Medical researchers in the United States who set out to demonstrate that a low-fat diet will reduce the risks of cancer and heart attacks were struggling yesterday to hide their disappointment. The results from their eight-year, government-funded study are in - and they show no such thing.
While this may be good news for lovers of butter and fans of bacon sandwiches for breakfast, it will surely befuddle the millions of health-conscious consumers around the globe who for years have skipped from one low-fat fad to the next in search of the perfect recipe for health, longevity and, of course, a tauter tummy. Just started the F2 diet? Don't bother. Freezer filled with low-fat yoghurt? Run for some Häagen-Daz.
That would seem - at first glance, at least - to be the only sensible lesson to be drawn from the study, which no one could describe as half-baked or skimpy. "It was the Rolls Royce of studies," agreed Dr Michael Thun of the American Cancer Society. The results, far removed from what the experts had expected, were reported yesterday by the Journal of the American Medical Association.
But before everyone dives for the chocolates, some sceptics - and some of its authors - point to potential problems with the study, notably that it did nothing to distinguish between different kinds of fat. They also question whether eight years was a long enough period to make the results meaningful.
Funded by the National Institutes of Health in the US, the sprawling experiment cost $415m in taxpayers' money and involved no fewer than 48,000 post-menopausal women, aged between 50 and 79 years old. The idea at the outset was straightforward: to prove scientifically what most of us instinctively believe to be true (or have been brainwashed to believe): that eating less fat is good for us.
Specifically, the team of researchers wanted to demonstrate a link between a low-fat diet and a reduced incidence of breast cancer and colon cancer and of cardiovascular problems, such as heart attacks and strokes. But when the numbers were in, they found nothing to prove the connection. Those women told to follow a low-fat diet had more or less the same rates of these diseases as those who continued to eat whatever they fancied.
In the words of Dr Thun, the results were "completely null over the eight-year follow-up for both cancers and heart disease". His organisation, for one, will as a consequence be be making no recommendations regarding reducing the intake of fat in your daily eating habits to protect against cancer.
"The results, of course, are somewhat disappointing," conceded Dr JoAnn Manson, a respected authority on nutrition and the chief of preventative medicine at Harvard's Brigham and Women's Hospital. "We would have liked this dietary intervention to have had a major impact on health."
It is also a bit of a blow to all the women - enough to populate a small city - who volunteered for the study, like 66-year-old Judy LaCour who lives close to Seattle and who was recruited in 1993. "I was surprised," she said, "I thought there would be more definitive answers about the value of the low-fat diet."
About 40 per cent of the women were randomly chosen for the low-fat regime. Their challenge was to cut the percentage of fat in their daily calorie intake to 20 per cent and up their consumption of fruit, vegetables and grains. "I was raised in a farm family where high-fat food was the norm, " Ms LaCour said. "It was a real culture shock for me when I first started." Everybody else stuck to their usual eating habits.
The women on the low-fat regime did show a rate of breast cancer that was 9 per cent lower than the control group, but the researchers considered the difference statistically unimportant. As far as cardiovascular issues were concerned, the one risk factor that did seem to change involved so-called LDL cholesterol. Known as "bad cholesterol", it can lead to heart disease. Women in the control group did show more of it, but not to an extent that would significantly increase their risk of a heart attack.
But otherwise, the health benefits for Ms LaCour and others who struggled to reduce their fat intake appeared to be zero. Not only did they have just as much breast, colon cancer and heart disease as the other women, they didn't lose weight either. In fact, their weights generally stayed the same. (Trimming waists and thighs, it should be pointed out, was never a goal of the study.)
Dr Manson was among those cautioning against reading too much into the study's disappointing findings. "These results do not suggest that people have carte blanche to eat fatty foods without health problems," she insisted. In other words, don't jettison your low-fat diet books just yet.
Part of the problem with the study may be that the women asked to reduce their fat intake to 20 per cent didn't quite manage that. In fact, by year six, they had on average slipped to a fat percentage level of 27 per cent. The control group was at 35 per cent at the start of the study and at 37 per cent by the end. The gap in fat intake between the two groups was not, therefore, as wide as the researchers hoped.
Then there is the whole tricky issue of bad fat versus good fat. This is an area of dietary science that was still in its infancy when the study began and today, most nutritional experts believe that what we really need to avoid is fried and processed foods that are often heavy in saturated and trans fats. Fats from nuts, fish and olive oil, we are now told, can even be good for us. Hence the heavy promotion recently of the Mediterranean Diet, which positively encourages the consumption of these types of fat.
"Just switching to low-fat foods is not likely to yield much health benefit in most women," Marcia Stefanick, professor of medicine at the Stanford Prevention Research Center, commented yesterday. "This shows that you can't rely on using low-fat substitutes to make a difference. You really need to think about what kinds of fats you're eating and the foods that should be part of your diet, such as vegetables."
