Christofer Backlin had gained 5 pounds, and it was all because of the muffins. Swallowing one last bite of crumbly cake, the 31-year-old resident of Uppsala, Sweden, closed his eyes and exhaled with relief. It was his 49th day and his 160th baked good (total tally: 40 chocolate, 40 vanilla, 40 lemon, 18 strawberry, 16 apple, 5 cinnamon, and 1 very unfortunate tropical flavor), and it marked the end of a bizarre, vaguely masochistic experiment. "Let's just say I won't be interested in muffins again for a while," says the medical PhD student, who had been forcing them down after every meal, every day for 7 weeks. One of his peers had quit the study, unable to stomach one more crumb, but Backlin never considered dropping out. "The world needs an answer," he says.
He's right. There was a final unresolved mystery in the decades-long search for consensus about fat, and it was time we put it to bed: Does saturated fat make us fat? We now know that a low-fat diet, tried en masse in the '80s and '90s, caused widespread weight gain. Trans fats are out, too, no debate there. Unsaturated fats are widely accepted as healthy. And—despite misleading headlines recently declaring that butter is back—we know that saturated fat does our hearts no good. While that last point continues to be fussed over, clearing the remaining blind spot—the impact of saturated fat on how we put on weight—promised to draw this endless ping-pong match to a close. So Backlin and 38 other brave participants put their waists on the line.
"Understanding dietary fat could save millions of lives if it helps us reduce obesity risk," says Ulf Riserus, an associate professor of clinical nutrition at Uppsala University and the mastermind behind the study. He set out to do an ambitious and unusual trial in which he monitored willing participants as they gained weight. Muffin weight.
During the study, each participant ate three or four daily muffins. Half the group was given treats baked with saturated fat (palm oil), and the other half ate ones made with polyunsaturated fat (sunflower oil). They would pick up desserts weekly or daily from the lab—researchers baked all 6,500 muffins themselves—and otherwise eat their regular diet, whether it was salad or pizza or sill på knäckebröd (pickled herring on crackers).
Even the ambitious Riserus, though, didn't anticipate the breakthrough result he got and how it would finally solidify a three-point approach to eating fat—to eating, period—that had been percolating for a while.
Source: Gretchen Vannice, Registered Dietitian Nutritionist. Illustration By Giulio Mencaroni
1. BUTTER WAS NEVER BACK
At this point you may be wondering: Is it really settled that saturated fat is bad for heart health? You may be aware of a big recent review that "exonerated" the stuff: Scientists from Cambridge looked at 72 studies comparing people who ate more saturated fat with those who ate less and found no cardiovascular advantages among the virtuous types who had cut back. So didn't Brie lovers have reason to rejoice, as all the "Butter Is Back" headlines claimed?
At this point you may be wondering: Is it really settled that saturated fat is bad for heart health? You may be aware of a big recent review that "exonerated" the stuff: Scientists from Cambridge looked at 72 studies comparing people who ate more saturated fat with those who ate less and found no cardiovascular advantages among the virtuous types who had cut back. So didn't Brie lovers have reason to rejoice, as all the "Butter Is Back" headlines claimed?
In short, no. Even the study's coauthor, a cardiovascular epidemiologist at Cambridge, acknowledges that the work was largely misconstrued and doesn't actually amount to permission to embrace saturated fat. The main problem with the study: It didn't look at the whole picture. Sure, the people who cut back on saturated fat had just as much heart disease as the others did. But what had those people filled the saturated-fat void with? Not healthy stuff but, rather, bread, cereal, and other refined carbs, per their food diaries. And we already know that eating too much sugar and starch is associated with obesity, diabetes, and coronary disease.
"If eating less saturated fat means eating more sugar, then of course cutting back on it isn't going to improve your health," says David Katz, founder of Yale University's Prevention Research Center. The study didn't show saturated fat to be harmless; it showed that replacing it with sugar and refined carbs is no better.
