Dieters hoping to shed the kilos should watch the clock as much as their calorie intake after scientists discovered that limiting the time span in which food is consumed can stop weight gain.
Confining meals to a 12-hour period, such as 8am to 8pm, and fasting for the remainder of the day, appears to make a huge difference to whether fat is stored, or burned up by the body.
Researchers at The Salk Institute in America said it adds more evidence to studies which show that eating late at night causes weight gain. They suggest restricting eating hours could help fight high cholesterol, diabetes and obesity.
"These days, most of the advice is, 'You have to change nutrition, you have to eat a healthy diet,"' said associate professor Satchidananda Panda
"But many people don't have access to healthy diets. So the question is, without access to a healthy diet, can they still practise time-restricted feeding and reap some benefit?"
The researchers studied 400 mice, ranging from normal to obese, that were placed on various types of diets and time restrictions.
They found that mice fed a high-fat diet, but allowed access to food for only 12 hours per day, were healthier and slimmer than mice given access to the same food for the whole day, even though the two groups consumed the same number of calories.
The results were the same even if the diets were high in fat, high in sugar, or high in fruit sugars.
The study also suggests that the odd blip is unlikely to make a difference. A late-night weekend takeaway, for example, is unlikely to harm the body's metabolism. However, regularly eating at night would have a big impact.
"The fact that it worked no matter what the diet, and the fact that it worked over the weekend and weekdays, was a very nice surprise," said the study's first author, Amandine Chaix.
Mice that had become obese by eating whenever they liked during the day lost 5 per cent of their body weight within just a few days of time restrictions being enforced. At the end of the 38-week study, they were 25 per cent lighter than the group that had continued to eat freely.
Although mice on a healthy diet did not lose more weight on a time-restricted diet, they gained muscle mass, according to the study, which was published in the journal Cell Metabolism.
"It's an interesting observation that although the mice on a normal diet did not lose weight, they changed their body composition," added Prof Panda.
"That brings up the question, 'what happens? Are these mice maintaining their muscle mass which might have been lost with free feeding, or are they gaining muscle mass?"
A second study found that sticking to a Mediterranean diet can protect the DNA from ageing. Researchers at Brigham and Women's Hospital in America found that a diet high in olive oil, fresh fruit and vegetables and nuts, was associated with longer telomeres.
Telomeres are the protective caps that sit at the end of chromosomes and prevent damage to the DNA. Previous studies have shown that short telomeres are associated with disease and advanced ageing.
"To our knowledge this is the largest population-based study specifically addressing the association between
Mediterranean diet adherence and telomere length in healthy, middle-aged women," explained associate professor Immaculata De Vivo.