UK GCSE level age ~14-16, ~US grades 9-10 Biology revision notes re-edit 17/05/2023 [SEARCH]

 Non-communicable diseases: 9. Measures of obesity - indexes and ratios - obesity linked to several diseases

e.g. non-communicable diseases including high blood pressure (hypertension), high LDL cholesterol, low HDL cholesterol, high levels of triglycerides, type 2 diabetes, coronary heart disease (CVD), stroke, gallbladder disease, and some potentially fatal

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(9) Measures of obesity  (just one measure of healthiness and well-being)

This section is re-edited from the section on

Keeping healthy: diet, exercise, diabetes, body indexes/ratios, diet deficiencies, calorific values

Introduction

The negative health effects of being overweight and obese, many of which can be fatal include:

High blood pressure (hypertension)

High LDL cholesterol, low HDL cholesterol, or high levels of triglycerides

Type 2 diabetes

Coronary heart disease

Stroke

Gallbladder disease.

Please note there is no such thing as the 'perfect weight', we come in all shapes and sizes, but there are limits within which we should be to be healthy!

In the medical profession, a doctor can't just simply say that somebody is overweight, without reference to some kind of statistical index, usually by one/both of the ratios described below.

Equally healthy people can have quite different weights, but there are some reasonably good indicators as to when your weight is not what it should be 'ideally'.

In rich developed countries we are often dealing with 'overweight' people eating too much rich fatty food, but in poorer underdeveloped countries we are dealing 'underweight' people, particularly young children suffering from malnutrition.

Malnutrition means lack of proper nutrition, caused by not having enough to eat, not eating enough of the right things, or being unable to use the food that one does eat.

 

The Body Mass Index

The body mass index is a 'rough' guide to help the medical profession decide whether is underweight, normal, overweight or obese.

The higher your BMI the more fat you are carrying - but not necessarily unhealthily.

Body Mass Index (BMI) = (body mass in kg) / (height in m)2

When measured, you then consult a table of BMI values to se where you fit in!

Table of BMI values (from https://www.vertex42.com/ExcelTemplates/bmi-chart.html)

Body mass index

Weight description

less than 18.5

underweight

18.5 to 24.9

normal

25.0 to 29.9

overweight

30.0 to 40.0

moderately obese

over 40.0

very obese

If you eat too much fatty sugary foods and don't take enough exercise, most people will put on weight and too much of it. You are taking in too much energy rich food for your daily needs.

The excess energy releasing food is stored as fat and gives you a raised BMI value.

Having a higher than normal BMI value increases your risk of developing type 2 diabetes and cardiovascular disease.

For more on this see The human circulatory system - heart, lungs, blood, blood vessels, causes/treatment of cardiovascular disease

Note of caution: Having a high BMI is not always unhealthy e.g. sports people train hard to build up extra muscle which is heavier than fat, so they will tend to have higher than 'normal' BMI values and would not be classed as overweight.

The BMI calculation is easy e.g. for a person with a body mass of 70.0 kg and a height of 1.80 m,

The BMI = m / h2 = 70 / 1.802 = 21.6 (3 sf, kg/m2), suggesting the person is 'normal'.

BUT, beware, we do come in all shapes and sizes, even people on healthy diets don't always 'fit in' with he BMI, but most doctors consider it a useful and reasonably accurate diagnostic tool.

Note from 2020 on the covid-19 flue pandemic: Research has shown that obese people are more likely to be seriously ill with the virus than non-obese people - more severe fever, more likely to be hospitalised and more likely to die!

The waist-to-hip ratio should also be taken into consideration (see below).

The waist-to-hip ratio

Comparing the circumferences of waist and hips is another measure of whether you are 'overweight' and concentrates around one area where we can accumulate to much fat.

This index is all about fat distribution.

waist-to-hip ratio = circumference of waist (cm) / circumference of hips (cm)

The higher your waist-to-hip ratio the more fatty tissue you are carrying around the middle of your body.

When measured, you then consult a table of BMI values to se where you fit in!

Make sure you measure both diameters with the same length units!

Table of waste-to-hip ratios (from https://www.healthline.com/health/waist-to-hip-ratio)

Health risk

waist-to-hip ratio (women)

waist-to-hip ratio (men

low

less than 0.81

less than 0.96

moderate

0.81 to 0.85

0.96 to 1.00

high (overweight)

over 0.85

over 1.00

The Waist to Hip calculation is easy e.g. for a woman of waist measurement of 32 cm and a hip measurement of 40 cm,

The waist to hip ratio  = 32 / 40 = 32 / 40 = 0.80 (3 sf, no units), suggesting the person is 'fine' (borderline low-moderate).

If you are female and your waist-to-hip ratio is over 0.85 you are classed as overweight.

If you are male and your waist-to-hip ratio is over 1.00 you are classed as overweight.

If you are above the moderate waist-to-hip ratio values you are carrying too much fat around your 'middle' - referred to as abdominal obesity.

Having a higher than normal waist-to-hip ratio increases your risk of developing type 2 diabetes and suffering from cardiovascular disease.

For more on this see The human circulatory system - heart, lungs, blood, blood vessels, causes/treatment of cardiovascular disease

Again, beware, we do come in all shapes and sizes, but most doctors consider it a useful extra diagnostic tool.

The body mass index (BMI) should also be taken into consideration (see above).


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