Obesity

It is natural and healthy for the body to store some fat. It does this by moving fat into special fat cells. Fat is needed to protect organs, as an energy store, and as a source of useful fatty molecules. But when too much fat is stored, this can be bad for a person’s health.

Over the past fifty years, obesity has become common in much of the developed world. This is a problem because it is linked to medical conditions including diabetes mellitus (view article here), and can lead to a reduced quality and length of life.

Because obesity affects over a quarter of the UK population and is on the rise, it is a very important public health issue.

Measuring Obesity

Body Mass Index

Every body is different. It is difficult to work out exactly how much body fat someone has, but it’s useful to have a quick method to work out whether someone might have a problem with obesity. For this reason, doctors sometimes use a measurement called Body Mass Index (BMI).

BMI is calculated using a person’s weight in kilograms and their height in metres: 

BMI = weight ÷ (height x height)

For most people, their BMI gives a reasonable measure of whether their body weight is healthy. BMI is judged as follows:

Classification    Body Mass Index (BMI)

Underweight       <18.5 kg/m2

Healthy               18.5 to 24.9 kg/m2

Overweight          25.0 to 29.9 kg/m2

Obese                 >30.0 kg/m2

A BMI of over 30 kg/m2 is normally considered obese. But BMI isn’t a useful measure for everyone – for example people with a lot of muscle may have a high BMI even if they don’t have a lot of fat. BMI is also affected by things like amputations and pregnancy. For this reason, BMI should be used with care.

Body shape

As well as the amount of fat someone has, the distribution of fat is important. Obese people whose fat is stored mostly around their middles will have fat stored around important organs. People with this type of fat are more likely to have health problems including heart disease, diabetes, and some cancers. Fat distribution can be judged by measuring the distance around the waist. This measurement is called girth. 

How common in obesity?

Obesity is very common. In the UK, the most recent estimates are that one in every four adults is obese. For children it’s about one in five.

The number of obese people has increased a lot in recent decades, not only in the UK but worldwide. It is thought this is mostly due to lifestyle changes, including diet. In the UK, it is predicted that if nothing changes, one in every two people will be obese by the year 2050 (Gov.UK, Department of Health and Social Care).  

Why is obesity a problem?

Obesity is defined as excess weight that causes risk to health. There are a large number of different ways in which obesity can affect health.

Metabolism and hormones

Obesity affects the behaviour of many different cells and body tissues. Changes in hormones (view article here) and metabolism can contribute to a wide variety of different conditions including type 2 diabetes mellitus (view article here), heart disease, stroke, some cancers (including breast, prostate and colon), and reduced fertility. 

Body mechanics

A larger, heavier body experiences different forces and moves in different ways. Obese people are more at risk of osteoarthritis, a condition that damages tissues in joints. It can also increase the risk of other conditions that cause pain and discomfort, or that reduce mobility. This can make it difficult for people with these conditions to get the exercise they need.

Obese people are also more likely to have sleep apnoea, a condition where breathing sometimes stops during sleep. This makes it difficult to get a good night’s rest. People with this condition feel very tired during the day.   

Mental health

Some people with obesity may also suffer from depression and social isolation linked to their condition. 

What causes obesity?

At the simplest level, obesity happens when a person’s body takes in more energy than it uses.  

We all take in energy from the food we eat. Energy-rich molecules from food are absorbed into the body, providing us with the energy we need to live.

Energy from food is used to drive the many biological processes that keep us alive and active. Energy is used to power growth and maintenance of cells, for brain activity, and for physical movements including breathing and running. And many other things besides. These processes convert the food’s chemical energy into thermal, kinetic and other forms of energy which can no longer be used to power our cells.

If more energy is taken in from food than the body needs, the spare energy is stored in the form of fat molecules.

Having a fatty energy store is useful in case there are times when we can’t eat enough for our energy needs. But if people keep eating more than they need, more and more fat is stored, eventually causing obesity.

So obesity is caused by people eating and taking in more energy than they need. However, this simple answer hides how complicated obesity really is. There are many different factors that affect how much energy is taken in, and how much is used. 

Genes

Obesity tends to run in families, and genetics is one of the reasons why. Our DNA can affect the amount and types of food we want to eat, how much energy our bodies require, and how our fat is distributed.

But genetics can’t explain the recent increases in obesity. We all get our genes from our parents, who got their genes from their parents. Mutation of individual genes is very rare, and as a population our genes have barely changed in the last 100 years.

There is one possible link to our DNA though: not genetics, but epigenetics. Lifestyle can change the way in which genes are used. And some of these changes can be inherited. Some epigenetic factors for obesity have been discovered, so lifestyle changes in previous generations could be one factor explaining increased obesity today.

But that still can’t be the whole story …

Diet

We take energy into our bodies from the food we eat. The chemical energy in food is measured in calories. Carbohydrates and fats are particularly high in calories.

Eating habits have changed a lot over the past 50 or more years. This is thought to be the main reason for more people becoming obese. Portion sizes are getting bigger, and people are less likely to cook meals from scratch. Pre-packaged and fast foods are often higher in calories than home-cooked meals. High-calorie snacks are cheap, and many soft drinks are full of high-energy sugars.

Eating more calories means we need to burn off more calories to keep our bodies in balance; but do we do that?

Activity and movement

Most of the calories we burn off are used to power muscle movement. Muscles use a lot of energy! This means our levels of physical activity are an important factor in whether we are burning off all the calories we are taking in.

Unfortunately, the average person today is less active today than in previous generations. We have more cars, so are less likely to walk, and more people work at desks. Having the internet means we can be entertained, socialise, work, study, go shopping, and pursue hobbies without even getting out of our chair! This is wonderful for the opportunities it brings. But it also means we have fewer reasons to get up and out and walk to other places.

