“Mmmm,” Amy Cragg, a marathoner competing in the Rio Olympics for the U.S., once tweeted about the chocolate raspberry flavor of GU (pronounced “goo”), an energy gel. “Tastes like frosting!”

For Cragg, GU was an essential part of her training regime before last year’s Boston Marathon. She alternated blueberry-pomegranate and orange creme “GU Brews” before and during the race. Clearly, she felt the gel was essential for her performance. She is far from alone.

Energy gels like GU have become high-profile staples in the diets of elite athletes worldwide — including many competing in the Rio Olympics. Cooked up in “energy labs,” they come in dozens of different forms, each sounding more appetizing than the next. (GU, one of the leaders in the industry, is now offering waffle-like performance foods called “Stroopwafels.” Yes, they look — and taste — exactly like miniature waffles.)

Venezuelan marathoner Luis Orta is on the record as a fan of CarbBoom! energy gels, particularly the banana-peach flavor. And U.S. triathletes Katie Zaferes and Lindsey Jerdonek have said they fuel themselves with vanilla GU and vanilla PowerBar gels, respectively.

Full disclosure: I am a die-hard GU user. Before any workout, when I know I’m about to push myself, there’s nothing that gets me ready to go better than sucking down a GU. It seems to tell me I will have the energy to power through when my legs start to feel heavy and I can hear my heart pounding. As one of my college teammates once joked, “GU is my religion.”

But has the science of exercise nutrition really reached the point that pocket-sized packages of goop can unlock anyone’s inner Olympian? And if a product comes from an energy lab, does that mean it is necessarily better than something you could find in your pantry?

If you ask registered dietitian Nancy Clark, a Newton-based sports nutritionist whose clients have included members of Olympic teams, as well as the Boston Celtics and Bruins, the answer is no.

“If you’ve eaten in the hour or two beforehand, that food will give you the energy that you need,” Clark said in an interview. “Most people who are just exercising for about 45 minutes can get by with just a banana.

“If you haven’t eaten anything … an energy gel can be a good way to give you a quick boost to get through a 45-minute workout,” she added.

So if you’re exercising for less than an hour a day, then GU may not deliver the enormous energy boost you’re looking for. Especially if you’re exercising at a sustainable pace, something that isn’t too taxing to maintain, she said. The bottom line is that GU is not a magic bullet for a recreational athlete — at least, according to the hard nutritional science.

But that doesn't mean energy gels have no place in the recreational athlete's toolkit.

Dr. William Roberts, a past president of American College of Sports Medicine, says that he uses GU when he goes skiing with his kids. It’s a portable, convenient way to get a quick energy boost when he’s been out on the slopes for a few hours. Roberts says that he can definitely feel the midday boost from his double chocolate mocha GU.

But that boost may have nothing to do with a specialized formula from an energy lab. The boost is simply due to giving your body some calories and sugar when it needs more fuel, said Clark.

“Most of those gels provide 100 calories of sugar. It comes in many different forms, but it’s sugar. That sugar provides fuel to help the brain stay focused. And it also provides fuel for muscles,” Clark said. “You could have a spoonful of honey, you could have a spoonful of maple syrup, you could have a swig of orange juice, it’s all the same stuff.”

Fitness die-hards on Reddit have been swapping homemade energy gel recipes for years, using foods like honey, molasses and brown rice syrup. Turns out it’s not as much about the specialized formula of energy gels like GU, as much as it is about getting sugar, and calories in general, into you body when you need them. The form those calories take is not terribly important, as long as you can stomach it.

From Reddit to credentialed experts like Clark, the message seems to be the same: At the end of the day, the special ingredients in GU are things that we can find in our pantries at home, but formulated in tiny, chemically compact doses.

-- GU advertises 50 milligrams of sodium, an ingredient that can help you retain water while you exercise. That’s just salt. For comparison, a piece of bread has 147 milligrams of sodium.

-- GU advertises 20 milligrams of caffeine, a legal stimulant that has proven effects on exercise performance. A Diet Coke has more than twice that amount of caffeine -- or if you don’t want the fizz, a couple of ounces of coffee contains 20 milligrams.

So the magic of GU may be not in the specialized chemical formula, but more in the convenient packaging. It is certainly easier to slip a small gel-pack into your pocket during a long run than it is to carry a cup of coffee and a slice of bread.

If you can handle the viscous texture, it will give you what you need to perform (or in some cases, merely survive) during your endurance race. And all in a tiny 1.1-oz packet. But if you’re not running a marathon, or even racing all out at breakneck speed, you probably won’t notice a difference between taking a specialized energy gel and just eating a good breakfast before your workout.

Here is a (lightly edited) transcript of Clark debunking the jargon on the back of a GU packet. My unwavering belief in the virtues of GU for every athlete also took a pretty hard hit.

Emma: So let me get this straight. Caffeine improves performance, in general. Sodium helps you retain water, in general. Amino acids help you rebuild muscle, in general. But the amounts of all these things in GU are so small that they’re not going to help you? Nancy: Precisely. It’s unlikely to make a significant difference. But there is a time and a place. If you’re out there for three, four, five hours, well, there’s still not enough protein to do much, and there’s still not enough sodium … but sometimes anything is better than nothing. Do you think there’s maybe a placebo effect for people who take this? I love GU. I’ve taken it before some races. And it sort of became a part of a racing ritual for me. So I’d take the GU, and then I would know that I’m racing and then I would go faster… And what did you have for breakfast before the race? I’d always eat the same thing. I always eat a bagel, whether it’s just practice or a race. So the GU just gave you a little more fuel in your tank. So when would you have it? Right before the race? Right before the start. Nancy: And when would you have your breakfast? About three hours before. Right. So, you’ve digested your bagel, and your body is ready for some more fuel. You gave it more fuel. But so that could be anything…It’s not the GU specifically. You could’ve had a banana. But then again, we look at digestibility. The harder you go, the more likely you are to prefer a gel over a banana.

In short, if drinking Diet Coke, eating a bagel, or taking a spoonful of honey gets you into that racing mode -- and you can tolerate it -- then maybe you’ve already unlocked the magic that these performance gels advertise.

So maybe for us mere mortals who are not Olympic triathletes, GU and other energy gels really are something like the exercise version of Santa Claus. They're a wonderful thing to believe in on the starting line, and during training. Just as believing in Santa gets us in the spirit of giving around the holidays, maybe GU gets us in the spirit of competing.

Readers, reactions? What's your experience?