A major US study has found that a low-fat diet won't stop cancer or heart disease. Have we all been passing up the bacon sandwiches for nothing? Fiona Tyrrell reports
A major US study involving over 48,000 women published last week concluded that a low-fat diet won't stop cancer or heart disease. The findings came as a big surprise to low-fat dieters across the world, health experts and the authors themselves.
While the results are good news for fans of the bacon sandwich and the Atkins diet, they fly in the face of strongly held beliefs of the health-conscious and the commonsense advice of health experts that eating less fat is good for you.
Published in the Journal of the American Medical Association last week, the study undertaken by the National Institutes of Health was the largest clinical trail of low-fat diets. It involved 48,835 post-menopausal women and cost $415 million to conduct.
The American researchers set out to test the widely held theory that a low-fat diet reduces the risk of cancer and cardiovascular disease.
The results indicated that there was no significant differences in the rates of heart disease or stroke or the risk of colorectal cancer between a group of healthy women who followed a low-fat diet and those who followed their normal diet over an eight-year period.
Although the women in the study who reduced their total fat intake had a 9 per cent lower risk of breast cancer, the difference was not large enough to be statistically significant, according to the authors.
Critics and the researchers alike say the study comes with a health warning. The diet used in the study focused on reducing total fat and, unlike diets used to reduce heart disease risk, did not differentiate between good fats found in fish, nuts and vegetable oils, and bad fats like saturated fat and trans fat found in processed foods, meats and some dairy products.
In addition, low-fat diets are notoriously difficult to maintain over a long period and participants did not meet the study's challenge to reduce average total fat intakes to 20 per cent.
By the end of the first year, the low-fat diet group had managed to reduce fat intake to 24 per cent but by year six this had risen to 29 per cent of calories from fat. This compared with the control group which had a fat intake of 35 per cent of calories.
When it comes to the fine print the study does, however, validate current nutrition recommendations, according to Barbara Howard, president of the MedStar Research Institute in Washington, US, where the study was carried out.
As a group, the women failed to reduce their fat intake enough to benefit from any major changes. However, women who did manage to reduce their overall fat intake significantly experienced a 15 per cent reduction in breast cancer and women also showed a reduced incidence of polyps, which are a pre-cursor of colon cancer, she says.
Irish experts caution against reading too much into the study's findings and argue there is no such thing as a magic bullet - our health over our lifetime is down to many factors including diet, lifestyle and exercise.
Looking at just one aspect of diet won't make a difference, it's your all-round lifestyle that counts, is the commonsense response from Margot Brennan of the Irish Nutrition and Dietetic Institute. "Nowadays we don't recommend any one change; we recommend an overall life change," she says.
In addition, low-fat diets are always a thorny issue as fat is not necessarily a bad thing, she says.
"It's not always about cutting out fat, but rather changing over to healthier fats," she explains.
When faced with the dizzying array of low-fat products on the shelves of a supermarket, always read the label, Brennan advises.
When fat is removed from a food it becomes less palatable and more often than not manufacturers of low-fat food products add more sugar and salt to make the food more tasty.
"The low-fat product is not always the healthiest and you may be far better off using a little bit of the ordinary product."
Many people feel they are making a healthier choice by using low-fat margarines or butters but lots of these products contain hydrogenated fats (trans-saturated fats), the real baddie when it comes to fats, she explains.
Hydrogenated fats are liquid oils that have changed at a biochemical level as a result of processing. Worse than saturated fats, such as butter and cheese, they cause an increase in bad cholesterol and a reduction in good cholesterol.
People should try to lean towards polyunsaturated and mono-unsaturated fats in their diets, she adds.
The traditional Mediterranean diet, which is full of olive oils, oily fish, nuts and seeds, is full of good fats and is the focus of much research attention at the moment, according to Brennan.
Responding to the study, the Irish Heart Foundation (IHF) said all aspects of dietary intake must be considered in relation to heart health and not one or some components in isolation.
In addition, attention must be paid to overall risk profile such as smoking, physical activity and alcohol intake, it said.
"This study does not change the current IHF recommendations of eating less saturated and trans-fat, less salt and sugar, more fruit and vegetables and more fibre-rich foods."
The IHF recommends a moderate diet of fat intake of 30 per cent of energy.
Current fat intake in Ireland is 37 per cent, according to the most recent figures from the Irish Universities Nutrition Alliance (IUNA).
The Irish Cancer Society agrees and that diet alone is not enough to stay healthy.
"How healthy we stay over a lifetime is down to many factors - things we can't change like our genes and things we can change such as our lifestyles. How active we are, what our weight is, whether we smoke, how much we drink, and how active we are on a daily basis," according to the health promotion manager of the Irish Cancer Society, Elaine Glynn.
The study "which seems to go against all previous studies" has a number of flaws, according to Glynn and she warns against throwing "the baby out with the bathwater".
The vast majority of evidence from studies in the past and from ongoing research indicates that high fruit and vegetable diets with high fibre which prioritise unsaturated fats are the best to follow to reduce cancer.
Aside from just looking at only one subsection of the population, the study looks at only eight years, which is a very short time when you consider that cancer develops over a period of a lifetime, she adds.
"It takes many years for the real benefits of healthy eating to take effect."
However, she describes the study as well designed and says further reports from the continuing study will be interesting.