When it worked, when those fat cats went into remission and no longer needed insulin, Einertson started to study whether his cat-friendly diet could help humans in bigger ways—like curing cancer, even.

Then he got a brain tumor.

Sure, Dr. Travis Einertson had prescribed his high-protein, low-carb "Catkins Diet" to thousands of Rochester’s pets.

He just never thought he’d need it to maybe save his own life.

In 2001, the Rochester veterinarian and co-owner of Heritage Pet Hospital was seeing a rising number of felines coming through his door with Type 2 diabetes.

"I was trained conventionally," he says during a midday coffee break, stoically gripping a towering travel mug of joe laced with heavy cream that is his only sustenance during one of his many ketogenic fasts.

"In veterinary school we learned that rates of diabetes were shooting up in cats, and we learned the conventional veterinary wisdom, which was to feed them a low-fat, high-fiber, so-called prescription diet dry pet food with big doses of insulin," says Einertson, who grew up in Loveland, Colo. as the son of a veterinarian. (His dad, Norm, worked with large and small animals with the USDA.)

Once Einertson started to apply these rules, however, he started to question whether the conventional wisdom was effective. "Sometimes the cat would do pretty well. You could get them to live for several years. More often you couldn’t keep their weight stable, they’d drink a ton, pee a ton, eventually develop neuropathy in their legs, and stop being able to walk."

Then Einertson read a study in a veterinary journal that suggested a low-carbohydrate, high-protein pet diet was effective in reversing symptoms for cats with diabetes. He told one of his families about it.

"They said they wanted to do it," he remembers, "and my heart kind of sank because it was completely contrary to my training. I didn’t want to be wrong and be responsible for their pet dying." Armed with his instructions, the daring pet owners ditched their expensive dry food and began to feed their cat a menu of exclusively canned fare instead.

"Within three months, the cat’s weight stabilized and his blood and urine tests all got better," says Einertson. "He never got sugar in his urine again. The next two cats I treated the same way, and [had] the same results."

To his delight, Einertson eventually realized the diet could do more than just treat diabetes. It helped the fat cats lose weight as well, causing animals to go from Garfield to sleek, vibrant predators. "My own cat was obese," he says wryly, "because I am a hypocrite. I was feeding her expensive, low-fat, high-carb [stuff]. She had gone from overweight to obese on this prescription diet for overweight cats and she was hungry all the time."

She would wake him up in the middle of the night to demand more food, he says. "When I put her on wet food, the fat melted off her body. She wasn’t waking us up at night. She could jump on high shelves again."

That was 2001.

Fast forward a year, and Einertson decided to test that diet on himself. At five-foot-nine and a former high school wrestler, by 2002 he weighed 187 pounds, up from 157 just a few years earlier. "I had torn through the seat of my third pair of pants by doing all the things you’re supposed to do," he says. "I was eating a low-fat, high-fiber diet, going to the gym regularly, and working out harder and harder. But I was hungry all the time and still gaining weight."

Like a lot of people battling the bulge, Einertson had also taken to eating less sugar, flour and starch in the course of his own day-to-day meals. He finally abandoned his years of failed adherence to the low-fat orthodoxy and found success through a high-fat, carb-skeptical approach. He shed 30 pounds in two months. Normally, for Einertson, that would have been the extent of his willingness to reorganize his life around diet. A soft-spoken outdoorsman, the 46-year-old husband and father of two teenagers was hardly the type to take up the latest diet craze for the sake of being different.

But then, in 2012, he began feeling painful electric shocks in his mouth. A visit to Mayo Clinic led to an initial diagnosis of trigeminal neuralgia, which meant that something was affecting one of the nerves in his brain. They scheduled an MRI for later that week. And that MRI revealed a grape-sized mass at the base of his brain.

"When they tell you something like that, it’s like an out-of body experience," he says. "I was sitting at this desk, at work, when I got the message, and I just didn’t know what to think."

