Time to Fatten Up Our Diets

Saturated and trans fat? No. But replacing carbohydrates with unsaturated fat could lead to a longer, healthier life.

Harvard Health Letter | September 2007

Fat of any kind packs in the calories. A single gram contains nine, compared with four in a gram of carbohydrate. So, yes, fat can be fattening if you eat too much of it. Of course, the same is true of carbohydrate. Extra calories that lead to extra weight, no matter where they come from, aren’t healthy.

Say, though, your calorie level is about right — you’re consuming as many as you burn up. Where is the best place to get them?

For years, the official dietary advice has steered Americans away from fats and thus toward carbohydrates. Important studies in the 1950s showed that countries where people ate a lot of saturated fat — the sort of fat in meat and dairy products — were more likely to have higher heart disease rates. Because saturated fat got a bad name, all fat did even though neither of the two large studies based at Harvard, the Nurses’ Health Study and the Health Professionals Follow-up Study, has found a link between the overall percentage of calories from fat in a diet and three of our biggest health woes: cancer, heart disease, and weight gain.

Good vs. Bad Fat

If we open the door to more fat in our diets, then which type of fat do we let in? The studies comparing countries done in the 1950s weren’t wrong about saturated fat being bad for the heart. Replace carbohydrates with saturated fat, and your “bad” LDL cholesterol levels will go up. So will your “good” HDL levels, although not enough to cancel out the LDL increase.

Swap out those same carbohydrates with unsaturated fat found primarily in vegetable oils, and you get the best of both cholesterol worlds: a decrease in LDL and an increase in HDL. Harvard researchers have estimated that if we were to replace a small amount of the carbohydrates we eat (the equivalent of 5% of our total calorie intake) with polyunsaturated fat, we’d lower our risk of developing heart disease by 30% to 40%. Foods with good fat include: nuts, avocado, fish, oils (Canola, Sunflower, Olive).

the really bad stuff

Some trans fat occurs naturally in meat and dairy foods but most is artificial. Trans fat is produced by partially hydrogenating — that is, adding hydrogen atoms to — vegetable oils (see sidebar below). Starting in the early 1990s, the tide began to turn against trans fat. Studies have linked high intake of trans fat to diabetes, dementia, gallstones, heart disease, and infertility.

6 Tidbits of Fat Wisdom:

Dr. Walter Willett's, chair of the Harvard School of Public Health’s nutrition department, research helped expose the harm caused by trans fat.

Here are six tips and insights from Dr. Willett:

1. Nutrition guidelines used to recommend that we get no more than 30% of our calories from fat. The federal government’s latest guidelines say up to 35% is okay. Dr. Willett would even go as far as 40%.

2. Limit your saturated fat intake to less than 8% of your total calories, which for most people comes out to about 17 grams of saturated fat a day. This still leaves room for a seven-ounce cheeseburger (12 grams of saturated fat) or ice cream (a scoop of the full-fat variety has 10 grams of saturated fat).

3. Health effects of monounsaturated and polyunsaturated fat seem to be about the same.
   

4. Although it seems to be on its way out, you still have to be on the lookout for trans fat. Dr. Willett calls it “metabolic poison.” The FDA is allowing food manufacturers to label their products as having no trans fat if there is less than 0.5 grams per serving. Check the ingredient list. If partially hydrogenated oil is on it, then there is still some trans fat in there, despite what the nutrition label says.

5. The tropical oils in small amounts are okay, and they’re certainly an improvement over trans fat. Remarkably, coconut oil and olive oil have similar effects on the ratio of LDL to HDL.

6. When it comes to chicken, go ahead and leave the skin on. Because of the polyunsaturated fat content, says Dr. Willett, “a little bit of chicken fat isn’t such a bad thing.” Chicken fat is 63% unsaturated fats, but fatty wild fish is the best.