Citrus fruits are nutritional champs in general, and grapefruits are their king. Besides being just physically more intimidating than their generally sweeter siblings, grapefruits go deep and long with fiber, antioxidants and other nutrients. And besides... how many other citrus fruits have their own diet plan?

Despite their size, grapefruits have one of the lowest calorie counts of any fruit (they contain a lot of weight-loss-inducing water). A study done at the Scripps Clinic, La Jolla, California, found that obese subjects who consumed half of a fresh grapefruit before meals lost significantly more weight than those who did not. You can chalk much of grapefruits' calorie-controlling superpowers up to their high fiber quotient. Eating fiber-rich foods such as grapefruits contribute to a feeling of satiety that keeps your appetite in check throughout the day.

Grapefruits are especially high in vitamin C, which in turn is high in antioxidants that keep your cells safe from infection, and helps the rest of you recover more quickly from the common cold. No slouch in the area of non-C vitamins either, one grapefruit provides more than a quarter of your daily vitamin A requirement as well.

Despite their sweetness, a half-grapefruit a day will keep your blood sugar in check. Insulin is the hormone in your body that is charged with reining in blood sugar levels. If you become insulin resistant (as over 30 percent of the population is), your body needs to manufacture more of it, your blood sugar levels rise, and you become more susceptible to contacting type 2 diabetes. One study showed how subjects who ate half of a fresh grapefruit before meals displayed a meaningful reduction in both insulin levels and insulin resistance, compared to a control group that did not eat grapefruit.

Eating grapefruit can also yield significant benefits for your heart health as well. Besides being high in potassium which has been shown to lower the risk of death from heart disease, grapefruits improve your total cholesterol and “bad” LDL cholesterol levels. The same study showed how people who ate grapefruit three times daily over the course of six weeks enjoyed significant reductions in blood pressure.

And here's one you didn't see coming: eating grapefruits may reduce your risk of developing kidney stones! The most common kidney stones form from calcium oxalate, and the citric acid which grapefruit has in abundance may be effective at preventing them by binding with calcium in the kidneys and flushing it out of your body. In addition, because the citric acid can increase the volume and pH of your urine, it contributes to an environment that is very unfriendly to the formation of kidney stones to begin with.