Body Story

• Diet and hunger

• Crisis conditions

The simplest way to lose weight is to go on a diet — or so we are led to believe. It seems to make sense: eat less, have less fat. And it does make sense up to a point.

Our bodies need energy to keep them going. They can get this energy, which is measured in calories and kilocalories, from food. If they do not get it from food, they will seek alternative sources, such as fat supplies. So if you limit your calorie intake, your body will start to use up its excess fat.

But there's a problem.

• Diet and hunger
Unfortunately, as far as your body is concerned, going on a diet is equivalent to facing a famine. Deprived of food, the body tries to conserve fat in preparation for hard times ahead. Instead of using up fat reserves to supply energy, it consumes short-term reserves of glucose, most of which are stored in the liver. But glucose molecules produce only half the energy that fat molecules produce, so the body craves more fuel.

However, hunger apart, for the dieter the early signs are good. Weight is being lost. The snag is that it's not fat that's being shed, it's water. The short-term glucose reserves being consumed are stored within large quantities of water, and as the glucose is used up, the water is released as urine. In the early days of dieting, the body loses an extra litre of water each day. It's only when the glucose reserves have run dry that fat begins to be burned.

• Crisis conditions
But even then, fat reserves are not sacrificed without a struggle. As fat cells are released into the bloodstream, they send a warning signal to the brain. The brain reacts by further increasing the body's appetite for fuel. The dieter feels ravenous.

Meanwhile, the brain imposes an energy cut. Mitochondria inside the cells burn less fuel in an attempt to conserve energy, and the dieter feels increasingly tired.

He or she will also feel dispirited. Since fat is considerably lighter than water, the rapid weight loss of the first few days of the diet does not continue. In fact, whereas losing 3kg of water will take around four days, losing the equivalent weight in fat will take about a month.

So, hungry, tired and downcast, many dieters crack and binge. Within no time at all, their fat and glucose stores are refilled. Their bodies retain water in which to store glucose and the pounds pile back on. They're back where they started.

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