As a culture, we have invented a multitude of ways to evaluate our bodies. We might compare our weight, clothing size, or waist-hip ratio either in an informal setting (like social media) or in a more formal setting, like the doctor's office. Sometimes the comparisons feel overwhelming or biased, while others seem like they should have more value. One of the tools - often used in clinical settings - is called your BMI, or body mass index.
BMI is a number calculated by using height and weight measurements. The number gives a general indication of whether your weight falls within a healthy range. It basically tells you if you're a healthy weight for your height. Your healthcare provider might calculate the number, but you can also calculate your own BMI or use a healthy BMI calculator to get your number.
Body Mass Index (BMI) Explained
In the 1980s, the National Institutes for Health (NIH) decided that they needed to define parameters for obesity. The organization knew that obesity was becoming more common, and in order to track the numbers more accurately, they needed to come up with a way to make its categorization very clear. So, the NIH used a mathematical formula created a decade before using height and weight measurements to put people into several groups: underweight, normal weight, overweight, and obese.
Today, healthcare providers often measure BMI at checkups because a higher BMI correlates with more chronic illness and a shorter lifespan. But in recent years, the use of BMI has become controversial. In fact, even medical experts have acknowledged the shortcomings of the tool.
For example, in one guidance document published by the Centers for Disease Control and Prevention, the report authors note that age, sex, ethnicity, and muscle mass can affect BMI and body fat. In addition, BMI only takes into account two measurements and doesn't account for where the weight comes from, such as excess fat, muscle, or bone mass. Lastly, body mass index does not provide any indication of how fat is distributed on the body.
However, despite these shortcomings, BMI is still widely used as a starting point for evaluating weight and its relationship to your risk for certain health conditions. But it is not the only way to evaluate your weight. If your BMI number is concerning to you, talk to your healthcare provider about other ways to evaluate your weight and health, such as body fat percent.
How to Calculate Your Body Mass Index (BMI)
You can calculate your BMI yourself with a pencil and paper, or you can use one of the many calculators available online. For any math enthusiasts out there, it is your weight in kilograms divided by height in meters squared. Here is the formula:
BMI = weight (kg) / height (m) 2
If you'd rather not do the math, no problem! You can look up your BMI on pre-calculated charts, or with online calculators.
BMI Calculation Charts
A BMI chart is a detailed spreadsheet of weights, heights, and the resulting BMI. You match your height to your weight and then find your BMI. Exercisers and coaches commonly use BMI charts. Some charts are very elaborate and even color coded. A BMI chart provides a quick and accurate result and can be a useful tool. Check out this BMI chart from St. Lukes Hospital to get an idea of where your number falls.
Healthy BMI Calculator
You may want a result specific just to you. In this case, you can use an online calculator to determine your BMI exactly. Pretty much every health website offers a free BMI calculator, including the Centers for Disease Control (CDC) and the NIH. You can also try this one:
Online calculators like these are all based on the formula above. You just get to skip the math! Now, let's talk about what your results mean.
What Is a Healthy BMI?
Body mass index charts and calculators usually come with a key at the bottom or after your result pops up. It will say where you fall on the underweight to obese scale. Here's how the numbers shake out:
- Below 18.5 = underweight
- Between 18.5 and 24.9 = healthy weight
- Between 25 and 29.9 = overweight
- 30 or over = obese
If you fall outside of the "healthy weight" range, don't panic. This is valuable information. If you know that your body mass index falls outside of the healthy range, you can set goals to make changes.
What to Do About a High BMI
Since your BMI is sometimes used to determine obesity, it can also indicate whether you're at risk for various obesity-related diseases like heart disease, stroke, and diabetes. If you and your healthcare provider determine that changing your weight may be a healthy choice for you, you can take steps to make changes. The most common approaches are diet and exercise.
Exercise for a Healthy BMI
Exercise provides a range of health benefits. One of those benefits is that it can help you to reach and maintain a healthy weight. The more you exercise, the more calories you burn. The more calories you burn, the less your body can turn into fat.
According to the Physical Activity Guidelines for Americans, adults should shoot for 150 minutes of moderate-intensity cardiovascular exercise plus two days of muscle-strengthening activity to stay healthy.
The recommendation of 150 minutes per week might seem overwhelming at first glance. However, when you break down the number, it can seem more manageable. Just 30 minutes per day, five times per week will satisfy the cardio recommendation, then add two 15-20 minute strength sessions and youve reached that goal. But perhaps you're coming up blank when you try to think of what exercises you should do. How about some suggestions?
Moderate-Intensity Cardio Exercise Examples:
- Brisk walk
- Mow the lawn (with a push-mower)
- Ride your bike
- Play a high-motion sport like tennis or basketball
- Swim laps
- Walk up and down a set of stairs
Cardio exercise is movement that increases your heart rate. You know you're working your heart at a moderate intensity if you can talk, but can't sing.
- Lifting weights
Try out a few different options and see what you like. If you enjoy your exercise, you'll be much more likely to stick with it.
Diet for a Healthy BMI
The calories you eat and drink either get used for energy or stored as fat. Your body uses calories for some life basics like breathing, digesting, and keeping your heart pumping. The rest of your calories are used for physical activity. If you don't use up all the calories you took in for the day, your body will tuck it away (in fat deposits) just in case you need it later.
The Dietary Guidelines for Americans 2020 - 2025 (DGA)recommends following a "healthy dietary pattern." This means balancing your diet to include a large variety of nutrient-packed foods. The food groups you should try to consume every day are vegetables, fruits, dairy, protein, grains, and oils. Here are some tips for keeping a good balance in your diet:
- Choose green leafy vegetables like spinach over starchy veggies like corn or potatoes.
- Eat plain yogurt with fruit added instead of flavored full-fat yogurt.
- Make sure each meal includes a vegetable.
- Trade out your butter for vegetable or canola oil whenever you can.
- Try sparkling water instead of soda.
If you want some more ideas, check out the DGA! If this feels overwhelming, try to make one change at a time. Be kind to yourself---creating new habits is hard. But you can do it!
Lowering your BMI may sound impossible, but if you try some of the suggestions above, you may find they're not so bad! Find a goal that works for you and remember that every little bit of weight lost will help your body work better and better.