The key appears to be exactly what you're replacing those carbs with.  
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For literally decades, a popular go-to diet for people looking to shed some unwanted weight has involved cutting back on carbs—from Atkins, to South Beach, to Paleo, or Keto.

And it works! Even U.S. News & World Report said so early this year when they evaluated the scientific cred behind the most popular diets. They ranked Atkins as #7 for “Best Fast Weight-Loss Diet” (and that spot was tied with other well-known diets like Jenny Craig and Nutrisystem). But it didn’t fare well when they ranked “Best Diets Overall” (Atkins came in #36 out of 40) or “Best Diets for Healthy Eating” (#38 out of 40).

Following Atkins and other low-carb diets over the long haul is getting a thumbs down in the scientific research world, too.

Recent research, which was presented at ESC Congress 2018 (but is not yet published) looked at the carb eating habits of nearly 25,000 Americans and compared rates of death, cerebrovascular (brain-related) disease, and cancer. They found that people who ate a low carbohydrate diet upped their risk of premature death. (And, interestingly, it turns out that “non-obese” and older (55 years and up) adults were at the highest risk of premature death when they followed a low-carb diet.)

So what’s so bad about low-carb diets? The researcher behind this study, Maciej Banach of the Medical University of Lodz, attributes it to what we replace those carbs with. He points to an uptick in animal protein, cholesterol, and saturated fat, as well as eating fewer fruits and getting less fiber.

Then, on the heels of that presentation, came a new study, published in the September issue of The Lancet. Those researchers’ findings supported Banach’s—people who followed a low carb diet (in this instance less than 40% of calories from carbs) upped their mortality risk. But the Lancet study went a little further: those who followed a high carb diet (greater than 70% of calories from carbs) also shortened their lifespan. The sweet spot in this study was for people who ate about 50 to 55% of calories from carbohydrates (or “moderate” amounts)—those participants had the lowest observed risk.

Credit: Rimma Bondarenko

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The researchers then went a little further and looked at where the fat and protein was coming from in the diets of people eating low carb. If participants ate a low carb diet and replaced those carbs with animal protein and fat, they further raised their risk of death. Roll up a few paragraphs to Banach’s hypothetical “why” and—poof—we now have data to support that thinking. Participants who ate a low carb diet and leaned on plant protein and fat (instead of animal-based sources) actually lowered their risk of premature death.

Bottom Line: You don’t have to shun low carb diets altogether. Following one will help you lose a few pounds quickly, but to be healthy in the long run (read: live longer), don’t make it a lifelong way of eating. And when you do go low carb, be mindful of what you replace those carbs with. Plant-based fat and proteins are ideal.

And, ultimately, that advice applies to how to eat healthy in general—don’t load up on animal protein and fat. Spread the love, save a cow and a chicken, and eat some plants.