Did you know that about two percent of American adults 20 and older are actually underweight? Admit it: You’re probably thinking, “Lucky dogs! I wish I had that problem!” right now.
But being underweight isn’t any better for your health than being overweight. And believe it or not, gaining weight — the right way, at least — can be just as challenging as losing weight.
Sure, you can start gobbling down bags of chips and boxes of donuts, but just like when you’re losing weight, the quality of the calories you’re consuming are just as important as the quantity. If you’re trying to gain weight, odds are you’re aiming to gain muscle mass, not fat.
(Note: There are medical conditions, like hyperthyroidism, that can affect weight gain, so consult your health care provider for treatment that’s appropriate for your situation.)
How Can I Tell if I’m Underweight?
When it comes to losing or gaining weight, it’s natural to want to focus on a specific number so you can say, “A-ha! Here is my goal. All I need to do is reach #pounds!”
But a lot of things can influence the number on the scale, like height, gender, age, and genetics. On top of that, the scale can’t tell the difference between muscle, fat, bones, organs, etc., so it can’t tell you how fit or healthy you are.
You’ve probably heard of body mass index (BMI), which is a simple height-to-weight ratio: your weight (in kilograms) divided by the square of your height (in meters). That number determines which general weight category you fall into, according the Centers for Disease Control and Prevention (CDC):
- Below 18.5 = Underweight
- 18.5 – 24.9 = Normal or Health Weight
- 25.0 – 29.9 = Overweight
- 30.0 and Above = Obese
Like your bathroom scale, your BMI doesn’t take into account those aforementioned things that can affect your weight or directly measure fat, so the CDC acknowledges that BMI is not the final word on your fat levels or health. But it can be used to determine your general weight category and the possible health risks associated with each.
Instead, it may be wiser to focus on your body fat percentage, which measures your body composition and how much of that is fat. When you’re trying to gain weight, it’s a good ratio to be aware of to make sure you’re gaining muscle, not fat. It can help you set realistic nutrition and fitness goals and expectations.
What’s Wrong With Being Underweight?
A certain amount of fat is essential for a healthy body. If you’re underweight, you may be missing essential nutrients, which can affect key body processes; in addition, low body weight in women could lead to the loss of a menstrual cycle.
Meanwhile, there are people who are at a healthy weight, but don’t have enough muscle on their frames, says Marie Spano, M.S., R.D., C.S.C.S., C.S.S.D., sports nutritionist for the Atlanta Hawks.
In people who perform limited strength training, as well as those coming off of injuries or illnesses, muscle mass can frequently be lower than is optimal for good health. And your risk of having too-low levels of muscle increases over the years.
After age 30, muscle mass can decline by three to eight percent per decade, contributing to metabolic issues, loss of strength and mobility, and the likelihood of falls as you age.
“Improving muscle mass can lead to gains in strength, endurance, and functional living,” Spano says.
How Fast Can I Gain Weight?
How much weight you can gain in a given amount of time depends on multiple factors, including your genetics, gender, age, and other factors.
But generally, if you’re trying to sustainably gain lean mass, most people can build between 0.25 and 0.5 pounds per week, explains Sam Simpson, C.S.C.S., C.P.T., co-owner and vice president of B-Fit Training Studio in Miami. Meanwhile, it’s possible to gain upward of two pounds of fat per week, although water weight would potentially be the cause of any further increases on the scale.
To determine where your weight gain is coming from (from fat vs. muscle), regularly measure both your weight as well as body fat percentage, recommends nutrition scientist Lisa Davis, Ph.D. Your gym may have a bioimpedance (BIA) device that’s available for use, or you can invest in an at-home scale that is equipped to measure body fat percentage as well.
How to Gain Weight the Healthy Way
Gaining weight in a healthy way — whether from fat or muscle — isn’t as simple as letting yourself go at the all-you-can-eat buffet or pumping iron 24/7. You have to take a targeted, science-backed approach that keeps your health at the forefront and yields the results you want.
1. Nix Processed Foods
Even if you’re trying to bulk up, it’s still important for your overall health that you’re filling your body with whole foods, says Davis. She notes that trying to gain weight by eating processed foods like soda, refined grains, bacon, and trans fats can increase your risk of conditions such as type 2 diabetes and cardiovascular disease. Instead, focus on healthy, balanced meals in proper proportions.
2. Increase Your Calories
“No one can be in a significant calorie deficit and build muscle,” says Albert Matheny, M.S., R.D., C.S.C.S., co-founder of SoHo Strength Lab.
To find out how many more calories you need to consume to gain weight, you need to first figure out your baseline, or how many calories you need to maintain your current weight, then add 300 calories to gain muscle mass. (And don’t forget the weight training; see #4)
3. Pay Attention to Macros
How you divvy up those calories between carbs, protein, and fat largely determines if your weight gained is from muscle or from fat.
Having an adequate amount of protein in your diet is necessary to build muscle. When you’re working out, you’re basically “breaking down” your muscles; the muscle-building phase happens when your body is repairing the damage — which is where protein comes in.
Protein is made up amino acids, which your body uses as the “building blocks” to create new muscle tissue. But how much protein should you be eating? To build muscle, consume between .5 and .9 grams of protein per pound of bodyweight per day — and no more than about 25 grams per meal.
To increase weight gain from fat, your macros should skew higher toward carbohydrates and fat, since it is the most calorically dense macronutrient, Davis says. The bulk of your fat should come from unsaturated sources like avocado, olive oil, and salmon.
An easier and faster way to increase lean mass is first to bulk, then lean out. Using this method, you only have to focus on one thing at a time — building, then leaning out, versus trying to build muscle AND prevent fat gain at the same time.
4. Strength Train at Least Three Times a Week
To build muscle, you should ideally strength train each muscle group at least two to three times per week. Otherwise, you will not be able to effectively build on your previous sessions and will actually backslide a bit between workout days. However, if you have been training for a few years, you may need to ramp things up to five or six days per week to keep progressing.
5. Perform Compound Lifts
“Isolation lifts and weight machines can be great for more specific physique goals of someone that has been lifting seriously competitively for many years, but for 99 percent of people, compound lifts will give you much more bang for your buck,” Matheny says.
That’s because compound (or multi-joint) lifts like squats, deadlifts, bench presses, and pull-ups tap a greater cross-sectional area of muscle, meaning you can lift and gain more from every rep. If you like to perform isolation moves, schedule them at the end of your workout as a way to further exhaust the muscles you prior worked during your compound lifts, Simpson says.
6. Focus on Hypertrophy Rep Schemes
To maximally increase muscle size, your training should take a hypertrophy scheme — a middle ground between max strength and muscular endurance. Simpson recommends schemes of three to six sets of eight and 12 reps, with loads heavy enough that you can just eke out your last rep of every set with proper form.
A requisite for muscle growth is to increase time under tension, he says. Time under tension is the total time your muscle resists weight during a lift. Give yourself up to 90 seconds to rest between each set.
7. Dial in Your Post-Workout Nutrition
“Remember your muscles don’t grow while you lift, they grow afterward in response to the stress of your workouts,” Matheny says. “Giving your muscle well-timed and sufficient protein to build and repair lean muscle while also carbohydrates and calories to support refueling of glycogen stores, hormone levels, and energy for your next workout.”
Generally, you should consume about 20 grams of protein with some carbs shortly after your workouts. Limit fats, which can slow down the absorption of protein. While recent research suggests that the post-exercise anabolic window may actually extend as long as several hours following exercise, there’s no harm in getting nutrients in early as long as you’re sticking to your overall caloric and macro goals.