We often hear about weight affecting our health. Being overweight puts us at a greater risk for serious and life-threatening conditions like heart disease, diabetes or stroke. Being underweight means that we’re not getting the nutrients we need, which can cause respiratory and digestive problems, and osteoporosis.
Many times, you can look at yourself in a mirror and know if you need to put on or take off weight. There are tools to help us (and our doctors) make this determination more scientifically. I’m talking about BMI, or Body Mass Index.
What is BMI?
BMI is a calculation of body fat in proportion to height. It uses your height and weight information to basically tell you if you’re at a healthy weight for your height.
How is BMI calculated?
There’s a simple formula for calculating BMI. BMI is universally expressed in terms of mass in kilograms to square meters and is determined using the following formula:
BMI = weight in kg/(height in meters) (height in meters)
For example, a woman who weighs 62 kg and is 1.64 m tall would have the following BMI:
62/(1.64)(1.64) = 62/2.6896 = 23.8
If, like me, you live in the United States and use the archaic, unintuitive, arbitrary Imperialist system, BMI is calculated the same way, but a conversion factor needs to be applied:
BMI = [weight in lbs/(height in inches)(height in inches)] X 703
Here’s a calculation of my BMI using this formula. I’m 5’5” inches tall (or 65 inches) and weigh 155 lbs.
[155/(65)(65)] X 703 = [155/4225] X 703 = 25.8
Yes, I have more body mass than the woman in the hypothetical example. Don’t judge me!
If you don’t want to calculate BMI yourself, there are a ton of calculators online that you can use. Simply enter your height and weight and the calculator does all the work for you. Many calculators also help you analyze your BMI and what it means, so they’ll ask you for other information, like your gender or age, to help with the analysis.
What does BMI mean for you?
In a nutshell, BMI helps you determine whether or not you’re a healthy weight. This chart can help you interpret your BMI results.
|18.5 – 24.9||Normal (this is the desired range)|
|25.0 – 29.9||Overweight|
|30 and above||Obese|
Taking a look at the 2 examples above, the first woman, with a BMI of 23.8, is within a normal or desired weight range. Her body mass is at a healthy level and she’s not considered overweight.
I, on the other hand, have a BMI of 25.8, which falls in the “overweight” category (again, don’t judge me!). However, I’m only slightly overweight which is good. It shouldn’t be too difficult for me to get back into the desired, healthier range (I hope!).
BMI only considers your weight and height, so it’s somewhat limited as a tool. It doesn’t include things like bone density. For example, I’m a small-boned person, so my BMI should probably be even lower than a fuller-boned person of my height – which makes me even more overweight! (I plead, don’t judge me!)
BMI also doesn’t consider muscle mass. Muscle weighs more than fat, so BMI could be misleading for you if you’re very muscular and fit. But for most people, BMI does provide a reasonable estimate of body mass.
Not only can your BMI level can have serious implications for your health but also your well-being. I think back to when I weighed a little less, and I had more energy and felt better in my body. Plus I felt a little better about myself when my jeans had more wiggle room than I do when they’re a little snug!
What does BMI mean for your fertility?
Experts agree that a woman’s BMI is strongly connected to her fertility potential.
Your doctor might tell you that you need to lower or raise your BMI before you can start treatment. It seems like it doesn’t matter if you’re over- or underweight, because we see people of all shapes and sizes get pregnant, right?
Wrong. All kinds of people can get pregnant and have a baby, but experts contend that BMI, fertility and conception are closely linked. Not being at a healthy weight can affect your ovulation, and issues with ovulation are the leading cause of female infertility. Thyroid dysfunction can also be a by-product of not being a healthy weight, which can affect the production of your hormones, including the reproductive hormones.
And, if you’re already predisposed to conditions that can affect your fertility, like PCOS or endometriosis, not being a healthy weight can exacerbate them.
Doctors like to see a woman’s BMI in the normal range (18.5-24.9) for pursuing treatment, and for having the greatest chance overall for success at conception.
A woman whose BMI is high (i.e., overweight) may have issues with insulin resistance which can cause hormonal imbalances that affect ovulation. Women with dangerously low BMI (i.e., underweight) are in danger of not ovulating at all.
In some cases, being over- or underweight can be the cause of a person’s infertility, so once they achieve a healthy weight, they have little or no difficulty conceiving. In the case of overweight women, studies have shown that by losing just 5-10% of your body weight can improve your chances of conceiving.
Strategies for Lowering BMI
The healthiest way to lose weight (and lower your BMI) – and keep it off – is through good old-fashioned diet and exercise. By diet, I mean how and what you eat, not following the latest diet craze. Many of the fad diets and crash diets might help you in the short term by getting the weight off, but many of those diets aren’t sustainable. Over time, people who follow those diets usually revert back to their old eating habits and the weight goes right back on.
You’ll make healthy lifestyle changes that last when you form new habits around how and what you eat, and by moving your body. These habits will stay with you forever.
The way we eat is a choice. Choose whole foods – whole fruits, vegetables and grains. Choose lean meats (preferably organic and grass-fed), if you eat meat. Choose healthy fats. Avoid processed and packaged foods, and refined sugars.
Regular and consistent exercise will burn off the calories. To lose weight you need to burn off more calories than you take in. While the standard rule of thumb is 150 minutes of moderate-intensity exercise a week to maintain your weight and health, you need to bump it up if you want to lose weight. Shoot for at least 200 minutes of moderate-intensity exercise – that’s about 3 ½ hours a week.
Strategies for Increasing BMI
If your issue is that you need to put weight on instead of take it off, you need to eat more! You need to do it sensibly, though. You might put on weight by eating rich desserts and drinking sugary sodas, but this isn’t healthy for you. You want to eat high-calorie foods that are rich in nutrients. Things like whole grains, fruits and vegetables, lean meats and healthy fats.
Perhaps not-so-ironically, these are many of the same foods you want to eat to lose weight, but to put on weight you will want to systemically increase your caloric intake. An online calculator can tell you how much more to eat to get the calories you need.
You want to make sure that some of the weight you’re putting on comes from muscle mass and not all from fat. So you’ll also want to have a good exercise plan to boost your BMI. Make sure your plan includes strength training, as this will help you build muscle mass.
As always, check with your doctor before starting any new diet or exercise plan, to make sure you take off or put on the weight safely.
To your health and fertility,
[originally appeared at B Fit, B Fertile 4/12/17]