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Why do we gain weight after drastic dieting?

ISLAMBAD (Online): A few years ago I proudly lost almost 15 per cent of my weight. 

However last week I stared with disbelief at my scale as I realised all my efforts were in vain and I had regained all of the previously lost weight.
This got me thinking about the mechanisms that underpin such dramatic fluctuations in weight (sometimes known as yo-yo dieting) and the defences the body uses for weight maintenance.

Even losing as little as 5 per cent of our body weight has a myriad of health benefits.

These include a reduced risk of heart attacks, lower blood pressure, improved glucose control in patients with diabetes, improved mental health and reduced risk of osteoarthritis and certain cancers.

Losing weight is associated with a number of health benefits but keeping weight off can be difficult because of changes to the metabolism

Therefore one would imagine the body would generally be supportive of weight loss.
If so, why is persistent weight loss and weight maintenance so difficult?

The control of weight is based on the balance between calorie consumption and the energy spent during our day to day living.
The brain’s weight control centre is in an area called the hypothalamus.
The hypothalamus integrates the incoming signals from the body (such as hormonal signals) and other parts of the brain and then controls weight by affecting hunger and satiety.

It also communicates with other parts of the brain that control metabolism (such as the pituitary gland and sympathetic nervous systems).
This complicated and fine-tuned system determines a ‘weight set-point’ which is the weight the body is accustomed to and then works to defend it by fine tuning our metabolism and our calorie consumption.

Danny Cahill (pictured left, before his 2009 appearance on The Biggest Loser, and right, after) lost 239lbs in 13 weeks on the show – but like 13 of the 14 contestants tested by scientists, he put weight back on

Energy consumption is divided into the resting metabolic rate (about 70 per cent of all energy used), the energy consumed in processing the food we eat (thermogenic metabolism) and exercise based energy expenditure.

A few studies have outlined the result of moderate weight loss. The body defends against weight loss by drastically reducing the energy expenditure.
The body also goes into a sort of ‘starvation mode’ to protect against lean body weight loss by preferentially depleting different energy stores including glycogen, fat and then eventually muscle.

The body spends a large percentage of energy in the maintenance of organ function, even when asleep.

In obese people, the resting metabolic rate significantly increases, perhaps to try to prevent further weight gain.

Unfortunately, when you lose weight, the opposite happens and the body’s metabolism turns right down.
This may occur through reductions in the active thyroid hormone (T3) and changes in the hormonal messages back to the brain promoting hunger.

A key finding in the above studies is the reduction in resting metabolic rate is disproportionately large, and potentially persists for long periods.
This explains why a return to a pre-weight loss lifestyle inevitably results in weight re-gain, and possibly more than was lost.

Only by maintaining a healthy lifestyle with calorie restriction of around 25 per cent and exercise can we avoid the inevitable.
The reduction in resting metabolic rate may be particularly problematic in people with severe obesity.

This led me to examine the published data on contestants with severe obesity in The Biggest Loser.

I wondered what had become of the contestants who had lost amazing amounts of weight over a relatively short period of time.
One study confirmed that despite the rigorous exercise programs, the drop in resting metabolic rate persisted.