These 3 foods are *the worst* for your metabolism, according to Jillian Michaels

When you take a look the ingredients that rev up your metabolism, a few stand out. Namely, fiber (particularly from “real” foods like fruits and veggies) and iodine-rich options like seaweed. For every metabolic superhero, though, there’s an alternative eat out there that works the opposite way, sabotaging your body’s calorie-burning prowess.

“The two things that are predominantly in control of your metabolism are your endocrine system and your hormone balance,” says Jillian Michaels, creator of the My Fitness app and former trainer on The Biggest Loser. Thus, when you chow down on something that disturbs these things, your metabolism gets thrown for a loop, too.

You may have already guessed some of the nutritional villains that Michaels names as the worst for your metabolism—cough, sugar, cough—but below you’ll get the full scoop from the celeb coach herself, with a bit of added insight from nutrition experts.

Keep reading to find out which foods you should avoid for a healthy metabolism.

1. Sugar

Not-so-shockingly, Michaels names sugar as one of the greatest culprits of a sluggish metabolism. Why? After savoring a dessert, she explains, your blood sugar spikes. This causes your cortisol and insulin hormone levels to increase, in an effort to level things out—and it can eventually lead to metabolic disruption if left unchecked long-term. “Hormones work in a symphony, and there are tons of them,” explains Michaels. “So ultimately, when we’re looking at metabolism, we want to make sure that we have the right hormones working for us, instead of against us.” 

According to Chicago-based dietician Amanda Lemein, MS, RD, LDN, the lack of fiber in sugary snacks is yet another factor that makes them a total no-go for a solid metabolism. “Things that we think of as sugar—like cookies, cake, pancakes, whatever—are broken down by our our bodies really, really quickly,” she says. Fiber-rich foods, however, are digested slowly—your body fights hard to break them down, kickstarting your metabolism in the process. 

2. Processed grains

Next on Michaels’ hit list: refined grains like white rice, highly processed breads, and white pasta. These have a similar affect on your body as sugar, breaking down quickly and causing insulin to skyrocket. And that’s not all, says Josh Axe, DNM, CNS, DC. “When consumed in excess, refined grains can provide you with high levels of certain compounds that may hurt your metabolism, including gluten, lots of starch, and phytic acid,” explains Axe, founder of Ancient Nutrition and DrAxe.com. “Many packaged grain products also contain lots of added sugar, salt, synthetic preservatives, and are ‘fortified’ with synthetic vitamins and minerals that can be hard to metabolize properly.” Moral of the story: Stick with whole, unprocessed grains when you get a carb craving. 

3. Processed Soy

Hold the vegan chicken tenders? “Soy is very toxic [to your thyroid],” Michaels claims. To be clear, scientists haven’t come to a consensus on this, but some studies do indicate that excessive soy consumption may negatively impact your thyroid—the gland in your neck responsible for regulating your body’s metabolic operations. (Especially if your iodine levels are low or you’ve already got some form of thyroid disfunction.) And to make matters worse, conventionally grown soy is also often treated with pesticides, which are also linked to thyroid issues. “The only time you should do soy is if it’s organic and fermented,” says Michaels. (Or you could always just turn to a soy-free Beyond Burger for your plant-based protein fix…)

Originally published on August 10, 2018; updated on January 24, 2019.

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