For years, nutrition experts have said that a healthy breakfast is a key start to the day. Not only do we think and perform better on the job, they tell us, it supports our well-being in many other ways.

Among these experts is Jessica Crandall, a registered dietitian and a spokeswoman for the Academy of Nutrition and Dietetics. "A lot of times, people think they know about nutrition because they eat," she says, "but you need large bodies of science and research to know what our bodies actually need."

And the research shows that there are good reasons to eat breakfast.

Fuel and Nutrition

The basic formula for breakfast: Pair carbs with proteins. The carbs give your body energy to get started and your brain the fuel it needs to take on the day. Protein gives you staying power and helps you feel full until your next meal.

It can be as simple as a combo of:

  • Whole-grain cereals or bread for carbs
  • Low-fat milk, yogurt, or cottage cheese for protein
  • Fresh fruit or veggies, again for the carbs
  • Nuts or legumes for even more protein

Should you eat before you hit the gym? Sabrena Jo, a personal trainer and a spokeswoman for the American Council on Exercise, says if you're the kind of person who wakes up hungry, try a snack before your morning workout. It will help you improve your performance and stave off fatigue and shakiness.

Keep it light though. Your body stops digesting when you exercise, and a full meal will slosh around in your belly. That can make you bloated or queasy, especially when you're doing a high-intensity workout.

"I would definitely eat something post-workout," Jo says. "A normal breakfast with some good carbohydrates and protein should be fine."

The most common mistake we make is not enough protein at breakfast. Crandall says adults need 20-30 grams of protein in the morning, which varies by gender and how active you are, to keep up our muscle mass and metabolism. That translates into a 6- to 8-ounce portion of Greek yogurt with a couple of spoonfuls of flaxseed, or an egg and a few links of turkey sausage.

Healthy Weight

Peanut butter on toast doesn't come close. That's the kind of meal, Crandall says, that has people over 40 wondering why their muscle mass is in decline as their waistline grows.

She also says that when you haven't had breakfast, you're more likely to get "hangry," which can lead you to overeat later in the day or choose unhealthy foods like those doughnuts someone left behind in the break room. The science seems to back her up. In 2017, a review in the journal Circulation found "an abundance of data" to show a link between skipping breakfast and being overweight.

Researchers at Cornell University a few years earlier, though, reported that breakfast skippers, despite their hunger, did not overeat at lunch or dinner. In this study, they saved an average of 408 calories per day. And a study of adults in Canada published in 2016 found that eating breakfast had little effect on rates of obesity or being overweight.

Perhaps twice as many Americans aren't eating breakfast now, compared with 40 years ago. Crandall says some people may be skipping breakfast due a trend called intermittent fasting. That's when they pass on meals to take in fewer calories and lose weight. There's a lot of hype about it, but, she says, there’s little evidence it works in the long run. Since your metabolism changes from morning to night, the same slice of bread eaten earlier in the day is actually less fattening.

She insists the bulk of the science favors a healthy breakfast. "It's not just about your weight. It's also about vitamins, minerals, and muscle mass. We have to think of larger pictures, of what food is really doing for your body versus 'I want a quick fix for weight loss.' "

Control Blood Sugar

Eating breakfast helps keep your blood sugar steadier throughout the day, whether you have diabetes or not. For people with normal glucose test results, this might help you avoid insulin resistance, which can lead to diabetes. Drops and spikes in your blood sugar can also affect your mood, making you more nervous, grumpy, or angry.

If you have diabetes, "Don't skip breakfast," says Osama Hamdy, MD, PhD, with the Joslin Diabetes Center. He says when people with diabetes miss their morning meal, they're more likely to get low blood sugar, also called hypoglycemia.

Hamdy says low blood sugar "is not a joke. This is a dangerous scenario." It can make you tired, anxious, irritable, or shaky. More serious symptoms include an irregular heartbeat and seizures.

His advice for people with diabetes is a breakfast that's easy on the carbs with balanced amounts of protein and fats. He suggests milk and oatmeal, or eggs and a piece of whole grain toast. The American Diabetes Association recommends including lots of fiber in your breakfast, about 7-10 grams, and limiting yourself to 400-500 calories.

People with diabetes should check their blood sugar to see the effects of their breakfast choices. For example, while some people do fine with oatmeal, it may cause spikes for someone else.

Good for Your Heart

Recent studies show a link between breakfast and heart health. In 2017, the Journal of the American College of Cardiology reported that people who skip breakfast are more likely to have atherosclerosis. That's when your arteries narrow and harden because of the buildup of plaque. It can lead to heart attack and stroke. These people were also more likely to have bigger waistlines, weigh more, and have higher blood pressure and cholesterol levels.

Maybe that's related to higher blood sugar, which, over time, can raise your odds for heart problems. Or maybe without breakfast you'll have a harder time getting the recommended amount of daily fiber.

Another study that found breakfast skippers have a higher risk of heart disease also pointed out that they were more likely to smoke, drink more alcohol, and exercise less, too -- unhealthy habits that can lead to heart problems.

Which raises a question: Is missing breakfast bad for you, or are people who don't eat breakfast worse off for other reasons?

Iva Smolens, MD, a thoracic and cardiac surgeon, says the current research doesn't fully answer that. She believes skipping breakfast is one of many cultural changes over the past few decades that have hurt our health.

"We're all leading these crazier lifestyles," she says. "We run out the door. We don't eat breakfast. You eat fast food in your car. The next thing you know, you've gained 20 pounds. Is it skipping breakfast that caused that, or is it everything combined? I think it's everything combined."

So eating breakfast may not solve the problem, but it's a good place to start.

Do Better at Work or School

"The other reason we tell people 'Don't skip breakfast,' " Hamdy says, "is when you kick-start your day, you need your metabolism to be up and working."

Regularly eating a healthy breakfast helps us pay attention, remember, and perform better. Children and teens concentrate better at school, get higher scores on tests, and are less likely to be tardy or miss school days.

Jo says a pre-workout snack can help your focus as well as your efforts.

Without breakfast, your body to goes into conservation mode, Hamdy explains. That's when your brain slows everything down because you don't have enough energy.

Research is ongoing into how breakfast affects the way your brain works.

Set Yourself Up for Success

Remember, pair carbs with protein, like a bowl of whole-grain cereal with milk and fruit. Don't have time for a meal at home? Pack a breakfast you can eat on the go, like a banana and trail mix with a carton of milk.

If you keep it simple and plan ahead, eating a healthy breakfast shouldn't take much time. Chop your breakfast ingredients while you've got the knife and cutting board out to prep dinner. Put out bowls or the blender before you go to bed. On Sunday, make a week's worth of hard-boiled eggs and keep them in the fridge.

You may be tempted to reach for a breakfast bar or protein drink, especially after exercise. While that's better than nothing, Jo's advice is to not make it a habit. "Use them rarely," she says. "They're not going to be as filling for the same amount of calories as you'd be getting from less-processed food."

Yet even the best plans can go astray. When you feel you have no choice but to miss breakfast, keep in mind that it's probably not the worst thing you'll do that day.

"We always say you can perform without breakfast," Crandall says. "You just won't perform well."

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