Why Diets Don't Work

Over the last half century, the diet industry has grown with the promise of miraculous weight loss. In the UK alone over £10million is spent every year on diet products. However, alongside this extraordinary growth, has grown the incidence of obesity and it is estimated that only 1 in 50 people following a weight loss diet achieve permanent weight loss.

To examine why this is happening let's look at a typical case study of someone wishing to go on a diet to lose weight.

First of all, this woman's BMR (Basal Metabolic Rate, basically how many calories she needs to survive) each day is roughly 2,100kcals (calories). This means that the diet is only allowing her half the calories she needs to function. The body will perceive this as starvation and will switch to "survival mode".

"Survival mode" refers to the body's physiological response to a perceived life-threatening situation (i.e. starvation). The body will make certain changes to ensure that what energy is available will last longer. It will prefer to retain its stores of fat as fat is essential to life and is used for insulation and keeping warm. The brain can only utilise carbohydrate for energy and can only access the glycogen (stored carbohydrate) stored in the liver. All stored glycogen in the body would be used up on the first day of the diet. This could be as much as 250grams of glycogen. Glycogen is stored in a very hydrated form (3grams of water for every 1gram of glycogen) and this water would also be lost.

So after 1 day of the diet, total weight loss is:
250grams glycogen+ 3x 250grams water = 1,000grams (1kg) but none of the weight loss is fat!!

Since the body is not being fed adequately, it slows down all of its processes to preserve as much energy as possible. In other words, the BMR slows down and the body burns less calories. This can be by as much as 20% and can occur within 24hours.

On the 2^nd day of the diet, the BMR is slower so the body requires slightly less energy than the day before. However, the requirement will still be above the 1,000 calories that the diet provides. In particular, energy supply to the brain will be in very short supply, so the body will be forced to manufacture the energy some other way. Glucose can be made quite easily but only by using amino acids which are the building blocks of proteins. Since dietary intake of protein is low, the body must break down lean muscle tissue in order to attain these amino acids. The amount of muscle tissue we have is vital to how high our BMR is. Loss of muscle tissue will mean that BMR will reduce even further, seriously compromising future calorie-burning. Muscle protein is bound with 4grams of water for every 1gram of protein. So assuming the muscle breakdown is 100grams, this will mean a loss of weight of 5 times this.

So after day 2 of the diet, total weight loss is:
1kg glycogen and water +500grams lean muscle and water= 1.5kg and still no fat loss!!

After 2 days then, the subject has lost 1.5kg (3Ibs) but the weight loss has come from stored glycogen, lean muscle tissue and water, NOT fat. The body will keep hold of its fat stores in case the starvation continues. Her BMR has also dropped significantly, meaning her body is not efficiently using energy and if she returned to normal eating, her body would struggle to utilise the extra calories and they would easily be stored as fat.

As the diet proceeds, weight loss will slow down and even stop. This shows that the body has managed to adapt to the situation albeit at the high cost of dramatically decreased BMR and severe health risks. The usual response to this hiatus in weight loss is to reduce calories even further, under the assumption that perhaps reducing 1,000kcals to 750kcals will "kick start" the weight loss again. This will indeed result in the weight loss starting up again, as the body once again has to learn to adapt to an even lower energy intake. Lean muscle mass, fluid levels and BMR will drop even further until weight loss plateaus again even on 750kcals. Now what?  500kcals??

Usually the response at this stage is to start eating normally again. However, the body perceives this as a binge and will easily store the extra calories as fat. So the weight that was lost during the diet will be a mixture of lean muscle, fluid, glycogen, and some fat, but the weight put back on, will be all fat. So after a few weeks of returning to "normal" eating, the individual will find that they are actually fatter than they were before they embarked on the diet.

So what's next? Perhaps our dieter pulls herself together and stoically goes on another diet! The result of this is that years down the line, and several diets later, she could be 2 or 3 stone heavier with 5-6% more body-fat than when she started her first diet.

Being "on a diet" suggests that at some point you are going to come off it. The only way to achieve permanent weight loss is a healthy, balanced eating plan that can be sustained for life.