BMI compares your weight to your height, and is calculated by dividing your weight in kilograms by your height in metres squared. It gives you an idea of whether you’re underweight, a healthy weight, overweight, or obese for your height.
BMI is defined as the body mass divided by the square of the body height, and is universally expressed in units of kg/m2, resulting from mass in kilograms and height in metres. If pounds and inches are used, a conversion factor of 703 (kg/m2)/(lb/in2) must be applied. When the term BMI is used informally, the units are usually omitted.
BMI may also be determined using a table or chart which displays BMI as a function of mass and height using contour lines or colours for different BMI categories, and may use two different units of measurement.
The BMI is an attempt to quantify the amount of tissue mass (muscle, fat, and bone) in an individual, and then categorize that person as underweight, normal weight, overweight, or obese based on that value. BMI provides a simple numeric measure of a person's thickness or thinness, allowing health professionals to discuss weight problems more objectively with their patients.
BMI was designed to be used as a simple means of classifying average sedentary (physically inactive) populations, with an average body composition. However, there is some debate about where on the BMI scale the dividing lines between categories should be placed. Commonly accepted BMI ranges are underweight: under 18.5 kg/m2, normal weight: 18.5 to 25, overweight: 25 to 30, obese: over 30. People of Asian descent have different associations between BMI, percentage of body fat, and health risks than those of European descent, with a higher risk of type 2 diabetes and cardiovascular disease at BMIs lower than the WHO cut-off point for overweight, 25 kg/m2, although the cut-off for observed risk varies among different Asian populations.
A BMI that places you in the higher range of overweight or obese tends to be a pretty accurate indication of body fatness. Carrying too much fat increases your risk of early death. High BMI levels usually correlate with an elevated risk of chronic disease, including type-2 diabetes, coronary artery disease, stroke, gallbladder disease, osteoarthritis, sleep apnea, chronic inflammation and depression.
A frequent use of the BMI is to assess how much an individual's body weight departs from what is normal or desirable for a person's height. The weight excess or deficiency may, in part, be accounted for by body fat (adipose tissue) although other factors such as muscularity also affect BMI significantly.
Body mass index, or BMI, is used to determine whether you are in a healthy weight range for your height.
It is useful to consider BMI alongside waist circumference, as increases or decreases in weight outside the healthy range may increase your health risks.
This tool shouldn’t be used for pregnant women or children.
Finding a Balance for a Healthy BMI
There's a lot of talk about the different components of food. Whether you're consuming carbohydrates, fats, or proteins all of them contain calories. If your diet focus is on any one of these alone, you're missing the bigger picture.
The Caloric Balance Equation
When it comes to maintaining a healthy weight for a lifetime, the bottom line is – calories count! Weight management is all about balance—balancing the number of calories you consume with the number of calories your body uses or "burns off."
- A calorie is defined as a unit of energy supplied by food. A calorie is a calorie regardless of its source. Whether you're eating carbohydrates, fats, sugars, or proteins, all of them contain calories.
- Caloric balance is like a scale. To remain in balance and maintain your body weight, the calories consumed (from foods) must be balanced by the calories used (in normal body functions, daily activities, and exercise).
Am I in Caloric Balance?
If you are maintaining your current body weight, you are in caloric balance. If you need to gain weight or to lose weight, you'll need to tip the balance scale in one direction or another to achieve your goal.
If you need to tip the balance scale in the direction of losing weight, keep in mind that it takes approximately 3,500 calories below your calorie needs to lose a pound of body fat. To lose about 1 to 2 pounds per week, you'll need to reduce your caloric intake by 500—1000 calories per day.
Recommended Physical Activity Levels
* 2 hours and 30 minutes (150 minutes) of moderate-intensity aerobic activity (i.e., brisk walking) every week and muscle-strengthening activities on 2 or more days a week that work all major muscle groups (legs, hips, back, abdomen, chest, shoulders, and arms).
* Increasing the intensity or the amount of time that you are physically active can have even greater health benefits and may be needed to control body weight.
* Encourage children and teenagers to be physically active for at least 60 minutes each day, or almost every day.
