There can't be many people who would willingly return to the days of food shortages and rationing, but that doesn't usually stop our mums and grans fondly recalling the stodgy puddings, bread and dripping and shepherd's pies of their wartime diet. Today, as we tuck into ready-made curries and lasagne, it's tempting to smile smugly and think we all know what's good for us now. But as nutritional experts believe - and the Hymers family from Otley in Yorkshire can confirm - it may well be that Mum knows best.

Dieticians have long argued that wartime rationing provided the healthiest diet the British population has ever eaten, leading to dramatic post-war improvements in the nation's health. But now that ration books are consigned to museums, nutritionists still believe there are valuable lessons we can learn from the 40s diet that could help us beat the biggest threats to health today.

The proof of the pudding lies in the experience of the Hymers family who volunteered to go back in time and spend nine weeks surviving on austere rations for the series The 1940s House , currently showing on Channel 4. Not only did all the adult Hymers lose weight and show modest health improvements by the end of the experiment but, six months after filming has ended, grandmother Lyn Hymers has stuck with her wartime regime and insists her health has benefited.

'I feel so much better,' says Lyn, 50. 'It really has become a way of life for me.'

Taking up the wartime challenge was no easy option for the Hymers. The family - Lyn and husband Michael, their daughter, Kirstie, 29, and grandsons Ben, 10 and Thomas, seven - previously ate a typical modern British diet. Their staple fare consisted of ready-made meals, tinned and frozen convenience foods and takeaways. Lyn rarely cooked, had no idea how to bake a cake and enjoyed smoking and drinking. Not surprisingly, both she and Michael, 52, were overweight and unfit.

After nine weeks of spartan rations and, without the benefits of modern time-saving conveniences, heavy physical labour, it is hardly surprising the adult members of the family lost weight. But after just nine weeks, medical tests also showed their cholesterol, blood pressure and bodyfat levels had fallen moderately and their muscles grown stronger.

More significantly, despite returning to their 21st-century home comforts, Lyn and Michael have continued their wartime regime, complete with Spam fritters and home-made cooking. While Michael feels more ambivalent about the benefits of his revolutionary lifestyle change, Lyn has now lost more than a stone, feels healthier, fitter and more energetic than ever before and has given up both alcohol and coffee, without the aid of any weight-reduction programme or exercise regime.

Instead of driving to the supermarket for weekly shopping, she now walks daily to her local bakery, grocer's and butcher's shops to buy fresh produce. She no longer buys convenience foods or ready-made meals, but cooks everything from basic ingredients. And while previously she threw away vast quantities of food each week, she now wastes nothing. One day for lunch she may make soup with fresh peas and the following day a broth from leftover pea pods. She is even converted to the delights of Spam, and although she still smokes, she has given up coffee and alcohol because she simply doesn't want them any more.

To her amazement, she has not regained the weight lost during the 40s experiment and feels healthier all round. 'I have battled weight all my life with different diets and going to Weight Watchers,' says Lyn. 'But whatever I did, the weight always yo-yoed back to its old level. This time it is just staying off and I am not hungry.'

In addition, she says, her teeth are whiter, her gums no longer bleed, her eyes are no longer bloodshot, she rarely becomes breathless and her skin is as clear as ever, without the aid of expensive creams.

The fact the Hymers lost weight and their short-term health improved confirms nutritionists' faith in the benefits of combining exercise with a diet high in carbohydrates and low in fat. But more importantly, nutritional experts also argue that a return to aspects of the wartime diet could, for all of us, be the secret to surviving modern-day killers such as cancer, heart disease, stroke and diabetes.

At first sight, the typical 40s meal of tiny meat portions, mounds of potatoes, carrots, cabbage and bread, followed by a stodgy pudding, may not sound like the pathway to true health. Yet, at the start of the war, the average British diet, with its higher carbohydrate and lower fat content, was closer to modern recommendations than today's diet, explains Susan Jebb, head of the Medical Research Council's human nutrition research unit, who advised on the television series. When war brought food shortages and rationing, the diet improved further, as people relied more on carbohydrates while fats and sugar were severely restricted.

