She may no longer be narrating the scandalous lives of Manhattan's elite, but Kristen Bell is still dishing secrets -- only now, they're about blood sugar, not Blair Waldorf.

At the Emmys, Bell's "Nobody Wants This" co-star Justine Lupe revealed the "Gossip Girl" alum's go-to biohack for eating carbs without the crash or the weight gain.

"You ask her anything about your glucose levels, you ask her how to plug up your system before you eat a bowl of pasta -- the woman knows what the heck to do," Lupe, 36, told E! correspondent Zuri Hall on Sunday.

Bell's method involves grazing on spinach or other leafy, fibrous greens before a carb-heavy meal. If those aren't available, Lupe said Metamucil or a shot of apple cider vinegar (ACV) also do the trick.

"It, supposedly, stabilizes your glucose," she noted. "You can thank Kristen Bell for that, everyone."

Turns out, she's onto something.

"Kristen Bell isn't wrong here," Amy Shapiro, a registered dietician and nutritionist, told The Post. "There's actually some science behind it."

Whether you're munching on leafy greens or taking a supplement like Metamucil, preloading your system with fiber can slow glucose absorption into the bloodstream, she explained.

"[This] leads to a steadier and slower rise in blood sugar instead of a sharp spike, which leads to a crash and further cravings," Shapiro said.

Meanwhile, studies show that ACV can improve insulin sensitivity and slow gastric emptying, largely due to its acetic acid content.

"This may blunt post-meal blood sugar spikes, especially after carb-heavy meals," Shapiro added.

A more stable glucose response can also boost mood, sharpen focus and make you feel fuller for longer, helping prevent overeating and unwanted weight gain.

Over time, Shapiro said this may lower the risk of developing insulin resistance, type 2 diabetes, obesity and cardiovascular disease.

"While it's not a 'magic bullet,' both strategies can make a measurable difference in glucose response for many people," she noted.

Whether you should choose ACV, leafy greens or Metamucil before your next meal depends on your lifestyle.

"It's easy to have leafy greens before a meal when dining out since you can simply order a salad," Shapiro said.

"If you prefer drinking water and don't mind adding fiber to it, Metamucil might be your go-to. It's a great way to boost fiber intake if your diet is low," she explained.

If you plan to use ACV, Shapiro recommends drinking it about 30 minutes before a carb-heavy meal.

"[But] if you don't like the flavor, which many people don't -- or the acid bothers your stomach -- it may not be the best tactic for you," she cautioned.

One hack she doesn't like? ACV gummies, which she said are popular but don't have the same effect as liquid vinegar.

"If I had to rank them, I'd put real food fiber (leafy greens) first, supplemental fiber (Metamucil) second and vinegar as an optional add-on," Shapiro said.

Still, adding fiber before carbs isn't a free pass to overeat.

"Healthy habits and balanced meals remain the most important," Shapiro noted.

For better long-term results, Shapiro recommends focusing on balanced meals that include protein, fat and fiber, while cutting back on ultra-processed carbs and sugary snacks.

She also stressed the power of regular physical activity -- one of the best ways to keep blood sugar in check.

"Even just 10 minutes of walking after a meal helps improve blood sugar levels," Shapiro said.

Kristen Bell's biohacking trick really works, says dietician -- it...