I eat 4 bananas, 2 eggs and dry fruits daily and have been going to the gym for the last 2 months, but I haven't gained much muscle/weight. However, I feel the power inside me, as I'm now capable of doing 12kg bicep curls, whereas on the first day, I couldn't even do 5kg. I'm not using any high-protein products and don't plan to for at least 6 months.

Do you have any advice on how to increase my muscles naturally?

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1gram of protein per lean bodyweight in lbs
or 2g per kg

must be caloric surplus to build muscle