Cod-liver oil isn’t the only dietary fat undergoing new scrutiny. The most notable example: Trans fat, found in many stick margarines and used in packaged and fast foods, was once viewed as a healthful alternative to butter. It is now banned from restaurant use in several cities because of the clear threat it poses to the heart. Researchers are also refining other long-held assumptions about the risks and benefits of various cooking oils, and the overall role of dietary fat in heart disease, cancer, and weight gain.
ACCEPTED WISDOM: Olive and canola oils are the healthiest fats.
NEW TAKE: Olive oil’s sterling reputation stems mostly from its association with the widely respected Mediterranean diet. Moreover, virgin and extra-virgin olive oils — those from the first pressing of the fruit — are rich in polyphenols, a class of antioxidants that may offer special health benefits. And olive, canola, and peanut oils contain mostly monounsaturated fats. Many people think that’s a boon, since monos tend to lower the “bad” LDL cholesterol without significantly lowering the “good” HDL, as do the polyunsaturated fats found in corn, safflower, soybean, and sunflower oils.
But many researchers now think that those assumed benefits are overblown. For one thing, the Mediterranean diet includes many healthful features beyond olive oil, such as produce, whole grains, and fish. Other research has recently undercut the presumed health benefits of antioxidants. And there’s little, if any, scientific evidence that people who consume mostly monos have lower rates of heart disease or other conditions. Indeed, some animal research suggests that polys may have a better overall effect on coronary health, for reasons that researchers don’t yet fully understand.
Because no particular vegetable oil stands out as superior overall, our consultants make it simple: Choose any vegetable oil that has no more than about 2 grams of saturated fat per tablespoon .
ACCEPTED WISDOM: Foods free from trans fats are much better than their previous versions.
NEW TAKE: Many restaurant chains now use a healthful mix of unsaturated oils for frying. But reusing those oils — as many restaurants do — also poses risks, since reheating oil modifies its molecular structure, making the fat more likely to stick to artery walls. And many “trans-free” restaurants still purchase french fries and other items that have been previously fried in trans fat. So you still need to be wary of restaurant fried foods, which pack a lot of calories no matter what they’re fried in.
The trans-fat-free products sold in the grocery store can be even more confusing. The Food and Drug Administration allows food labels to list 0 grams of trans fat if a product contains less than half a gram of trans fat per serving. But if you eat large or multiple servings of those supposed “trans-fat-free” products, it’s easy to exceed the American Heart Association’s recommended maximum for trans fats just 2 grams a day if you consume a 2,000 calorie diet.
Trans-fat substitutes now used in crunchy cookies, flaky pie crusts, and other baked goods are also cause for concern. Some manufacturers use palm oil, since it’s semisolid like trans fat. But palm oil is one of the least healthful vegetable oils because it contains high amounts of saturated fat. Other manufacturers now combine fully hydrogenated soybean oil, a nearly solid fat, with a liquid oil to yield a semisoft fat. While the combination contains no trans fat and doesn’t appear to affect cholesterol levels, researchers still don’t know what its long-term health impacts might be. So our consultants say that at this point, the health benefits of these two trans-fat replacements are unclear.
To avoid trans fat and minimise confusion about its alternatives:
— When selecting trans-fat-free prepared foods in the grocery store, choose those with the lowest amount of saturated fat. If palm or fully hydrogenated oil are used in the products, they’ll show up as saturated fat on the nutrition panel.
— When dining out, ask the waiter what kind of oil the restaurant uses in the items you order. If possible, choose dishes that don’t contain trans fat.
ACCEPTED WISDOM: A very low-fat diet is the best way to protect the heart.
NEW TAKE: A few trials have found that people with existing heart disease who cut back on fat to less than 10% of total calories can reverse the progression of clogged coronary arteries. But those trials typically combined a low-fat diet with other measures, such as regular exercise and stress reduction, which likely contributed to the apparent benefit.
Moreover, very low-fat diets have mixed effects on cholesterol levels. While they do sharply lower harmful LDL cholesterol, they also lower beneficial HDL cholesterol and raise the level of triglycerides, another kind of fat that may contribute to heart disease. In fact, the American Heart Association (AHA) recently increased the acceptable upper limit for fat from 30-35% of your total calories.
However, it’s still vital to cut back on saturated fat, the kind that comes mostly from meat and dairy products. Saturated fat clearly raises LDL and increases coronary risk. In fact, at the same time that the AHA loosened restrictions on total fat it tightened the limit on saturated fat, reducing the recommended maximum daily intake from 10-7% of calories. No more than 1% of your calories should come from trans fat, found in partially hydrogenated vegetable oils, since trans fat not only raises LDL but also lowers HDL and increases inflammation in the body.
The vast majority of your fat calories should come from unsaturated fats, the kind found in most fish, nuts, seeds, and vegetable oils.
ACCEPTED WISDOM: Cutting back on fat can prevent cancer.
NEW TAKE: Most studies have now largely exonerated dietary fat — total, saturated, or otherwise — from playing a significant role in causing cancer. For example, in the respected Women’s Health Initiative, researchers randomly assigned some 20,000 postmenopausal women to receive intensive dietary counseling. The women did lower their total fat intake. But after 8 years, they didn’t significantly cut their risk of breast or colorectal cancer compared with a similar group of women who didn’t get that counseling and didn’t reduce their fat intake. Most other studies evaluating the effect of dietary fat intake on preventing other malignancies has yielded similarly disappointing findings.
However, people who already have breast or prostate cancer may want to cut back on fat. Evidence does suggest that limiting fat intake to less than 15% of calories may prevent those cancers from progressing or recurring.
ACCEPTED WISDOM: Cutting back on fat is the most important dietary step you can take to lose weight.
NEW TAKE: Cutting calories counts more. Reducing fat intake can contribute to that effort, since 1 gram of fat packs 9 calories compared with 4 calories in a gram of carbohydrates or protein. But fatty foods usually contain protein, and that combination makes you feel fuller longer, so very low-fat diets can be hard to maintain.
Indeed, most research suggests that people who eat moderate amounts of fat are at least as successful at losing weight as those who restrict fat intake sharply. For example, the National Weight Control Registry, which tracks 6,000 successful dieters nationwide, reports that members today usually consume more fat than previous members did. They typically consume 30% of calories from fat compared with 24% about a decade ago. Yet registry members are still successfully keeping the weight off. So, provided you keep your total calorie count down, eating a moderate amount of the right type of fat is OK for dieters.
To determine if you’re overweight and to get guidance on how many calories and how much saturated fat you should consume based on your age, height, weight, gender, and activity level, visit the American Heart Association’s dietary Web site at www.myfatstranslator.com
For more information on Choosing the Right Vegetable Oils and When to Use: Fatty-fish Supplements, please see Utusan Konsumer, Jan-Feb 2008
Read more about dangerous trans fat in the CAP Guide, Toxic Trans Fat in Processed Food