Breakfast comes at a terrible time of day to make a rational decision. We're rushed. We're groggy. And we're famished.

We know it's good for us -- 90 percent of Americans think it's the most important meal -- yet fewer than half of consumers actually eat breakfast on a regular basis, according to the International Food Information Council.

Unlike other meals, however, breakfast is unique in that it can set the tone for your entire day -- for better or for worse. The trick is knowing how to eat it.

There is no perfect morning meal because the best breakfast depends on your body and individual nutritional needs, but you can't go wrong by eating "a moderate meal of mixed foods," said Richard Mattes, a professor of food and nutrition at Indiana's Purdue University. Start experimenting, using our guide below to see how common breakfast combos will affect your day.

Really bad: no breakfast at all.

Some people say they're not hungry when they wake up, but because you've fasted all night your metabolism -- and fat-burning ability -- slows down. Those who skip breakfast are also more likely to be overweight and consume more fat and calories the rest of the day, said Dr. Susan Biali, a dietetics specialist in British Columbia. Bypassing breakfast also makes you less productive and less likely to excel at school or work.

Very bad: coffee or tea only.

A daily cup of coffee or tea can give you hydration and a jolt of caffeine. Research has also linked both drinks to a variety of health benefits. Though it might hold you over until lunch, "it's only the hot liquid that is filling your stomach, tricking you into feeling satisfied," said Janel Ovrut, a registered dietitian in Boston. "You likely wind up overeating come lunch, when you're famished." To jump-start your metabolism, add a piece of fruit, Ovrut said.

Bad: coffee or tea, and a doughnut.

It's quick, easy and yummy, but you'll pay a steep price for the 90-minute sugar high. Doughnuts are a famously high-calorie, high-fat, high-carbohydrate breakfast that will leave you feeling "stuffed, sluggish and even sleepy," said New York registered dietitian Constance Brown-Riggs. Bagels, muffins and sugary cereals also "spike your blood sugar and set you off on an energy roller coaster for the rest of the day," said Tara Coleman, a clinical nutritionist in San Diego. A breakfast bar and orange juice might seem healthier, but "it's not much better than eating a candy bar and sugar cubes," said Dr. John La Puma, a physician and chef. Avoid sugary foods in the morning altogether.

Better: a bowl of low-sugar, high-fiber cereal with skim or low-fat milk, banana, whole-wheat toast and jam, and coffee.

Choose cereals that have at least 3 grams of fiber and less than 10 grams of sugar, such as Cheerios, Kashi's GoLean, All Bran or Fiber One. But even though this breakfast provides fiber, protein and vitamins, it's high in processed sugar, wheat and caffeine, said registered dietitian Ilona Fordham. "It won't provide long-term energy," she said. By lunch, you'll be hungry and might feel like overeating all day long.

Best: a hard-boiled egg and a bowl of slow-cooked oatmeal topped with berries, walnuts, raisins, flaxseeds or sunflower seeds -- with coffee or tea.

This meal is a nutritional powerhouse and easy to pull off if you make the oatmeal and the eggs the night before. Fiber and protein help slow down the digestive process, making you feel full longer and keeping your blood sugar steady. "The protein from the milk and nuts, combined with the healthy carbohydrates, will eliminate any sugar crashes for at least three hours," said Melissa Hawthorne, a Houston registered dietitian. To make this meal even better, add good fats by spreading peanut butter or avocado on whole grain toast or an English muffin.

Is it OK to eat a big Sunday brunch?

Fortunately, the weekend binge -- eggs, bacon, sausage, pancakes and more -- isn't likely to have a huge negative effect because "eating healthy is all about balance," said Timothy Harlan, a professor of medicine at the Tulane University School of Medicine in New Orleans. Sunday brunch is a special part of countless family rituals, he said. That alone can have health benefits. "It's the same with eating out," he said. Also, with a brunch, you'll eat only two meals on Sunday. So even if your meal consists of fatty and caloric foods, you have a chance to take in fewer overall calories.