Why Do Diets Fail?

Essential Information for Intending Dieters

Sep 9, 2009 Allan Johnson

Food should be enjoyed – we anticipate tasty meals and spend a great deal of time in the kitchen or eating out. Eating is good news for our digestive system, which evolved over millions of years to extract what we need to thrive, storing the best bits and dumping the rest. In times of imminent food shortages, it was an advantage to be overweight. It kept you warm too! Nowadays, we carry the extra weight for no good reason, upsetting our otherwise tolerant metabolism, leading eventually to chronic health problems such as high blood pressure, diabetes and heart disease.

The Background Science

To kick-start our bodies into converting stored fat into energy so that we lose weight is not easy. We all store large amounts of “healthy fat” that we do not need to lose. It may end up in all the wrong places, but it is still needed as a food reserve, heat insulation and as a protective layer. There is enough fat in a healthy adult to allow us to run non-stop for 3 days and nights, but don’t try this at home!

When we get hungry, our liver changes a stored sugar (called glycogen) into glucose to maintain our blood sugar at normal levels. If this did not happen, we would quickly collapse into a hypoglycaemic diabetic coma. Fortunately, there is about 24hrs supply of glycogen in a healthy liver, which a novice marathon runner uses up in about 2 hours before “hitting the wall” and changing to fat metabolism for the rest of the race. For most of us, this method of accessing our fat stores is rather drastic, so we need to compromise.

Some Useful Tips and Warnings

• Gentle exercise, such as walking, which burns a combination of fat and glycogen, is a very slow way to lose weight .To burn off a pound (450g) of fat requires approximately 3500kcals of energy expenditure, equivalent to about 14hrs of brisk walking! However, spread this over a fortnight and you are in business.

• Consuming 3 pieces of chocolate (100kcals) will compensate for 30 minutes of brisk walking, so don’t increase your snack allowance after exercise.

• If you are exercising seriously, your muscle mass will increase and you may actually put on weight because muscle weighs more than fat! Nevertheless, a good level of fitness has other benefits, such as improving your cardiovascular output and lowering your blood pressure. Overweight people can become very fit if they choose an appropriate form of exercise.

• The answer is to combine some dietary restriction with exercise. That way the body will have to access its fat stores to meet your needs. This will produce more than the odd pang of hunger, so buy some attractive low calorie snacks in advance, such as fruit or cereal bars, washed down with fruit juice diluted with water.

• Hunger is a perfectly normal sensation, which most of us have lost the capacity to endure.

The Hazards of Rapid Weight Loss

If you try to lose more than 1kg (2.2lb) per week by cutting back the calories, this will hit your glycogen reserves, which are stored in a hydrated form in your liver and muscles. The depletion of glycogen is accompanied by water, and your weight will fall quite quickly for a short time. Once you start to burn some fat, the weight loss will slow down, which is very discouraging for novice slimmers. Even worse, the body resists changes in weight by slowing down your metabolism to help you gain weight when you resume a normal diet. For this reason, many people find their slimming diet results in weight gain (1).

Further problems

If you follow these guidelines and still cannot lose weight, ask yourself the following questions:

1. Have I underestimated my food intake and not taken account of all snacks and drinks? When controlled surveys are done to monitor diets, this is one of the commonest problems, especially in front of the TV late at night!
2. Have I set an unrealistic goal? Your body has a genetically determined “set point” against which it regulates its weight. Large variations will always be difficult to achieve if your “excess fat” is actually normal body fat.
3. Weekend splurging - many dieters abandon their diet at weekends and more than compensate for their calorie deficit on days six and seven.
4. Aim for a 500kcals shortfall per day, every day (2). This is roughly equivalent to:

• a large helping of apple crumble and custard
• 2 slices of fruit cake
• a 100g bar of chocolate
• 2 large pieces of sponge cake
• 120g of cheddar cheese
• 120g of grilled bacon
• 110g of double cream
• 2 large pork sausages
• 1 large portion of chips
• 2 pints of strong lager or beer
• 3 large glasses of wine

One indulgent weekend meal, preferably at lunchtime will not make much difference, but a massive binge (alcoholic or otherwise) will destroy the arithmetic - and upset your liver!

To get the result you want, plan long-term rather than short-term. Like opening a savings account, make a steady contribution to the cause that will stay put and let the passage of time do the rest. Tell all your friends and family of your change in lifestyle and keep them informed of your progress at regular intervals. You can’t give up now!

References

1. Bean A. 2006. The Complete Guide to Sports Nutrition. A & C Black London.
2. Food Standards Agency 2008. Manual of Nutrition. TSO London.