Body composition varies from individual to individual. Body weight is a combination of fat and lean tissue (water, muscle and bone). It is not possible to take direct measures of body composition of live individuals so assessments are made indirectly “Weight” loss or gain itself says nothing about the composition changes in the body. Weight measures are inexpensive, easy and accurate. Being overweight is not necessarily the same as being over fat. Lean body mass is denser than body fat.

What is a Healthy Weight?

Here are some important aspects of a healthy weight
• a weight that is appropriate for a person’s age and physical development
• a weight that a person can achieve and maintain without excessive diet restrictions or constant “dieting”
• a weight that a person feels satisfied with
• a weight that is congruent with a person’s genetic makeup and family history or body shape and weight
• a weight that promotes healthy eating habits and allows for participation in regular physical activity

A person is considered underweight when he/she has insufficient amounts of body fat to maintain health. In this state. he/she has a weight that is below an acceptably defined weight for a given height.
A person is considered overweight is when he/she has a moderate amount of excess body fat. In this state, he/she has a weight that is greater than some accepted standard for a given height but is not considered obese.

A person is considered obese when he/she has excess body fat to the extent that it is adversely affecting his/her health. In this situation, a person has a weight that is substantially greater than some accepted standard for a given height.

How “Healthy” Body Weights Are Determined

How much should a person weigh?

Is a person’s weight, jeopardizing his/her health? These are not easy questions to answer. Generally, healthy weights have been established by looking at weights associated with lowest mortality rates and establishing criteria for healthy weights. These include:
1. A weight within a health BMI range
2. Fat distribution associated with low risk of illness or death
3. No medical condition present that suggests a need for weigh loss
For many people, body image and weight is a more important issue than health and weight.

Body Mass Index (BMI)
BMI compares weight for height and is calculated using the following formula:
BMI = Weight in kg/Ht in m2
BMI Interpretation is as follows:
<18.5- underweight – at risk for health problems 18.5 - 24.9 - healthy weight range - least risk for devloping health problems 25 - 29.9 -overweight- at risk for health problems 30 -34.9 -obese- high risk for health problems 35-39.9 obese- very high risk for health problems >40 obese- extremely high risk for health problems
Note: BMI has limited value when used for people who have very large muscle mass for a given height. BMI is also not intended for us on children younger than 18 yrs old or on pregnant or lactating women. BMI is also not accurate for adults who are naturally very lean or seniors over 65 yrs old and certain ethinc groups.

Is Distribution of Body Fat Related to Health?

For the average man a reasonable body fat range is10-25%. The average woman has a reasonable body fat range of 18 – 32%. Athletes have a lower body fat that is advantageous for performance. Female athletes have a fat range of 15 -20% (some are even lower) while male athletes are 5-10%.
People living in cold climates may benefit from higher body fat percentages and pregnancy needs higher fat stores.
Low body fat is associated with hormonal abnormalities, infertility, depression, abnormal hunger regulation and the inability to maintain normal body temperature.

What is the Ideal?

The media strongly influences our perceived body image and people often turn to fashion or culture rather than health. The body shapes that society values have changed over time. When food was scarce, fashion dictated being overweight was a sign of prosperity and well-being. When food was plentiful, being slimmer is usually favoured. Our culture holds high value on thinness
There is a movement towards the acceptance of a wider range of body shapes. Thin does not necessarily equate with health. A person should have enough fat for their needs but not too much so as to be at increased health risk. Fat distribution may be more important and than total fat in determining health.

Apple vs Pear shape

Central obesity or the storage of fat around the abdomen (apple) is associated with increased risk of diabetes, heart disease, stroke and hypertension. Fat around the thighs and hips (lower body fat-pear shape), is more common in women and seems to pose less of a health risk. Two measures the Waist to Hip Ratio and Waist Circumference can be used to assess fat patterning.

