Millions of us will have entered the new year with the goal of losing weight.
But if you’re banking on a crash diet — where you eat fewer than 1,200 calories a day — be warned that it might not work.
Even if you initially shift the balance this month, you’ll likely pile the pounds back on.
That is according to Dr. Christopher Gaffney of Lancaster University, a senior lecturer in physiology, who says the approach slows the body’s metabolism – the rate at which it burns calories.
Crash diets can damage your metabolism, making it difficult for you to lose weight once you return to normal eating
Plus, it disrupts hormone levels and causes a drop in energy, says Dr. Gaffney.
On average, women need to consume 2,000 calories per day to maintain their weight, while men need 2,500.
So following a crash diet, where intake can be reduced to as little as 800 calories per day, usually works initially because dieters burn more calories than they consume.
A 2018 study recruited 278 obese people who followed a crash diet of 810 calories per day for three months.
The results showed that this group lost 11kg, while those who simply reduced their portion size only lost 3kg.
However, these effects are virtually impossible to maintain.
A 2011 studyResearch into the benefits of intensive calorie restriction for type 2 diabetes patients found that those who ate just 600 calories a day for two months lost an average of 15kg.
However, three months later the participants regained approximately 3 kg.
To write The conversationDr. Gaffney said that overall, eight in 10 people who diet gain back all the weight they have lost. Some even end up heavier than when they started.
One reason for this is that crash diets wreak havoc on metabolism, a process responsible for converting food into energy.
When the body receives dramatically fewer calories than it is used to, it adapts and burns fewer calories – a survival mechanism that has evolved over hundreds of years and is sometimes called starvation mode.
As a result, crash dieters can lose weight quickly in just a few weeks. But when the body enters this mode, progress suddenly stops.
Even after a diet is ended, the decline in metabolism can continue for years.
In addition, crash diets cause a host of unpleasant short-term effects, such as fatigue, making it challenging to undertake any activity.
Eating less during a crash diet lowers metabolism and can even increase the hormones that help retain fat
Continuing to eat minimal calories causes changes in hormone levels, releasing more of the stress hormone cortisol, which can cause the body to store more fat within a few months, says Dr. Gaffney.
Crash diets can also lower levels of the hormone T3, which is produced by the thyroid gland and is vital for regulating metabolism.
‘Together, all these changes ensure that the body is better able to gain weight when you start consuming more calories again. And these changes could last for months, if not years,” he warned.
Instead, those looking to lose weight should take a gradual and sustainable approach, which leaves them with enough energy to exercise and has less impact on metabolism.
According to Dr. Gaffney, an ideal diet will only reduce body weight by about 0.5 to 1 kg per week.
While dieting, he suggests eating more protein to feel full longer.