13 items a nutritionist says you should buy at Costco - and the one item you shouldn't

"Costco is famous for their rotisserie chicken, which has been steady at $4.99 for years," Kylie Sakaida, a registered dietitian nutritionist, told Insider. "It's such a great option for people who need a portion of that for dinner and use the rest for lunch the next day."

She added that the chicken is already fully cooked and seasoned, so people don't have to worry about undercooking it.

Seeds of Change comes in a microwavable pouch, so it's simple to cook.

"Because of the quinoa and brown rice, it has a good amount of fiber and protein," Sakaida said. "I tasted it myself. It tastes just as good as freshly made rice."

"The Kirkland peanut butter is one of my favorite things at Costco because it's such a large portion, and it's also not going to have any of those unnecessary additional ingredients like palm oil in it," Sakaida said.

Sakaida said they have great ingredients, are higher in fiber, and have whole grains.

"You can use their mix to make waffles and pancakes because they are higher in protein, higher in fiber, so they leave you satisfied for a lot longer than something like the Eggo's brand," Sakaida said.

Sakaida described this as Costco's version of Sargento's Balanced Breaks. The Kirkland Signature brand's pack offers protein, fiber, and carbohydrates.

"This snack has a lot of components that make it balanced and satisfying," Sakaida said. "It's also portable, which I think is a huge draw."

Costco sells large bags of almonds, walnuts, and pistachios under its generic name brand.

"I always like to recommend portioning that out into snack baggies," Sakaida said. "You can do your own trail mix by adding sunflower seeds and dried fruit, so that you have something ready to go and something super cheap, too."

They're made from vegetables including sweet potato, beets, and plantains.

"Root vegetable chips have more fiber than something like a potato chip," Sakaida said. "They're crunchy, they're crispy, they're salty, and they're going to be a little more satisfying than potato chips."

These bars come in all flavors including, chocolate brownie and cookies 'n cream, according to Costco's website. Each bar has 21 grams of protein.

"They're a really good alternative if you like Quest bars," Sakaida said. "The price is better in comparison to Quest bars and it has really similar nutrition facts."

RXBars come in many flavors, including peanut butter chocolate, blueberry, and chocolate sea salt.

"RXBars are popular because they have a very short ingredient list," Sakaida said. "They don't have a significant amount of added sugars. The only sweetener comes from dates, and their protein comes from nuts or egg whites. They also have a good amount of fiber."

Since it's Greek yogurt, these frozen dessert bars are higher in protein and lower in saturated fats. They come in a variety of flavors, including mint chocolate chip, chocolate chip cookie dough, and black raspberry chip.

"It tastes so good," Sakaida said. "I've only heard really great things about it, and I myself am a fan of the taste."

Beyond the fresh produce, Sakaida said there are a ton of frozen vegetables like broccoli, bell peppers, and even a frozen stir fry vegetable blend at Costco. Also, there are frozen blueberries, cherries, strawberries — all of which stay fresher for longer when they're frozen.

She also mentioned Costco carries frozen açaí bowl packets that are portion-sized.

"As far as produce, Costco does a really great job at providing a lot of options for people," Sakaida said.

Sakaida said she loves the frozen fish options at Costco, which include Atlantic salmon, sea bass, and mahi-mahi. She also mentioned there are frozen meat-less options like plant-based nuggets, salmon burgers, and edamame.

"These are really good options for people who might not plan ahead super well," Sakaida said. "They can just leave frozen protein options in their freezer, and they can just defrost it when they are ready to use it because they can be left in the freezer for a few months."

According to the manufacturer, the product "has been shown to increase calorie burning (thermogenesis), kick-start your fat burning ability (fat oxidation), and supply powerful antioxidant protection."

However, Sakaida said she would not recommend it.

"People are often misled by this type of information where they think if I take this supplement, I will lose weight and lose fat, but that's not necessarily how it works," Sakaida said. "I'd recommend staying away from that at all costs."

While green tea-based supplements are considered natural, the FDA does not strictly regulate dietary supplements and there is limited research on their effectiveness. You should consult a doctor before taking a weight-loss supplement.