What causes obesity?

Our bodies need energy to function every day. This energy is measured in calories and comes from our food and drink. Our bodies need energy for daily functions like breathing, sleeping and digestion. We also use energy when we move and use more energy with greater physical activity. Everyone’s energy requirements are different. These are based on things like body size, age and activity levels.

But if we take in more energy (calories) than we use, then this extra energy is stored as body fat. Storing more body fat causes us to gain weight, and too much can lead us to being overweight or obese.

The cause of obesity is not as simple as eating too much and moving too little. Obesity is complex with many different causes. For some people, being overweight can be linked to other things. Such as a health condition, medications, or having a genetic predisposition. But one of the biggest influences on our weight is the world around us.

The world around us affects how healthy we are

While we might think we’re in control of what we eat, we’re all being influenced by the world around us more than we realise. It could be while we are on the go, when eating in a restaurant, or when doing a food shop.

If unhealthy options are the easiest, cheapest, or only things available, then weight gain becomes more likely.

The world around us makes it more difficult to be a healthy weight:

• Confusing food labels, and more fat, sugar and salt in our food make it harder to find healthy options.
• Unhealthy food adverts and 2 for 1 offers encourage us to eat more unhealthy foods. 
• Bigger portions and fast food on the go tempt us to eat more and in bigger amounts.

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The world around us also affects how active we are. Increased use of cars or public transport and more jobs where we sit still, can mean that we are moving less.

Find out more about how being active helps to keep a healthy weight.

Why are more people overweight or obese now?

In the UK, more than 6 in 10 adults (aged 16+) are overweight or obese. The proportion of people overweight or obese has increased over time across the UK.

Over time food has become available in bigger portions with more calories. There are also new ways in which people can access fast food. Such as through delivery apps and more food outlets on our high streets. Food advertising and marketing has also become more sophisticated. Food adverts, price promotions, and where products are in a store, all have an impact on our behaviour.

These things can make it harder to be healthy. This is one of the main reasons that more people struggle to maintain a healthy weight.

What can reduce overweight and obesity?

It’s important to reduce overweight and obesity to lower the risk of many health conditions. These include diabetes, heart disease and 13 types of cancer.

There are things we can do to keep a healthy weight. Making small changes and forming long-term healthy habits, can make a big difference.

We know that keeping a healthy weight is more difficult for some groups than others because of things outside of their control. Our health inequalities article explains why it’s harder for some people to eat healthily.

We need the government to help make it easier for everyone to be healthy.

Cancer Research UK has been campaigning since 2016 for Government-led change.

In 2020 the government launched a new obesity strategy for England. This aims to halve childhood obesity by 2030.

It promised to:

• Restrict junk food marketing on TV and online.
• Restrict how and where unhealthy food and drink can be promoted in stores. For example, in England, junk food is now banned from being sold at shop checkouts.
• Require large restaurants, cafes, and takeaways to show calories in foods.
• Start a new Better Health campaign to support people in creating healthier habits.

There’s still a long way to go for changes across the UK, but we are seeing steps in the right direction.