Can I increase my daily protein intake by drinking lots of milk? A friend drinks 2-3 liters a day and highly recommends it.
Milk doesn't have a lot of protein. For example, whole milk is 49% fat, 30% carbs (sugar), and a measly 21% protein. If you want to increase the protein intake then you want to eat protein rich foods such as:
Here are some protein sources; note not all of them are high protein but they do show you the calorie/carbs/fat breakdown.
The main reason a lot of people like to add milk is because it requires no cooking or preparation and it's easy to take in liquid calories. It can be part of a healthy diet but I wouldn't recommend drinking large quantities for reasons outlined in this answer.
Also note, if you are trying to gain weight then protein isn't that relevant. Instead you should focus on increasing your calorie intake. Part of that increase WILL be protein, but keep in mind:
More Protein != More Muscle.
Why milk isn't a high protein food
Taken from discussion below
~12.6 cups of whole milk have 1839 calories, 100 grams of fat, 163 grams of sugar, and 100g protein. On the other hand, 380 grams of Tuna has 440 calories, 1g fat, 0g carbs, and 100 grams of protein. So yes, if you want to increase your protein intake, then you should eat a high protein food. I mean any food can become 'high protein' if you eat enough of it. Fun fact, whole wheat bread has the same protein % by weight, ergo whole wheat bread has gobs of protein. I know Mark Ripptoe is a cool guy and all but at one point math wins over dogma
Milk is calorically dense, nutritionally awesome, has gobs of protein, and is simple.
Use whole milk.
The answer depends on what your overall goals are, and what you are doing with your training. So, let's look at a couple of different people with different goals:
Jack is a marathon runner. He runs for miles on end, and is into endurance. Jack needs to keep his electrolytes up, make sure he has carbs for energy. He still needs protein, but his muscles only need to be so strong, so his primary concern is energy. On the surface it sounds like Jack would benefit from a whole lot of milk, but he really only needs enough protein to maintain the muscle he has.
Joe on the other hand is a power lifter. Joe is taxing his muscles pretty hard, and constantly increasing weights. Joe needs both a lot of protein and a lot of Calories because the process of building muscle burns more Calories than maintaining it. Additionally, those muscles need the energy to lift the heavy weights. There is also a very strong correlation between lifting heavier weights and more body weight. This is why things like the Wilks Coefficient exist, because a 140lb guy lifting 140lbs requires more effort than a 200lb guy lifting the same 140lb. That and the process of lifting weights burns a lot of Calories in a relatively short time. Joe is the guy who needs to be drinking lots of milk.
Now, please understand that when Mark Rippetoe or any other weightlifter is recommending GOMAD (Gallon of Milk a Day), they are not recommending it for more than a month or two at a time. Drinking that much milk only works when you put in the effort at the gym.
For long term sources of protein, as a weightlifter, look at:
The bottom line is be intelligent about what you eat and why. Don't simply take someone's word for it, but find out the purpose behind the recommendation, the side effects, the time frame recommended, etc.
Milk is not evil, but it is not the end all and be all either. When you are trying to gain weight, GOMAD (or the 2-3L a day) can be an effective means to do so--particularly if you have a hard time gaining weight. It won't be all muscle, but it will be more muscle than fat if you are putting in work at the gym. There will also be a fair amount of water retention.
If you don't have problems gaining weight, then no GOMAD is not what you want. You want to control the rate of gaining weight so that it is mostly muscle. Stick with regular food for your protein intake.
Yes. The strength training classic "Super Squats" recommends a gallon a day. Milk is a great way to get protein and calories. A couple caveats: A lot of milk might not agree with you. (Might make you fart like crazy!) It can also have a lot of sugar and calories so if you are really obese, I wouldn't recommend a lot of milk, but you can of course just drink skim. Also, you might want to consider protein powders with milk instead of so much milk. The gallon of milk idea kind of went away with the invention of protein powder.