Coconut milk is the water inside of a coconut and is pretty standard from brand to brand. It stands at around 50-100 calories per cup, with 5-10 grams of fat per serving depending on the additives.
What the majority of people call coconut milk is actually coconut water and comes from the liquid inside of a coconut, as opposed to being squeezed from the grated meat like actual coconut milk is. Coconut water is low calorie, but real coconut milk has a very high fat content and over 500 calories a cup. This is very seldom used as a drink, so coconut water is commonly referred to as coconut milk. It's important to remember that it changes not only from brand to brand, but from flavor to flavor. Unsweetened coconut milk is healthier as it has fewer calories and grams of fat, and flavored or sweetened brands have more of both.
Comparing three of the most popular coconut milks' nutrition facts, the average per cup is 50 calories, 5 grams of fat and 3 grams of sugar for unsweetened, and 80 calories, 5 grams of fat, and 7 grams of sugar for sweetened or flavored options. Coconut milk is high in saturated fats and natural sugars, both of which are healthy in moderation and help support a healthy diet.