After an avalanche of criticism, the authors published a revised version. Some experts are calling for it to be revoked entirely. Decades of research show that saturated fat raises cholesterol, which in turn may increase heart disease risk. The Cambridge study did little to refute that.
2. SATURATED FAT IS A BIG WAIST
When the results of Riserus's muffin study came in, they were beyond damning. While both muffin groups experienced similar weight gain—that's what happens when you eat 750 extra calories a day for nearly 2 months—the volunteers eating the saturated-fat muffins built more fat, and far more of the dangerous kind around the internal organs; meanwhile those eating polyunsaturated-fat muffins built three times more muscle mass, which makes it easier to lose weight and stay healthy. "We were surprised that the differences in abdominal and liver fat accumulation were so clear," says Riserus.
When the results of Riserus's muffin study came in, they were beyond damning. While both muffin groups experienced similar weight gain—that's what happens when you eat 750 extra calories a day for nearly 2 months—the volunteers eating the saturated-fat muffins built more fat, and far more of the dangerous kind around the internal organs; meanwhile those eating polyunsaturated-fat muffins built three times more muscle mass, which makes it easier to lose weight and stay healthy. "We were surprised that the differences in abdominal and liver fat accumulation were so clear," says Riserus.
The trial impressed nutrition scientists internationally, including Walter Willett, chair of the department of nutrition at Harvard School of Public Health. "If the results hold up in longer-term studies," he says, "replacing saturated fat with unsaturated fat could have important benefits for obesity risk."
So saturated fat dangerously pads the waistline—but why? The research team suspects that it might turn on genes that block fat burning and promote fat storage or turn off genes that do the opposite. This might have been a good thing for a hunter-gatherer bulking up for the cold, hard winter; not so much when you're trying to zip up a pencil skirt on the way to your desk job.
3. THE GOOD STUFF MATTERS MOST
The fact that subjects who ate sunflower-oil muffins built so much more muscle—muscles from fat?—was an even bigger surprise. Until this point, only animal data had suggested that this could happen. Riserus and his team think that polyunsaturated fat might somehow turn on genes that stimulate protein synthesis.
The fact that subjects who ate sunflower-oil muffins built so much more muscle—muscles from fat?—was an even bigger surprise. Until this point, only animal data had suggested that this could happen. Riserus and his team think that polyunsaturated fat might somehow turn on genes that stimulate protein synthesis.
The benefit adds to the growing list of what you stand to gain from eating more healthy fat. Earlier this year, the Academy of Nutrition and Dietetics urged us to increase heart- and brain-essential omega-3 fats (the equivalent of two to three servings a week of salmon or sardines). And if you're sick of hearing about the fat-filled Mediterranean diet, too bad: A recent trial showed that diets with increased olive oil or nut intake reduced heart trouble. Some research even indicates that good fats can inoculate us against the ill effects of bad ones. In a 2012 UCLA study, people who ate hamburgers topped with avocado saw a smaller spike in triglycerides and inflammatory substances than those who ate burgers without the healthy-fat add-on.
All this consensus leaves you with an easy-to-follow edict: Eat positively. As in, stop thinking about what to cut out of your life and start focusing on what to add. Fill your diet with unsaturated vegetable oils, nuts, and fish and you naturally keep saturated fats to a minimum, Willett advises. You also crave far fewer refined carbs.
"Future dietary guidelines will emphasize real food, not individual macronutrients," says Frank Hu, a professor of nutrition and epidemiology at Harvard. He also suggests looking at the big picture because, as the "butter is back" study showed, focusing on one single food can start a crazy-making domino effect.
Even Fredrik Rosqvist, a doctoral student who coauthored the muffin study, agrees. "Overall diet quality is more important than single nutrients," he says. His own study may have singled out saturated fat as a cause of dangerous ab flab, but the end message echoes what top nutritional minds everywhere are emphasizing: Eat healthy foods, including fats, and the nutrients take care of themselves.
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