Written by Bonnie Gifford
Bonnie Gifford
Nutritionist Resource Content Team

Last updated 5th December 2022 | Next update due 4th December 2025

Obesity or severe obesity are terms used for people who are overweight or very overweight, with an excessive amount of body fat. Around one in four adults in the UK are currently obese. We explain more about obesity, the risks and causes of being overweight, and how working with a nutritionist can help you to reach a healthy, sustainable weight.

What is obesity?

The term obese is generally used for people with a BMI of 30 or over. Typically caused by having too many calories (through eating or drinking too much) and not exercising enough, someone who is considered to be obese has excessive fat that could risk their health. 

According to the World Health Organisation, each year over 4 million people die as a result of being overweight (having a BMI of 25 or over) or obese. In 2016, it was estimated that there were over 650 million adults worldwide that were classified as obese. 

Why is obesity a problem?

Obesity can lead to increased health risks. These can include being at a greater risk for a number of different diseases and conditions, including type 2 diabetes, coronary heart disease, stroke, and some types of cancer (particularly breast or bowel). It can also lead to lower quality of life and psychological issues including low self-esteem and depression. 

Nutritionist who can help with obesity

Am I obese?

There are a number of different ways you can check to see if you may be clinically obese. One of the most common ways healthcare professionals measure if you are a healthy weight is by calculating your body mass index (BMI). Your BMI looks at your weight in relation to your height, age, and sex. It does not take into account your muscle mass, build, or other factors. 

While healthcare professionals find BMI to be a useful tool in quickly identifying potential health risks, it is worth remembering that this measurement alone does not provide a detailed, full picture of your health. Some experts believe that BMI alone can be confusing and an oversimplification. We explain more about other ways you can track your physical health

Calculating your BMI

You can use the free NHS BMI healthy weight calculator to check your BMI, as well as to find out more information about what your BMI number means. For most adults:

  • under 18.5 means you are underweight
  • 18.5 to 24.9 means you are considered to be a healthy weight
  • 25 to 29.9 means you are overweight  
  • 30 to 39.9 means you are obese
  • 40 or above means you are severely obese

BMI alone is not typically used to diagnose obesity. This is because you may have a particularly high muscle mass, resulting in a higher BMI without a high percentage of body fat. 

Measuring your waist

Waist measurements are often used as a good indicator of whether you may be overweight, moderately obese, or severely obese if your BMI is 25 or over. According to the NHS, men with a waist size of 94cm or higher, and women with a waist size of 80cm or more are more likely to develop obesity-related health problems. 

Is my weight already affecting me or putting me at risk?

If you have concerns that you may be overweight or obese and this has put your health at risk, seek advice from your GP. They may start asking about any symptoms you may have experienced and tests may be carried out in order to rule out any other potential issues.

Taking steps to promote healthy weight-loss is important. This can help to reduce your risk of developing other health conditions and obesity-related problems, which can, over time, cause problems with day-to-day activities. Other issues that can be related to obesity can include:

  • breathlessness
  • snoring
  • increased sweating
  • difficulty with physical activity
  • feelings of tiredness or lethargy
  • joint or back pain
  • feelings of isolation, low confidence, or low self-esteem
  • negative impact on relationships with friends, family or colleagues

Over time, there can also be psychological effects, which can not only influence your self-image, but can also lead to other issues such as anxiety and depression. 

Serious health concerns and conditions can also develop due to obesity. These can include:

  • type 2 diabetes
  • high blood pressure or high cholesterol (which can lead to coronary heart disease or stroke)
  • asthma
  • metabolic syndrome (combination of high blood pressure, diabetes, and obesity)
  • cancer
  • gallstones
  • reduced fertility or pregnancy complications (gestational diabetes, pre-eclampsia)
  • GORD (gastro-oesophageal reflux disease)
  • osteoarthritis (painful and stiff joints)
  • sleep apnoea
  • kidney or liver disease
  • reduced life expectancy (between three to 10 years depending on severity)

Childhood obesity

The World Health Organisation (WHO) has reported childhood obesity to be one of the most serious challenges for public health this century. WHO regard obese children and adolescents to be living with an increased risk of developing weight-related health conditions. 

According to the latest figures from The National Child Measurement Programme in England 2020-21 report, 14.4% of children aged four to five years old (reception age) are obese. Amongst children aged 10-11 (year six pupils), 25.5% were found to be obese.  

Childhood obesity can lead to ongoing issues with obesity as children grow up, as well as leading to potential health problems. Research has suggested that children that are a healthy weight may be healthier, more self-confident, and better able to learn. They are also at lower risk of low self-esteem and experiencing bullying. 

