Is it true that mothers and their daughters’ resemblance on BMI is a sure thing? It’s easy to assume that a daughter might take after her mother’s eating habits and have a similar BMI as her mother, for many reasons. But they might not be the reasons you’d think. But first, let’s make it clear what BMI is.

BMI or body mass index is nothing more than the measure of a person’s weight in relation to her height. A person’s weight in kilograms is divided by a person’s height in meters, squared (which is simply a person’s height times itself—if I’m 1.5 meters tall, I would take 1.5 times 1.5). The resulting number is her BMI.

A normal BMI is anything from 18.5 to 24.5, and 25 to 29.9 is considered overweight, with anything above that considered obese. A BMI below 18.5 is considered underweight. BMI is a good general measurement for most people, although very muscular people usually measure as overweight or obese because BMI doesn’t distinguish between muscle weight and fat weight.

So, back to mothers and their daughters’ resemblance on BMI, does it guarantee that a daughter will be overweight if her mother has a high BMI? Will a normal weight mother raise a normal weight daughter? Will the daughter be underweight if the mother is too skinny? While nothing is certain 100% of the time, there are some factors that push those answers more toward a yes than a no.

Genetics do play a part in a person’s tendency toward staying thin or gaining weight. Hereditary factors like body type are impossible to change. Tendency toward a slow metabolism can be boosted by exercise, good nutrition and a healthy lifestyle, but genetics will help determine how easy or difficult keeping a high metabolism may be for a daughter.

The environment is a huge factor. When a mother is overweight, for example, and she generally cooks for the family, the family eat what she eats to a large degree. So it’s easy to see why mothers and their daughters’ resemblance on BMI is often very similar. Living with a person, especially someone with the influence a mother has on a daughter, also tends to shape a person’s attitudes. So if the mother is very active, eats healthy and stays physically fit, it’s more likely than a child, especially a daughter, will do the same.

Conversely, a mother who is overweight, rarely gets exercise and doesn’t seem overly concerned with weight loss or health is likely to bring up her daughter with the same outlook. In both cases, it’s no surprise that their BMIs might be similar.

So not only do the attitudes about food and fitness filter down from mothers to daughters, the type of food eaten, and even the amount of food eaten, can filter down, too. Mothers and their daughters’ resemblance on BMI charts is no coincidence, and only shows the need for families to be aware of their health and fitness even when children are small.

With all the talk about it these days, you might be wondering, “What is BMI?” There’s no magic to it, no secret formula, even though sometimes the way it’s talked about it sounds like some sort of mantra for weight loss and health. BMI isn’t a meditation or an exercise or diet plan, it’s simply the measure of your body mass.

It compares your weight and height, and boils that ratio down to a number. Depending where your number is on the scale, it tells you if you’re underweight for your height, overweight, or obese.

So what is BMI, in general? BMI, or body mass index, is a tool of body mass measurement that was created in the early 1800s by Adolphe Quetelet. This is why sometimes you might see BMI referred to as the Quetelet index. Adolphe Quetelet was mathematician, statistician, and an astronomer, among other things.

He developed the BMI while working on social physics. The BMI is still used today with very few variations on his original invention.

What is BMI, specifically? BMI doesn’t measure body fat, but instead compares a person’s weight and height to estimate a healthy body weight for that person’s height. It’s widely used to determine if someone is technically overweight or obese. Though it’s the not the final tool in diagnosing obesity or overweight, because it’s not without its flaws for certain body types, it’s still in use in the medical community.

The formula for BMI is simple: Take your height in meters squared (your height times itself) and then divide your weight in kilograms by that number. For example, if I’m 5 feet tall, that’s about 1.5 meters. 1.5 squared (1.5 times 1.5) equals 2.5. If I weigh 120 pounds, that’s about 54.5 kilograms. So I need to divide 54.5 by 2.5 which gives me a result of 21.8 as my BMI. So what does that number mean? A BMI of 18.5 or below indicates that an individual is underweight. The normal weight range is from 18.5 to 24.9. Overweight people will calculate a BMI of 25 to 29.9. A BMI of 30 or greater indicates obesity. Someone five feet tall weighing 120 pounds falls into the normal weight range.

Where BMI fails is with extremely muscular people. It doesn’t distinguish between muscle and fat, instead using total weight as the measure. So according to the BMI, bodybuilders are likely to measure as obese which is inaccurate. Most athletes like wrestlers, footballs players and any athletes with a large amount of lean muscle are going to measure as overweight or obese. But for most people, BMI is a fairly accurate measure of their level of underweight or overweight.

Now that you know the formula, you know that BMI is as simple as a single math problem, and a single number. Next time you’re faced with the question, “What is BMI?” you’ll know there’s no magic to it, it’s simply a measure of a person’s body weight compared to his or her height.