Because we move less in our normal lives, sports and other forms of planned exercise have become really important. Not only because they help burn up our extra calories, but also for of all the other health benefits that exercise brings. 

Medical conditions

Some drugs can increase the risk of obesity as a side effect. This includes oral contraceptives, anti-psychotic drugs, anti-epileptics and steroids, and some diabetes medications.

Less often, a medical condition can itself lead to obesity. Many of these conditions are related to unbalanced hormones. For example, in Cushing’s Syndrome high levels of the hormone cortisol (view article here) lead to weight gain. Other conditions that can lead to obesity include hypothyroidism (an underactive thyroid gland), reduced sex hormones (e.g. during menopause), and some rare genetic conditions (e.g. Prader-Willi syndrome).

Medical conditions that make it difficult to exercise can also affect a person’s risk of obesity. 

Ways to treat obesity

There are many different ways to treat obesity. But it can be very difficult to lose weight, and any treatment programme must be a long-term commitment. For this reason, people are advised to talk to their GP about the best options before making any big changes. Usually a combination of approaches is best.

All the treatments described below work by changing the balance of the amount of energy taken in versus the energy used by the body.

• To lose weight, it is necessary to take in less energy than is being used. The body will then break down its fat stores to find the extra energy it needs.
• To maintain a healthy weight, it is necessary to take in the same amount of energy as is being used.

Treatments work by either changing what is eaten, changing how much of it is absorbed, or changing how much energy is used by the body. 

A healthy diet

The most important step to long-term weight loss is for the person to reduce the amount of energy taken in from food. This can involve them eating smaller portions, and/or eating foods with less fat and carbohydrate. It’s important that these changes are made in a way that still gives a healthy, balanced diet with a mix of nutrients.

Very low calorie diets can cause problems unless they are carefully designed and monitored, so these should only be used with medical supervision.

Exercise programmes

Exercise is an important part of any weight management programme. It helps build muscle, increases metabolic activity, and improves general health. Aerobic exercise is the most helpful for people who are obese – this can include activities like brisk walking or swimming. It is recommended that people should aim for 30-60 minutes of continuous aerobic exercise, at least five times per week.

Counselling

It can be very difficult to change eating habits. Professional counsellors can help by leading in-depth discussions about the changes needed. This type of treatment can include help with snacking and other eating behaviours. The person must be highly motivated to change, and the counsellor must be dedicated and willing to keep in touch long term.

Medication

There are a few different drug treatments available to help with obesity, which work in different ways. These are given alongside diet and exercise changes for maximum effect.

One common drug is taken as a capsule at mealtimes. It blocks the action of digestive enzymes that help break down fats. This means that less fat is absorbed from the gut. Because of the way it works, this drug can have some side effects like flatulence (wind) and discomfort. It can also affect the frequency and consistency of bowel motions (that’s the medical term for poo).

There are also drugs that reduce appetite.

Normally when we eat, the body uses hormones like glucagon-like peptide 1 (GLP-1) to signal when we are full and should stop eating. A new type of drug (GLP-1 analogues) mimic the action of GLP-1. When these drugs are injected, the person feels full and stops wanting to eat more.

GLP-1 analogues also increase levels of the hormone insulin (view article here), which reduces blood sugar. For this reason, the drugs are also used for people with type 2 diabetes mellitus, or who are at risk of developing this disease. People often have side-effects when they start taking GLP-1 analogues, but these tend to settle down after a few weeks. 

Surgery

In cases where people are unable to control their weight using the above methods, surgery may be an option. Surgery is very effective for long-term weight loss, but it comes with risks and long-term side effects. It is also not appropriate for everyone.

In the UK, weight-loss surgery is used for people who are very obese, and/or have health conditions directly linked to their obesity, including type 2 diabetes mellitus.

There are four main types of weight-loss surgery: gastric balloon, gastric band, sleeve gastrectomy and Roux-en-Y gastric bypass (RYGB). All of these methods work by reducing the size of the stomach.

Gastric balloon

In this procedure, a small balloon is swallowed. Once inside the stomach, the balloon is inflated with salt water. The balloon takes up space inside the stomach, reducing its volume so that people feel full more quickly.

Gastric band

Gastric band surgery involves placing a tight band around the top part of the stomach. The band squeezes in on the stomach like a belt, creating a small pouch at the top with a narrow opening through to the rest of the stomach. Food can still get through, but it is slowed down. Once the top part of the stomach is full, the person will feel full and want to stop eating. 

Sleeve gastrectomy

Sleeve gastrectomy is a surgery that keeps the stomach’s full length while removing most of its width, narrowing it to a sleeve shape. Again, this reduces the volume of the stomach, so that less food is needed for people to feel full.

Roux-en-Y Gastric Bypass (RYGB)

RYGB surgery reduces the top part of the stomach to a small pouch. This pouch is then plumbed directly into the small intestine, taking a short-cut past the main part of the stomach.

Life after weight-loss surgery

People with successful surgeries need to be careful afterwards. They need to eat food in small amounts and make sure they chew it properly. They also need long-term follow up to make sure they are doing well and getting the nutrition they need.

Side effects can include acid reflux (acid coming up from the stomach) or problems with low blood sugar after meals. There is also a condition called ‘dumping syndrome’ where food enters the intestine too quickly, leading to nausea, sweating, diarrhoea, or weakness after eating.

Sleeve Gastrectomy and RYGB are particularly effective but are serious procedures - they carry risks similar to any major surgery.