Perhaps no other nut grows in such a bizarre manner as the cashew. Their trees, which reach heights of around 20 feet, grow in tropical climates throughout the world. The top 3 countries for production are Vietnam, Nigeria, and India. Since they aren't grown in the United States, most people have no clue that they actually grow in pods which are to the bottom of an "apple" as pictured above.
Is the cashew apple fruit edible and good for you? Technically it not a real fruit, but what's known as a false fruit. The nut is the reproductive seed of the tree and the apple is there to divert an animal's attention away from it (so it eats or attempts to eat the apple rather than the nut). This is where nature has yet another trick up her sleeve... the fruit is edible, but it doesn't taste good. This means an animal may take a test bite, determine the tree does not produce edible food and move on (and therefore never discovering the yummy and nutrious nut).
What does cashew fruit taste like? Unlike real apples, these are described as rotten, horrible, and disgusting are common adjectives used to describe them. Leaving a tart aftertaste, many liken it to that of a rotten papaya or guava. So can you eat a cashew fruit apple? Yes, contrary to what some have said, they are not poisonous and despite their bitter taste, many people do eat them.
In Thailand, this fruit is sold by many street vendors. Cashew apple juice is actually used in both alcoholic and non-alcoholic juice beverages in South America. In countries such as India and Brazil, you can purchase jams and chutneys made from them, though other ingredients such as sugar are used to make the taste more appealing. You will not find fresh cashew fruit for sale in the United States and it's unlikely you ever will. With little to no demand and the fact that it perishes extremely fast make it an unprofitable fruit for import.
Based on their nutritional facts, you could say they are both good and bad for you. Good, since 100 grams of the raw apple contains anywhere from 146 to 372 mg of vitamin C (60 mg is your RDA). Bad, because their high tannin content (more in the red, less in the yellow varieties) interferes with your body's absorption and processing of protein. Aside from the C, their content of vitamins and minerals is not particularly stellar. The amount of total antioxidants they have (ORAC value) is quite low relative to most fruits.
One study has suggested that cashew apple juice may help with burning fat during high intensity exercise. As a result, some clever marketers have peddled products with it for weight loss, trimming belly fat, and other promises which are quite dubious since only one study does not necessarily mean factual claims. Plus, because of the tannin's interference with protein synthesis, any increased fat burning may be offset by a decrease in fitness and athletic performance.
Research Support, Non-U.S. Gov't: In Vitro Cell-Mediated Antioxidant Protection of Human Erythrocytes by Some Common Tropical Fruits PDF 2012