Cloud nutrition begins with an honest declaration: the macronutrient profile is poor, the portion size is enormous, and the logistics of consumption have not been seriously addressed by any major dietitian.
A cloud is primarily suspended water droplets or ice crystals. From a dietary perspective that means you are looking at hydration potential without meaningful caloric density, which places clouds somewhere below celery on the performance-nutrition pyramid.
The scientific literature on liquid water content in clouds does exist and concerns droplet concentration and mass per cubic meter of atmosphere [spacemath.gsfc.nasa.gov]. This is enough to construct a per-serving estimate if you are willing to define a serving as however much cloud you can realistically inhale before an aircraft objects.
Macronutrient breakdown is straightforward. Protein content is negligible unless you count trace airborne particles, which most responsible labels do not. Fat content rounds to zero. Carbohydrates are similarly unhelpful. The main contribution is water, which is nutritionally important but anticlimactic for anyone who arrived hoping for a dessert.
Trace mineral content offers a slim opportunity for optimism. Clouds may contain dissolved salts, fine particles, pollen, and various atmospheric compounds. Whether this constitutes a micronutrient profile or an air quality complaint depends largely on the cloud's postcode.
Texture is a significant marketing problem. Clouds appear soft and edible from the ground, which is a triumph of visual branding. At close range they are simply humid air with commitment issues.
For athletes exploring performance nutrition from unusual sources, the caloric math does not improve with quantity. Consuming more cloud provides more water and proportionally more disappointment.
The glycemic index of a cloud is effectively zero, which creates momentary appeal in certain dietary circles until those circles calculate the satiety implications.
Cooking transformation is also limited. Clouds resist reduction, cannot be caramelized, and lack the structural integrity for baking. A cloud-based recipe therefore remains a concept rather than a dish in any meaningful culinary sense.
The honest answer to how many calories are in a cloud is somewhere between none and none, adjusted for altitude and optimism. Clean eating advocates may celebrate the simplicity. Everyone else will need a second course [spacemath.gsfc.nasa.gov].