What is overweight and obesity?
Body mass index (BMI) is a calculation used to measure whether an individual has a healthy weight for their height.
For most adults, a BMI of:
- 18.5 to 24.9 means you're a healthy weight
- 25 to 29.9 means you are living with overweight
- 30 to 39.9 means you are living with obesity
- 40 or above means you are living with severe obesity
For adults from Asian, Chinese, Middle Eastern, Black African or African Caribbean families, these ranges are lower:
- 23-27.4 means you are living with overweight
- 27.5 or above means you are living with obesity
A waist measurement can be used to see whether you have a healthy level of body fat around your abdomen. If your waist measurement is less than half your height, this indicates you are at a lower risk of associated health problems such as type 2 diabetes and heart disease.
BMI is useful for most people for indicating whether they have a healthy weight. In some cases, BMI may be less useful, and additional tests may be needed. For example, someone who has a lot of muscle mass, such as an athlete, may have a healthy level of body fat but have a high BMI due to their higher muscle meaning they have an increased body weight.
Can living with obesity affect my kidneys?
Living with obesity can directly affect your kidneys as puts strain on the kidneys which need to work harder to meet the demands of a higher body weight. This can be harmful to the kidneys and means people living with obesity are at an increased risk of chronic kidney disease (CKD).
You are also more at risk of other health conditions linked to kidney disease if you are living with obesity, including type 2 diabetes and high blood pressure. Diabetes and high blood pressure are the two most common causes of CKD in adults.
Living with obesity also increases your risk of other serious health problems, including heart attack and stroke.
What causes obesity?
Obesity is caused by consuming more calories than the body uses. These additional calories are stored as fat. Calories are contained in the food and drink we consume and are used by the body to fuel activity.
The reasons why someone develops obesity are complex and will depend on the individual and is influenced by their environment.
Obesity is becoming more common. There are many reasons for this. For example, processed and convenience foods, and sugar-sweetened drinks, which are often high in calories, are cheap, convenient, and highly advertised, are consumed more in modern living. For some people, healthy food is less available at an affordable price, and they may be exposed to more advertisement of unhealthy foods. Activity levels are also lower in modern living, for example, we spend more time on electronic devices, and many jobs require less physical activity.
Certain genes and medications can cause some patients to gain weight, which can lead to obesity. Some health conditions are also associated with weight gain, but this can usually be controlled if the condition is well managed.
What are the treatments for obesity?
Lifestyle changes can help you to lose weight safely. You should speak to your GP for advice who may also be able to refer you for more specialist support.
Lifestyle changes can include:
- Diet. Eat a healthy, balanced diet and avoiding high calorie, unhealthy foods. A healthcare professional such as your GP or dietician can make recommendations for your diet. You can find more information on how to eat a balanced diet on the NHS website: How to eat a balanced diet - NHS. If you have kidney disease always speak to your renal dietitian before making any changes to your diet.
- Regular exercise. The NHS recommends at least 150 minutes of moderate exercise a week, so try to do at least 30 minutes activity or exercise at least five days per week. Increasing the physical activity you do will increase the calories burned by your body.
It may take a few months to begin losing weight after making these lifestyle changes.
Sticking to a diet and exercise plan on your own can be tough. Joining a weight loss group can help by providing support and encouragement. If you are interested in joining one of these groups you can ask your GP for more information.
Some people may also find counselling and other healthcare support services helpful to help make lifestyle changes and lose weight.
If lifestyle changes aren’t helping with weight loss, your healthcare professional may recommend weight management medicines. These include GLP-1 medicines. You should only take these if prescribed by a healthcare professional.
If you are living with severe obesity and lifestyle changes and medicines aren’t helping, you may be offered weight loss surgery. This works by decreasing the size of the stomach, so you feel fuller.
Help for you
It can be hard to lose weight successfully but setting yourself realistic goals, regularly monitoring your weight and receiving encouragement from family and friends can help you persevere.
Speak to your GP if you want help and advice about how to lose weight.
You can also find practical tips – including a free 12-week NHS diet and exercise plan on the NHS website. Always remember to speak to your kidney consultant or kidney dietitian before starting a diet plan or new exercise programme if you are on a restricted diet due to kidney disease.
For more information and lifestyle advice for kidney patients you can visit:
References
NHS. Obesity [online]. Nhs.uk, England; Feb 2023 [Accessed 31 December 2025]. Available from: Obesity - NHS
NICE. Keep the size of your waist to less than half of your height, NICE recommends [online]. Nice.org, England; [Accessed 31 December 2025]. Available from: Keep the size of your waist to less than half of your height, NICE recommends | NICE
Kovesdy, CP. Furth, SL. and Zoccali, C. Obesity and Kidney Disease [online]. 2017; 8;4. [Accessed 31 December 2025]. Available from: <PMCID: PMC5433675>
NIDDK. Causes of Chronic Kidney Disease in Adults [online]. NIDDK.nih.gov, US; Feb 2025 [Accessed 31 December 2025]. Available from: Causes of Chronic Kidney Disease in Adults - NIDDK
WHO. Obesity and overweight [online]. WHO.int. [Accessed 31 December 2025]. Available from: Obesity and overweight
NHS. What is weight loss surgery? [online]. Nhs.uk, England; Feb 2024 [Accessed 31 December 2025]. Available from: What is weight loss surgery? - NHS
Lee, A. Michelle Cardel, BS. And Donahoo, WT. Social and Environmental Factors Influencing Obesity [online]. 2019. [Accessed 22 January 2026]. Available from: <PMCID: 25905211>
Reviewed March 2026 by Professor James Burton from Leicester
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