A standard dinner at David Harper's house: a tuna nicoise salad (hold the potatoes) served with a glass of red wine. David Harper, author of Biodiet

David Harper, a cancer researcher and kinesiologist, has been on a high-fat ketogenic diet since 2013.

He says the sugar-free eating plan has helped him slim down even though he eats a lot of fat.

Harper has written a new book, "Biodiet," about how to follow the trendy keto diet in a healthy, science-backed way.

One of the problems with modern "Western" diets, he says, is that they tend to promote inflammation, obesity, and disease by relying too much on sugar and other carbohydrates.

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Start the day off with a piece of toast, a bit of margarine and jam, and a glass of fresh orange juice? Definitely not, says the cancer researcher David Harper.

The kinesiology professor hasn't eaten toast in more than six years: He started following a high-fat, low-carb ketogenic diet strategy in 2013, and he says he's never looked back.

Harper says both he and his wife, Dale Drewery, rely on fat to power them through the day.

"I eat full-fat cream in everything," Harper told Business Insider, adding that he consumed lots of nuts and seeds, green beans, "organ meats" like liver, and up to a dozen eggs each week.

The keto diet Harper follows is designed to force the body into a state of ketosis, in which it uses fat for energy and produces ketones, instead of relying on carbohydrates and turning them into glucose. (It's essentially the same switch our systems make when starving.)

Harper and Drewery have written a new how-to book about going keto, called "Biodiet," which was released in May. In it, the couple suggest that our modern diets are formulated around too much sugar and too few veggies.

Harper refers to carb-heavy diets as a modern "axis of illness," a reference to the term "axis of evil" that President George W. Bush used to describe Iran, Iraq, and North Korea. When it comes to our health, Harper insists, the "three common enemies" we're at war with are obesity, insulin resistance, and inflammation.

"At the core of the axis of illness is a weapon of mass destruction," Harper writes. "The high-carbohydrate diet most of us have been eating our entire lives."

According to Harper, this carb-loaded eating regimen promotes a vicious cycle of disease and disability in our bodies.

"As these conditions worsen, they feed upon one another: obesity contributes to insulin resistance, which in turn worsens obesity; inflammation aggravates obesity, promoting more inflammation; insulin resistance causes more inflammation, which worsens insulin resistance," he writes in the book.

The 'axis of illness' on our plates

Harper and his "Biodiet" coauthor and wife, Dale Drewery. Biodiet authors David Harper & Dale Drewery

On a well-formulated keto diet, the idea is that no more than 5% of a person's daily calories come from carbs, while about 70-80% is made up of fat. Harper said he and Drewery would often split a fat-marbled steak for dinner or pair a bit of chicken (fatty skin left on) with low-carb shirataki noodles made from Japanese yams.

Harper thinks cutting carbs in this way will help him and Drewery live to a ripe old age and stay sharp, trim, and satiated.

"We're not eating a lot of packaged foods - we're not eating a lot of processed foods," he said.

Harper says he also avoids pasta, potatoes, and sandwiches, along with some naturally carb-heavy items like beans and apples. The latter part of that approach can be controversial, since many studies suggest that people who eat more fiber - a carbohydrate present in many vegetables, whole grains, and pulses - tend to live some of the longest lives.

Harper said he got his daily fiber from veggies like cauliflower, peppers, and salad greens - "anything that grows above the ground that's not a grain or a fruit or a bean, other than green beans," as he put it.

Those are not carb-free foods, since even lettuce and peppers contain some carbs, including natural sugars.

"You're going to get some sort of residual carbs in the nuts that we eat and in the vegetables we eat," Harper said. "But most of the carbohydrate that's in there is going to be fiber."

The rest of the carbs in those veggies, he said, isn't enough to make a big impact "in terms of staying in ketosis, so I don't worry about it."

Eating fat does not necessarily make you fat

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For a long time, the conventional wisdom was that if you restrict calories - no matter whether they be from fat, carbs, or protein - then avoiding weight gain should be a cinch. Cut down on dense, 9-calorie-per-gram fats; fuel up on 4-calorie-per-gram carbs and a little protein instead; get some exercise; and voilà: a winning low-fat lifestyle.

But Harper said "we've tried that for 40 years, and it's not working."

Carbs are not inherently evil, but scientists are coalescing around the idea that sugar, be it natural or artificial, isn't good for our bodies in big doses.

In reality, high-sugar, high-carb foods don't keep us full as well as items with healthy fats. Because quick-burning carbs like white bread, white rice, and sweet cereals are digested quickly, it's easier to overeat and send blood-sugar levels soaring. Over time, people who rely on these foods tend to get more cases of diabetes, gain more weight, and develop more heart problems than people who opt for whole grains and fresh produce.

Recent research even showed that sweet, all-natural juice could be almost as bad for our livers and blood-sugar levels as soda, and may contribute to disease and early death in a similar way.

The public-health push to eat "low-fat" - which was especially popular in the 1980s and '90s - led some people to replace fatty foods like bacon and butter with low-fat alternatives that were often loaded with sugar to maintain taste. That now seems to have been a misguided and often lobbyist-driven diet agenda that caused people to gain weight.

"That is unfortunately a myth, that eating fat makes you fat," Harper said. "But it's a myth because it makes sense. Fat calories are twice as dense."

Keto or not, we should all probably eat more veggies

Today, more than one in three Americans battles diabetes or prediabetes, and the numbers are rising. A 2017 Harvard study suggested that 57% of US kids would be obese by the time they're 35.

Many doctors agree that keto diets can help people combat those chronic diseases.

"Keto is undeniably the best way to deal with Type-2 diabetes and insulin resistance," the cardiologist Ethan Weiss, who follows a keto diet plan himself, recently told Business Insider.

But even fervent keto-followers like Harper and Weiss caution that the keto plan is not for everyone.

Some people have metabolic disorders that make it impossible for their bodies to use ketones as fuel, so they must eat carbohydrates to live. Other people take certain medications, carry certain genes, or have kidney issues that can all make keto eating dangerous for their health. Anyone thinking about trying a new, restrictive eating regimen like the keto diet should consult a doctor and a nutritionist.

Nutritionists and doctors generally agree, however, that nobody's system should run on sugar alone. Adding more fresh veggies to your plate is almost always a beneficial change, as is lowering your intake of ultra-processed snacks.

"If you don't want to be ketogenic," Harper said, "just get sugar and starch out of your diet, and make sure you're eating real food, not processed food."

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