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Why doesn’t NutriMirror allow users under 18?

NutriMirror's Terms & Conditions require that all users be at least 18 years old. Teens and parents sometimes wonder why we have this limitation, so we've created this page to explore some of the technical issues that would need to be addressed if we were we to build an alternate version of the site for younger users.

Defining an Appropriate Weight

Despite the shortcomings of the well known Body Mass Index table for adults, it has the advantage of being straightforward and easy to use. Just find the spot on the graph where your weight and height meet, and there you have it: a quick indicator of whether you might be underweight, normal weight, overweight, or obese.

For children, however, things get much more complicated. Growing bodies are going through major and rapid changes, and what might be considered a normal BMI for an adult could be inappropriate for a child, and vice versa. And a child with a BMI in the overweight category might find that only one month later that same BMI is considered normal.

comparison of adult bmi graph with children's bmi for percentile graph

Take a look at the three graphs above. The one on the left is for adults, with heights on the left and weight on the bottom. The second two graphs are for children, one for boys and one for girls. To use these latter two graphs you must first compute a standard BMI number with the following formula:

BMI = weight in kilograms / (height in meters * height in meters)

Once the BMI is known, you find the location on the appropriate graph by charting BMI on the left and age on the bottom. The curvy lines running through the graph are percentiles comparing BMI numbers to others in the population of the same age. Anything between the 5th and 85th percentile is considered "normal" and anything between the 85th and 95th might be overweight.

Use the form below to calculate a BMI for someone between the ages of 2 and 20 years old. We'll place the BMI on the appropriate graph for you.


Birth date:

Height:  feet    inches  or    cm  

Weight:  pounds  

In addition, the placement on these children's BMI graphs, whether in the "normal" range or not, comes with the caveat that it should not be relied upon as the only indicator of health. A physician who can take into account additional factors affecting a child's fitness and appropriate development should always be consulted.

Metabolic Rate Calculations and Calories Burned

As with the BMI charts above, it's easy to estimate an adult's resting metabolic rate. A number of formulas are available. None are 100% accurate, but they provide a reasonable, workable estimate. They look something like this:

Women: BMR = 655 + (4.35 x pounds) + (4.7 x inches) - (4.7 x age)
Men: BMR = 66 + (6.23 x pounds) + (12.7 x inches) - (6.8 x age)

NutriMirror then adjusts this number according to your lifestyle activity level, and makes additional adjustments each time you log an exercise.

These formulas, however, are calibrated for adult bodies only and are inappropriate and misleading for children. Instead, calorie recommendations for children are much more general, along the lines of the following (from the American Heart Association):

1 Year 2-3 Years 4-8 Years 9-13 Years 14-18 Years
Female 900 kcal 1000 kcal 1200 kcal 1600 kcal 1800 kcal
Male 900 kcal 1000 kcal 1400 kcal 1800 kcal 2200 kcal

Note: Increase calories by 0-200 kcal/day if moderately physically active; Increase by 200-400 kcal/day if very physically active.

Children and Calorie Restriction

Much of the focus on NutriMirror is on weight loss for adults, although we try to make weight loss more a byproduct of healthy nutrition and a balanced lifestyle. Still, many of our users out of necessity have implemented moderate calorie restrictions into their daily diets. As a result a common refrain on the site is "no fewer than 1200 calories per day for women" (or 1500 calories per day for men). That is the absolute minimum amount of calories needed to maintain a healthy adult diet.

For those 18 and under, however, whose bodies are still growing, more energy is required than that 1200 or 1500 minimum. Refer again to that chart above for girls aged 14 to 18, where the recommendation is 1800 calories for a sedentary lifestyle (and more for an active lifestyle). Eating less than these recommended levels during this critical time of life can lead to severe developmental problems resulting from nutrient limitations, including (but not limited to) osteoporosis and increased risk within just a few years of overweight and obesity.

The common sense recommendation for a teenager who hopes to lose weight is therefore not to "diet," but to maintain a healthy, active lifestyle. Eat your recommended calories (making sure they are healthy, nutritious calories) and increase your activity level. Your body will take care of the rest.

Nutrients for Growing Bodies

NutriMirror's recommendations for nutrients such as vitamins and minerals are customized for each member based on the Dietary Reference Intake tables provided by the Food and Nutrition Board, Institute of Medicine, National Academies. This means that each member sees different percentages and different red and green indicators for different nutrients depending on several factors: age, sex, and whether pregnant or lactating.

Look at the following table for an example:

Dietary Reference Intakes for Iron

Recommended Intakes for Individuals*
Age Male Female Pregnant Lactating
1-3 yrs.7 mg7 mg
4-810 mg10 mg
9-138 mg8 mg
14-1811 mg15 mg27 mg10 mg
19-308 mg18 mg27 mg9 mg
31-508 mg18 mg27 mg9 mg
51-708 mg8 mg
70+8 mg8 mg

*These Recommended Dietary Allowances are set to meet the needs of almost all (97 to 98 percent) individuals in the groups listed in the table above.

As you can see, a woman's recommendations for iron are signifcantly higher than a man's, while a teen boy needs more than an adult male, and a teen girl needs less than an adult female.

Take a look at our nutrient pages (click here) and you'll see similar variations for many of the vitamins and minerals tracked by this site.

Since NutriMirror requires members to be 18 or older, this variation in nutrient recommendations for users under the age of 18 is not currently reflected in any of our member food logs and reports.

Recommendations for People Under 18

While we at NutriMirror have discussed a number of ways to provide a service valuable to younger users, we are currently focused on developing and expanding the main site. So any features aimed at younger users are not a priority at the moment. However, if you are a parent of young children and you use this site, rest assured that your children are already benefiting from your focus on nutritious eating — partly from the meals you prepare, but even more from the example you are setting. Keep eating well and in appropriate amounts, keep yourself active, and your children will learn to do the same.

If you are a teen and you are hoping to use this site, unfortunately it's not ready for you at this time. But there is a wealth of information available on the Internet that can help you.

Link To NutriMirror

Use the following code to add a link to this page to your own web site or blog:

<a href="http://www.nutrimirror.com/children-bmi-under-18.php" title="Diet and Body Mass Index (BMI) information for children 18 and under">Diet and Body Mass Index (BMI) information for children 18 and under</a>

Or use the following code to link directly to NutriMirror's front page:

<a href="http://www.nutrimirror.com" title="food journal">NutriMirror</a>

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