The bottom line is… each person's body is unique and may have different caloric needs. A healthy lifestyle requires balance, in the foods you eat, in the beverages you consume, in the way you carry out your daily activities, and in the amount of physical activity or exercise you include in your daily routine. While counting calories is not necessary, it may help you in the beginning to gain an awareness of your eating habits as you strive to achieve energy balance. The ultimate test of balance is whether or not you are gaining, maintaining, or losing weight.
You may also find it helpful to weigh yourself on a regular basis. If you see a few pounds creeping on, take the time to examine your lifestyle.
Improving Your Eating Habits
When it comes to eating, we have strong habits. Some are good ("I always eat breakfast"), and some are not so good ("I always clean my plate"). Although many of our eating habits were established during childhood, it doesn't mean it's too late to change them.
Making sudden, radical changes to eating habits such as eating nothing but cabbage soup, can lead to short term weight loss. However, such radical changes are neither healthy nor a good idea, and won't be successful in the long run. Permanently improving your eating habits requires a thoughtful approach in which you Reflect, Replace, and Reinforce.
- REFLECT on all of your specific eating habits, both bad and good; and, your common triggers for unhealthy eating.
- REPLACE your unhealthy eating habits with healthier ones.
- REINFORCE your new, healthier eating habits.
Reflect, Replace, Reinforce: A process for improving your eating habits
· Create a list of your eating habits. Keeping a food diary for a few days, in which you write down everything you eat and the time of day you ate it, will help you uncover your habits. For example, you might discover that you always seek a sweet snack to get you through the mid-afternoon energy slump. It's good to note how you were feeling when you decided to eat, especially if you were eating when not hungry. Were you tired? Stressed out?
· Highlight the habits on your list that may be leading you to overeat. Common eating habits that can lead to weight gain are:
- Eating too fast
- Always cleaning your plate
- Eating when not hungry
- Eating while standing up (may lead to eating mindlessly or too quickly)
- Always eating dessert
- Skipping meals (or maybe just breakfast)
· Look at the unhealthy eating habits you've highlighted. Be sure you've identified all the triggers that cause you to engage in those habits. Identify a few you'd like to work on improving first. Don't forget to pat yourself on the back for the things you're doing right. Maybe you almost always eat fruit for dessert, or you drink low-fat or fat-free milk. These are good habits! Recognizing your successes will help encourage you to make more changes.
· Create a list of "cues" by reviewing your food diary to become more aware of when and where you're "triggered" to eat for reasons other than hunger. Note how you are typically feeling at those times. Often an environmental "cue", or a particular emotional state, is what encourages eating for non-hunger reasons.
Common triggers for eating when not hungry are:
- Opening up the cabinet and seeing your favourite snack food.
- Sitting at home watching television.
- Before or after a stressful meeting or situation at work.
- Coming home after work and having no idea what's for dinner.
- Having someone offer you a dish they made "just for you!"
- Walking past a candy dish on the counter.
- Sitting in the break room beside the vending machine.
- Seeing a plate of doughnuts at the morning staff meeting.
- Swinging through your favourite drive-through every morning.
- Feeling bored or tired and thinking food might offer a pick-me-up.
1. Circle the "cues" on your list that you face on a daily or weekly basis. Going home for the Thanksgiving holiday may be a trigger for you to overeat, and eventually, you want to have a plan for as many eating cues as you can. But for now, focus on the ones you face more often.
2. Ask yourself these questions for each "cue" you've circled:
- Is there anything I can do to avoid the cue or situation? This option works best for cues that don't involve others. For example, could you choose a different route to work to avoid stopping at a fast food restaurant on the way? Is there another place in the break room where you can sit so you're not next to the vending machine?
- For things I can't avoid, can I do something differently that would be healthier? Obviously, you can't avoid all situations that trigger your unhealthy eating habits, like staff meetings at work. In these situations, evaluate your options. Could you suggest or bring healthier snacks or beverages? Could you offer to take notes to distract your attention? Could you sit farther away from the food so it won't be as easy to grab something? Could you plan ahead and eat a healthy snack before the meeting?
3. Replace unhealthy habits with new, healthy ones. For example, in reflecting upon your eating habits, you may realize that you eat too fast when you eat alone. So, make a commitment to share a lunch each week with a colleague, or have a neighbor over for dinner one night a week. Other strategies might include putting your fork down between bites or minimizing other distractions (i.e. watching the news during dinner) that might keep you from paying attention to how quickly — and how much — you're eating.
