Low-carb diets like the ketogenic diet are popular strategies for rapid weight loss and appetite control.

Keto diets require eaters to essentially forgo all carbohydrates and fuel up on fats and limited amounts of proteins instead.

Because sugar is a carb, many keto dieters drastically reduce their sugar intake — but they eliminate healthier carbs too.

Nutritionists are starting to notice that people who live the longest tend to incorporate more plant-based foods, including some fiber-rich carbs, into their diets.

It's another reminder that focusing on healthy, plant-based, whole foods is a better long-term strategy than dieting.

Scientists and dietitians are starting to agree on a recipe for a long, healthy life. It's not sexy, and it doesn't involve fancy pills or pricey diet potions.

Fill your plate with plants. Include vegetables, whole grains, healthy fats, and legumes. Don't include a lot of meat, milk, or highly processed foods that a gardener or farmer wouldn't recognize.

"There's absolutely nothing more important for our health than what we eat each and every day," Sara Seidelmann, a cardiologist and nutrition researcher at Brigham and Women's Hospital in Boston, told Business Insider.

Seidelmann recently published a massive, blockbuster global study of the eating patterns of more than 447,000 people around the world. What she discovered — and what is probably not a huge surprise — is that no matter where you live or what your daily diet is like, banning entire food groups and thinking you can cheat your way into good health might work for a while, but it could also send you into an early grave.

The popular ketogenic diet, which involves strictly limiting carbs to less than 50 grams a day (that's no more than two apples' worth) and subsisting primarily on high-fat foods, is one of those restrictive diets that could have harmful long-term consequences.

Other low-carb weight-loss diets that fall into this category include paleo, Atkins, Dukan, and Whole 30. Nutrition experts say that besides their potential for harm, these popular diets are really hard to follow.

[Read More: The keto diet could make certain cancer treatments more effective in mice, a study found — and a human trial is moving forward]

Some benefits of going keto are difficult to dispute. Following a high-fat, low-carb diet can be a solid strategy for rapid weight loss and blood-sugar control. The keto diet can also be great for children with tough-to-control epileptic seizures. For decades, people have seen stellar results managing those conditions on a keto diet with the help and guidance of professionals.

But there's some limited evidence that going low-carb might also lead people to become less tolerant of glucose and develop diabetes, though more research is needed.

What we do know, based on carefully conducted laboratory testing of overweight men, is that going keto probably doesn't help burn more body fat than a regular regimen. Instead, it forces people to dramatically curb their sugar intake (remember, sugar is 100% carbohydrate) and kick processed foods to the curb. Those are both good habits for overall health and blood-sugar levels, and they can help reduce your likelihood of developing cancer.

But like taking aspirin, eating a special high-fat, low-carb diet probably shouldn't be an everyday habit for otherwise healthy people. Our bodies simply aren't designed to fuel up on fats, unless we're literally starving. Even Josh Axe, a keto evangelist, has said it's not a diet that should be followed for more than a few months at a time.

Finally, low-carb diets make it easy to neglect key nutrients like magnesium, calcium, and potassium that can be plentiful on less restrictive diets with fresh, high-carb foods like beans, bananas, and oats.

More studies suggest that people who eat whole, nutrient-rich foods live the longest and have a lower risk of cancer

Flickr/Rusvaplauke

More research that backs up Seidelmann's was presented in August at the European Society of Cardiology Congress.

Researchers who presented at that conference studied the self-reported eating patterns of nearly 25,000 people in the US and compared their results with studies involving more than 447,500 people. Again, they found that those who ate a moderate amount of carbohydrates were more likely to live longer than either low-carb or high-carb dieters.

"Our study suggests that in the long-term, [low-carb diets] are linked with an increased risk of death from any cause, and deaths due to cardiovascular disease, cerebrovascular disease, and cancer," Maciej Banach, a professor at the Medical University of Lodz in Poland who helped write the study, said in a release.

A third study published this week in the journal PLOS Medicine that surveyed the eating habits of 471,495 Europeans over 22 years found that people whose diets had lower "nutritional quality" (i.e., fewer fresh vegetables, legumes, and nuts) were more likely to develop some of the most common and deadliest forms of cancer, including colon, stomach, lung, liver, and breast cancers.

[Read More: Silicon Valley's favorite diet can lead to kidney trouble — here's how to go keto without getting sick]

Basically, we're learning there's no shortcut to healthy eating

It can be tricky calculating the precise kind of diet that leads to a long life. Part of the problem is that (thankfully) we don't live our lives in highly controlled laboratory conditions. Until that terrifying day arrives and we all become well-studied lab rats, we have to rely on long-term observational data, usually in the form of surveys, to know more about which diets are the best long-term plans.

In study after study, survey data from around the world has shown that people who stick to limited amounts of meats, dairy, and processed foods while fueling up on fiber-rich plant-based foods including vegetables, whole grains, nuts, and, yes, even carb-heavy beans have some of the best health outcomes. Seidelmann describes their diets as being rich in "whole foods."

"They were not processed," she said of the diets of people in her study who lived the longest. These people would consume whole-grain rice, not white varieties. They'd eat plants like fruits and vegetables, not more-processed versions like fruit juice or smoothies.

"You have the intact fiber; you have a lot more nutrients," Seidelmann said.

Fiber isn't just good for keeping your gut moving — scientists feeding diets rich in fiber to mice are discovering that the carbs, which can't be absorbed by the body, can help protect aging brains from some of the damaging chemicals associated with Alzheimer's and reduce inflammation in the gut. They're confident that the health benefits of eating more fiber extend to humans too.

But a plant-based regimen with lots of fiber can be tricky to maintain on a low-carb diet, because some of the highest-fiber foods are also high in carbs, such as savory beans, crunchy peas, and sweet fruits.

"It is not a common pattern to eat very low-carb, strictly plant-based," Seidelmann said. "At least in the Western world, it tends to be more animal-based. That just is what it is."

People on low-carb diets often turn to more butter and meat for sustenance, which can increase blood pressure and, in the case of processed meats, contribute to cancer. Meat and dairy can also contribute to inflammation in the body, which can help cancerous tumors form and grow.

The new scientific findings all support what parents, trainers, and coaches have been saying for years: eat less junk, and continue to be skeptical of the latest miracle diet, be it keto or any other passing fad.