Dear EarthTalk: what's the skinny on fat these days? I saw a major magazine cover image recently that was suggesting fat wasn't so bad for us after all?

Author:Bellwether, Marcy

Going "fat-free" might seem like an effective, safe way to lose weight when considering that fat contains nine calories per gram, compared to four calories per gram in carbohydrates and proteins. But if you take into account the fact that approximately 60 percent of human brain matter consists of fats, eating reduced fat or fat-free foods high in sugar and refined carbohydrates no longer seems as appealing for our health.

"The brain thrives on a fat-rich, low carbohydrate diet, which unfortunately is relatively uncommon in human populations today," reports David Perlmutter, author of Grain Brain. "Mayo Clinic researchers showed that individuals favoring carbohydrates in their diets had a remarkable 89 percent increased risk for developing dementia as contrasted to those whose diets contained the most fat. Having the highest levels of fat consumption was actually found to be associated with an incredible 44 percent reduction in risk for developing dementia."

Granted, certain types of fats are more beneficial than others. "Good" fats include monounsaturated fats, found abundantly in olive oil, peanut oil, hazelnuts, avocados and pumpkin seeds, and polyunsaturated fats (omega 3 and omega 6), which are found in flaxseed oil, chia seeds, marine algae oil and walnuts.

"In the '70s and early '80s ... we were not talking about low-fat diets. We were talking about replacing saturated fat with a healthy fat, polyunsaturated fat," says Walter Willett, professor of epidemiology and nutrition at the Harvard School of Public Health. "But somewhere in the mid-1980s, we lost that message. It's perhaps partly because some nutritionists felt it was too complicated to talk about different types of fat, and developed the notion we should just reduce all types of fat across the board."

With over five million Americans currently living with Alzheimer's disease, researchers are examining which dietary fats may help prevent dementia. Olivia Okereke at Brigham & Women's...

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