Watermelon

Watermelons are mostly water — about 92 percent — but this refreshing fruit is soaked with nutrients. Each juicy bite has significant levels of vitamins A, B6 and C, lots of lycopene, antioxidants and amino acids. There's even a modest amount of potassium. Plus, this quintessential summer snack is fat-free, very low in sodium and has only 40 calories per cup. .

"Foods that are high in antioxidants and amino acids allow your body to function optimally," said Angela Lemond, a Plano, Texas-based registered dietitian nutritionist and spokesperson for the Academy of Nutrition and Dietetics. "Antioxidants help prevent damage, and cancer. Amino acids are the basic building block for protein, and protein is used in virtually every vital function in the body."

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Lycopene has been linked with heart health, bone health and prostate cancer prevention. It's also a powerful antioxidant thought to have anti-inflammatory properties, according to Victoria Jarzabkowski, a nutritionist with the Fitness Institute of Texas at The University of Texas at Austin.

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Citrulline (found in the white flesh near the rind) is a valuable amino acid that converts to the amino acid arginine. These amino acids promote blood flow, leading to cardiovascular health, improved circulation, and according to research at Texas A&M University, erectile dysfunction improvement (you'd probably have to eat a lot of the fruit to get a Viagra-like effect, though).