Obesity

What is obesity?

If you're obese, it means you weigh much more than is healthy for you. It happens because you eat more calories than your body uses. The extra calories are stored as fat.

Obesity is more than being just a few pounds overweight. It can cause serious health problems.

Being obese is more than being just a few pounds overweight. Obesity can cause health problems such as diabetes, high blood pressure, arthritis, and heart disease. And it makes some people feel bad about themselves.

Losing weight isn't easy. You'll need to change the way you eat and the amount of exercise you get. But if you make these changes, you'll be healthier.

Key points about obesity

• Obesity is a serious medical condition.
• Losing even a small amount of weight can lower the risk to your health.
• Cutting down on calories, getting more exercise, and learning good eating habits can help you lose weight.
• Medical treatments might also help.
• You're more likely to lose weight if you get help from a health professional.
• If you're very obese, surgery can help you lose a lot of weight. But there are risks with surgery, so doctors usually recommend it only if your weight is a danger to your health.

What's a healthy weight?

When doctors talk about a "healthy" or "ideal" weight, they mean a weight that lowers your risk of getting serious health problems, such as heart disease or high blood pressure. It's not based on how thin you would like to look. ¹

Most doctors use the body mass index (BMI for short) to figure out whether you're at a healthy weight. Your BMI is a single number that's worked out from your height and weight.

This table shows what the different BMI scores mean.

BMI	What it means
Less than 18.5	Underweight
18.5 to 24.9	Healthy weight
25 to 29.9	Overweight
30 or greater	Obese

You might have read that there are problems with using someone's BMI to find out if they're overweight. For example, an athlete who's very muscular might have a BMI that suggests they're overweight, even though they're healthy. That's because muscle is heavier than fat. However, for most people, working out their BMI is a quick and simple way of finding whether their weight is healthy.

How your body uses food

Food gives you energy. The amount of energy in food is measured in calories (short for kilocalories, or kcal).

Your body needs energy all the time, especially for moving and keeping warm. Different people need different amounts of energy. The amount of energy you need depends on your metabolic rate. And the more active you are, the more energy you use.

Your brain helps you stay a healthy weight. It helps to balance how much you eat with how much energy you burn. Your brain sends out "hungry" or "full" signals that make you want to eat or stop eating.

What happens in obesity?

Being obese is not the same as being a few pounds overweight. Doctors say someone is obese if their BMI is 30 or higher (see the table above). For most people, having a BMI greater than 30 means they're at least 30 pounds overweight.

If you're obese, it means you're eating more calories than your body is using up as energy. Your body stores the extra calories as fat.

Doctors aren't sure why some people eat more food than they need. There are probably lots of reasons.

One theory is that early humans probably had to go for long periods without food, so our bodies needed to be able to store fat easily in order to survive. But nowadays we can get food easily. Some scientists think that our bodies haven't had enough time to evolve and adapt to a plentiful supply of food.So, our bodies still work as if we might have to face a famine.

And for some people who are obese, their "full" and "hungry" signals may not work properly.

For some people, this happens because of a medical condition, or because of side effects of medications. Medical conditions that can cause obesity include having an underactive thyroid. Medicines that can make you put on weight include some antidepressants and corticosteroids.

"It must be my glands"

Like many people who are overweight, you might feel that you don't eat a lot. You might think that your weight problems must be due to something else, such as a "slow metabolism" or your "glands." ⁵

Some medical conditions can make you more likely to put on weight. But you can only become obese by eating more calories than your body uses.

Medical conditions such as hypothyroidism and medications such as steroids make it more likely that you'll put on weight. Some conditions make you feel more hungry. Other conditions slow down your metabolic rate, so you use fewer calories. And some of these conditions affect your glands.

If you have one of these conditions, you might find it more difficult to keep your weight down. It's important to get medical help.

"But I don't eat that much"

The bad news is that you only have to eat slightly more calories than you use for the weight to add up.

• The average American over age 25 takes in only 0.3 percent more energy than they use each day. This about 150 calories, which is the number of calories in a small soda.
• Over time, this extra energy adds up. It's stored as fat.
• By the age of 55, that average American has gained 20 pounds.

If the amount of fat in your body increases gradually, your body doesn't seem to notice that you're putting on weight. Your appetite might stay the same.

Obesity and our lifestyle

There are two things about our Western lifestyle that are linked to more and more people becoming obese:

• Modern fast-food culture
• Lack of physical activity.

Because we're less active than people were in the past, and because fatty and sugary foods are so widely available, it's very easy to gain weight. Some doctors think it would make a difference if unhealthy foods were more clearly labeled. Others think that fast-food ads aimed at children should be banned. These things might make it easier for people to eat a healthy diet and avoid being overweight. But you'd still need to make sure you didn't eat more calories than you needed.

Obesity: why me?

Anybody can become obese if they eat more calories than they use. But there are certain things that make this more likely. These are called risk factors. Some of these you can control, others you can't.

Here are some of the things that make it more likely that you'll become obese. It's probably a combination of these factors that lead to obesity in most people.

Your parents and your genes

You're at risk of obesity if one or both of your parents is overweight or obese. This might be because you share the same genes as your parents. Or it could be because family members tend to eat the same things and have a similar lifestyle.

The ob gene

Genes are in every cell in your body. They tell cells how to grow and what to do. The ob gene tells the cells in your body that store fat to make a chemical called leptin. Leptin tells the brain how hungry or how full you feel. It also helps your body burn the food you eat to keep you warm.

Researchers think that some people who are obese might have a faulty ob gene. So these people don't make enough leptin. This makes it harder for them to control how much they eat because they don't sense when they feel hungry or full. This makes them more likely to be obese. ¹¹

But this problem is rare. Most people with obesity don't have this problem.

Comfort eating

You might eat too much as a way of dealing with painful or difficult emotions. Perhaps you eat when you feel unhappy or bored, even if you don't feel hungry. This is often called comfort eating. It can be hard to break this habit.

You might also eat too much if you have a mental health condition, such as depression or anxiety disorder, or if you feel bad about yourself (have low self-esteem).

Other risk factors

Many things make it more likely that you'll gain too much weight. If you're overweight, there's a risk you might become obese.

• Your sex: Women are slightly more likely to be overweight than men are.
• Your ethnic group: Women who are Mexican-American or African-American are particularly at risk.
• Age: Men and women are most likely to gain weight between the ages of 20 and 40.
• Menopause: The changes in levels of hormones during menopause can make it easier to gain weight.
• Drinking too much alcohol: Alcoholic beverages are high in calories.
• Quitting smoking: Quitting smoking is good for your health, but you might gain weight afterward.
• Being married: Married people are more likely to be overweight than those who stay single.
• Having children: Women are likely to gain about 2 pounds each time they have a baby.
• Poor education: People who do less well at school are more likely to get obese later in life.