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Good fat, bad fat

(article, Megan Holden)

We all know that too many calories leads to too many pounds. But if your calorie consumption is about right — that is, you’re burning as many calories as you consume — the question then becomes, What foods make the best fuel?

Recent findings from the Harvard-based Nurses’ Health Study and the Health Professionals Follow-Up Study have found no link between our overall intake of fat calories and our three biggest health threats: cancer, heart disease, and weight gain.

These studies conclude that we can live longer, healthier lives if we replace carbohydrates in our diets with healthy fats. Increasing our consumption of unsaturated fats (found primarily in vegetable oils) and reducing our consumption of carbs (including pasta, refined baked goods, and other processed foods) is, apparently, the ticket to good health. Most unsaturated fats not only increase good cholesterol (HDL) but also help lower bad cholesterol (LDL), which in turn protects the body from disease.

Based on these findings, Walter Willett, the chair of the Harvard School of Public Health’s nutrition department, goes so far as to recommend that we get 40 percent of our calories from fat (as opposed to the current federal maximum of 30 percent). In short, it’s time to shelve those low-fat diets.

There’s no denying it: Fats are essential to our health. Our bodies require fatty acids for almost everything, from brain, liver, and eye function to building cell membranes. Fats in our meals also slow down our digestion so the body can absorb more nutrients, providing a steady energy source and a feeling of satiety. 

Not all fats are equal, however. In general, fats can be divided into two groups: the bad guys (trans fats and, to a lesser extent, saturated fats) and the good guys (unsaturated fats). This means limiting our intake of saturated fat to about 8 percent of our total calories; for most people, this is about 17 grams of saturated fat per day. Trans fats should be eliminated completely; don't eat anything with "partially hydrogenated oil" on the ingredients list.

Most of our calorie swapping should be aimed at increasing the good fats found in vegetable oils, nuts, and seeds. When monounsaturated and polyunsaturated fats are eaten in place of carbohydrates, these good fats improve blood-cholesterol levels by decreasing LDL and increasing HDL. 

The occasional hamburger is fine. In fact, the saturated fat in beef (as well as chocolate made from cocoa butter) includes stearic acid, which converts quickly to healthy monounsaturated fat and doesn’t increase LDL levels much.