Waist to Hip Ratio and Waist Circumference

The ratio is an indicator of fat distribution and is calculated by dividing the waist circumference by hip circumference. Women with a waist to hip ratio of > .80 are at high risk as are men with a ratio of >1.0. For the waist circumference, a man’s risk is increased when his waist circumference is greater than 102 cm (40 inches) and for women increase risk is associated with measures greater than 88 cm (35 inches).
A recent study* demonstrated the waist to hip ratio was the best indicator of risk for heart attacks. This study also found that BMI was not a good predictor for heart attack risk. When obesity was considered using the waist to hip ratio rather than the BMI, the number of people at risked tripled. The link between increased waist to hip ratio and increased risk of heart attack was a consistent finding in all 52 countries involved in the study.

The reason increased abdominal fat increases the risk of heart disease, stroke, hypertension and diabetes may be that abdominal fats seem to be more active than hip/thigh fat. When mobilized, abdominal fat goes directly to the liver rather than into the general circulation which other fat does. The liver takes abdominal fat and converts it to VLDL and then LDL.

As lipids rise, hormones are released that result in increased heart rate and increased blood pressure. Fat metabolism interferes with insulin metabolism and insulin levels and blood glucose levels tend to rise too.
*Yusuf, S et al. Effect of Potentially Modifiable Risk Factors Associated with Myocardial Infaction in 52 Countries( the INTERHEART study): Case control study. Lancet 2004:364:937-52.

Measuring Body Fat

Calipers are used to measure body fat by fat folds (skin folds). Measurements are taken as several sites including the triceps, biceps, subscapular and suprailiac. The thickness of skin fold reflects the amount of body fat (almost half of fat is under the skin). Measures are taken and compared to standards. Fat folds give a good estimate of body fat and a fair assessment of the location of the fat. It is best used to monitor changes in an individual over time. If there is a gain in body fat, there is a corresponding increase is the skin fold measure. If a person loses body fat, there is a decrease in skin fold measure.

One limitation of this method is that the calipers are too small to measure the skin folds on obese people. To be accurate, this method also relies on well trained technicians. Fat fold measures correlate directly with heart disease.

BIA – Bioelectrical Impedance Analysis involves sending a very low level of electrical current through a person’s body. Lean body mass is mostly made up of water. Water is a good conductor of electricity so the rate at which an electrical current is conducted provides an indication of a person’s body composition. The leaner person is less resistant to the current. There are limitations with this method but under ideal conditions BIA can estimate body fat with an error of 3-4%.

Hydrodensitometry or underwater weighing measures a person’s weight on land and underwater.-not the most convenient thing to do! This method is primarily used in research settings. It is considered on of the most accurate methods of determining body composition. Body fat can be estimated within 2-3%.
Near Infrared Reactance is base on the priciples of light absorption and reflection. A probe is attached to the biceps. Then an infraed beam penetrates the arm and is reflected back into the probe. This method is widely used in health clubs but the accuracy is very poor and the value of any result have to be questioned.
Pod Bod is a machine the uses air displacement to measure body composition. This technology is expensive and is used primarily in research settings. The results seem to be accurate for caucasians but overestimates body fat in some other ethnic groups.

Health Risks Associated with Body Weight and Body Fat

Too little or too much body fat is associated with health risks. People who are underweight or extremely overweight have a high risk of illness and early death.

Underweight
A person with minimal nutrient and energy reserves has difficulty dealing with physical stress such as surgery or illnesses. Underweight women also tend to be infertile.

Overweight
There are multiple health risks associated with being overweight including diabetes, hypertension, cardiovascular disease, sleep apnea, gout, gallbladder disease, liver malfunction, complications after during pregnancy and after surgery.
People who are overweight place a high cost on the health care system.

Cardiovascular Disease
There is a strong association between overweight and increased risk of heart disease and high blood pressure. With weight loss these people see better control of blood lipids and decreased blood pressure.

Diabetes
Type II diabetes is much more likely to develop in an obese than non-obese person. Insulin resistance associated with central obesity. Weight loss contributes to better blood glucose control.

Cancer
There is an increased risk of cancer with increased body weight. It is believed this is because the elevated levels of hormones could influence cancer development.