Breakfast is the most important meal of the day. You’ve heard it, I’ve heard it, my stomach’s heard it, too. But my stomach doesn’t care, and I’m not alone. According to the American Journal of Clinical Nutrition, a quarter of Americans skip breakfast.

So what are we doing to ourselves? Well, it depends on whom you ask.

According to Dr. Emily Cooper of Cooper Center for Metabolism, you aren’t doing yourself any favors by skipping breakfast. “When people skip breakfast, a good percent will start disruption in insulin secretion,” Cooper said. In other words, low blood sugar, which can cause fatigue, brain fog and “exaggerated emotional response,” also known as a crappy mood. Having a meltdown? Maybe you just need a smoothie, according to Cooper’s thinking.

People have many reasons for skipping breakfast — they’re rushing to get out the door in the morning, they don’t have reliable food access or maybe, like me, their circadian rhythm is such that their ghrelin — that’s the hunger hormone — doesn’t kick in till later. Cooper doesn’t care. Skipping breakfast is a deal-breaker for her patients.

She practices what she preaches. She’d already had “two pieces of good local bakery sourdough whole grain toast with tahini and apricot jam” and was enjoying a bowl of raisins before 7 a.m. when I spoke to her. That’s complex carbs, protein, iron and healthy fats.

But not every breakfast choice wears that kind of halo. Sugary cereal and processed meats, for example, deliver calories but few nutrients. Even so, Cooper says bad breakfast beats no breakfast.

“If you don’t get enough to eat early in the day, ghrelin levels rise later. Your body is trying to make up for all the stuff you’ve missed,” she explained.

You’re hungry, even hangry, which can lead to making poor choices. You’re liable to grab something that gives you the immediate lift you need, maybe an iced Frappucino, extra whip. So here you are mid-morning, loaded with calories, fizzing with caffeine and sugar, but without enough nutrients to sustain you. You’re a hot mess for your 3 p.m. Teams meeting.

Keep that roller-coaster pattern up, and, studies indicate, including one from Cleveland Clinic, you’re looking at potential weight gain and diabesity — obesity-caused diabetes. That morning toast sounding better to you?

Dr. Jonathan Rosand has seen those studies, too. As co-founder of Massachusetts General’s McCance Brain Care Center and professor of neurology at Harvard Medical School, it’s his business to understand factors that may lead to depression, stroke and dementia. Does skipping breakfast make the list?

When I spoke to Rosand, he had eaten his oats this morning but said it’s OK that I hadn’t. He said, “I don’t know. There’s a lot of evidence” between missing breakfast and cognition. In other words, skipping breakfast won’t make me stupid. Unlike Cooper, he focuses not on the when but the what: “Getting more stuff that’s good for you — a diet rich in vegetables and leafy greens,” as well as other foods linked to brain health, including fatty fish, berries and walnuts, which are rich in omega-3s and — caffeine fans, rejoice! — coffee and tea.

Check in with yourself, Rosand advises. “How do you feel? Are you cloudy? Clear?” If you’re feeling fine, don’t worry.

But Rosand suggests that breakfast isn’t a bad idea for children, teens and anyone with health issues. Science backs him up on this. The American Academy of Pediatrics has found that kids who eat breakfast typically learn better at school, have fewer behaviour issues and buck the teen obesity trend by maintaining a healthy weight.

Despite that, many of Yasi Ansari’s younger patients regularly skip breakfast. For Ansari, a registered dietitian nutritionist in Los Angeles, it’s a concern. “The problem with not getting our needs met, especially in the adolescent years, is that it can lead to unhealthy eating habits, unhealthy relationships with food,” she said. “Not getting their needs met during this time period can also put individuals at risk of stunting their growth and not being able to perform their best in the classroom or out on the field.”

But, she admitted, the data is inconclusive. When working with patients, she considers other factors: “Are they meeting enough of their nutrition needs throughout the rest of the day? Do they make time for movement in their day? Are they getting enough sleep? Is there a work-life balance? What do foods at lunch and dinner look like?” Ansari advises eating “at regular intervals,” but just as important is to “listen to what your body needs.”

Rosand agrees. “Listening to your appetite — that’s helpful,” he said. “Much of what you’re inclined to do for your body is probably OK.”

And now the big IF is intermittent fasting. This eating trend du jour indicates fasting, skipping meals or stretching out the time between them forces your body to work more efficiently, so you’re running on ketones and fatty acids for energy, not glucose (sugar). Most people choose to stop eating around 8 p.m. and not eat again until noon the following day, meaning they skip breakfast.

Intermittent fasting isn’t proven for weight loss, but studies like one in the New England Journal of Medicine show it can benefit the body. It decreases the risk of major diseases, including diabetes, reduces inflammation, and potentially leads to living healthier and longer.

Does skipping breakfast mean you’re in the ketone-burning club? Quite possibly. And it’s the most common way to practice intermittent fasting. Just don’t tell Cooper. “I’ve never been a fan. All these kinds of trends people get into — nothing good comes of it. It doesn’t make metabolic sense.”

If you’re a member of the breakfast-skipping tribe, you’re in good company.

St. Thomas Aquinas wasn’t a morning meal fan either. He believed breakfast led to gluttony, one of your seven deadly sins, and was immoral. Pete Wells, the New York Times restaurant critic, doesn’t think breakfast is immoral, but he just doesn’t eat it. Stands to reason. He tastes food — a lot of it — for a living. It’s not what he wants to do on his time off.

If you’re expecting a lecture from nutrition and public health expert Marion Nestle, guess again. Nestle doesn’t do breakfast, either. “I prefer eating when I’m hungry, and I rarely get hungry before 10:30 or later,” she said.

As for all those studies talking about breakfast being the most important meal of the day, Nestle advises reading the fine print. Who’s funding the study? Money for The International Breakfast Research Initiative, an exhaustive database of breakfast patterns and outcomes, came from Cereal Partners Worldwide in the U.S. and Canada by General Mills.

To eat breakfast or not to eat breakfast?

“One of the challenges when counselling people on a diet is our all-or-nothing culture,” Rosand said. “That’s not how we live.”

Do you want to start eating breakfast? Great! “Make small changes over the course of weeks, months,” Rosand added. “Look for ways to improve.”

Still not sold on the benefits of breakfast? That’s fine, too. “The goal is to feel comfortable, take better care of ourselves,” Rosand said. “Let’s give ourselves a break.”