Patient information from BMJ

Obesity - diet and exercise

Last published:May 20, 2025

Obesity means having more body fat than is healthy. It usually happens when you take in more calories than your body uses as energy. These extra calories are stored as fat.

Losing weight takes time and effort, and requires making changes to your diet and activity level. While it can be challenging, these changes will help you feel better and reduce your risk of serious health problems.

You can use this information to talk with your doctor about which approach to weight loss is best for you.

What is obesity?

Being obese means being very overweight. This can greatly increase your chances of serious health problems such as:

• diabetes

• high blood pressure

• arthritis

• cancer, and

• heart disease.

Obesity happens when you eat more calories than your body uses. These extra calories are stored as fat, leading to weight gain. The types of food you eat, portion sizes, and how active you are all play a role in weight gain.

Lifestyle choices are the main cause of obesity. You might think that obesity is caused by something else, like a slow metabolism. It's true that some people gain weight more easily than others due to genetics. Hormonal issues, medicines, and specific genetic conditions can also cause weight gain in some people. But these don’t cause obesity on their own.

Most doctors use the body mass index (BMI for short) to work out whether you're at a healthy weight. Your BMI is a single number that's worked out based on your height and weight. Doctors say someone is obese if their BMI is 30 or higher. 

What are the symptoms of obesity?

If you are obese, you carry a lot of extra weight on your body. Carrying this extra weight may make you feel tired, or short of breath, or make your joints ache. You may also get skin irritation where your skin folds. If you’re female, you may find that your periods become irregular.

Having extra weight around your waist has also been linked to having a higher chance of problems with your blood sugar, blood pressure, or cholesterol. This in turn may increase your chance of having heart problems.

What are the treatment options for obesity?

If you’re obese, your doctor will recommend various strategies to help you lose weight. Losing weight can reduce your risk of serious health problems.

You can lose weight by making lifestyle changes. This includes:

• Improving your diet

• Exercising more

• Engaging in talking treatments.

Combining these three strategies will give you the best chance of losing weight. Your doctor will help you create a plan that works for you. Doctors sometimes refer to this as a weight loss programme.

Dietary changes

There are many different weight loss diets, but they all focus on reducing the number of calories you eat. The goal is to eat fewer calories each day than your body uses.

This could mean eating smaller portions, and choosing foods with fewer calories. Men are usually advised to eat around 1200 to 1500 calories a day to lose weight. For women, the goal is usually 1000 to 1200 calories.

Common types of weight loss diets include low-fat diets, low-carbohydrate diets, the Mediterranean diet, and supervised diet plans. Supervised diet plans are structured programmes that offer support, meal guidance, and regular check-ins to help you stay on track.

Some research suggests that low-carbohydrate/high-protein diets work better than low-fat diets for the first 6 months, and that people find them easier to stick to. But there isn't much good evidence about what works best over the long term.

Physical activity

You’re likely to lose more weight if you exercise at the same time as changing your diet. Dieting or exercising alone doesn’t work as well.

If you’re able to, try to be active for 30 minutes a day, 5 days a week. This could include activities like going for a walk. Strength exercises, such as lifting light weights or using your own body weight, can also help.

Start slowly and build up at your own pace. Small changes, like taking the stairs instead of the lift, can make a difference too.

There are many exercise programmes you can follow, both with and without supervision. Your doctor can help you find one that works for you.

Talking treatments

Talking treatments involve having regular conversations with a professional who is specially trained to help people with obesity. These treatments can help you change the way you think about food and exercise.

One of the most effective types of talking treatment is behavioural therapy. In this type of therapy you will focus on identifying and changing unhelpful thoughts and behaviours, while learning about healthier habits. You can have sessions either virtually or in person, but many people find in-person sessions with a therapist to be more helpful. Weighing yourself regularly can also help you stay on track.

What happens next?

If you're obese, losing weight can be challenging and takes time. Keeping the weight off can also be hard. It's often easier if you get help from your doctor and follow a weight loss programme.

Doctors usually recommend that people lose about 10% of their body weight over the first 6 months. If your BMI is 30 to 35, this will mean losing between 0.25 and 0.5 kilograms each week. If your BMI is above 35, you may need to lose between 0.5 kilograms and 1 kilogram a week.

Different weight loss programmes can have different results. Research shows that:[1]

• People who change their diet without doing more exercise typically lose around 5% of their body weight in 6 months. Over the next 4 years, they tend to keep off about 3% of that weight.

• People who exercise more without changing their diet usually lose around 2.7% of their body weight in 6 months, and keep off around 1% over the following 2 years.

• People who change their diet and do more exercise lose around 8.5% of their body weight in 6 months, and keep off around 4% over the following 4 years.

• People who follow supervised diet plans lose around 9.6% of their body weight in 6 months.

• People on very low calorie diets lose around 16% of their body weight in 6 months. But most people regain this over time. Over the next 3 years they keep off around 5% of that weight.

Your best chance of maintaining weight loss is to stay on a programme with regular support from a health professional.

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