BMI is the body mass index used to gauge your weight according to your height. Low BMI is typically associated with lower weight and high activity levels. But recent research findings suggest that some individuals can maintain a low BMI even though they eat less and are less active. Why? Because they have a naturally fast metabolism and tend to eat less.

How did these findings counter earlier thinking about BMI? 

This study observed 173 participants with normal BMI levels. Approximately 150 were considered “healthy but underweight,” with a BMI of 18.5. They screened them to see if they had any eating disorders, were ill, had HIV, or were on medication that caused them to lose weight. 

For two weeks, scientists measured their food consumption and physical activities. When they compared the underweight group with the other group, scientists found that the healthy underweight people ate at least 12% less food and were also 23% less active. Usually, a high BMI is how doctors measure obesity. 

Scientists expected these underweight people to be very active and consume a lot of food. But, as it turned out, these individuals ate less and did less, yet still had a high resting metabolic rate and elevated thyroid hormones. 


What is BMI?

Body mass index is calculated by dividing your weight (in kilograms) by your height in meters squared. A normal BMI is 18.5 to 24.9. Conventional wisdom says the higher your BMI, the more at risk you are for heart disease, type two diabetes, breathing problems, high blood pressure, and some cancers. Over the years, BMI has been a good tool for measuring obesity and overweight. BMI does have limitations. BMI mistakenly assumes you have a higher body fat if you have a muscular build or are an athlete. For older people who have lost muscle, the BMI overestimates body fat. The best way to get an accurate BMI is to use a BMI calculator. 

Is BMI a good measure of health? 

Some researchers feel that using BMI to measure overall health is useless today. It was popular in the 1800s and utilized with little change since then. But many doctors think it’s an inaccurate measure of a person’s health. That’s because someone’s body mass index doesn’t consider the weight’s location on the body. For instance, a female may carry weight mainly in her chest or thighs, which doesn’t put her at risk for specific health problems like heart disease. Proponents of a new system for measuring overall health suggest using body shape along with your BMI and something else like blood work or blood pressure measurements to gauge fitness. So BMI may be suitable as a partial measure of health combined with other factors. 

What is metabolism?

Your metabolism is the process in your body that breaks down and creates energy for you to live. Metabolism is how quickly your body expends energy and burns calories. 

  • Every activity: Your metabolism creates energy to do your everyday life activities. 
  • Exercise: Exercise burns more calories.
  • Bodily functions: At rest, your body still uses up energy to function. It’s called the basal metabolic rate (BMR). Your BMR is, in part, determined. by your genes. 

Some people inherently have a faster metabolism. They can eat more than others yet not gain weight. Your metabolism depends on your age, gender, activity, and genetics. You can increase your metabolism for a short time with exercise, proteins, green teas, and spicy foods. Eating breakfast and not skipping your meals will also help improve your metabolism. Getting enough sleep and drinking water is also essential. Your eating habits also significantly contribute to your weight gain or loss. 

Is it better to have a faster metabolism?

Not necessarily.

If you have a faster metabolism, it means your body burns more calories when you’re resting than someone with a lower metabolic rate. However, the quicker your metabolism, the more calories your body needs. A fast metabolism isn’t good or bad for your health. Maintaining healthy eating habits is crucial so you get enough calories to nourish and sustain your body. Good eating habits help increase your metabolism. 

Does being underweight due to a fast metabolism have health risks?

According to other studies, being underweight has as many health risks as being overweight. Underweight individuals may struggle with poor eating habits, leading to not getting enough calories. As a result, you may lack vitamins and minerals. If your BMI is less than 18.5, you don’t weigh enough. Weighing too little may cause:

  • Osteoporosis: Sometimes called brittle bone disease, osteoporosis makes you prone to bone fractures, skin, teeth, and hair problems. 
  • Getting sick a lot: You’ll lack sufficient calories if you make unwise food choices. Poor nutrition takes away your ability to fend off infection and illnesses. As a result, you’ll be more likely to catch a cold or virus. 
  • Fatigue: Another symptom of being underweight is constant tiredness. If you don’t get enough calories makes it difficult to keep up your energy. 
  • Anemia: If you’re underweight, you’re prone to anemia. This disease occurs if your body doesn’t produce enough red blood cells. Low red blood cells lead to headaches, fatigue, and dizziness. You may also have absent or irregular menstrual periods and even infertility. 
  • Stunted growth: Lacking the necessary calories and nutrients leads to poor development and stunted growth. 
  • Risk of mortality: Being underweight increases your risk of lack of healing if you have an accident or trauma compared to someone with a higher BMI. 

