For years, fat was demonized as dietary “Public Enemy Number One.” Despite the essential roles it plays in the body, including temperature regulation, hormone production and protection of organs, we were told it was also responsible for weight gain and a host of health woes. As a result, the public shied away from the macronutrient and instead stocked their kitchens with skim milk, fat-free snacks and low-fat dressings. This approach backfired spectacularly.
You may have noticed that fat is making headlines again and is rising above its bad-for-you reputation. New research and popular diets like paleo and ketogenic have caused the fat stigma to wear off. An endless parade of social media images flaunting avocado toast and all-things coconut oil suggests people have done a nutritional 180° on what was once a dietary villain. But just how healthy is this shift?
Many people are more confused about fats than ever. Here, we explore the latest research and pose some big questions to the experts to clear up a handful of the most common fallacies.
The Myth: Eating Fat Won’t Make You Fat
The reality: “Eat fat, get fat” had been the theory guiding American diets for several decades. Today, mounting evidence suggests that this conventional wisdom during the fat-phobic era was dangerously misguided and may have had the unintended side effect of fueling the current obesity epidemic and associated conditions like diabetes (Bazzano et al. 2014).
A 2016 meta-analysis of randomized controlled trials published in the British Journal of Nutrition determined that people on a low-carb diet (which presumably means higher intakes of fat) tend to lose more weight than those on a low-fat diet (which presumably means eating more carbs) (Mansoor et al. 2016). In another major analysis of the available data, Harvard researchers concluded that low-fat dietary interventions are not more effective at promoting long-term weight loss than higher-fat diets, including the olive-oil-loving Mediterranean style of eating (Tobias et al. 2015).
“Many people simply replaced fat with something worse, that being processed foods full of refined carbs and added sugars, which are more strongly linked to weight gain,” says Michelle Babb, MS, RD, author of Anti-Inflammatory Eating for a Happy, Healthy Brain (Sasquatch Books 2014). Butter and olive oil were out of favor; bread, rice, cereal and pasta were in. “Not only did that shift take a metabolic toll on the body; it also created a culture of chronic overeating, since fat is essential for satiety, so low-fat eating just left us wanting more,” notes Babb. When fat enters the small intestine, it signals the release of peptides YY and CCK, two hormones that work to reduce appetite (Maljaars et al. 2009).
In what seems to be rebellion against those decades-old credos, the message we’re now getting seems to be “Fat is where it’s at!” and you can eat it to your heart’s content without repercussions. But before you open the olive-oil floodgates, be mindful that while eating some fat certainly is encouraged as part of an overall healthy eating plan, these studies don’t grant anyone an all-access pass. Once you eat enough fat to meet what your body needs for functions like metabolism, Babb notes, it is not as if extra calories from fat will simply vanish. “Eating an excess of calories in any form—be it from fat, protein or carbohydrate—will result in weight gain.” And at 9 calories per gram compared with 4 calories in the same amount of carbs and protein, it’s not hard to see how easy it can be to go overboard on calorie-dense fat, be it from almond butter or trendy nut-covered smoothie bowls.
Bottom line: Breaking from earlier editions, Dietary Guidelines for Americans 2015–2020 makes no recommendation about total fat intake. But as a rule of thumb, Babb says, people should aim to get 20%–30% of their daily calories from fat, which should be enough to dull hunger without overdoing it. So, if you eat 2,000 calories per day, shoot for 50–65 grams or so of fat. And if a few extra handfuls of nuts or spoonfuls of full-fat yogurt are causing the scale to nudge upward, it might be time to reconsider the number of fatty calories you’re consuming.
The Myth: Fat-Free Or Low-Fat Is Healthier
The reality: The low-fat craze led to the formulation of thousands of lower-
fat products, from yogurts to cookies, that still have a major presence on store shelves. “But when the fat is reduced or removed from a food, you lose much of its flavor,” explains Babb. “So to make up for the flavor shortage, manufacturers often add sugar, artificial flavors and salt, which is hardly a nutritional upgrade.”
For instance, the calorie savings in reduced-fat peanut butter is negligible owing to its higher sugar numbers. When you opt for fat-free salad dressings, you won’t fully absorb the fat-soluble antioxidants—like lycopene and beta-carotene—that are found in vegetables. Fat-free yogurt tends to have more tang than those containing fat, making it more tempting to reach for sweetened versions. In fact, people who gravitate toward full-fat dairy products like yogurt and cheese may have lower rates of diabetes according to those who prefer low-fat versions, per an American Journal of Clinical Nutrition study (Ericson et al. 2015). We may need some fat to go along with the calcium, vitamin D and other nutrients in dairy to reap the full rewards. “New evidence suggests that emulsifiers used in some processed low-fat foods may disrupt our microbiome in a way that can impact our health and weight loss efforts,” adds Babb.
Bottom line: As long as you are mindful of portions, Babb says, there is no reason you can’t enjoy foods that are closer to their natural, full-fat state.
