How can i lose weight before beach fastest. exercise or diet?

Both: A combination of exercise and a healthy, balanced diet will help you drop the pounds quickest. Doing one or the other is tougher and ends up with rebound weight gain or an unhealthy diet. Stay away from "fad" diets, as they rarely keep the pounds off.

Nutrient dense foods: Eat foods that are nutrient dense (like meat, fish, poultry, eggs, cheese, low starch vegatables and water) avoid foods that are not nutrient dense (like starches and sugars, including fruit) nutrient dense foods will increase your basal metabolic rate. On the other hand, starches and sugars impair thyroid metabolism via affects on your liver (which helps activate thyroid hormone).