Before making any changes to your child’s diet, do make sure to discuss this with your doctor. There may be other conditions affecting their weight that need to be accounted for. However, if their dietary habits are a concern, a nutritionist may be of help. They will be able to support and advise you on what changes need to be made in order for them to follow a calorie-controlled diet and live an active lifestyle.

As a parent, you can support your child in making healthier choices by encouraging them to be more active, and helping them to learn more about food, nutrition, and the importance of a balanced, healthy diet. If your child is worried about their own weight, listening to them is key in helping them to feel supported, in control, and heard. 

Modelling healthy behaviours with food, ensuring you understand child-sized portions, and encouraging less screen time and more sleep can all be helpful. 

What are the main causes of obesity (and what can I do about them)?

Though there are many factors that can affect a person’s weight. Obesity does not develop overnight. Consuming high amounts of fat and sugar but not burning enough energy through physical activity will in time result in the body storing it as excess fat.

Your metabolic rate is the amount of energy or calories your body needs to burn in order to function normally. There is a common misconception that overweight and obese individuals have a low metabolic rate, when in fact more often than not, obese individuals have a normal to high metabolic rate - this is because the body uses more energy to carry the excess weight.

Poor diet

One of the primary reasons people gain weight can be their diet. When we are eating food, our body sends signals to indicate fullness, this sensation can be ignored if we are eating something we enjoy. A recent study found that an area of our brain linked to addiction and reward lights up when we are faced with carb-rich, fatty foods. Eating what we think to be ‘rewards’ can be harmful to our health, for example:

  • eating large amounts of processed or fast food
  • drinking an excess of alcohol
  • eating larger portions
  • drinking fizzy or sugary drinks
  • comfort eating

These foods in excess can result in rapid weight gain; products with high sugar and fat content can result in an increased risk of developing health problems later in life. A balanced, calorie-controlled diet consisting of fresh fruits, vegetables and regular exercise can help reduce the risks and promote healthy weight-loss.

Typically, an average man needs around 2,500 calories a day to maintain a healthy weight, while an average woman needs around 2,000. 

Counting calories isn’t always effective for weight loss

While calorie-controlled diets are often the route people take when trying to lose weight, research has shown that calorie restriction can lead to a slower metabolism, increased hunger hormones (ghrelin), and a decrease in our ‘feeling full’ hormones (leptin). When we focus on calories, we not only feel hungrier, but are less likely to feel full or satisfied. 

Looking at your relationship with food, making long-term, sustainable lifestyle changes, and learning more about nutrition, healthy eating, and a balanced diet can all be effective, alternative ways of losing weight and overcoming obesity. 

Lack of physical activity

Physical activity not only helps our body burn off any excess energy which may be stored as fat but it is also necessary to keep our bodies in optimum condition.

The NHS recommends adults aged 19 to 64 should do some kind of physical activity every day. If you struggle to exercise more often, doing so just twice a week can reduce your risk of heart disease or stroke. It’s advised that you should:

  • Do strengthening exercises that works all your major muscle groups at least twice a week.
  • Exercise for at least 150 minutes moderately or 75 minutes vigorously each week.
  • Exercise for similar lengths of time over four to five days minimum, or every day if possible.
  • Reduce how long you sit, lay down, or remain stationary for long periods. 

If you have any existing medical conditions, concerns, or haven’t exercised in a while, speaking with your GP first may be advisable. 

Environmental and genetic factors

While in most obese people, there has been no single genetic cause identified, some studies have shown that there are more than 50 genes associated with obesity. For some people, genes can account for 25% of their predisposition to be overweight, while for others, it can be as high as 80%

Those with one or more parents classified as overweight or obese may be at a higher risk of becoming overweight or obese themselves. This can be due to genetics, environment, or learning unhealthy eating habits or behaviours. While for most of us, our brains send a signal when our bodies are full, over time, we can ignore or stop recognising these signals. 

Medical problems

Other medical problems can lead to or affect your likelihood of developing obesity. Prader-Willi syndrome and Cushing syndrome can lead to obesity. For example, Prader-Willi can leave people feeling constantly hungry, while their lower muscle mass means that they need fewer than normal calories. 

Polycystic ovary syndrome (PCOS) or having an underactive thyroid can make weight gain easier for women. Some chronic illnesses and chronic pain disorders, such as arthritis, can lead to decreased activity, which can increase your likelihood of gaining weight. 

Some prescription medications can also lead to weight gain. If you are worried that you may be experiencing a side-effect from medication, it’s important to speak with your GP before making any changes. You should not stop taking medication without first consulting with your GP or healthcare provider. 


