There are many things that affect body weight, including what and how much food and drink is consumed, physical activity levels, as well as things like family history, medication and the food environment that surrounds us.
A healthy diet contains the right amount of nutrients and calories to achieve and maintain a healthy weight. The number of calories that each person needs varies, and depends on a number of factors, including sex and life stage (e.g. such as during childhood, adolescence and pregnancy).
It’s difficult to know what an individual’s ideal weight should be. The most widely used method to measure and categorise a person’s body weight is body mass index (BMI). BMI is categorised into ranges:
- under 18.5 - this is described as underweight
- between 18.5 and 24.9 - this is described as the ‘healthy range’
- between 25 and 29.9 - this is described as overweight
- 30 and over - this is described as obesity.
While BMI can provide an indication of whether a person has a healthy weight for their height, it doesn’t measure body fat directly or consider factors such as muscle, age, sex or ethnicity; it doesn’t indicate an individual’s overall health.
Overweight and obesity occurs when the calories consumed are regularly above what the body requires to function and perform daily tasks. People living with overweight or obesity have an increased risk of developing a range of health conditions, including type 2 diabetes, high blood pressure, heart disease, liver disease, stroke and some cancers. Please see the NHS inform page on obesity for more information.
If someone is underweight, it could mean that their dietary intake is not meeting their needs, and they may be missing out on important vitamins and minerals, and may result in a weakened immune system that can make someone more susceptible to catching a cold, flu or other infections.
For more information on underweight, please see the NHS website – Underweight Adults.