A man gains weight by eating more calories than he burns daily. But don't just chow down on donuts and pizza. Eating healthy protein, dairy, whole grains and starchy vegetables will help you look and feel healthier when you need to put on pounds.

From his cut physique in “American Psycho” to his emaciated look in “The Machinist” to his bloated bod for his upcoming role in “Backseat,” we’ve seen Christian Bale completely transform his look numerous times.

The basics of muscle gain and fat remain the same, regardless of your gender. To become lean, you need to strength train and follow a healthy diet.

When men approach middle age, they tend to gain weight, especially around the midsection. While this is avoidable, several factors fall into place during this time of life, leading to an increase of fat storage and loss of muscle tone.