If you’re lean, there’s a good chance you’re busy all the time during the day. You might fidget and always be in motion more than someone who is overweight. If you can’t seem to sit still, you may have learned this tendency or are just genetically wired to move a lot. Overweight people tend to be sedentary, making it more difficult to lose body fat. 

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What are alternatives to BMI?

Here are some other tried-and-true methods to measure your BMI. These tests are more popular now in light of this new information on metabolism.

Waist circumference measurement

This old-fashioned alternative to BMI is one of the best ways to measure your abdominal fat. Carrying extra weight around your stomach puts you at risk for heart disease and other medical problems such as 

  • Type two diabetes
  • Liver problems
  • Dementia
  • Cancer

You measure your natural waist. Women with a waist measurement of around 35 inches and men with a mid-section over 40 inches have almost double the risk of experiencing cardiovascular disease, for instance. 

Body adiposity index

The body adiposity index doesn’t use your weight. For this measurement, you multiply your hip circumference by your height. Many feel this is a better measurement of overall health than BMI. As a result, some health care professionals often rely on this factor. 

Waist-to-hip ratio

This ratio is also an accurate way to calculate extra body fat, especially around your belly. First, measure your natural waist and the widest part of your hips using a tape measure. Then you divide your waist circumference by your hip circumference. Most people convert this to metric. So, if you have a 30-inch waist (76cm), and you divide it by your hips 38″ (97cm), then you have a waist-hip circumference of approximately 78cm. Here’s a chart to gauge your health. 

Women hip to waist ratio:

  • Low waist 31.4 inches (80cm) or lower
  • Moderate 31.88-33.4 inches(81cm to 85cm)
  • High 33.8 inches (86cm or higher)

Men hip to waist ratio.

  • Low 37.4 inches (95 cm) or lower
  • Moderate 37.7 inches(96cm)
  • High 39. 7 inches (100cm)

Be careful not to short-circuit your metabolism

Just as there are ways to increase your metabolism, common mistakes slow it down. 

  • Lack of sleep: Not getting enough sleep will cause metabolic issues. Your metabolism will slow down, so you’re burning fewer calories. It increases your cortisol which causes your body to store fat. As a result, you’ll eat more because your body lacks energy. The result is weight gain. 
  • Too much caffeine: Although caffeine can boost your metabolism, too much of it makes your metabolism sluggish. 
  • Eating habits: Not eating high-fiber foods like fruit can affect your metabolism. 
  • Keep your house too warm: Keeping your house cooler kicks up your metabolism, so it has to work harder. Sleeping in a cool room at night can help you burn brown fat, the most challenging fat to lose.
  • You didn’t eat enough food: Conventional thinking is the less you eat, the better. But it can backfire on you by slowing down your metabolic rate. Healthy eating can help you have the energy you need plus burn calories. 
  • You skipped the sun: Exposing your body to sunshine for thirty minutes gives you 10,000 IU of vitamin D. This weight loss vitamin alters the formation and storage of fat. In addition, it increases serotonin, so you feel good and lose weight. 

metabolism myths

Final thoughts on metabolism and the surprising BMI study

Body mass index has been used for many years to measure a person’s fat, bone, and muscle levels. Today many doctors feel it’s outdated, so they suggest different ways to gauge a person’s health. Metabolism is the body’s thermostat that regulates burning calories and giving your energy. Healthy eating habits maintain and increase your metabolism. Staying healthy is vital for the energy you need to do what you love with the people you love.