12 healthy ways to gain weight safely and build muscle fast, according to dietitians

• If you want to gain weight quickly, eat an additional 500 calories a day.
• If you have a fast metabolism, you might need to eat even more calories to gain weight.
• Once you're gaining weight, begin strength training to ensure you're adding muscle and not fat.

Being overweight is a more common issue for Americans — but being underweight can be just as unhealthy.

In fact, being underweight — a BMI of 18.5 or lower — can lead to health complications like a weakened immune system or fragile bones.

Many different factors can contribute to being underweight, like genetics, taking certain medications, not eating enough, or recovering from a serious illness.

If you need to gain weight or want to for aesthetic purposes, it's important to do so in a way that ensures you're getting proper nutrition. Here are 12 tips for gaining weight in a healthy way.

1. Eat more calories

To gain weight, you'll need to eat more calories than you burn. On average, you'll need an additional 3,550 calories to safely gain one pound of body weight. If you're looking to put on a pound a week, that's about 500 additional calories a day.

Weight gain goals will differ by person and should be discussed with your doctor or a registered dietitian, but in general, a weight gain of about half to one pound a week is considered safe, says Jaime Gnau, RDN a biomedical sciences clinical instructor at Missouri State University's dietetics program.

Here is a breakdown:

Your metabolism also plays a role. If you have a fast metabolism, your body burns more calories at rest, which can make gaining weight difficult. People with a fast metabolism will need to eat more calories than the average person to gain weight.

2. Choose high-calorie fruits and vegetables

Whether you're trying to gain, lose, or maintain your weight, eating a well-rounded diet of fruits, vegetables, protein, and grains is key to getting adequate amounts of vitamins and minerals.

An easy way to meet your daily fruit and vegetable requirements is to opt for high calorie produce like:

• Dates (66 calories per date)
• Raisins (120 calories in 1/4 cup)
• Black beans (220 calories in 1/2 cup)
• Bananas (112 calories per fruit)

3. Eat energy-dense foods

One way to consume more calories without feeling overly full is to eat energy-dense foods, Gnau says, which have more calories per gram.

Energy-dense foods include:

• Avocados (240 calories per fruit)
• Nuts, like almonds (180 calories in a ¼ cup)
• Olive oil (120 calories in one tablespoon)
• Dried fruit, like apricots (90 calories for about five pieces)
• Whole milk (about 150 calories per cup)

Important: Even if you're trying to gain weight, it's important to consume mostly nutritious foods. Baked goods, like pie, cake, and cookies are also high in calories and fine to consume in moderation, Gnau says. But these foods contain added sugars, which can increase your risk of heart disease and diabetes, so it's best to limit your intake.

4. Drink your calories

Beverages like smoothies or protein-packed shakes can also help add calories to your daily intake. Some examples of high-calorie beverages include:

• Smoothies with peanut butter, chia seeds, fruit, yogurt, and whole milk.
• 100% fruit juice which has more calories than whole fruit. Healthy people can include a serving — one cup — of 100% juice each day as one of their fruit servings.
• Unsweetened protein powder, which can be added to drinks, oatmeal, or yogurt.

5. Add extras like condiments, sauces, and toppings

Adding sauces and toppings to foods can help bump up your calorie intake, Gnau says. Some condiments and toppings to add to meals include:

• Topping chili with shredded cheese (about 110 calories per ¼ cup).
• Spreading peanut butter (about 190 calories for two tablespoons) or almond butter (about 190 calories for two tablespoons) on toast or pancakes.
• Preparing roasted vegetables with olive oil (120 calories per tablespoon).
• Topping salads with sunflower seeds (85 calories per tablespoon) and shredded cheese (about 110 calories per ¼ cup).

Important: Adding extras can help boost calorie intake, but be aware of added sugars, sodium, and saturated fat in sauces and condiments.

6. Increase protein intake

As you gain weight, you'll add both fat and muscle.

Muscles are made of protein, so eating more protein while strength training ensures the extra calories go more toward building muscle and less toward fat.

A small 2012 study examined the effects of low, moderate, and high protein diets on weight gain. Participants ate a caloric surplus for eight weeks, with one group receiving a 5% protein diet, another a 15% protein diet, and another a 25% protein diet.

Individuals in the highest protein diet group gained about 14 pounds, while those in the lowest group gained about seven pounds. Body fat composition was the same across all groups.

Quick tip: In general, 0.5 to 0.8 grams of protein per pound of body weight has been shown to help with weight gain.

