For Skinny Athletes: How to Gain Weight Healthfully

author : Nancy Clark
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Although you cannot change your genetics and your tendency to fidget, you can boost your calorie intake. Here are five tips to help you bulk-up healthfully.

“My 8th grade son is 5'6” and weighs 108 lbs. He thinks drinking Muscle Milk will provide bulging muscles.”

“No matter what I eat, I cannot seem to gain weight. What am I doing wrong?”

“How many extra calories do I need to gain weight…?”

If you are among the few skinny folks who have a hard time bulking up, you may be feeling frustrated you can't do something as simple as gain a few pounds. For underweight athletes, the struggle to bulk up is equal to that of overfat people who yearn to trim down. Clearly, genetics plays a powerful role in why some athletes have so much trouble gaining weight (and keeping it on). 

Some athletes are genetically fidgety; they don’t like to sit still. Not only are they active with sports, but they are also active when sitting. For example, when I am counseling skinny clients, I observe them constantly tapping their fingers and shifting around in the chair—activities that burn calories. 

The technical term for these spontaneous movements is Non-Exercise Activity Thermogenesis or N.E.A.T. NEAT includes fidgeting, pacing while you wait for the bus, standing (not sitting) while you talk with a teammate, being animated when you talk to friends, or tapping your fingers when watching TV. If you overeat, NEAT helps you dissipate excess energy by nudging you to putter around the house, choose to shoot some hoops, or (yikes!) feel motivated to vacuum the house. NEAT can predict how resistant you'll be to gaining weight (1).

Historically, athletes have been told that consuming an extra 500 to 1,000 calories per day will lead to a gain of 1 to 2 pounds per week. Nature easily confounds this mathematical approach. For example, in a weight gain study where the subjects were overfed by 1,000 calories per day for 100 days, some people gained only 9 pounds, whereas others gained 29 pounds (2). NEAT likely explains the difference.

Researchers don't understand the source of this increased activity, but they do know that people with higher VO2max (a measure of athletic potential) are genetically predisposed to spend more time being active throughout the day. Hence the natural ability to be active for long periods (think marathon runners) might be connected to both NEAT and leanness. In contrast, unfit people (with a lower VO2 max; think couch potato) tend to do less spontaneous movement, and that can lead to weight gain (3).

Five tips for boosting calories

Although you cannot change your genetics and your tendency to fidget, you can boost your calorie intake. Here are five tips to help you bulk-up healthfully.

1. Eat consistently. Do NOT skip meals; doing so means you'll miss out on important calories needed to reach your goal! Every day, enjoy a breakfast, an early lunch, a later lunch, dinner, and a bedtime meal. 

2. Eat larger than normal portions. Instead of having one sandwich for lunch, have two. Enjoy a taller glass of milk, bigger bowl of cereal, and larger piece of fruit.

3. Select higher calorie foods. By reading food labels, you'll discover that cranapple juice has more calories than orange juice (170 vs. 110 calories per 8 ounces); granola has more calories than Cheerios (500 vs. 100 calories per cup); corn has more calories than green beans (140 vs. 40 calories per cup).

4. Drink lots of juice and low-fat milk. Instead of quenching your thirst with water, choose calorie-containing fluids. One high school soccer player gained 13 pounds over the summer by simply adding six glasses of cranapple juice (1,000 calories) to his standard daily diet. 

5. Enjoy peanut butter, nuts, avocado, and olive oil. These foods are high in (healthy) fats, and can be a positive addition to your sports diet by helping knock down inflammation. Their high fat content means they are calorie-dense. Add slivered almonds to cereal and salads, make that PB&J with extra peanut butter, and dive into the guacamole with baked chips (without the ‘bad” trans and saturated fats).

6. Do strengthening exercise as well as some cardio. Weight lifting and push-ups stimulate muscle growth so that you bulk-up instead of fatten up. Sooner or later, exercise will stimulate your appetite so you'll want to eat. Exercise also increases thirst so you'll want to drink extra juices and caloric fluids.

Weight gain supplements?

What about buying weight gain drinks? Save your money! As you can see from the chart below, they are expensive and offer nothing you cannot get via food. A hefty PB&J with a tall glass of milk adds about 1,000 calories for about $1.50. You’d spend about $5.50 getting those calories from Muscle Milk that you mix yourself from powder, or $14 if you pick up ready-to-drink bottles of Muscle Milk at the convenience store. 

To make your own weight gain drink in the morning, blend 1 quart of lowfat milk with 4 packets of Carnation Instant Breakfast and 1/2 cup powdered milk (1,000 calories total). Toss in a banana or other fruit for more calories. Drink half at breakfast and take the rest with you in a travel mug. Easy! 

The cost of calories

Gaining weight can be expensive if you choose lots of commercial protein shakes or sports supplements. You can get the same results with standard foods. 

Foods at home

Serving size



Cost/100 cals

1 cup Granola +
1 cup 2% milk

1 bowl




Peanut butter & jelly sandwich

3 Tbsp PB; 2 Tbsp jelly; 2 slice oatmeal bread




Chocolate milk, 1% fat

16-ounces (tall glass)




Carnation Instant Breakfast

1 packet mixed into 8 ounces 2% milk




Welch’s 100% Grape juice

16-ounces (tall glass)




Muscle Milk, powder

2 scoops


$1.78 / serving**







Drinks bought on the run






16-ounce bottle


(at supermarket)


Carnation Essentials

11-ounce bottle, ready to drink


(based on 4-pack)



8-oz bottle


(based on 6-pack)


Muscle Milk, Ready to Drink

14-ounce bottle


(at CVS)


* based on ½ gallon price**based on 5-lb tub of powder ($57)


By following these rules, you should see progress. But honor your genetics: If your father was slim until age 40, then you might follow the same footsteps. Most people do gain weight with age as they become less active, more mellow, and have more time to eat. Granted, this information doesn't help you today, but it offers optimism for your future. 

Nancy Clark, MS, RD, CSSD (Board Certified Specialist in Sports Dietetics) counsels both casual and competitive athletes at her office in Newton, MA (617-795-1875). Her best-selling Sports Nutrition Guidebook and food guides for new runners, marathoners, and soccer players offer additional information. They are available at See also


1) Levine JA, Ebernath NL, Jensen MD. 1999. Role of nonexercise activity thermogenesis in resistance to fat gain in humans. Science. 283(5399):212-4.

2) Bouchard, C. 1990. Heredity and the path to overweight and obesity. Med Sci Sports Exerc 23(3):285-291.

3). Novak CM, Escande C, Burghardt PR, Zhang M, Barbosa MT, Chini EN, Britton SL, Koch LG, Akil H, Levine JA 2010. Spontaneous activity, economy of activity, and resistance to diet-induced obesity in rats bred for high intrinsic aerobic capacity.  Horm Behav 58(3):355-367


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date: September 25, 2012

Nancy Clark

Nancy Clark, MS, RD, an internationally known sports nutritionist and nutrition author, is a registered dietitian (RD) who specializes in nutrition for exercise, health and the nutritional management of eating disorders.

avatarNancy Clark

Nancy Clark, MS, RD, an internationally known sports nutritionist and nutrition author, is a registered dietitian (RD) who specializes in nutrition for exercise, health and the nutritional management of eating disorders.

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