Here are more ideas to help you replace unhealthy habits:
- Eat more slowly. If you eat too quickly, you may "clean your plate" instead of paying attention to whether your hunger is satisfied.
- Eat only when you're truly hungry instead of when you are tired, anxious, or feeling an emotion besides hunger. If you find yourself eating when you are experiencing an emotion besides hunger, such as boredom or anxiety, try to find a non-eating activity to do instead. You may find a quick walk or phone call with a friend helps you feel better.
- Plan meals ahead of time to ensure that you eat a healthy well-balanced meal.
4. Reinforce your new, healthy habits and be patient with yourself. Habits take time to develop. It doesn't happen overnight. When you do find yourself engaging in an unhealthy habit, stop as quickly as possible and ask yourself: Why do I do this? When did I start doing this? What changes do I need to make? Be careful not to berate yourself or think that one mistake "blows" a whole day's worth of healthy habits. You can do it! It just takes one day at a time!
Maintaining a Healthy BMI
If you've recently lost excess weight, congratulations! It's an accomplishment that will likely benefit your health now and in the future. Now that you've lost weight, let's talk about some ways to maintain that success.
The following tips are some of the common characteristics among people who have successfully lost weight and maintained that loss over time.
Watch Your Diet
· Follow a healthy and realistic eating pattern. You have embarked on a healthier lifestyle, now the challenge is maintaining the positive eating habits you've developed along the way. In studies of people who have lost weight and kept it off for at least a year, most continued to eat a diet lower in calories as compared to their pre-weight loss diet.
· Keep your eating patterns consistent. Follow a healthy eating pattern regardless of changes in your routine. Plan ahead for weekends, vacations, and special occasions. By making a plan, it is more likely you'll have healthy foods on hand for when your routine changes.
· Eat breakfast every day. Eating breakfast is a common trait among people who have lost weight and kept it off. Eating a healthful breakfast may help you avoid getting "over-hungry" and then overeating later in the day.
. Get daily physical activity. People who have lost weight and kept it off typically engage in 60—90 minutes of moderate intensity physical activity most days of the week while not exceeding calorie needs. This doesn't necessarily mean 60—90 minutes at one time. It might mean 20—30 minutes of physical activity three times a day. For example, a brisk walk in the morning, at lunch time, and in the evening. Some people may need to talk to their healthcare provider before participating in this level of physical activity.
Stay on Course
. Monitor your diet and activity. Keeping a food and physical activity journal can help you track your progress and spot trends. For example, you might notice that your weight creeps up during periods when you have a lot of business travel or when you have to work overtime. Recognizing this tendency can be a signal to try different behaviours, such as packing your own healthful food for the plane and making time to use your hotel's exercise facility when you are travelling. Or if working overtime, maybe you can use your breaks for quick walks around the building.
. Monitor your weight. Check your weight regularly. When managing your weight loss, it's a good idea to keep track of your weight so you can plan accordingly and adjust your diet and exercise plan as necessary. If you have gained a few pounds, get back on track quickly.
. Get support from family, friends, and others. People who have successfully lost weight and kept it off often rely on support from others to help them stay on course and get over any "bumps." Sometimes having a friend or partner who is also losing weight or maintaining a weight loss can help you stay motivated.
Why is BMI Important?
BMI (Body Mass Index) is important as it is widely regarded that your chances of having a longer and healthier life are improved if you have a healthy BMI.
If your BMI is high, you may also have an increased risk of developing type 2 diabetes, as well as other metabolic diseases such as hypertension, high cholesterol and heart disease.
Relationship of BMI with diabetes
Research shows strong links between a high BMI and type 2 diabetes, with the risk of the condition rising with each increase in BMI.
A review of over 12,000 people in the United States, published in 2014, showed that people with a BMI of 25-29.9 had a 50% increased risk of diabetes compared to people with a BMI of 18.5-24.9.
