Low-carbohydrate diets are all the rage in the Western world, and they always seem to be... While the foundational claim – eat fewer carbs – hasn't changed over the past few decades, the marketing has shifted. "Atkins," "Stillman," "Paleo," "Keto;" pick what sounds most appetizing and eat your way to health nirvana, or so devotees proclaim.

And any of these diets could very well prove successful for an ardent follower, but not for the reasons that are regularly touted. Our bodies are not evolutionarily predisposed to thrive on a "Paleolithic" diet. The ketosis brought on by eating extremely low amounts of carbohydrates is not metabolic magic. Rather, people who switch to these diet regimes see improvements simply because they are probably transitioning from a haphazard, unbalanced diet to one that's actually nourishing. If they experience significant weight loss, it's because they reduced calories as a side effect of the diet change.

Yale University neurologist Steven Novella provided a wonderful analogy to explain this on his podcast The Skeptics' Guide to the Universe. Controlling the body's weight is a lot like adjusting the speed of a car, he said, "It’s basically a function of how much you’re applying the gas versus the brake." In other words, how many calories are you eating vs. burning?

Low-carb purveyors commonly point to studies (almost always conducted on rodents) suggesting that their chosen diets alter metabolic pathways, boost certain hormones, lower your appetite, and burn more fat. That may all be true, Novella says, but it's mostly meaningless when you examine effects on the whole human body.

"Yeah, all of that is at work… but that’s in the background. The driver doesn’t need to know the coefficient of friction of the brake pads. All you really need to know is that you apply the gas to go faster and you apply the brakes to go slower."

It's the same with diet, Novella concludes.

"Knowing about all of the various mechanisms of homeostasis and energy control in the body is useful for scientists and for complicated questions like disease states… but for the average person you don’t need to know all that stuff… What you need to know is calories in, calories out. That’s the predominant effect when we’re talking about weight control. How many calories are you eating and how many calories are you burning? All of the other stuff has a negligible effect."

Novella's analogy is supported by systematic reviews and well-controlled trials. Low-carb, reduced-calorie diets might show slightly better results than other diets, but the difference equates to an extra pound or two of weight loss over an entire year. It seems silly that this tiny difference fuels a $300 million industry of books, podcasts, supplements, and foods.

The secret to a long and healthy life is not in eating like your ancestors, starving your body of carbohydrates, or fine-tuning the many metabolic pathways of your body with supplements. No, it's following the speed limit on a well-paved road winding through a beautiful countryside. And don't forget to enjoy the scenery.