Anyone, at any age, can be obese. But as we get older, hormonal changes, decreasing muscle mass, and a less active lifestyle can increase your risk of becoming obese. These changes can also make it more difficult to keep off excess weight, meaning you may need to be more conscious of what you eat and how frequently you exercise. 

Social and economic factors

Where you live and how you grew up can both be linked with your likelihood of becoming obese. If you are in a built-up area with few safe places to walk, it can lead to relying on driving or public transport. If there are few free, cheap or only expensive places to exercise, you may be less likely to prioritise exercise. If you weren’t taught about eating healthily, balanced meals, how to cook, or even how to budget your money to create healthier meals for less, you may struggle to make better food choices. 

Lack of sleep or increased stress

When we don’t get enough sleep (or sleep too much), it can cause changes in our hormones that increase our appetite. This can leave you craving high-calorie, high-carbohydrate foods, which can lead more easily to weight gain. 

If you are struggling with stress, this can not only decrease your quality of sleep, but can affect your overall mood and well-being. This can lead to trying to self-soothe with food, or using food as a way to cope with how you are feeling. Over time, this can become an unhelpful habit. 

What treatments are available for obesity?

If you are committed to making a change and losing excess weight, you first have to accept that it takes time and patience. While the initial weeks often see rapid results, a successful long-term weight-loss requires a change in diet and an increase in physical activity.

It is important to consider the following when adopting a change in lifestyle:

  • Are you motivated?
  • Is your goal realistic?
  • Are you prepared to track your progress?

Recommended treatment for obesity includes:

  • Speaking with your GP for further advice about services in your area. This can include weight loss groups, exercise on prescription, and further recommendations for tests or specific specialist support.
  • Diet. Making healthy changes to reduce your calorie intake by up to 600 calories a day is typically recommended by the NHS. Fad diets, diet programmes, and other ‘extreme’ diets that encourage very low-calorie (under 800) intake or cutting out food groups are often not recommended, as these are not sustainable. Instead of focusing on teaching you sustainable, healthy eating habits, these offer quick but short-term results that can leave you feeling ill and frustrated.  
  • Exercise. Physical activity can help improve your overall health and sense of well-being, as well as helping to manage and prevent a number of different health conditions. 

How can working with a nutritionist help reduce obesity? 

Working with a qualified nutritionist can help. A nutritionist can offer tailored support, advice and guidance. They can help with:

  • Creating a balanced diet plan tailored to you.
  • Advising you on sustainable changes you can make to your diet, lifestyle, and daily routine.
  • Helping you to learn more about a balanced diet, getting enough nutrients, and the importance of exercise alongside nutritional changes.
  • Focusing on weight-loss, nutrition, weight management, and healthy eating.
  • Providing ongoing support and advice to help you continue to succeed with and maintain weight-loss.
  • Encouraging you to set realistic weight goals. By setting smaller milestones, you can feel a sense of progress and achievement sooner, which can boost and sustain motivation.
  • Teach more about mindful eating.
  • Help you to recognise situations and temptations that can lead to overeating, unhelpful food choices or habits.
  • Monitor your progress.
  • Help with ongoing weight management advice and guidance. 

Different nutritionists specialise in different areas. Some also offer support for those experiencing other weight-related conditions or concerns, as well as follow-up support following bariatric surgery (such as gastric bypass, intragastric balloon, sleeve gastrectomy, and laparoscopic adjustable gastric banding). 

A nutritionist can support and help you lose weight whilst maintaining it long-term. A nutritionist will often begin by discussing your dietary habits and activity levels, your lifestyle and emotional well-being in order to distinguish what may be affecting your eating habits.

Usually, a nutritionist will begin by compiling a detailed case history of your diet, lifestyle and any health issues. This may include asking you to complete a food diary before the initial consultation in order for them to determine where the problems may lie. The food diary will most likely involve you noting down what you eat, how often and your portion sizes.

At this stage, the nutritionist may ask you to complete some medical tests to ensure your health and well-being. They will discuss with you the issues that may need to be considered within your nutrition programme, these could include special dietary requirements or current or past health conditions. The other points to consider include your physical activity levels, your mental well-being and flexibility.

After the above have been considered, the nutritionist will create a calorie-controlled diet plan and activity programme that are both realistic and achievable. Over time, your progress will be monitored and the nutritionist will be there to offer ongoing support and advice. Extreme lifestyle changes are tough so regular consultations are advised, multiple visits enable you to stay motivated and committed.

Contacting a nutritionist will not only benefit and support the start of your weight-loss journey, but they will also be there to ensure the changes you have made will be maintained long-term. Throughout your progress, the nutritionist will make adjustments to your plan in order to adapt to your new lifestyle and eventually, you will have reached a point where you feel you can continue your healthy lifestyle without the extra support.

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