How Low Can You Go ?
An American study throws doubt on the benefits of a low-fat diet.
Confused by recent news that a low-fat diet may not help prevent cancer and heart disease after all?
Beth Hobson is.
"I've been on a low-fat diet for four years now," says the 44-year-old part-time worker at a fitness centre. "Does that mean I can go back to eating full saturated fats? I should go home and eat a pizza tonight?"
By no means, say scientists.
The real culprits in our diets, they say, are the hardened fats in margarine and shortening as well as saturated fats in meat.
In addition, people seeking healthy lifestyles should look beyond eliminating fat and actively incorporate more fruits, vegetables, whole grains and exercise.
"It's all about balance in all ways," says Dr Jacques Rossouw of the American National Heart, Lung and Blood Institute.
Nor should those adjusting their eating habits to prevent bad things from happening expect quick results. "The effects of a change in diet are going to take a long, long time," he says.
Rossouw was project director of a $US415 million study in which 48,835 post-menopausal women aged 50 to 79 were assigned to eat either a low-fat diet or anything they wished.
Researchers following the women over eight years found no statistically significant differences between the two groups in rates of colon cancer, breast cancer, heart attack and stroke - all the things doctors hoped a healthy diet would prevent.
The study, published in a recent issue of the Journal of the American Medical Association, surprised and puzzled many consumers who are growing weary of shifting advice about food.
"Whenever I try to pursue some nutritional strategy, it seems that there's always some new study that comes out years later reversing it," says freelance writer Betty Boyd, 32.
Cheryl Anderson, a nutritional epidemiologist at the Johns Hopkins Bloomberg School of Public Health, says it would be a mistake to think you can just eat what you want and be OK.
"If you're only watching total fats, you may miss the subtlety of what types of fats you're eating," Anderson says.
Like many other scientists, Anderson notes that the study was conceived before evidence emerged that two particular types of fat may be the chief dietary evils in heart disease.
One, called trans fat, is created when hydrogen is added to vegetable oils that harden into margarine or shortening. Trans fats are often used in commercial baked goods such as doughnuts, pastries and biscuits. They also show up in the french fries and fried chicken made by most fast-food chains.
The other, saturated fat, is usually solid at room temperature and comes mostly from animal sources in meat, poultry, and whole milk and whole-milk cheeses. Saturated fats are also found in certain plant oils, such as palm, palm kernel, coconut oils and cocoa butter.
Both types of fat contribute to elevated blood cholesterol levels and increase heart disease risk, research shows. A strategy that simply cuts back on all dietary fats - as the women in the study did - ignores this distinction and other knowledge that experts say they've gained.
"Ten years ago, our mindset was to lower the fat - the lower the fat, the better. That clearly has changed," says Dr Michael Miller, director of the Centre for Preventive Cardiology at the University of Maryland Medical Centre.
"Our approach has been not to restrict [total] dietary fats, but to restrict saturated fats and to eliminate the absolute worst kinds of fats - trans fats."
Miller recommends that dieters lean more toward unsaturated and polyunsaturated fats. They're found in olive oil and avocados; in fatty fish such as wild salmon, sardines and albacore tuna; in nuts such as almonds, walnuts and pistachios; and even in dark chocolate.
But even good fats should be consumed in moderation, because they're also rich in calories, Miller notes. "The total fat content [of one's diet] could be 30 or 35 per cent of your calories," he says.
"The best way to cook, in fact, is to steam your products," he says. Microwaving, grilling or sauteing are also OK.
Animal products are another source of saturated fats. "Choose lean cuts and no more than three or four ounces [85 to 115 grams] per serving. Instead of doubling your meat, double the green vegetables. Anything that's colourful is good for you - except Froot Loops."
The women in the study, most of whom were overweight, might have stayed healthier had the protocol also forced them to lose weight and get more exercise, says Dr Roger Blumenthal, director of the Johns Hopkins Ciccarone Preventive Cardiology Centre.
"We don't want people to get the wrong message, that diet doesn't mean anything," he says. "But diet without weight loss probably is very unlikely to have a significant health benefit. Combine diet with better exercise habits."
Bonnie Liebman, director of nutrition at the Centre for Science and the Public Interest in Washington, says she worries that consumers will be misled by the study.
"What I fear is that people will hear all fats are OK. This message could really do harm. It could undo a lot of the progress we've made over the years."
- The Washington Post