This just in: Sleep is not for the weak. According to Reese Witherspoon’s fitness trainer Ashley Borden, making sure you get those extra Zzs is crucial to tackling your workout.

“I always tell my clients that I would rather them get sleep instead of working out on four hours of sleep,” Borden told mindbodygreen.com. “Studies have shown that between 7.5 and eight hours of sleep every night helps the body repair itself and regulate inflammation in the body.”

Borden, who has also worked with the likes of Christina Aguilera, Mandy Moore, and Ryan Gosling, said sleep also affects your metabolic process.

“[Not getting enough sleep] produces a higher amount of the inflammatory stress hormone, cortisol,” she said in the interview. “Cortisol has its time and place in our bodies, but not at night. Cortisol heightens our alertness, the last thing we need when we crave sleep.”

Aside from sleeping in, Borden also recommends that her clients avoid sugar and load up on greens.

“Sugars are inflammatory and trigger more sugar cravings, along with increasing inflammatory cortisol levels, which cause belly fat,” she said. “Choose vegetables that are all the colors of the rainbow and focus on dark green veggies, too. These give us phytonutrients, which have many antioxidant assets that can put a stop to cell damage, which helps strengthen our immune system, prevents cancer, has a positive effect on our hormones, and improves our overall health and vitality.”

And even though temperatures are dropping, Borden says it’s important to take your workout outdoors.

“Getting outdoors for even 10 minutes provides the body with a natural dose of vitamin D,” she said. “Being outside also provides amazing mental stimulation.”

One way she gets her clients moving? An outdoor workout that sounds like something Witherspoon’s Wild character, Cheryl Strayed, would approve of.

“I have taken clients out for power walks with a backpack full of mini bands and bands with handles to create a hillside neighborhood circuit workout,” she said.