From Vincent Iannelli, M.D.,
Your Guide to Pediatrics.
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About.com Health's Disease and Condition content is reviewed by Kate Grossman, MD

Parents often wonder how their kids gain so much weight so quickly, especially when their diets aren't that terrible. After all, your kids don't need to be eating a big bag of chips, a double serving at each meal, or a bedtime snack every night to become overweight. Although that would usually do it, more often it is smaller things that creep up on you and a few extra calories add up day after day until your children become more and more overweight.

Understanding how many calories it takes to gain a pound of fat can help you understand how this happens.

One pound of fat is equal to about 3500 calories.

That means that if you eat an extra 350 calories of food a day, which is about equal to a large piece of cake or a medium milk shake, you would gain an extra pound every 10 days (350x10). Or you would gain a pound in about 20 days if you eat or drank an extra 175 calories a day (175x20).

On the other hand, eating 175 fewer calories a day would mean that your kids could lose a pound every 20 days.

Or if they kept their diet the same, but burned an extra 175 calories a day by exercising more, then again, they could lose a pound in about 20 days.

How about if your kids are gaining weight? If you calculate how quickly they are gaining weight, it can help you to figure out how much they may be overeating. If they are gaining a pound every 10 days, then they are likely overeating by about 350 calories a day. Of course it is a little more complicated than that, since that doesn't factor in how much or how little they are exercising or the fact that younger kids should normally be gaining some weight, so talk to your Pediatrician before adjusting your child's diet based on this calculation.

Losing Weight

If your child is overweight, he likely needs to lose more than a pound, but you will likely be more successful starting with small steps, then looking for quick weight loss with drastic changes.

Can you find little things in your child's diet that you could change?

How about changing to a lower fat milk? Just going from whole milk to 1 percent milk, if your kids drink 3 cups a day, will save about 150 calories a day, which can translate into a pound every 20 days.

Or if your get your kids to stop drinking soda each day, that 12 ounce can of soda will save you 155 calories a day, or a pound in about 23 days.

These small changes, although they may not seem like much, will add up quickly and help your kids lose weight, just as easily as they helped them to pile the pounds on.

For more information, see our guide to childhood obesity. And our Calorie Calculator can help you figure out how many calories your kids need each day.