It was a meningioma, they said, a cancer in the lining of his skull.

While the condition is often benign, his was Grade II, a type that was more likely to return. Worse, after 15 hours of surgery, his doctors said they could not get all of it—they had to leave a little less than half of it in place—and would have to operate again someday if it began growing.

"That was disappointing," Einertson says. So was the fact that he had to endure six-and-a-half weeks of radiation, which was designed simply to keep the mass from growing. But, as a curious student of science and one who had come to suspect carbohydrates in the diet were involved in the diseases of civilization, Einertson began reading about how to starve cancer. And he found a little understood, compelling and relatively safe (if challenging) dietary-oncology treatment called the ketogenic diet.

He had learned that while knowledge of the genetic story behind cancer grabs all the attention, it doesn’t change the fact that cancer still needs to eat. What if you could starve it? In fact, what if you could selectively starve cancer while feeding the rest of your body? Because cancer is not hungry for just any kind of food. That’s right. Cancer is a carb addict, too.

He decided to take his own diet—the one he’d created for overweight cats—and reformulate it to fight his own cancer. The diet was based on similar principles and concepts from what he’d worked with for cats over the past decade, though he dropped the protein intake from "high" to "moderate" for humans.

"I think the American diet is too full of sugar, refined carbohydrates, and vegetable oil," he says, recounting his immersion in dietary books by journalists and science writers Gary Taubes and Nina Teicholz. "The vegetable oils create carcinogenic compounds when heated, which can damage mitochondria and create cell mutations. Carbohydrates spike your blood sugar which spikes your insulin, which promotes cell growth and division. Ask anyone in a lab. If you want to increase cell growth in a petri dish, add some insulin."

It was all just interesting science when he was treating feline diabetes. Then he got those electric shocks in his mouth, and it became personal.

Einertson tilts his head slightly and downward as he tells you all this. It lends the appearance of deep thoughtfulness, but, while he is indeed a thoughtful listener, it turns out to be a side effect. His tumor surgery left him with double vision if he stares at you straight on.

Once he’d received the standard care (radiation, in his case), Einertson began considering changes he could make to help slow the growth or even shrink the mass in his brain. He read Good Calories, Bad Calories by Gary Taubes, "maybe five times" and met the author at Mayo. He thought about the way that eating carbohydrates—and we’re mostly talking about refined and easily digestible carbohydrates here, like high-fructose corn syrup—has risen in tandem with a demonizing of dietary fat from animal sources—and all of it accompanied by rising rates of obesity, diabetes, stroke, heart disease and cancer.

He found a talk by Dr. Thomas Seyfried, the Boston College professor of biology and the author of Cancer as a Metabolic Disease, then another by Dominic D’Agostino, a biologist at the University of South Florida. Eventually a question occurred to him: What if you could selectively starve a tumor of all energy, and still feed the rest of your body? Who wouldn’t want to do that?

Because as it turns out, selectively starving cancer through the avoidance of carbohydrates and a turbo-ingestion of animal and dairy fat is indeed possible. A host of studies have already proven to be effective in slowing the growth of tumors, in mice at least.

Here’s how it works: As the Nobel-winning scientist Otto Warburg first discovered in the 1920s, a defining characteristic of cancer is that it acts like a sprinter, not a jogger. What that means is, most cancer cells can only burn fuel via the so-called anaerobic pathway—the faster, ravenous energy system we use to keep cells going when we’re working harder than our oxygen can keep up with.

This anaerobic reliance on what is called fermentation glycolysis may be an adaptive quality to cancer, or it may be an accident, but it is nothing if not an Achilles heel. After all, as part of this one-track metabolic pathway, cancers primarily consume glucose, and a lot of it. You don’t need to eat the carbohydrate-rich foods that put glucose in your blood. In some respects, your body doesn’t even expect you to eat refined carbohydrates, much less for nearly every meal, every day as we do in much of the Western world. Normal cells, in fact, make it seem like eating carbohydrates in high quantities is a physiological disaster.