Obesity was linked with increased rates of diabetes between 2.5 and 5 times higher than people of normal weight, with the highest risk being those with a BMI of 40 or more. The results found:
* BMI 25-29.9 (overweight): 50% higher type 2 diabetes risk
* BMI 30-34.9 (obesity class I): 2.5 times more likely to get diabetes
* BMI 35-39.9 (obesity class II): 3.6 times more likely to get diabetes
* BMI 40+ (obesity class III): 5.1 times more likely to develop diabetes
BMI and other long term health risks
The World Health Organisation (WHO) lists a high BMI as a major risk factor for heart disease, stroke, bone and joint problems including osteoarthritis and a number of cancers, including breast, colon and endometrial cancer.
Large scale surveys, such as SHIELD (Study to Help Improve Early evaluation and management of risk factors Leading to Diabetes), conducted in the USA in 2004, show clear associations between a raised BMI and increased risks of hypertension (high blood pressure) and dyslipidaemia (high cholesterol) in addition to type 2 diabetes.
How health care professionals use BMI Formula
BMI is checked regularly by doctors to assess if people are at a healthy weight, with advice dependent on what your BMI reading is:
* Below 18.5 BMI: advised to eat more to gain weight within a normal range
* Between 18.5-25: you are of normal weight
* Between 25-30 BMI: advised to lose weight and exercise more to reduce risk of obesity
* Over 30 BMI: specific diets and weight loss programmes suggested, as well as referral to a dietician.
In the UK, you may be considered for bariatric surgery in the following cases:
* Having a BMI over 35
* Having a BMI over 30 and having recently been diagnosed with type 2 diabetes
People of Asian origin may be considered for weight loss surgery if they have been diagnosed with type 2 diabetes within lower BMI brackets than 30.
Follow-up appointments will be carried out to ensure your diet, medication and level of support is appropriate to prevent weight being regained.
Determining Your BMI
You can calculate your BMI yourself, using just your height and weight. Use the following formula to calculate it by hand:
A healthy BMI is between 18.5 and 24.9. If you register below 18.5, you may be diagnosed as being severely underweight. A BMI of between 25 and 29.9 puts you in the category of overweight. If your BMI is 30 or greater, you may be diagnosed with obesity, depending on how muscular your build is.
BMI Can Misdiagnose
People who are extremely muscular, such as athletes and bodybuilders, may register a high BMI even though they are exceptionally healthy. Increased muscularity makes you weigh more than average for your height, so the equation results appear as if your BMI is too high. Your doctor should be able to visually assess your muscular condition and offer alternative methods for evaluating your risk of disease, such as blood tests.
BMI can also miss people who have a high body fat percentage but a normal weight. If you have 20 percent fat as a man, or 30 percent fat as a woman, but your BMI is in the normal range, you are still at risk of many of the same ailments associated with obesity. You have a condition known as normal-weight obesity. Sedentary people and older adults are at particular risk for this condition.
Alternative Measures of Fat
Waist circumference is a relatively easy and non-invasive way to perform a quick analysis of a person's health risk due to being overweight or obese. A waist size that's larger than 40 inches on a man or 35 inches on a woman indicates that you likely carry excessive belly fat, which puts you at a higher risk for weight-related diseases. Measuring your waist size may be a way to catch those who have normal-weight obesity.
Body composition measurements, including those taken with skinfold calipers or a body fat scale, can also give you a rough idea of the amount of body fat you carry in relation to lean body mass. More in-depth analyses -- such as DEXA scans and hydrostatic weighing -- are more accurate, but they're expensive and require specialized equipment.
How to Measure Your Waist
Your BMI is a great method of deducting your weight, but measuring your waist is also important to assess for potential risks of disease.
Carrying too much abdominal fat around your waist can lead to obesity-related diseases such as coronary heart disease, high blood pressure and diabetes.
Using a tape measure, there are four steps to follow to accurately measure your weight:
* Locate the top of your hip bone and the bottom of your ribs
* Take a deep breath out
* Place the tape measure between these points and pull it tight around your waist
* Read your measurement
For children, the best way to determine their BMI is by letting the doctor determine it.
The BMI is only a tool. It doesn’t mean that you will develop heart disease. There are other risk factors that go into the disease process, but weight is one of the factors that can be changed by you. Losing weight eliminates obesity from the equation in your life. With that gone, the odds are better that you will not develop health issues at a young age or in the future.