Do you need to exercise to gain muscle weight?

My BMI is really low and I need to gain at least 5 kilograms just to be on the edge of the normal category (and another 5-10kg to be in the middle of the normal category)

I have less than minimal understanding of how nutrition works, but what I’ve got is that you can either have fat or muscle weight.

Adding fat is much easier, but just 2 or 3 kg of additional fat and your body fat percentage goes way up and you start looking fat, even though my BMI would still be underweight.

As can be seen from the title, I don’t know how muscle weight works, do you have to exercise to get it or can you get it even by just eating with some basic walking and stuff, at least if you’re underweight like me? I’ve read somewhere that you shouldn’t exercise if you’re really underweight, so that would make sense I guess.

Also, the main thing for building muscles I should look for is protein, right?

You will add some muscle mass just by eating more, if only because as you get heavier, you need bigger muscles to move your bulk around.
But, if you want to preferentially gain muscle mass, you need to exercise as you eat more, or you are going to get fat, rather than strong.

I just want to be at least 5kg heavier, so what should I do to get the weight as quickly, but safely as possible?

Eat lots of protein (drink a protein shake or two every day), and exercise the major muscle groups (legs, chest , arms, back), especially legs. Concentrate on strength-building exercises (6-8 reps to failure), and don’t do a lot of strenuous cardio (you need to do some). 5kg is a fair amount of muscle to put on, but if you are as underweight as you say, then you should be able to do this in a few months. Getting the advice of a personal trainer would be valuable.

Not just lots of protein but lots of calories, period.

Yep.

How really underweight are you? In general if you are not in good shape or have health problems it’s a good idea to get a doctor’s OK before ramping up from no exercise onto an intense exercise program. Aside from that I would follow **beowulff’s **suggestion.

Consuming “good” fats will also have it’s place. Mix a few spoons of coconut or avocado oil into your shakes.

Yeah building muscle will be extremely difficult without ample amounts of all three macronutrients (well, after the initial muscle gain that typically occurs when a sedentary person begins exercising). The key is to choose calorie dense and nutritional foods

My BMI is 16.7, 170cm and 50kg , underweight is a BMI less than 18.5 (based on this at least https://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm )

What exactly are calories? Isn’t that just a unit of energy value of either proteins or carbs or fats? And what’s the role of fats and carbs in building muscles?

Yes, and alcohol as well. The roles of fats and carbs in muscle building are numerous. By consuming adequate calories from fats and carbs, you “spare” the protein you eat to be used for building muscle, rather than simply burned for energy. Also, adequate good fat intake, counterintuitively, aids in your body burning fat. Fat plays a role in hormone regulation as well.

Although I agree with all of this, I wouldn’t advise adding a lot of fats to a beginners diet without doing a nutrition survey first. Most Western diets are already pretty fat-laden. Adding some MCTs would be ok.

Notice I said “adequate” calories from carbs and fat, not “lots”. And I should have specified I was talking about “good” fats, with most calories from mono-and polyunsaturated fats and at least some saturated fats. He’s quite underweight as is.

Generic exercise won’t help you gain weight. Walking, biking, running, etc won’t really add much muscle. To add 5kg, you’ll need to actually do a weightlifting program. And it’s not enough just to lift a few weights every now and again. To actually build muscle you’ll need to make sure you’re lifting enough weight to stimulate muscle growth. Too little weight and you’re just doing an aerobic workout. Too much weight and you’ll injure yourself. And you’ll want to make sure you adequately work all the muscles in your body so you stay balanced.

Do you have a friend who does weightlifting? Starting out with someone more experienced will give you a much better chance of success. If you don’t know someone who works out, I strongly recommend you get a personal trainer for a little while. Although you can figure weightlifting out on your own, you’ll have to really understand the concepts to properly execute them. Use your friend or trainer as a resource to determine what your diet should be.

One other thing to keep in mind is that if you don’t use your muscle, you lose it. Once you gain muscle, you’ll need to exercise the muscles on a regular basis or your body will reclaim the protein. So be sure you think long-term and look at ways to keep exercise as part of your life even after you met your BMI goal.

In addition to the risk of injury, lifting too heavy doesn’t allow you to engage enough muscle fibers needed to really build muscle. That’s why the typical powerlifter doesn’t resemble the typical bodybuilder; different training protocols. As a general rule of thumb (emphasis on ‘general’), 8-12 reps is the sweet spot for muscle fiber recruitment. Lower reps, say below 6, is ideal for building strength. The ideal solution is to incorporate both training styles across your workouts.