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diet, Health information, obesity, overweight


A growing problem

Obesity is caused by overeating and lack of exercise and it’s a global issue: over two billion people (39% of the global population) are overweight and 670 million obese. Half of the world’s overweight children are in Asia and, maybe surprisingly, eight of the 20 countries with the fastest rising rates of adult obesity are in Africa.

Most of the countries with the highest proportion of obese and overweight people are in just two regions of the world: Oceania and the Middle East, although the USA, Turkey and Malta also sneak into the top 20. Amongst OECD countries, the USA is in pole position with the UK 8th: one quarter of UK adults are obese and one in five children aged 10-11.


The most common classification is the Body Mass Index (BMI). It is calculated by dividing your weight (in kgs) by the square of your height (in metres). So if you weigh 70kg and are 1.75m tall, then your BMI=22.8. You can check your BMI here.

BMI is interpreted as follows:

  • 5 – 24.9: healthy weight
  • 25 – 29.9: overweight
  • 30 – 39.9: obese
  • 40 & above: severely obese

These thresholds generally apply to white Caucasians. People from other ethnic groups may have lower thresholds.

The BMI formula is far from perfect – in particular, it doesn’t discriminate between fat and muscle so very muscular people appear to be overweight and older people (who lose muscle mass) can have deceptively low scores. Methods such as whole body MRI scans (to spot harmful intra-abdominal fat stores) and even underwater weighing are more accurate methods, but they’re expensive and complicated to do.

A better measure of excess fat is waist circumference, and in particular the ratio of waist to hip, but there’s no standardised way to measure it. In general, men with a waist circumference over 94cm (37in) and women over 80cm (31.5in) are more likely to develop weight-related health problems.

BMI shouldn’t be used for children because their bodies are still developing.

Why it matters

As well as being uncomfortable, being overweight is bad for your health causing problems like shortness of breath, reduced exercise tolerance, increased sweating, snoring, joint & back pain plus psychological problems such as depression and low self-esteem.

Obesity is also a major risk factor for acid reflux, gallstones, reduced fertility and problems during pregnancy, sleep apnoea (where you intermittently block off the airways during sleep, leading to long term lung problems), type 2 diabetes, high blood pressure, high cholesterol, asthma, liver & kidney disease, heart disease, breast, bowel and ovarian cancer and stroke.

Obesity reduces life expectancy by between 3 and 10 years and contributes to 1 in every 13 deaths in Europe.


This is the simple bit. For almost everyone, you’ll get fat if you eat too much and don’t exercise enough. How you avoid that can be much more complicated since modern lifestyles and economics make it very hard for some people to adopt a healthier lifestyle.

In general, people add about one pound of weight (0.5 kg) every year after they reach 30, and most of it is fat, not muscle. It doesn’t sound much but by the time you’re 50, you’ll be 10kg heavier. And as well as overall fat increasing as you age, more of it is “white” rather than “brown” fat (brown fat is better at burning calories).

It’s worth noting that, although often claimed otherwise, the tendency to put on weight as you get older is not because your resting (or basal) metabolism slows down (at least, not much). Our basal metabolic rate (BMR) is determined by height, sex and genetics and there’s not much you can do about it unless you have a condition such as an underactive thyroid gland and need to take supplements. Although some rare genetic conditions such as Prader-Willi syndrome cause obesity, the vast majority of people can lose weight even if they have a genetically driven tendency such as, for example, a large appetite. It’s just more difficult.

It’s worth noting that various medicines including steroids and medicines used for epilepsy, diabetes and mental illness can predispose to weight gain. And smoking is a potent appetite suppressant, so people often put on weight when they stop (although being overweight is less harmful than smoking).

Losing weight

The best way to lose weight is to eat less and exercise more.

The energy value of food is measured in calories. A physically active man needs about 2,500 calories a day and women about 2,000, to maintain a healthy weight. Although it sounds a lot, it doesn’t take long to reach the total. A large takeaway burger plus fries and milkshake is about 1,500 calories – and that’s just one meal.

A good rule of thumb if you want to lose weight at a safe and sustainable rate (0.5 to 1kg a week) is to reduce your energy intake by 600 calories a day. Although there are plenty of food supplements around that claim to burn up calories more efficiently, you only use up about 10% of calories in consuming the food that you eat and increasing your caffeine and protein intake or eating more chilli doesn’t change it much.

Exercise, however modest, burns up calories and after a strenuous workout, the body continues to burn even more. This post-exercise phase makes an important contribution to weight loss, but it requires a higher-intensity workout.

The Department of Health recommends that adults complete two-and-a-half hours of moderate-intensity aerobic activity (eg: cycling or fast walking) every week. This can be broken down into smaller periods such as 30 minutes a day for five days a week. Children over the age of five should get at least one hour of vigorous-intensity exercise each day.

Medical treatment

If lifestyle changes alone don’t help you lose weight, you may need medical help. Orlistat is the only drug proven to reduce weight. It works by preventing about a third of the fat in food being absorbed in the gut. The fat’s passed in the faeces instead, which can lead to pretty unpleasant side-effects.

Orlistat can help reduce weight gain, but doesn’t generally help you lose weight. It’s usually provided on prescription for people with a BMI over 30 (or over 28 if there are other risk factors like high blood pressure. It’s rarely used for pregnant or breastfeeding women. Women using the oral contraceptive pill (OCP) need to use other forms of contraception because orlistat can prevent the OCP being absorbed.

If none of these approaches work, then weight loss (bariatric) surgery may be needed.

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