It's likely you'll put on weight over the festive season - and equally likely you'll struggle to lose it.

But many people will still embark on New Year diets, possibly losing a bit of timber, and then putting it back on again, in the classic yo-yo fashion.

However, although such yo-yoing is very common, new research suggests it could also be dangerous.

Increased risks

A US study found women in the 'normal weight' range who lost and regained weight had about a three-and-a-half times higher risk of sudden cardiac death - where the heart's electrical system abruptly stops working - than women whose weight remained stable.

Yo-yo dieting was also associated with a 66% increased risk of death from coronary heart disease, where blood vessels to the heart become blocked with fat, in the normal weight women.

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The research, which studied more than 158,000 post-menopausal women over an 11.4-year period, didn't find an increase in either type of death among overweight or obese women who yo-yo dieted, otherwise known as 'weight cycling'.

"Weight cycling is an emerging global health concern associated with attempts of weight loss, but there have been inconsistent results about the health hazards for those who experience weight cycling behaviour," said Dr Somwail Rasla, lead author of the study at Brown University.

What’s going on?

Rasla suggests that as people gain weight, cardiac risk factors, such as blood pressure and glucose levels, often increase, and the body eventually makes adjustments to compensate for the changes.

But when people yo-yo diet, the body may not have time to make those adjustments.

Another theory, developed after a trial using mice, suggests yo-yo dieting may have an impact on DNA. "We found that mice exposed to weight cycling behaviours ended up with damage to their DNA," notes Rasla.

Don’t ditch the diet

However, if you're overweight, it's not wise to completely abandon diets either, as evidence shows that being overweight in mid-life also increases the risk of dying from both types of heart disease.

The best solution, therefore, has to be to embark upon a healthy diet which aims to achieve a steady, regular, small weight loss, rather than the rapid, major loss that a crash diet aims for.

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Nutritionist Cassandra Barns points out that as well as negatively impacting physical health, crash diets followed by weight gain can affect mental health, leading to guilt and low self-esteem.

"This can result in an unhealthy relationship with food," she warns. "By cutting back on calories to extreme levels while yo-yo dieting, you can be at risk of malnourishment, and you may be more tempted to overindulge in the likes of alcohol when 'off' your diet.

"Also, when our weight fluctuates regularly, we often diminish muscle mass, which is crucial for a high metabolic rate when resting."