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Five Tips To Help Your Skinny Child Bulk Up

Is your child genetically fidgety? Adding calories can be expensive


Recently, I got an email from a mother with a son in 8th grade who is 5'6" but weighed only 108 pounds.  She said he thinks drinking Muscle Milk will provide bulging muscles, but no matter what he ate, he could not seem to gain weight and she wanted to know what he was doing wrong, and how many extra calories did he need to gain weight.

If your child is among the few skinny folks who have a hard time bulking up, he may be feeling frustrated that he can't do something as simple as gain a few pounds.  For underweight athletes, the struggle to bulk up is equal to that of over-fat 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).

A NEAT explanation

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 your child overeats, NEAT helps them dissipate excess energy. NEAT can predict how resistant your child will be to gaining weight.Historically, athletes have been told that consuming an extra 500 to 1,000 calories per day will lead to 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 VO-2max (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 child's genetics and their tendency to fidget, you can boost their calorie intake. Here are five tips to help your child bulk-up healthfully:

  1. Eat consistently. Do NOT skip meals; doing so means they'll miss out on important calories needed to reach their goal! Every day, they need to 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 more calories than green beans (140 vs. 40 calories per cup).
  4. Drink lots of juice and low-fat milk. Instead of quenching their thirst with water, offer them calorie-containing fluids. One high school soccer player gained 13 pounds over the summer simply by 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 child's 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).  Peanut butter on bread
  6. Do strengthening exercise as well as some cardio. Weight lifting and push-ups stimulate muscle growth so that a child bulks-up instead of fattening up.  Sooner or later, exercise will stimulate their appetite so they'll want to eat. Exercise also increases thirst so they'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 your child cannot get via food. A hefty PB&J with a tall glass of milk add 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 low-fat 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. Have your child drink half at breakfast and take the rest with them in a thermos. 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  Calories  Price  Cost/100 calories 


1 cup granola + 1 cup 2% milk


1 bowl  500  $1.00 $0.20 
 Peanut butter & jelly sandwich


3 tbsp PB; 2 tbsp jelly; 2 sl oatmeal bread 


650 $.95 $015
 Chocolate milk 1% fat 16 ounces (tall glass) 300  $.60* $0.20
 Carnation Instant Breakfast 1 packet mixed into 8 ounces 2% milk 250 $.80 $0.32
 Welch's 100% grape juice 16 ounces (tall glass) 280  $1.00* $0.36
 Muscle Milk (powder)  2 scoops 310  $1.78/serving** $0.57
 Drinks bought on the run        
 Nesquick 16-ounce bottle 300  $1.79 (at supermarket) $0.60
 Carnation Essentials 11-ounce bottle ready to drink 260  $1.75 (based on 4-pack) $0.67
 Ensure  8-ounce bottle 250  $1.50 (based on 6-pack) $0.60
 Muscle Milk, ready to drink  14-ounce bottle 230  $3.59 (at CVS) $1.56

* based on 1/2 gallon price

** based on 5-lb tub of powder ($57.00)  


By following these rules, your young athlete should see progress. But honor your child's genetics: If his father was slim until age 40, then he might follow in 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 your child today, but it offers optimism for their 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 www.nancyclarkrd.com. See also www.sportsnutritionworkshop.com.


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

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

3. Novak CM, Escande C, Burghardt PR, et al. Spontaneous activity, economy of activity, and resistance to diet-induced obesity in rats bred for high intrinsic aerobic capacity. Horm Behav 2010;58(3):355-367

Posted October 22, 2012 




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