Now, I believe the rules on the Nutrition Facts display are that ingredients have to be listed in descending order of amount, so in theory the first ingredient (celery) should be the single largest ingredient. Now because the math is much easier, I’m going to just assume the density of this green liquid is the same as water, and thus assume it weighs 474 g. Below I’ve listed each ingredient, (its kcal per 100g), a potential guesstimate as to how many grams of the food are in the liquid, and the resulting calorie total.
Celery (13) - 105g = 13.65 kcal
Cucumber (10) - 90g = 9 kcal
Spinach (23) - 85g = 19.55 kcal
Kale (49) - 75g = 36.75 kcal
Parsley (36) - 60g = 21.6 kcal
Dandelion (33) - 59 = 19.47 kcal
13.65 + 9 + 19.55 + 36.75 + 21.6 + 19.47 = 120.02–pretty damn close to that 120 listed on the bottle. So in essence, assuming celery is the number one ingredient by weight, and the known nutrition value per gram of the remaining vegetables, you can easily show mathematically there is no reason at all to question how the 120 kcal came to be. Note particular weight should given to Spinach / Kale / Parsley / Dandelion, while they are the bottom four ingredients by weight, they are far more energy dense per gram than the top two ingredients (celery / cucumber), so most likely the lion’s share of the calories come from those. If I actually knew the relative price of the input vegetables, I could make a better guess as to the distributions, since I’m sure most of the calorie padding comes from the cheapest, densest of the ingredients.