When we're not swooning over celebrities' drop-dead outfits or gorgeous complexions, we're envying their six-pack abs and tight AF tushes. Without a doubt, Hollywood's hottest stars make a flawless physique look effortless -- like they could eat doughnuts on the reg and still look fabulous. But one peek inside our favorite A-listers' kitchens tells us otherwise. In fact, many celebrities known for their smokin' bods have stringent diets with long lists of foods they will not eat (we're looking at you, Gisele). We caught up with some celebrity trainers and nutritionists to find out what foods their clients never eat -- and why.

Who Avoids It: Megan Fox

Why: Prepare for complete and utter devastation, cheese lovers, because when it comes to dairy, even traditionally healthy options like Greek yogurt and cottage cheese are a no-go for washboard abs.

"While many people consider dairy to be a protein, the body will utilize it first as lactose, or milk sugar," explains Philip Goglia, nutritionist to stars like Kim Kardashian and Cara Delevingne. "These sugars found are inflammatory, and can cause sugar sensitivities and digestive issues, like bloating and gas."

Goglia also points out that adults don't have the ability to utilize diary products to their full nutritional potential, and are all, to some degree, lactose intolerant. "In fact, dairy products inhibit the full use of our oxygen pathways, which is why athletes avoid dairy before or immediately after workouts," he explains.

Who Avoids It: Jessica Biel

Why: You know those easy, on-the-go protein bars, microwaveable meals, and meal replacement shakes? According to Goglia, processed foods are all crap -- no matter what their health claims.

"As manufactured foods, these items are generally more difficult to digest, and through the reduction of calories, can cause cravings for higher sugar or higher fat foods to compensate for daily energy needs," Goglia says. While grabbing that protein bar might seem like a healthier choice than reaching for say, that BLT (extra B please) -- Goglia says the best diet foods are real food. "Stick to one-ingredient foods like yams, oatmeal, chicken, fish, lean steak, vegetables and fruits," Goglia says. "There are no better diet foods than these."

Who Avoids It: Taylor Schilling

Why: This next diet no-no might come as a shock, considering you can't go anywhere without hearing about another celebrity juice cleanse. While fresh squeezed and cold-pressed juices do offer some nutritional benefits, Los Angeles based nutritionist Ilana Muhlstein, R.D. with Explore Cuisine, says that, in general, juice cleanses are the antithesis of healthy.

"I find them to be ridiculous, expensive and totally nonsensical," Muhlstein says. "They don't include fiber from the fruits and vegetables, which is where the bulk of the benefits are held. They leave people starving and deprived, and can cause a super unhealthy relationship with food."

In fact, "Orange Is the New Black" star Taylor Schilling, point-blank told People, "I don't roll with the juice cleanses. I will never do that. I like chicken and beans." Goglia supports Schilling's stance, and adds that because juice is so low in fiber, it rapidly penetrates the bloodstream, causing an immediate rise in blood sugar, which will ultimately result in a loss of energy and lethargy in a matter of minutes.

Who Avoids It: Gwyneth Paltrow

Why: If you're vegetarian or vegan, soybeans might be a primary source of protein for you, but according to Goglia you're not getting a whole lot of bang for your buck. "There are amino acids (the building blocks of protein), but those amino acid structures within soybeans are difficult for us to absorb," Goglia explains. "First and foremost, soy is a starch and sugar [two things you want to avoid when trying to slim down]. It's high in estrogen, and it's been linked to numerous cancers, (primarily breast cancer) in both men and women. Any products high in estrogen like wheat and soy are unfavorable choices."