I want to gain around 10 kg in one month, is this possible?
If so, what would be the healthiest way of doing so?
I'm 23 years old and weigh 56 kg with a height of ~6 ft.
I would not suggest gaining that much weight in one month. You are not going to build more than 1 pound of muscle in one month which means you'll be gaining over 20 pounds in a month.
That is very unhealthy! That type of weight gain will negatively effect your hormone levels...increasing your estrogen level, lowering your testosterone, and slowing your thyroid.
It's a really bad idea.
While I'm no expert on this, there have been a couple very intriguing articles I read on this.
From the blog of Tim Ferriss, a post titled "From Geek to Freak: How I Gained 34 lbs. of Muscle in 4 Weeks"
Here are the six basic principles that made it happen:
Follow Arthur Jones’ general recommendations for one-set-to-failure from the little-known Colorado Experiment, but with lower frequency (maximum of twice per week) and with at least 3 minutes between exercises.
Perform every repetition with a 5/5 cadence (5 seconds up, 5 seconds down) to eliminate momentum and ensure constant load.
Focus on no more than 4-7 multi-joint exercises (leg press, trap bar deadlift, overhead press, Yates bent row, dips, incline machine benchpress, etc.) and exercise your entire body each workout to elicit a maximal hormonal (testosterone, growth hormone + IGF-1) response.
Eat enormous quantities of protein (much like my current fat-loss diet) with low-glycemic index carbohydrates like quinoa, but drop calories by 50% one day per week to prevent protein uptake downregulation.
Exercise less frequently as you increase strength and size, as your recovery abilities can only increase 20-30%, while you can often increase fat-free muscle tissue up to 100% before reaching a genetic set-point.
Record every workout in detail, including date, time of day, order of exercises, reps, and weight. Remember that this is an experiment, and you need to control the variables to accurately assess progress and make adjustments.
There are a few popular approaches to gaining weight quickly. GOMAD (Gallon Of Milk A Day) is a pretty popular method advocated by Mark Rippetoe in his Starting Strength program. Dozen Eggs a Day (DEAD) is another method which I'm currently playing with myself. One thing to keep in mind about DEAD vs. GOMAD is that w/ GOMAD you'll be getting a lot more calories which will certainly assist in the weight gain (although there will be a fair amount of fat gain). Mass gains will usually result in gaining some amount of both muscle and fat.
On many medical weight-gain programs, eating "doubles" will help weight gain. Meaning basically eating twice what you'd normally eat during a meal. Two sandwiches for lunch, etc. Also, another method to gain weight is to add in some meal replacements as snacks or as a second lunch/dinner/meal. Because the meal replacement has all the components of a meal, adding it to your diet tells your body that you've eaten another meal.
I'm not sure about 10kg in one month, but I know of one person who added 11kg in 8 weeks. It was the Gallon of Milk a Day (GOMAD) diet, where in addition to your normal food, you have 1 US Gallon of whole milk a day. Split it up between meals of course. In addition to the milk, you need to do some strength training which will trigger your body to use most of that milk for your muscles.
Now, Nick (the guy who gained 11kg in 8 weeks) dealt with lactose intolerance, and I think his review of the experience is a fairly balanced view of things.
Bottom line: your goals are very ambitious. While it provides you with something to shoot for, you may have to be OK with a slower pace. If you have a naturally high metabolism, you will have to eat so much food you will get sick and tired of eating.
Consider a cheap creatine (monohydrate) supplement for increased water retention. That should net you another 1-3 kg in no time.
If you work out, it should help a little with strength/endurance as well. And you really do want to spend some time in the gym. Even if you'll mostly be gaining fat, some muscle mass is better than none.