Carb backloading is a buzzy ketogenic diet alternative—but is it too good to be true?

For years, conventional diet wisdom has proclaimed that simple carbohydrates, like white rice and pasta, are bad. (And they’re said to be especially nefarious at night.) But one on-the-rise trend bucks this belief in favor of the exact opposite approach—carb backloading.

Here’s how it works: During the day, your carb intake is meant to be as minimal as possible, resembling the keto or Atkins diet. But after an evening workout, you’re actually encouraged to load up on the starchy stuff—spaghetti, pizza, whatever carb-tastic food your heart desires. It’s all part of a plan that promises fat loss and lean-muscle gain.

“Proponents of this kind of diet find [it beneficial to] time your carbohydrate intake with your optimal insulin sensitivity,” explains integrative and functional dietitian and nutritionist Ryan Whitcomb, MS, RD, CLT, owner of GUT RXN Nutrition.

But the thing is, it’s just a theory—for now.

Here’s how carb backloading (supposedly) works, what the research says, and what you need to know before you try it for yourself.

What is carb backloading?

First, a little lesson in what happens when you digest carbs. When carbohydrates are broken down into glucose in your small intestine, this glucose needs to be brought from the bloodstream into your cells, explains Whitcomb.

This is where insulin comes in—it’s a hormone released by the pancreas, and its job is to shuttle glucose to your muscles and tissues. When insulin sensitivity is high, it means that your body is releasing the right amount of insulin to transport glucose where it needs to go. Some research suggests that insulin sensitivity is higher in the morning than it is at night.

According to proponents of carb backloading, this is a double-edged sword. While more glucose absorption in the muscles is a good thing, they believe more glucose absorption in the tissues is a bad thing—because you’re essentially “fueling” fat tissue.

The idea is that you can hack these natural fluctuations in insulin sensitivity by avoiding carbohydrates as much as possible until nighttime. As a result, your body will use its fat stores for fuel during the day, à la keto.

The TL;DR version of all this? Fast from carbs in the day, work out and feast on carbs at night.

An important part of this equation is also an evening strength training session. By carbo-loading right after an evening workout, carb backloading proponents claim glucose will go to your muscles first (because they’ll need it the most), so you don’t lose muscle mass.

The carb backloading plan also controversially suggests that simple carbs are better than complex carbs. Complex carbs, like whole grains, are digested more slowly—and most nutrition pros consider this a good thing, as it helps you avoid major blood-sugar spikes and drops. But carb backloading proponents say that the digestion process interferes with your body’s ability to build and repair muscle while you sleep. (Of course, if you’re consistently going above your daily calorie needs during evening pasta binges, that’s going to outweigh any potential fat loss benefits of carb backloading.)

The TL;DR version of all this? Fast from carbs in the day, work out and feast on carbs at night.

But where’s the evidence that carb backloading works?

While carb backloading sounds good in theory, there’s little research that backs up its effectiveness. That said, there are a few commonly cited studies that may suggest benefits in some people: In one six-week study of a group of 10 women, those who ate more of their calories at their evening meal preserved more lean muscle mass and lost more fat than those who had larger morning meals. (The latter group lost more overall weight, but more of it was lean muscle mass.)

Another study of 78 police officers found that after six months, those who ate most of their carbs at night lost more weight than those on a different weight loss plan. However, their calorie and carb intake was self-reported, which can lead to major inaccuracies as far as study results are concerned.

But overall, “the problem with these studies is that they’re typically either of short duration or of a small sample size,” says Whitcomb. “This means the results cannot be extrapolated and applied to the larger population.” The scientific consensus: There’s just not enough convincing evidence to say that carb backloading is totally legit (yet). 

The potential downsides to carb backloading

Whitcomb’s chief concern is that by avoiding carbs all day, you’re missing out on most sources of fiber, like fruit and whole grains. “This is a terrible idea, because general guidelines suggest that most women need 25 grams per day, minimum,” he says. For one, fiber promotes healthy digestion and elimination. “[But] the primary role of fiber is to feed the microbiome, so when you avoid that all day long, you starve the bugs in your gut,” Whitcomb explains. And, as you’ve probably heard, healthy and diverse gut bacteria are a cornerstone of good health.

Plus, since the carb backloading protocol favors simple carbs, you’re not getting much fiber there, either. And even if you were, trying to eat those 25 grams of fiber all at once would feel pretty uncomfortable for your digestive system, says Whitcomb.

From a practical point of view, there are a couple of other drawbacks. Maybe working out at night doesn’t suit your schedule. Evening workouts can interrupt your sleep, which ends up working against any fat loss or muscle gains. And as anyone who’s tried a low-carb diet can attest, minimizing carbs all day can feel pretty miserable. (Hey, keto flu.)

Bottom line: Take carb backloading with a grain of salt.

Keeping in mind the potential pitfalls, you can still try carb backloading if it sounds like a good fit for you. “There’s not a lot of evidence to show that carb backloading works—but that doesn’t mean that it doesn’t work,” says Whitcomb. “Every person is different, and there’s no one diet that’s going to work best for everyone.”

For most people, a healthy balance between carbs, protein, and fat throughout the day is the best approach, he says.  But the limited research on carb backloading might also suggest that eating carbs at night isn’t necessarily as bad as we all once thought. And that’s definitely good news.

Another way to get keto diet benefits without swearing off bread: carb cycling.  Or you could just embrace carbs and use them to reduce sugar cravings, like Kayla Itsines does.