AUDIE CORNISH, HOST:
Now to a story that challenges some common advice about dieting. In recent years, nutrition scientists have been rethinking fat. Many have concluded it's not the enemy we've been led to believe it is - not for our hearts, not for our waistlines.
NPR's Allison Aubrey tells us about a new study that adds to the evidence.
ALLISON AUBREY, BYLINE: Lots of people, including me, once assumed that if you ate fatty foods - say, avocados, nuts, full-fat dairy or oily salad dressings - that you'd get fat.
DAVID LUDWIG: We've been told for decades that if you don't want fat on your body, don't put fat into your body. It's a very appealing notion. The problem is, it's wrong.
AUBREY: That's David Ludwig of Harvard Medical School and Boston Children's Hospital. Back in 2012, he published a study in the Journal of the American Medical Association, which was one nail in the coffin for the low-fat diet paradigm. His study showed that when people add in lots of healthy fats to their diets and take out refined carbohydrates - such as bagels and crackers, which had become staples of low-fat eating - they did better, including on measures of heart health.
LUDWIG: We saw improvements in HDL-cholesterol and the possibility of lowered chronic inflammation.
AUBREY: And there was another advantage - the higher-fat, lower-carb approach seemed to rev up people's metabolism. Ludwig found that those who stopped eating so much starch burned off about 150 more calories a day compared to people eating a high-carb, lower-fat diet.
LUDWIG: Too much refined carbohydrates - white bread, white rice, potato products - all those foods that have crept into our diets as we've followed the low-fat craze, has undermined our metabolism and caused us to become hungrier and ironically, burn off fewer calories.
AUBREY: What's thought to happen in the body is this - too many refined carbs send a signal to the body to release a lot of insulin. That extra insulin locks up calories inside fat cells, where they cannot be used for energy.
LUDWIG: So that's a recipe for both increased hunger, but also feelings of fatigue and tiredness. It's a double-whammy for weight gain.
AUBREY: So this brings us to a new study, published today. Researchers at Tulane University tracked what happened over a one-year-long period when overweight men and women - a diverse mix, including African-Americans and Caucasians - followed a low-carb approach. Study leader Lydia Bazzano says once you swap out bready carbs, what you're swapping in is more protein and more fat. So what kinds of meals were they eating?
LYDIA BAZZANO: Typically, in the morning they were eating eggs. We had a lot of recipes with eggs in them.
AUBREY: And for lunch and dinner, the low-carb dieters were directed to eat lots of vegetables - salads, proteins including fish and meat, prepared with generous portions of healthy fats.
BAZZANO: Olive oils, canola oils, vegetable oils.
AUBREY: As well as small amounts of butter and other animal fat. In total, fat made up a sizable portion of their overall calories; in the range of 40 to 43 percent.
Now, Bazzano says many people might say, this doesn't sound like a weight-loss diet, with all the fat.
BAZZANO: It's not the general perception.
AUBREY: Yet, when she tracked how much weight the low-carb dieters lost over one year, it averaged about 12 pounds. This compared to only about 4 pounds of weight loss for those following a low-fat diet, even though the two groups were eating about the same number of calories.
BAZZANO: It's more than double, yes. So this was, yes, surprising.
AUBREY: And it offers more evidence that when it comes to right-sizing our waistlines it's refined carbs, more so than fat, that many Americans could cut back on.
Allison Aubrey, NPR News.
CORNISH: You're listening to ALL THINGS CONSIDERED from NPR News.
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