We've reported a lot this year about how there's a major rethinking of fat happening in the U.S.
Turns out, eating foods with fat — everything from avocados and nuts to dairy fat — doesn't make us fat.
But eating too many carbohydrates — particularly the heavily refined starches found in bagels, white pasta and crackers — does our collective waistlines no favors.
A new study published in the Annals of Internal Medicine adds to the body of evidence that cutting back on carbs, not fat, can lead to more weight loss.
Researchers at Tulane University tracked two groups of dieters for one year. The participants ranged in age from their early 20s to their mid-70s and included a mix of African-Americans and Caucasians.
The low-carb group, which reduced their carb consumption to about 28 percent of their daily calories, lost almost three times as much weight as the low-fat dieters who got about 40 to 45 percent of their calories from carbs.
The low-fat group lost about 4 pounds, whereas the low-carb group's average weight loss was almost 12 pounds. Participants in the two groups were eating about the same amount of calories.
Lydia Bazzano, one of the study authors and an associate professor of epidemiology at Tulane, says she had anticipated some difference in weight loss between the two groups. But the size of the effect — the nearly 8-pound difference in weight loss — was surprising, she says.
So, what kinds of meals were the low-carb dieters eating?
"Typically in the morning they were eating eggs," says Bazzano. Other breakfast items included small portions of high-protein, high-fiber bread, with either butter or other kinds of oily spread.
As for lunch and dinner, the low-carb dieters ate lots of vegetables, salads and protein, including fish, chicken and some red meat. They had generous portions of healthy fats such as olive oils, canola and other plant-based oils.
Fat accounted for a sizable part of their diet: from 40 percent to 43 percent of their total daily calories, including about 12 percent from saturated fat.
Bazzano says with so many people still abiding by low-fat recommendations, a diet so high in fat might not sound like a good weight-loss strategy. "It's not the general perception," she says.
But, in fact, there are a spate of studies that have come to the same conclusion about the benefits of swapping a low-fat, high-carb strategy for a pattern of eating that emphasizes healthy fats and lower carbohydrate consumption.
It's not just waistlines that respond. The low-carb, healthy fats approach has been shown to cut the risk of heart disease.
One big study published in the New England Journal of Medicine found that a Mediterranean diet rich in olive oil cut the risk of heart attacks and strokes by 30 percent, compared to a low-fat diet.
Research published last year in the Journal of the American Medical Association, which compared a low-glycemic-index diet — which minimizes refined starches — with a more traditional low-fat diet, also documented advantages.
"We saw improvements in triglycerides, [good] cholesterol, and the possibility of lower chronic inflammation" among the lower carb group, JAMA study author David Ludwig of Harvard Medical School and Boston Children's Hospital told us.
Here's the fascinating part: Ludwig also found that when people stopped eating so many refined carbohydrates, they burned off about 150 more calories per day, compared to those eating a higher carb, lower fat diet.
"Too much refined carbohydrates — white bread, white rice, potato products — all the foods that crept into our diets as we've followed the low-fat craze has undermined our metabolism," says Ludwig.
In other words, the high-carb, low-fat pattern of eating "caused us to become hungrier and burn off fewer calories," he says.
What's happening in the body when we follow this pattern of eating is still the subject of much research, but Ludwig says the thinking goes like this: Eating too many carbs can overstimulate the release of insulin and direct more calories into storage in the fat cells.
"It's a double-whammy for weight gain," Ludwig says. "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, but the problem is it's wrong."
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. Transcript provided by NPR, Copyright NPR.