Everyone knows about the importance of calories - how many you consume or remove from your daily diet - in the struggle to lose weight. But new research and scientific evidence is throwing up interesting challenges and new twists to the perennial tale of "how to lose weight". It's time now to peer behind the "theoretically right diet".

One of the latest gems in the tale is that sleep deprivation is tied to weight gain. The results of a study conducted at Columbia University in the US - on the relationship between sleep patterns and obesity - were reported early in April 2005 at the annual meeting of the North American Association for the Study of Obesity. The study's findings say that people who sleep two to four hours per day are 73 per cent more likely to be obese than those who get normal sleep (seven to nine hours). Five hours of sleep a day makes you 50 per cent more likely to be obese, and six hours brings this likelihood down to 23 per cent.

The finding defies apparent logic because we burn fewer calories while we're asleep. The key factor here is to understand the beneficial effects of adequate sleep on body weight - achieved by the regulation of bodily chemicals during sleep. Says lead researcher of the study James E Gangwisch, "Getting more sleep actually has a protective effect against obesity."

Another study at the University of Chicago (published in November 2004) shows that sleep deprivation contributes to overeating and weight gain. During the research, participants were restricted to four hours of sleep per night and their food intake and activity levels were strictly monitored. After merely six nights of sleep deprivation, they demonstrated a decrease in leptin (a hormone that communicates satiety or fullness to the brain - when levels are high, the brain knows you are full, when levels are low, the brain thinks the body needs nourishment) ranging from 19 to 26 per cent.

Participants with the greatest decrease in leptin reported feeling the hungriest and they craved for carbohydrate-rich foods, while those with less significant leptin decreases reported being the least hungry. Both studies indicate that when you are not getting enough sleep, it becomes more difficult to control your appetite and the risk and likelihood of overeating is consequently greater.

Drinking enough water everyday also plays a significant role in keeping weight in check or losing it. Besides the well-known facts that drinking a lot of water makes you feel full and flushes out the toxins, latest scientific evidence says more. Researchers in Germany - Michael Boschmann, MD, and colleagues from Berlin's Franz-Volhard Clinical Research Centre - report that adequate daily water consumption increases the rate at which people burn calories (The Journal of Clinical Endocrinology and Metabolism, December 2004). The general recommendation of 8 to 10 glasses a day stands, whether you go in for a hi-carb or a hi-protein weight-loss plan.

Another aspect to watch out for is eating what you don't put on your plate. "Eating amnesia", or forgotten nibbling, says research, can undo all your weight loss efforts. Stolen bites like a handful of a friend's popcorn at the movies or finishing off a child's leftover snack can rack up a few hundred uncounted calories, which can put on pounds fast. Eating while distracted is also included in this kind of amnesia.

When women who normally watch their portions had lunch in different situations, researchers found that they ate 15 per cent more - 72 additional calories - if they ate while listening to a detective story compared with when they ate alone and free of any distractions (reported in American Journal of Clinical Nutrition, April 2001).

In trying to lose weight, most people target excess calories. But they often overlook something equally important - psychological stress. Dr Pamela Peeke, MD, (assistant professor of medicine at the University of Maryland Medical School in Baltimore, US) explains how stress can be deadly for weight loss in her book, 'Fight Fat After Forty'.

"When you face a threatening situation, your body secretes adrenaline to initiate the 'fight-or-flight' response. Adrenaline readies muscles for action, triggers the metabolism of fat reserves for energy and suppresses appetite. Once the danger is past, cortisol takes over. This hormone increases appetite, so that your body can replace the used-up energy. The end result is that when the stress abates, we eat to replace energy that was never used - building up more toxic fat," she writes.

Continued stress also leads to higher levels of cortisol in the body, which encourages goading of fat in the body. Peeke's advice - "To lose weight and keep it off, strive for stress reduction as well as calorie reduction".

In Delhi, weight-loss consultant Dr Shikha Sharma gives general guidelines in view of emerging research. There are all those common mistakes that everyone makes, including skipping breakfast, not eating enough, going on drastic diets, starving all day, snacking on high cal foods, ignoring fibre in the daily diet, wolfing on junk, and not reading the labels (on fat content) carefully enough. "The best approach," says Sharma, "involves stress management, sensible eating, exercise and sleeping enough every day. In effect, a complete lifestyle makeover