When Bridget Jones slavishly recorded her lists — “Food consumed today: 2 pkts emmenthal cheese slices, 14 cold new potatoes, 2 bloody marys, 12 Milk Tray” — it turns out she was way ahead of medical science. According to the American Journal of Preventive Medicine, dieters who keep a food diary can double their weight loss. The study followed 1,700 overweight people over six months, and revealed that those who wrote down everything they ate lost an average of 13lb.

“Recording what you eat can really help you lose weight, because a lot of the time, you’re not conscious of your behaviour,” says Azmina Govindji, a consultant nutritionist and author of The Hot Body Plan. “Some eating habits are situational — for example, having tea and a chocolate biscuit while watching your favourite television programme. We do it on autopilot. If you know that you actually have to record every item you eat, it gives a split-second pause for thought. You think, ‘Do I really want to write this down?’ ”

It’s a trend that is sweeping America, with a plethora of websites, such as thedailyplate.com, that allow users to log their food sins into a digital confessional that even calculates the calories for you. Julia Cameron, author of the creativity bible The Artist's Way, has gone a step further with The Writing Diet, a self-help book that explores the link between eating mindfully and living a happy life.

“Through the use of a food journal, we often become aware of patterns that are self-destructive,” Govindji says. “We become more authentically honest with ourselves, and we start asking the question ‘What’s eating me?’ instead of ‘What can I eat?’ ” Even people who believe that they are resolutely healthy can get a shock when they see everything written down in black and white. “Mothers who eat the last few chips on a child’s plate, or the single woman who reaches for the Häagen-Dazs when she’s feeling lonely in front of the TV, start to see where their diets are going wrong,” she says.

These emotional triggers can often come as the biggest surprise. To this end, Govindji gets clients to keep a “food and mood” diary, so they write down not only every mouthful they eat, but the time of day and how they were feeling at that moment. “Once someone spots a pattern, then they can do something to change it,” she says. The most common patterns she uncovers are in those who eat naughty foods because they are bored, hormonal or depressed.

Which brings us to an obvious flaw in the food diary. Surely mere mortals are tempted to cheat? “Well, yes, we’re all human. If someone is going to see an expert, they are obviously going to be concerned to be seen in a good light,” she concedes. “But if you’re just doing this at home for yourself, what would be the point of lying? You’re setting up a dialogue with yourself, so there's no point. It can just be for your eyes only.”

In any case, new research from the University of Wisconsin-Madison has revealed a way around the tendency to fib — the photo diary. Taking a digital snap of every meal was shown to be an even more powerful and accurate weight-loss tool. One volunteer told the researchers: “I had to think more carefully about what I was going to eat because I had to take a picture of it.

I was less likely to have a jumbo bag of M&M’s. It curbed my choices. It didn’t alter them completely, but who wants to take a photo of a jumbo bag of M&M’s?”

Who, indeed. But the good news, according to Govindji, is that you don’t have to keep this up for very long. “Two or three days is enough to get a real understanding of how and why we eat what we do.”

A food day in the life of . . .

Marcus Wareing, chef at Marcus Wareing at The Berkeley

Breakfast 1 cup of tea, 1 pain au chocolat

Before lunch 4 cups of coffee

Lunch Taste of white onion soup, nutmeg foam, 2 grissini, 1 slice of Poilâne bread and butter. Tastings (a spoonful or slice): 4 types of bread, 15 different dessert flavours, lamb, beef, scallop, sea trout, pork crisps, duck crisps, veal, pig’s trotters, salad, pomme purée, pork belly, pork crackling, lamb crackling, chicken, navet, beetroot, mushrooms, cabbage, baby gem, fennel, tomato, radish, potato, onions. 6 home-made chocolates, 1 bottle of sparkling water

Afternoon 2 cups of coffee, 2 cups of water

Dinner Tastings repeated as above, except for the bread, chocolates and desserts. Sample of lamb dish with braised lamb, bacon, fennel, cabbage

After work 1 cup of tea and a bowl of Shreddies with semi-skimmed milk at 1am

Jo Wood, founder of Jo Wood Organics

Before breakfast Kick-start the day with 1 cup of green tea

Breakfast Sheep’s yoghurt mixed with a dessertspoon of organic flaxseed, a dessertspoon of mesquite meal and organic honey to sweeten. 1 double expresso

Lunch Roast lamb, green cabbage and parsnip purée at Jerry Hall’s house. 1 roast potato — I can’t resist. Chocolate mousse, 1 cup of coffee, 1 glass of red wine

Dinner Home-made chicken and vegetable soup with brown rice in it. All the vegetables were from my garden

Other drinks I drinks lots of water, green tea and oolong tea

India Knight, journalist and author

Breakfast 2 eggs and 2 rashers of bacon. 1 cup of earl grey tea. Water

Lunch Kedgeree with curly kale. Water

Dinner Steak and salad (with olive oil and balsamic dressing). 3 glasses of red wine

Snacks 1 handful of cashew nuts, 1 piece of cheddar, 1 slice of birthday cake (children’s party), one latte, three more cups of tea, more water

Henry Holland, fashion designer

Breakfast Peanut butter on 2 slices of brown toast (low GI), 1 skinny white americano

Lunch Mixed salad with chicken at a lunch meeting. I always choose the chicken option on any menu

Afternoon 1 Wispa and 1 americano to wake me up at 3pm

Dinner Sweet potato and coconut soup from a new soup recipe book, with hot bread — too much hot bread — and hummus

Other drinks No alcohol. I rarely drink, unless I’m out for the night, when I drink vodka and cranberry or white wine — although someone recently told me a bottle of white wine has the same number of calories as a Big Mac. Whoops!

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