Examples of high-protein foods include:

• Salmon (29 grams of protein in five ounces)
• Eggs (6 grams of protein per egg)
• Beans (6 grams of protein per ½ cup of black beans)
• Nuts (6 grams of protein her ¼ cup)

Excess protein can increase the chance of dehydration so be sure you're drinking plenty of water when increasing protein intake. Gnau recommends limiting your protein intake to no more than 35% of your daily calories. It's also a good idea to talk with your doctor or a registered dietitian to develop an individualized plan.

7. Start lifting weights

Strength training can help you gain weight by building muscle, says Jenna Coker-Jones, a health and fitness coach with her own private practice.

Quick tip: Jones recommends weight training at least three to four days a week and lifting heavy enough weights that you can only do six to eight reps at a time.

Try to avoid intense cardio, like running, because it could burn the additional calories you're eating and prohibit weight gain. Instead, opt for low-impact cardio like walking.

"Walking is such an important resource that many don't use it for training," Jones says. "You get the benefits of being outside and it's a great addition to strength work if you want to do less cardio and more gaining."

8. Go for full-fat dairy

Reach for whole milk, as well as full-fat cream, yogurt, and cheeses. These higher-fat versions are a good way to consume more calories while also getting essential nutrients like protein.

One cup of whole milk contains about eight grams of protein and close to 150 calories. A cup of skim milk also has around eight grams of protein, but only about 90 calories.

If you're doing strength training, it can aid in both recovery and building muscle. In a small 2013 study, researchers found that men who consumed milk beverages after resistance training had a greater protein accretion in their muscles than those who consumed a soy beverage. This protein accretion and synthesis is essential for increasing muscle mass.

Also, a small 2010 study of young women found that drinking fat-free milk after heavy resistance exercise led to greater muscle mass and strength gains than drinking a carbohydrate beverage.

In fact, a 2019 analysis found that dairy consumption led to a decrease in fat mass and an increase in lean body mass. That means it can help you gain muscle weight, rather than fat.

Note: Cheeses like cheddar and parmesan are lower in lactose than other dairy products, making them a good option for people who are lactose intolerant.

9. Don't be afraid of carbs and starches

Healthy carbs and starches can increase your caloric intake while providing beneficial nutrients.

For example, grains like buckwheat and quinoa are rich sources of protein and minerals like potassium and magnesium.

Getting more complex carbohydrates can also fuel strength workouts and may help with the process of protein turnover, which helps you build and maintain muscle.

Bulk up your meals with the addition of healthy carbs and starches like:

• Whole grain or whole wheat breads and cereals
• Oats
• Brown rice
• Potatoes
• Pasta

10. Make some mealtime swaps

If you want to eat more during your meals, you might try eating off a bigger plate. Some research has suggested that larger plates and tableware can cause people to eat larger portions. However, a small 2019 study found no connection between plate size and consumption.

While the research goes both ways, eating from a bigger plate might be useful if you're intentionally trying to consume more calories.

You can also try eating your food in a strategic order. Rather than filling up on low-calorie veggies first, get your dense proteins out of the way. This will help you meet your caloric needs before you get too full.

11. Eat and snack frequently

Eating more frequently can help you consume more calories and maintain your body's energy levels.

Having more, smaller meals throughout the day can also be helpful if you find it hard to consume large meals in one sitting.

A large 2017 study found that eating more than three meals per day was associated with an increase in body mass index (BMI), while people who only ate one to two meals a day had a decrease in BMI.

12. Try weight gainer products

If other diet and lifestyle changes aren't helping you gain weight, there are also weight gainer products and supplements that can help. They include products like Optimum Nutrition Serious Mass weight gainer protein powder and Naked Mass weight gainer protein powder.

However, supplements aren't regulated by the FDA, so you might want to talk to your doctor or dietician about finding a product that is right for you.

The best whey protein powder

• Best overall: Naked Whey Protein, $95 on Naked Nutrition

• Best for mixing: Cellucor Whey Protein Isolate, $70 on Amazon

• Best-tasting: Optimum Nutrition Gold Standard 100% Whey, $75 on Amazon

Insider's takeaway

If you need to put on weight safely and healthily, focus on eating more nutritious energy-dense foods, increasing your protein intake, and lifting weights. Everyone's goals will be different, but in general, a healthy range for weight gain is about 0.5 to 1 pound per week, Gnau says.

Always check in with your doctor before changing your diet and workout routine. A registered dietitian can also help develop a plan to help you meet your goals.