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Body weight

Many Canadians weigh too much – more than half of Canadian adults (ages 18 and older) and nearly one-third of children and youth (ages 5–18) are overweight or obese. An unhealthy diet that is too high in calories and lack of regular physical activity can lead to being overweight and obese. People who are overweight or obese have a high amount of body fat and are at greater risk of developing health problems such as diabetes, high blood pressure, heart disease, stroke and certain types of cancer.

Being a healthy weight helps you feel fit and flexible, have more energy and lowers your risk for weight-related health problems.

What is a healthy body weight?

A healthy body weight will be different for everyone, so check with your doctor about what a healthy body weight is for you. Being at a healthy body weight does not mean being skinny, but you might be surprised to learn how much “extra” weight makes you obese or even just overweight from a medical point of view.

Body mass index (BMI) and waist circumference are 2 common tools that healthcare professionals use to find out if you are overweight or obese.

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Body mass index

A tool called body mass index (BMI) can be used to help decide when adults may be at risk for developing health problems because they are underweight or overweight. BMI uses a chart based on weight and height. BMI is calculated by dividing people's weight (measured in kilograms) by their height (measured in metres squared). The result is looked up in the table to determine the risk of developing health problems.

Health risk and body mass index (BMI)
GroupBMI (kg/m2)Risk of developing health problems

underweight

less than 18.5

increased risk

normal weight

18.5–24.9

least risk

overweight

25–29.9

increased risk

obese

obese class I

obese class II

obese class III

30 or more

30–34.9

35.0–39.9

40 or more

high risk

very high risk

extremely high risk

Source: Health Canada

BMI is not used the same way for people under 18 or women who are pregnant or breastfeeding. Finding out a child’s BMI is different than for adults. Children and adolescents are still growing and their amount of body fat changes as they grow. BMI charts are also different for boys and girls. Talk to your doctor to find out if your child is underweight or overweight for their age.

Drawbacks of using BMI

BMI is not a perfect tool. There are some drawbacks to using it as a measure of obesity.

  • BMI is an indirect measure of body fat.
  • BMI does not necessarily reflect the changes that occur with age.
  • BMI and body fat actually differ for men and women. Women often have a greater percentage of body fat, but this is not reflected in height and weight measurements.
  • BMI may not reflect the difference between excess body fat and muscle mass. For example, lean people, such as athletes, with high muscle mass sometimes have high BMI scores.
  • BMI may be based on self-reported height and weight, which can affect accuracy.

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Waist circumference

Waist circumference (WC) is another indicator of health risk associated with excess abdominal fat (fat around the belly). Excess fat around the waist and upper body (an "apple" body shape) is associated with a greater health risk than having more fat in the hip and thigh areas (a "pear" body shape). WC is measured around the abdomen from the bottom of the lower rib and the top of the pelvic bone while a person is standing.

In general, the risk of developing health problems, including cancer, increases as WC increases above 102 cm (40 inches) in men and 88 cm (35 inches) in women. Even though a person's BMI may be in the normal weight range, a high WC indicates some health risk. Excess abdominal fat increases the risk of colorectal cancer and may increase the risk of pancreatic, post-menopausal breast and uterine (endometrial) cancer.

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Being overweight or obese and cancer

Research shows that being overweight or obese increases your risk of cancer.

Breast cancer – the effect of obesity on breast cancer risk depends on whether a woman has reached menopausemenopauseThe time in a woman’s life when her ovaries stop producing estrogen and she has not had a menstrual period for 12 months. Most women start menopause between 45 and 55 years of age.. Post-menopausal women who are overweight or obese have a higher risk of developing breast cancer than women who are a healthy weight.

 

Colorectal cancer – colorectal cancer occurs more often in people who are overweight or obese than in those who are a healthy weight. This increased risk of colorectal cancer has been reported for men with a high BMI, but the connection between BMI and the risk in women seems to be weaker.

Esophageal cancer – people who are overweight or obese are more likely than people who are a healthy weight to develop cancer of the esophagus.

Gallbladder cancer – studies have shown that being overweight or obese is a risk factor for gallbladder cancer.

Kidney cancer – studies have shown a link between kidney cancer (renal cell carcinoma) and being overweight or obese.

Uterine (endometrial) cancer – overweight or obese women have a greater risk of developing uterine cancer than women who are a healthy weight.

Pancreatic cancer – studies show that people with a higher BMI are at increased risk of developing pancreatic cancer.

Liver cancer – studies have shown that obesity is associated with increased risk of liver cancer.

Prostate cancer – studies have shown that being overweight or obese increases the risk of advanced prostate cancer.

There also appears to be a weak link between thyroid cancer and increased BMI.

Researchers do not know exactly how being overweight or obese increases a person's risk of developing cancer. It may be different for each specific type of cancer. It is thought that obesity may cause changes in the level of hormoneshormonesA substance that regulates specific body functions, such as metabolism, growth and reproduction., such as the sex hormones (like estrogenestrogenA female sex hormone that causes the female sex characteristics to develop (such as breasts) and is necessary for reproduction., progesteroneprogesteroneA female sex hormone that prepares the uterus (womb) for pregnancy and the breasts for lactation following childbirth. and androgensandrogensA type of hormone that regulates the growth, development and function of the male reproductive system (the group of organs involved in having children). Androgens also control the development of male physical traits.) or insulin. This may account for an increased risk of developing breast, colorectal or uterine cancer.

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Reducing your risk

About one-third of all cancers can be prevented by eating well, being active and maintaining a healthy body weight. A healthy, well-balanced diet and regular physical activity are 2 of the best ways to reach and maintain a healthy body weight. People who are overweight or obese should avoid gaining more weight and try to lose weight by eating healthier and exercising more.

To help you maintain a healthy body weight:

  • Follow Canada's Food Guide and eat a well-balanced diet that includes a variety of vegetables and fruit and lots of fibre each day, but has little fat, little sugar and less processed food.
  • Try to drink at least 6–8 glasses of water (or other caffeine-free fluid) each day. When you are physically active or when it is hot outside, drink more water.
  • Follow physical activity guidelines for your age group.
  • Talk to your doctor or a registered dietitian if you need to lose weight. Small, gradual changes to what you eat and how active you are can make a difference.
    • Try not to skip meals because this may cause overeating later.
    • Replace high-fat foods, beverages and snacks with low-fat choices. Choose leaner cuts of meat. Avoid high-calorie foods.
    • Eat smaller portions and plan meals around vegetables, fruit and grain products.
    • Be aware of diets and exercise products that promise quick and easy results. Most diets fail because staying at a healthy weight depends on more than just cutting down on the amount of food you eat or exercising for a short period of time.

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