BMI: A Starting Point for a Healthy Weight

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The health risks of obesity have been in the news lately, including in our latest report showing a link between obesity and ovarian cancer risk. The stories have sparked a lot of conversation about BMI (Body Mass Index), a number used to easily determine a person’s body fatness. Young man measuring his weight on weighing scale in clinic

Maybe you know your own BMI. But what is BMI and what does it mean to you?

The formula for BMI is:
weight (kilograms) divided by height (meters)2
weight (pounds) divided by height (inches)2  x 703

A BMI of 18.5 – 24.9 is considered healthy; 25-29.9 overweight and 30 and above obese.

BMI is very useful for studies looking at a large number of people and trying to determine if, on average, BMI links to disease risk or health status in some way. But for individuals, BMI is a starting point to determine whether your weight is in the healthy range for you.

The groups of people with higher BMIs do have higher risk for getting certain cancers when compared with the lowest BMI groups over time. Researchers sort out other factors that influence disease risk, like smoking and amount of physical activity, to determine that it is the extra body fat causing the higher risk.

Yet for each person – especially if you are in the overweight range (25-29.9) – BMI does not always correlate with how much body fat you have. That is why athletes may be overweight or slightly obese, but not have excess body fat. And it is also not a good predictor for the elderly. Children and teens have a different formula for determining healthy ranges. For most people, though, it is a pretty accurate measure.

If you are wondering whether your BMI measure is an accurate measure of your body fatness, you might consider some of the factors that affect your body fatness or your health risk. These are health habits that may help you maintain more muscle and keep body fat at a healthy level:

1. Being regularly physically active and doing activities that are muscle building (weight training for example)

2. Eating a healthful diet that contains plenty of plant-based foods like vegetables, fruits, whole grains and legumes and avoiding or limiting high calorie, highly processed foods that have added sugars, fat and salt.

3. Doing at least 30 to 60 minutes of moderate physical activity (can carry on a conversation, but couldn’t sing)

4. Avoiding or limiting alcohol to no more than 1 standard drink/day for women; 2 for men.

5. Don’t smoke. (Some studies show that smokers have more waist fat than non-smokers, even when they weigh less.)

Most people don’t need to have their body fat tested, but if you are concerned, there are other ways to have your body fat tested but these also have drawbacks. The calipers method uses skinfold thickness, but is only accurate if done correctly. Bioelectrical Impedance (BIA) uses electrical signals to measure body fat. You might have access to these in fitness centers or at your doctor’s.

You can check your BMI on AICR’s BMI calculator.


Author: Alice RD

Alice G. Bender, MS, RDN, is the Director of Nutrition Programs at AICR. She helps put the science of cancer prevention into action by providing tips and tools to choose nutritious and delicious foods. Alice has guided thousands of individuals to healthier lives through diet changes and choices.

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