Carbohydrates put sugar in your blood, which causes the body to release insulin, a hormone meant to help cells use glucose as fuel by pulling sugar from the blood. Insulin then blocks fat cells from releasing energy, keeping you hungry. Eating mostly fat and a little protein with virtually no carbohydrates, according to Einertson, causes the body to consume from a slow, sustained release of energy stores in the form of fatty acids and ketones. Because ketones are readily available when no insulin is present, they are likely the energy system prehistoric man was designed to use in a natural food environment (as food availability rose and fell from day to day).

This is why skipping meals altogether, as Einertson does for five days every other month, causes the body to release even more ketones, a process that likely places a high stress upon cancer.

The ketogenic diet was invented (or at least improved upon—and named—by Mayo doc Russell Wilder) at Mayo Clinic nearly 100 years ago as a treatment for epilepsy, and is used to this day for treatment-resistant seizures in children.

While some nutritionists believe that we need carbohydrates to provide our brain with the glucose it needs to function, others point to the fact that ketones are eventually converted into glucose downstream, enabling brain cells to eat their needed food without requiring carbohydrates. For that second group, this can also mean that cancer, without those carbs, is denied its pathway to energy.

Another negative perception of ketogenic eating comes from the fact that the diet requires high levels of dairy and animal fat. Worried they will gain weight or about a supposed relationship between saturated fat and heart disease, people are no longer used to eating the fat from their bacon.

Last February, however, none other than the president of the World Heart Federation, Salim Yusuf, told a crowd of cardiologists that, when it comes to heart disease, eating beef is neutral to cardiovascular risk, while eating dairy fat is protective.

"It’s interesting," says Dr. Adrienne Scheck, when asked about Einertson’s story. "To the best of my knowledge, people have not tried it with meningioma."

Scheck, an associate professor of neurobiology at the Barrow Neurological Institute in Phoenix, is the lead scientist in a series of studies examining the effects of a ketogenic diet on mice with glioblastoma, the deadliest of brain cancers. She believes that as long as the standard of care is employed (chemo, radiation), a ketogenic diet can’t hurt, and may just help.

"When you look at molecular changes, the diet does a big basket of things," she says, citing beneficial changes—and the activation of cancer immune responses in animals with tumors—she has observed through her research. "The truth is, it is not just food, it’s a metabolic therapy."

In the early years of Einertson’s experimental diet, his tumor continued to grow, albeit slowly. After adding intermittent fasting to his diet, in 2015, his tumor stopped growing. By 2016, the tumor had begun to shrink. Today, five years after being diagnosed, his tumor has shrunk from 21.2 millimeters to 19.5 millimeters.

Today Einertson seeks out only the most marbled cuts of meat. "I pick out the fattiest steaks," he says. "It fills you up and it’s nutrient dense. Because my wife and kids trim the fat on their meat, I eat their fat, too."

What he no longer eats—what he skips entirely or at least minimizes—are all of the things that get laid out at office parties, served up out of vending machines, and sold in convenience stores, including candy, cereals, crackers, cookies, bars, soda, juice, chips, beer and bread. "Cancer thrives on sugar," he explains. "I want to get my blood glucose as low as I can."

He misses beer, but the rest, not so much.

With the exception of a ketogenic nutritionist who treated epilepsy, he’s been forced to take up these steps towards starving cancer on his own. "I’ve only met one oncologist who knows who Otto Warburg is," he says. "My radiation oncologist completely dismissed it, and said it is not evidence-based."

It may not be evidence-based, but so far, Einertson likes what he’s seeing. In June, his latest MRI showed the size of his tumor unchanged.

And none of it would have happened if he hadn’t tried it out on cats to such success first.

"I might be kidding myself," he says. "Let’s say my diet has nothing to do with my tumor staying the same size, and even shrinking. That it’s all a placebo effect. At least I have a strategy that’s nontoxic and proactive. I really believe I have a way to beat this thing."