Body mass index (BMI) has become quite the buzzword in the health and fitness industry, often cited as a quick reference point to assess your health status.
But what actually is BMI, and is it always accurate?
In this Fitness First guide, we'll walk you through everything you need to know about BMI, with tips on maintaining a healthy score.
What is body mass index (BMI)?
Your BMI, which stands for body mass index, is a measure of body fat in relation to your height and weight. BMI isn't a totally accurate indicator of your overall health, but it can be used to estimate whether you're at a healthy weight.
How to calculate your BMI
To calculate your BMI, all you need to know is your height and your weight. You simply divide your weight in kilograms by your height in meters squared. For example, if you're 70 kilograms (11 stone) in weight and 1.75 metres (69 inches) in height, you would calculate your BMI as follows:
70kg / (1.75m²) = 22.86
So, your BMI would be 22.86.
To make things easier, you can use an online calculator like the NHS healthy weight calculator. Doctors and health professionals can also calculate this for you.
What is a healthy BMI?
According to the NHS, a healthy BMI is between 18.5 and 24.5 for most adults.
Based on your BMI, you can fall into one of the following categories:
- Below 18.5 — underweight range
- Between 18.5 and 24.9 — healthy weight range
- Between 25 and 29.9 — overweight range
- 30 or over — obese range
Being underweight can pose serious health risks like nutritional deficiencies and decreased immune function. But on the other hand, high BMI can lead to an increased risk of various health issues, including heart disease, high blood pressure, type 2 diabetes, and certain types of cancer. That's why keeping your BMI score healthy is so important.
Is BMI always accurate?
BMI can be a handy reference point to check on your progress and ensure you're achieving your weight loss or gain goals. However, it may not always be accurate, and some extra factors do need to be considered when calculating it.
For example, some professional athletes may have a BMI that suggests they're overweight due to muscle weighing more than fat. Also, people with low muscle mass but high body fat might fall within a normal BMI range, masking potential health risks associated with excess fat.
Factors such as age, sex, ethnicity, and bone structure can also significantly impact BMI accuracy. For instance, as people age, muscle mass usually decreases, and fat can increase without a significant weight change.
For a clearer picture of your health, it might be a good idea to chat with healthcare professionals who can provide a more holistic assessment. Looking at other things like body fat percentage, muscle mass, and waist-to-hip ratio can give you a clearer picture of your health.
Tips for maintaining a healthy BMI
Generally, the basic rule of maintaining a healthy weight is to consume the same or slightly fewer calories than you burn. Use a calorie calculator to work out roughly how many calories a day you use (you will need to enter details of your exercise routine and your working environment) and then stick to eating only that amount, or a little less or more, if you want to lose or put on weight.
See our top tips for reducing or increasing your BMI below.
How to reduce your BMI
Here’s some advice for losing weight if your BMI is high:
1. Reduce your daily calorie intake
Taking control of your calorie intake is a solid first step to losing weight and reducing your BMI.
To start, work out how many calories you're currently eating — a food diary or online tracker can help with this. Then, determine your daily caloric needs using a calorie calculator.
According to official NHS guidelines, consider reducing your daily intake by around 600 calories to lose weight safely.
Remember: it's all about balance; make sure you're consuming enough to sustain your energy levels, but try to cut back on extras like sugary drinks and snacks. Keeping a food diary could be eye-opening to see where extra calories are potentially sneaking in.
2. Avoid crash diets
While crash diets might tempt you with rapid results, they aren't a long-term solution and can be harmful to your health. Crash diets tend to severely restrict calories or eliminate entire food groups, leading to nutrient deficiencies as your body misses the essential vitamins and minerals needed to function properly.
When you slowly adapt to smaller portions or healthier food options, it's easier for these changes to become part of your daily routine rather than feeling like a chore or restriction. It's more sustainable, and you're more likely to keep the weight off.
3. Move more
Burn up your body's excess fat by taking part in regular cardio workouts like high-intensity interval training (HIIT), spinning, powerwalking or even freestyle dance. Cardiovascular exercises are perfect for weight loss, as they're usually high-intensity, meaning you can burn a substantial number of calories in a relatively short time.
Even tiny tweaks in your daily routine, like walking instead of driving or taking the stairs instead of the lift, can make a significant difference. These small changes can help you burn more calories throughout the day, gradually contributing to weight loss over time and a reduced BMI. Plus, they seamlessly integrate into your day, making them sustainable habits for long-term health benefits.
4. Eat more fibre
Fibre-rich foods, like vegetables, whole grains and fruits, keep you feeling full for longer, leaving less room for higher-calorie ingredients. They help keep your cravings in check, so you're more likely to make better food choices, which can be a big help in managing your weight.
How to increase your BMI
If your BMI is on the low side, you may be underweight. Of course, there could be various reasons why, so it’s best to consult with your doctor before making any major dietary or lifestyle changes.
Here are some healthy ways to increase your BMI:
1. Add healthy calories
The most effective way to gain weight and consequently increase your BMI is to consume more calories than your body needs. Healthline suggests increasing by 300-500 calories daily above your maintenance level for steady weight gain.
Incorporating nutrient-dense foods such as avocados, nuts, seeds, and eggs, which are high in calories, can contribute significantly to your daily calorie intake without requiring you to eat huge portions.
To learn more about healthy eating, read our beginner's guide to protein and nutrition.
2. Eat more frequently
Consider spreading out your food intake by having five to six smaller meals throughout the day instead of sticking to the traditional three larger ones. This approach can make increasing your calorie intake feel more manageable and less overwhelming.
It might be helpful to set specific times for these meals, ensuring a consistent intake of calories. Even if you're not feeling particularly hungry, sticking to a regular eating schedule can assist in gradually boosting your caloric intake, which, in turn, will contribute to healthily increasing your BMI.
3. Build muscle
Incorporating strength training into your routine effectively contributes to weight gain by adding muscle mass instead of just fat. As you progress, your increased muscle mass will not only help in increasing your BMI but also improve your overall physical fitness.
It's a good idea to work with a trainer initially to ensure that you're performing exercises correctly and targeting the appropriate muscle groups. At Fitness First, our personal trainers can help you create a workout plan tailored to your goals.
To learn more, read our guide on the benefits of lifting weights.
Maintain a healthy BMI with Fitness First
At Fitness First, we can guide you on your journey toward achieving a healthy BMI in a supportive environment. We have a wide range of classes, personal training sessions and more available for you, no matter your fitness level.