interview, that seems to foster perseverance in seeking recovery from an incurable condition: “Early life experiences in coping with adversity that may inoculate people against hopelessness and prompt them to believe that if they would just keep trying they would succeed.” Or as the son of one patient profiled in the book put it: “Courage is knowing you’re licked and doing it anyway.”

That patient was Dr. Terry Wahls, who overcame a progressive form of multiple sclerosis for which medicine had little to offer. Once confined to a reclining wheelchair despite trying a range of conventional treatments, Dr. Wahls researched, then adopted, a diet that eliminated grains, dairy and sugar but included 12 cups a day of berries and vegetables supplemented with grass-fed beef, organ meats and oily fish. She combined this with neuromuscular electrical stimulation and exercise.

Within a year, Dr. Wahls had ditched her motorized assists and started riding a bicycle. Eight years later, she shows no signs of her disease. Last summer, the National Multiple Sclerosis Society, which has been tracking research into diet and inflammation, committed more than $1 million to study the effect of her diet on M.S.-related fatigue.

Ms. Meadows summarized the overriding lesson derived from the people in her book: “You have a choice to keep going when others say you can’t. They had no reason to think they could succeed, but they just wouldn’t give up.”

Ms. Meadows said this was not something she understood when her son Shepherd was given a diagnosis at age 3 of polyarticular juvenile arthritis, a crippling condition affecting multiple joints. She and her husband were told he was unlikely to outgrow it. Facing a choice of doing nothing or treating him with a potent drug that “made him feel bad and did little for his arthritis,” she learned about a child with the same condition who was helped by avoiding gluten and dairy products and taking fish oil, probiotics and a Chinese herb.

“With nothing to lose – if it helped one child, maybe it will help ours,” Ms. Meadows said they had to try it. “In terms of hope, an example of one is very important.” And as she reported four years ago in an article in The New York Times Magazine, Shepherd got better.

Eventually, with the help of a self-styled healer named Amy Thieringer, who emphasizes the need to calm fear and anxiety when trying to counter food sensitivities, Shepherd was gradually reintroduced to gluten and dairy and “now eats everything without any problems, no more painful, inflamed joints,” his mother said.

Although Amanda Hanson was warned by her son Hayden’s allergy specialist that attempting Ms. Thieringer’s treatment for the boy, who had life-threatening allergies to 28 different foods, would be playing Russian roulette with his life, she felt she had no choice but to try.

Inspired by the testimony of other mothers facing a similar problem, and knowing that doctors had no solution for Hayden’s allergies, Ms. Hanson bought into the Thieringer program known as allergy release technique. Borrowing ideas from cognitive behavioral therapy, Ms. Thieringer first worked to ratchet down Hayden’s fear of certain foods before introducing them in tiny increments until he could consume them in normal amounts without a reaction. Now 16, Hayden has had no bad reaction to any food since completing the program six years ago.

As a careful journalist, Ms. Meadows make no claims for cures. Her book is not prescriptive, though it describes the science that might explain the unlikely recoveries she has written about. “I’m a journalist reporting on the fact that there is a whole community of people who are looking for, and in some cases finding, answers to health problems on their own.”

There is another important message in this book worth mentioning, and that is the enormous obstacles to producing ironclad evidence for the kinds of approaches that brought relief to the people Ms. Meadows interviewed. The treatments often involved a combination of interventions and few if any profit-making products. Thus, no company is likely to pay for the needed studies, which would also probably be too costly and complicated for government agencies to underwrite.