Sometimes it feels like celebrities all have perfect metabolism and never gain any weight, but that’s not true. They struggle with the same issues as we do — they just have better access to nutritionists and health coaches to keep their diets in check. The secret tip to their weight loss? It’s not about what foods they eat, but what foods they avoid.

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Gwyneth Paltrow, who’s quite vocal about her clean eating habits, even the ones that are a little controversial, doesn’t eat soy. For the past decade, soy has been touted as the better alternative to milk, but beware. As an ingredient, it’s technically not very healthy.

“Soy is not a health food,” Gwyneth’s health coach Dr. Frank Lipman said. “If it’s not fermented, I don’t recommend it.”

So why is soy bad for you? It depends on the type of soy product you’re buying. Soy burgers or energy bars? Not a good choice.

“If you want to maximize your potential benefits from eating soy, then eat natural, minimally processed sources,” Heather B. Patisaul, an endocrinology and biology researcher at North Carolina State University told U.S. News. “That way, you get the full mixture, including the protein, fiber, isoflavones and other ingredients. Tofu, tempeh and edamame are some of the best sources.”

As for soy milk, the ones you buy at the store might have questionable ingredients in them, so it’s best to check labels, do your research, and find out which brands are OK and safe to consume on your weight loss journey.

Check out the gallery below to see other foods celebrities avoid to maintain their weight.