By now, most of us might be ready to throw up our arms in despair. We loved the Atkins Diet - meat and cheese are great, potatoes and pasta are a disaster - until its founder, Robert Atkins, keeled over weighing 258lbs. Suddenly he looked like a charlatan. We have had the South Beach Diet, the Tapeworm Diet (honestly - Maria Callas apparently ate parasites to get herself slim) and the fibre-all-day diet. Eventually all of them are either debunked or fall from favour. It was long thought that lots of fibre would protect us from colon cancer. Wrong, say the newest studies. Certain vitamins were meant to block cancer too. Wrong again.
But surely nothing is as discombobulating as this latest news: that everything we thought we knew about fat might be codswallop too. What are we to do?
Dr Peter Libby, a professor at the Harvard Medical School, may have a commonsense answer. He thinks we should be far more worried about the volume of food on our plate than about what food groups, vitamins, proteins or fats are represented on it. Nothing, he says, fascinates us "so much as the notion that what you eat - rather than how much you eat - directly affects your health".
In other words, when you sit down to dinner tonight, be it fish dinner, steak or tofu, simply eat less. Oh yes, and chuck out the cigarettes, forego the whisky and Red Bull and do a bit of exercise from time to time.
Six 21st-century diets and what they claim to do
You Are What You Eat
Who's behind it? Gillian McKeith
How does it work? "Good" carbohydrates like brown rice and wholewheat bread and pasta are included, as are "good" fats (known as essential fatty acids), such as the ones found in nuts, seeds, fish and avocados. These are essential for breaking down other types of fat which would otherwise be stored in the body.
What the critics say: "I think what I found most objectionable was the bullying, patronising tone... In my professional opinion, anyone following her advice to the letter will be permanently hungry, thoroughly miserable and most probably will suffer from perpetual indigestion," said one disgruntled biochemist.
Celebrity fans: Gwyneth Paltrow, Madonna, Michelle McManus, Kerry Katona
The Atkins Diet
Who's behind it? Robert Atkins
How does it work? Dr Atkins believed that too much carbohydrate causes the body to produce too much insulin, and this in turn leads to hunger and weight gain. On the diet, you're allowed 15-60g of carbohydrates a day - including pasta, bread and fruit - but you're encouraged to eat protein and fat. The diet works on the principle that by reducing high-carbohydrate foods, we can alter our metabolism and shed weight.
What the critics say: Dr Atkins was clinically obese when he died. Nutritionist Dr Susan Jebb condemned the diet as "nonsense and pseudo science". Health psychologist Dr Jane Ogden described fans of the diet as "delusional".
Celebrity fans: Renée Zellweger, Jennifer Aniston, Geri Halliwell and Robbie Williams.
The South Beach Diet
Who's behind it? Dr Arthur Agatston, who says: "Forget low carbs and low fat and think right carbs and right fats."
How does it work? The principle is that the more weight you carry, the higher the risk that your body will become insulin-resistant. The side effect of this is that the body stores more fat, particularly around the tummy, hips and thighs. The diet works by teaching you to rely on the right carbohydrates (fruits, vegetables and wholegrains) and reduce the intake of "bad" carbohydrates (cakes, biscuits).
What the critics say: Dieters who avoid carbohydrates often experience significant weight loss during the initial stages of this diet, but it has a diuretic effect and this may be due to water loss, not fat loss.
Celebrity fans: Nicole Kidman
The Hay Diet
Who's behind it? Dr William Howard Hay
How does it work? The underlying cause of many health problems is the wrong chemical condition in the body. Dr Hay classified foods into three types (protein, neutral and starch) according to their requirements for efficient digestion. Mixing protein and starchy carbohydrates at the same meal, for example, leads to them being incompletely digested, leading to toxicity and weight problems. Vegetables and fruit form a large part of the diet, but fruit must be eaten in isolation.
What the critics say: A University of East Anglia study found "no scientific evidence or reason to believe the 'protein fights carbohydrates' theory".
Celebrity fans: Liz Hurley, Catherine Zeta-Jones.
The Gl Diet
Who's behind it? It started as a clinical trial, when Dr David Jenkins of the University of Toronto looked at the effects of different types of carbohydrates on diabetes patients. It was launched in 2004.
How does it work? GI stands for glycaemic index, a scale of 1 to 100 that describes the speed at which we digest carbohydrates. Foods with a low glycaemic index, such as porridge or beetroot, release glucose slowly and evenly. High GI foods provide a quick hit and encourage the body to release insulin, which then converts the excess glucose into fat.
What the critics say: Very little. The medical industry considers the GI diet to be one of the most sensible and healthy plans around.
Celebrity fans: Kylie Minogue and Anthony Worrall Thompson.
The Zone Diet
Who's behind it? Nutritionist Dr Barry Sears.
How does it work? A strict low-fibre, low-carb regime. Sears believes that by regulating insulin, we maximise fat loss and reduce the chances of heart disease. One of the most complicated diets around, it relies on a ratio of 40% protein, 30% carbs and 30% fats.
What the critics say: You have to eat six complicated meals a day, so even in Hollywood, where it initially proved a big hit among celebs, models and those with time on their hands, it had little staying power.
Celebrity fans: Jennifer Aniston - "I got addicted to it. It wasn't a good thing."