Nearly everyone's heard of the grapefruit diet. It's a short-term approach to weight loss (low carb, healthy proteins) with one unique feature. For 12 days you're supposed to eat a serving of grapefruit with every meal. It appears that by adding grapefruit to a protein-based meal, your metabolism gets kicked into overdrive.

This diet's a quick fix and it's really for those folks looking to drop a few pounds quickly. But I've always had a hunch that there's something worthwhile about this diet just waiting to be discovered. Sure -- grapefruit is healthy. It's packed with vitamins. But why does adding it to your diet seem to spur on weight loss?

Well -- a new study published in the medical journal Diabetes zeroed in on one secret ingredient in grapefruit responsible for that sudden boost in metabolism.

More than just an antioxidant
Grapefruits contain a type of flavonoid called naringenin. It's basically an antioxidant that seeks and destroys free radicals (those nasty agents that promote cancer). But as followers of the grapefruit diet can tell you, naringenin also boosts your metabolism.

In fact, the new Canadian study examined exactly how naringenin works and why it promotes weight loss. Scientists divided healthy mice with normal body weight into four groups. They fed one group a normal, healthy diet. The second group received a high-fat, high-calorie diet. The third and fourth groups received a high-fat, high-calorie diet along with a naringenin supplement.

After just four weeks, the mice on the high-fat, high-calorie diet became obese. In addition, they became insulin and glucose intolerant.

On the other hand, the two groups who received the naringenin supplement fared much better. Despite the same high-fat, high-calorie diet, these mice didn't gain weight like their counterparts. In addition, the naringenin mice didn't develop key health factors linked to Metabolic Syndrome.

What's Metabolic Syndrome?
Sometimes called "Syndrome X," it's when you have significant fat around your belly as well as high blood pressure, high cholesterol, and insulin resistance. According to some published reports, as many as 40 percent of adults over age 60 have Metabolic Syndrome. And many experts believe that once you've got it, you also significantly increase your risk of suffering diabetes, heart disease, and stroke.

But the mice taking naringenin didn't get metabolic syndrome. In fact, they lowered their triglyceride and cholesterol levels. They also continued to metabolize glucose normally and they never developed a resistance to insulin.

So how did naringenin work such magic? Did it block the absorption of the fat? Did it suppress the appetite?

Well, in fact, none of the above. The naringenin mice never absorbed the fat because their livers got kicked into high gear and flushed out what they didn't need for energy.

Words of caution
Now -- before you go off and start eating grapefruit with every meal, there are a few things you need to know:

1. First off, this study involved mice. As a general rule, I don't put a whole lot of stock into a study's findings if it's only proven to work on mice. Scientists still have a long way to go to prove that naringenin works the same magic in humans. But given what we already know about grapefruit, I've got a pretty good hunch that scientists will eventually find that this powerful antioxidant does have a positive affect on human metabolism.

2. Secondly, the mice didn't drink grapefruit juice every day. They took naringenin extracts. So it's tricky to determine how much you or I would need to get the same benefits of naringenin. According to the study authors, you'd have to drink roughly six to eight glasses of grapefruit juice a day to get the equivalent to what the mice took. And that's a lot of grapefruit juice. It's probably a better option to take a grapefruit juice capsule, like the mice did. But they're hard to find.

3. Thirdly, grapefruit juice is pretty powerful stuff. In fact, it blocks the absorption of certain types of drugs, like statin drugs and calcium channel blockers. (Unfortunately, men and women taking these drugs are the ones most likely to benefit from naringenin.) So make sure to consult with your doctor before adding naringenin to your diet, especially if you take any type of prescription drug.

4. Lastly, be sure to add a good probiotic capsule before meals if you begin a naringenin regimen or start eating grapefruit regularly. As I said before, grapefruit juice is pretty powerful stuff and can be hard to digest. But the probiotic will help regulate your digestion and soothe your stomach.