In may online examination you will found this question, Here we have provided Questions, options and Answer. Also at the end you can read explanation answer.

Question:

weight gain occurs when a person consumes too much/many __________.

or

weight gain occurs when a person consumes too much/many blank

or

weight gain occurs when a person consumes too much/many

Options:

A)calories B)fat C)carbohydrates D) protein

ANSWER IS:

CALORIES

There are many people who interested in weight gain. So weight gains occurs when we consume more calories consistently every day then our body reaquire or burn each day.
Again Consumption of calories depend on your physical activity and body size. Let say your body need 2000 calories every day, but you are consuming 3000 calories consistently.
Then there are higher changes that your body will gain weight.
If every week your weight gain 0.2 kg – 0.9 kg per week then it is safe weight gain.
Rapid weight gain might contain some other side effects.

So as per conclusion:
Weight gain occurs when a person consumes too much/many calories.