Alternately, and this is what I do, you can multiply 3.9% by the total volume of the beer (355mL for a standard bottle I think), to get the volume of pure alcohol. Then multiply this by the density of ethanol, 0.789 g/mL, to get grams of alcohol.
To make things easier, you can shorten this if you only drink beer from the common 355mL bottles: just multiply the alcohol percentage by 280 (roughly .789 * 355) to get your alcohol grams. This works best for me since the alcohol in the beer I drink ranges from 4 - 10%
1) eat real food - more vegetables, moderate meat, moderate fruits, less grains, less sugar, less vegetable oils.
2) exercise - moderate intensity cardio, sprinting, heavy lifting, dedicated stretching and mobility.
3) live - relax, de-stress, meditate.
Disclaimer: I'm not professionally qualified to make any formal recommendations. I've just done my homework and I'm my own guinea pig. All of my data, unless otherwise cited, comes from a sample size of n=1 (me).