It should come as no surprise that weight loss isn’t one-size-fits-all, nor does it revolve exclusively around food. Stress and mental health play an important role, as do genetics, levels of physical activity, hormones (especially for menopausal women), and, yes, sleep.

We sat down with the founder of PHD Weight Loss, Ashley Lucas, and her husband, Doug Lucas, in order to better understand the impact that sleep, exercise, and nutrition have on weight loss and weight gain.

Is there one that’s most important? If so, which? Is it better to sleep in or pull yourself out of bed for an early-morning workout?

We’re covering it all.

Before we dive in, a bit about Ashley and Doug. The two met in undergrad, where they were both pursuing a fine arts degree in ballet at the University of Utah. Ashley went on to dance with the Aspen Santa Fe Ballet, then the Richmond Ballet. Eventually, she was invited to New York...but ended up in the ER instead.

“My body had a breakdown and panic attack,” explained Ashley, “and the doctor basically said that I was over-exercised and under-fed. I was a master chronic dieter to try and maintain the body shape that I needed for the sport.”

This is what eventually propelled Ashley into the field of nutrition. After earning a PhD in sports nutrition and chronic disease from Virginia Tech—where she specialized in energy metabolism—she taught for a few years before heading back to school to become a Registered Dietitian. Upon completing her dietetic internship, she began working in Durango, Colorado with elite athletes to help them improve their performance and maintain an optimal body composition. Along the way, Ashley realized that the very work she was doing with athletes had the potential to make an even more significant impact on those struggling with excess weight and inflammation. And PHD Weight Loss was born.

After undergrad, Doug went to medical school to pursue the path of orthopedic surgery. He began practicing as Ashely was building PHD Weight Loss—during which time they both realized that there was a need there for medical support.

“There’s decades of opinion and bad research in the weight loss world, so it made sense for me to come in and explain those things and help people feel better about going against some of the dogma that’s existed over the last 50 years or more,” explained Doug. “In doing that, I realized that there's a need for that type of practice, so now I’ve started seeing patients in ‘a precision health practice’ at Optimal Human Health where we coach people through lifestyle changes and diet as well as genetics and medication/supplement optimization.”

Below, Ashley and Doug weigh in on sleep, exercise, and nutrition for weight loss.

“Studies have shown that people who sacrifice shuteye and eat the same amount as people who sleep adequately weigh more and have increased cortisol (stress hormone) secretion,” (1) explains Ashley. “So if we see a client who is eating right on track with our meal plan but not losing weight, then the first thing we ask is about sleep and stress management. If they’re not sleeping adequately and/or not managing their stress adequately, they can follow a healthy diet by filling their bodies with ALL the right foods at ALL the right times, and they still won't see success."

READ MORE: 7 Reasons You May Be Tired Even Though It Feels Like You Slept Well

“I would say the number one is food,” says Ashley. “Because how you eat is going to drive your cravings and your hunger levels. So food is definitely the most important, followed by quality and hours of sleep, then exercise. You can’t eat Twinkies and then sleep 10 hours a day.”

Doug agrees.

“If someone is trying to lose as much weight as possible, they have to have the nutrition piece at least somewhat figured out. But at the same time, if you’re not sleeping well and your circadian rhythms are thrown off, the elevated cortisol is going to drive cravings. You’re going to feel terrible and be in a worse mood. In other words, you can have the best nutrition advice in the world, but if you’re strung out, if you’ve slept two hours, you have cravings, your stomach’s screaming at you. And you’ll have no choice but to listen.”

Here’s the science behind why.

Your body receives signals from hunger hormones such as ghrelin (increases our cravings) and leptin (causes feelings of satiety), which means a disrupted sleep cycle can diminish feelings of fullness and lead to patterns of overeating—especially when it comes to snacking on high-caloric and high-carb foods. In fact, a study conducted by the American Heart Association (2) found that people who slept an hour and 20 minutes less consumed 549 more calories than the control group. However, what didn’t change between the groups was the amount of energy expended, which suggests that those who slept less (and consumed more) weren’t burning additional calories.

In addition to affecting how much you eat, sleep can also affect what you eat. In a study conducted by the University of Chicago, researchers tested the hypothesis that sleep loss is associated with an activation of the body’s endocannabinoid system, which serves as a key component of “hedonic pathways” that regulate decision-making processes for food intake. The study compared four nights of normal (i.e. 8.5 hours) sleep against restricted (i.e. 4.5 hours) sleep, with results showing that the sleep-deprived group consumed nearly twice as much fat and protein as the control group. (3)

In order to understand why sleep deprivation impacts food desire, you have to talk about the brain—specifically three reward centers that control what’s called “appetitive evaluation”:

  1. Anterior cingulate cortex
  2. Lateral orbital frontal cortex
  3. Anterior insula cortex

During periods of poor sleep quality and sleep deprivation, activity in each significantly reduces. The result is a progressive increase in desire for weight-gain promoting and blood-sugar spiking foods (i.e. high-caloric and high-carbohydrate). (4)

READ MORE: Sleep Deprivation + Men’s Health: What’s The Connection?

Nutrition may be at the top, but when Doug consults with patients, he doesn’t position the three pillars of health in a hierarchical 1-2-3 structure. Instead, he takes sleep and spreads it out across the bottom.

“I tell my patients that this is the foundation,” explains Doug. “Because research shows that with a lack of sleep, you can’t follow a nutrition plan and you can’t follow—or you almost shouldn’t follow—an exercise plan because you’re adding more stress to your day.”

“I would say sleep is more beneficial,” posits Ashley. “Without enough sleep, your body’s in such a high state of stress and cortisol is so high that even if your workout is good, you’re stressing your system so much that the resulting hunger and cravings will cause you to over-eat whatever calorie allotment you burned. It won’t go to your muscles.”

“Without enough sleep, your body’s in such a high state of stress and cortisol is so high that even if your workout is good, you’re stressing your system so much that the resulting hunger and cravings will cause you to over-eat whatever calorie allotment you burned. It won’t go to your muscles.”

Ashley Lucas, PhD, RD

“It’s not just about the calories,” adds Doug. “And at the same time, if you start a workout on little sleep and a lot of stress, then you add more stress to it, you’re going to overcompensate and then overeat based on that. So it won’t be helpful if your goal is fat burning and fat loss.”

Wondering if your sleep struggles are a sign of a sleep disorder? Here are six symptoms to keep an eye out for.