British people derived 32 per cent of their calories from fat in the 40s - almost spot on the 33 per cent level now recommended by government - compared to 40 per cent today, says Dr Jebb. Although we are now more likely to spread polyunsaturated fats, such as margarine, on our bread than the butter or dripping of the war years, overall fat consumption is still too high, she says. Similarly, whereas war families consumed 55 per cent of calories as carbohydrates, the figure today is down to 45 per cent. We now eat about half the potatoes and a third of the bread typically consumed during the 40s. And although we partly compensate with pasta and rice, this is still insufficient, she argues.

These two major shifts in British diet are held partly to blame for our high incidence of several killer diseases. Nutritionists agree that too much fat can lead to raised cholesterol and obesity, which put us at risk of heart disease, stroke and diabetes. Eating more carbohydrates provides essential fibre, which can protect against some cancers. It is also more likely to fill us up without making us resort to unhealthy biscuits, cakes and other bad habits. Higher vegetable consumption also protects against certain cancers.

Experts estimate that up to a third of all cancers are caused by dietary factors. Since 1950, cancer deaths have grown from 17 per cent to 25 per cent of all mortality, and while treatment has improved survival in many cases, incidence is still rising. Diabetes and obesity have also both increased significantly and although deaths from heart disease are now falling, they have not dropped as fast as many experts believe feasible.

'Many people ate a lot better during the war,' says Dr Jebb. Ironically, although we now enjoy more choice and variety in what we eat, diet has generally worsened. 'It is certainly possible to eat more healthily now than then, but not all of us choose to do it.'

There were other health advantages to the wartime diet, too. Although fruit was a rarity, there were free supplies of fruit juice, milk and vitamins for children. The standardised wartime national wholemeal loaf contained far more fibre than traditional white bread and was fortified with calcium, while vitamins A and D were added to margarine. At the same time, fair shares meant many poorer families ate a better diet than before. The difference in death rates between rich and poor reached its narrowest gap in the 20th century after the war, before widening to its current gulf.

'It was the best diet we have ever had in Britain,' declares Aubrey Sheiham, professor of dental public health at University College London. The government based rationing on sound nutritional principles, while equal shares ensured the benefits were enjoyed by all. After the war, there were dramatic reductions in diabetes and dental decay, which can both be linked to better diet, he points out.

Obviously, health trends have not all moved in one direction. We now live longer than ever before and have largely seen off infectious diseases such as TB, measles and polio. Yet the greatest increases in life expectancy during the last century happened during the war decades, according to Richard Wilkinson, professor of social epidemiology at Sussex University.

From 1911 to 1921 and again from 1940 to 1951, life expectancy increased by between six and seven years - more than double the rise in other decades, he says. In the 40s, deaths from many causes, including heart disease, diabetes, flu and pneumonia, fell significantly. He believes full employment, higher earnings, more equality and social cohesion all played a part in this dramatic health improvement. The wartime diet was clearly another factor. 'Food certainly is part of the more general picture.'

On the home front

Rationing was introduced in 1940 and lasted 14 years. For most of that time, meat, cheese, butter, cooking fats and sugar were heavily restricted, but potatoes, other root vegetables and bread were freely available. People ate a diet much higher in carbohydrates and lower in fats. After rationing ended, people rushed to buy butter, sugar and white bread. The National Food Survey, conducted since 1950, shows our consumption of fruit has slowly risen over the past 50 years, but that consumption of bread, cereals, potatoes and other vegetables has steadily fallen. We eat fewer visible fats, but consume hidden quantities in processed foods, takeaways and restaurant meals.

 The 1940s House continues on Thursdays at 9pm on Channel 4. You can tour a replica of the house at the Imperial War Museum, Lambeth Road, London SE1 (020 7416 5320) until 3 June.