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Why crash diets don't work

Published by Bupa's health information team, healthinfo@bupa.com, April 2008

Sadly, there's no such thing as a quick fix. Crash diets might help you lose a few pounds at first, but they won't help you to stay at a healthy weight in the long run. As soon as you stop restricting your calorie intake, you will usually put the weight straight back on again.

How much weight should you lose?

You can use the BMI calculator as a general guide to see if you need to lose any excess weight. You can also measure your waist-hip ratio using a tape measure to see if you need to lose weight. You can do this by dividing the measurement of your waist (lower part of your ribs) by that of your hips (at the widest part). This shouldn't be over 0.9 for men or over 0.8 for women.

If you are overweight and want to be a healthier weight, the trick is to set realistic goals. Weight loss of around 0.5 to 1kg (1 to 2lb) per week is about right. Any more than this and you may become demotivated with too harsh a regime. If your diet is too restricted, you might not be getting enough vital vitamins and minerals either.

If you lose weight too quickly, you tend to lose a lot of lean body tissue as well as fat. When this happens, your metabolism slows down, which means that your body needs fewer calories to function day to day. That's why the weight piles back on so quickly once you go back to your usual eating habits. Your body has adjusted to a lower calorie intake, so excess calories are stored as fat.

On the other hand, you might become demotivated if you are only losing less than half a kilo per week. This may mean you need to make further alterations to the habits which caused you to become overweight. By measuring your waist and hips with a tape measure at regular intervals you can keep track of your weight loss so you can lose weight at a healthy rate.

Changing your lifestyle

You don't become overweight by eating the occasional chocolate bar or cream cake if you have an otherwise healthy, balanced diet. Becoming overweight and slimming down to a healthy weight (and then maintaining it) is really about lifestyle habits. Successful weight loss is more to do with shifting these patterns than with poring over the precise calorie content of every food you eat.

Most people find it easier to lose weight by using a two-pronged approach that combines increased physical activity with a lower-calorie diet. To lose weight, you need a balance where more calories are going out (through activity) than are coming in (through eating). To stay at a healthy weight you need to keep the two in balance across the weeks and months.

How to be more active

Some activity is less useful than others. Exercise machismo where you exercise to painful levels ("feeling the burn") sits firmly in the less useful category, especially if you are starting to be active for the first time, or are returning to exercise after you have been sedentary for a long time. A relatively unfit person running hard for 10 minutes a couple of times a week is unlikely to shift much weight. In fact, it could even be dangerous.

According to the Department of Health, to stay healthy you need to do at least 30 minutes of moderate exercise, such as brisk walking or swimming, five times a week. You can break this up into shorter chunks of 10 to 15 minutes throughout the day if that's easier for you. Building some activity into your daily life, such as walking the kids to school instead of driving, is a relatively painless way to help you get to a healthy weight and stay there.

Trimming the calories

On the eating side of the equation, eating less fat is probably a good place to start. Weight for weight, fat has more than twice the calories of carbohydrates and protein. So remember to satisfy your hunger with bread, potatoes, rice and pasta when trying to lose excess weight. Try to find low-fat alternatives to creamy sauces and buttery toppings, and choose cooking methods that keep the overall fat content low. Roast potatoes, chips, fried bread and buttery basmati do not count as healthy carbohydrates! And don't forget that a mountainous portion of healthy pasta still stacks up a lot of calories. Serving food on smaller plates can help encourage sensible portion sizes.

Watch out for "low-fat" foods that are either not low in fat at all ("75 percent fat free" still means 25 percent fat) or contain lots of salt and sugar instead. Equally important is to aim to include at least five portions of fruit and vegetables in your daily diet. Not only are fruit and vegetables rich in essential vitamins, minerals and fibre but, steamed, boiled or raw, they are both filling and low in calories.

If you find it difficult to go it alone, remember that support is available. You could join a reputable slimming club, for example, or get advice from your GP. Your GP may be able to refer you to a nurse or dietician for further advice.

Are you obsessed by your weight?

It's true that, as a nation, the UK has an increasing problem with obesity, and many people would benefit from losing some weight. But it's equally important to emphasise the dangers of becoming obsessed with losing weight. In its extreme form, this can lead to eating disorders such as anorexia and bulimia.

People with anorexia starve themselves. Symptoms include an intense fear of gaining weight, lower than normal body weight and the person saying they are fat even when they are very thin. Someone who is bulimic typically eats exceptionally large amounts of food then vomits, and may take laxatives or diuretics to purge him or herself. These problems can be life-threatening, and anyone who is affected needs to seek medical help as these individuals have an altered perception of themselves and food. For more information see related links.