The Myth: Coconut Oil Is A “Superfood”
The reality: Often demonized for its super-high saturated fat content (91% of calories), coconut oil has experienced such a renaissance that according to a joint survey by The New York Times and the polling firm Morning Consult, 72% of Americans now consider the solid, white fat to be healthy (Quealy & Sanger-Katz 2016). But when you separate the science from the sales pitch, coconut oil is not nearly the health-boosting, fat-fighting miracle that its fans want it to be.
“There’s no strong evidence directly tying coconut oil to either a greater or reduced risk of cardiovascular disease,” says Patrick Wilson, RD, PhD, assistant professor of exercise sciences at Old Dominion University in Norfolk, Virginia. He explains that while studies show coconut oil intake raises levels of total cholesterol and LDL (“bad”) cholesterol, some of these studies found that HDL (“good”) cholesterol also increases, so overall cholesterol numbers may not worsen or improve. “Combined with information from epidemiological studies, this suggests that coconut oil, at most, has a small impact on heart health on its own.” Notably, officials at the American Heart Association still say we should steer clear of coconut oil, citing concerns about its potential impact on cardiovascular health (Sacks et al. 2017).
In addition, coconut oil is touted as a weight loss marvel owing to its medium-chain triglycerides (MCTs). The human body handles MCTs differently from other fats and prefers to burn them for energy rather than store them (St-Onge et al. 2003a; St-Onge et al. 2003b). But coconut oil contains rather modest amounts of MCTs compared with the amounts used in most studies showing fat-loss benefits, so research has been widely misinterpreted.
“If you simply add generous amounts of coconut oil to your diet without cutting calories elsewhere, you’re likely to gain weight—not lose it,” cautions Wilson. “With that said, replacing other oils and fats in your diet with coconut oil may lead to small reductions in bodyweight of 1–2 pounds over a few months, but that is not a game-changer for most people.”
Bottom line: It’s likely that coconut oil is neither a heart surgeon’s worst nightmare nor a magical panacea (Eyres et al. 2016). If you like its flavor or the moistness it adds to baked goods, it’s probably fine to include modest amounts (no more than a tablespoon daily) as part of an overall healthy eating plan.
The Myth: Fat Is The Best Fuel
The reality: A growing group of athletes has been pursuing and proudly trumpeting the fat-adapted approach to athletic success. In short, fat adaptation involves eating severely restricted amounts of carbs (as little as 10% of calories) in conjunction with a complementary increase in fat (up to 75% of calories) to induce a physiological shift where a body in motion is more efficient at burning fat during exercise to help “banish the bonk.” The fat-first ketogenic diet is at the forefront of this movement.
Advocates say this provides a bigger reserve of energy to push through long training bouts, whereas loading up on pasta, pancakes and bagels before big races—a common high-carb fueling strategy of many athletes—inhibits fat utilization and can lead to premature fatigue and brain fog. A 2016 study in the journal Metabolism found that ultramarathoners and Ironman® distance triathletes who consumed a high-fat diet (70% fat, 10% carbs) for 9–36 months burned fat at much greater rates during a 180-minute run at 64% of VO2max than those who followed a lower-fat diet (25% fat, 59% carbs) (Volek et al. 2016).
But before you trade in gels for guacamole, Wilson says athletic endeavors that demand high-intensity efforts can suffer in this fat-centric approach. “While including loads of fat in your diet will undoubtedly increase the amount of fat you burn during exercise, it also impairs your body’s ability to burn carbohydrates.” That’s a big deal because, as Wilson points out, fewer chemical reactions are required to convert carbs to a usable form of energy (ATP) than are needed for fat, making carbohydrate a much more efficient energy source when you need to switch to a higher gear. “It doesn’t matter how good you are at using fat as a fuel source; if you’re performing lots of repeated high-intensity work, your body wants to be heavily reliant on carbs.”
In a recent review of 61 studies, the vast majority showed that diets relying on more calories from carbs than from fats were optimal for athletic performance (Stellingwerff & Cox 2014). None found that carb-rich diets hurt performance. In contrast, most of the research to date shows that shunning carbs in favor of fat is not likely to get you to the finish line faster (Burke et al. 2017; Havemann et al. 2006; Urbain et al. 2017; Zinn et al. 2017). Wilson points out that a low-carb, high-fat diet may improve performance if it helps an overweight athlete to lose weight. “But that’s not a unique benefit of low-carb diets. Any diet that leads to weight loss could substantially influence performance under the right circumstances.”
What’s more, very-low-carb diets can take weeks to adapt to, and in the meantime, people often experience a host of unwelcome side effects, ranging from fatigue and constipation to mood swings that can affect training.
Bottom line: If a sport of choice involves long periods of low- to medium-intensity exercise like ultrarunning and mountaineering, Wilson says reducing dependence on carbs by being fat-adapted may work for some, but for those who need to push all-out—as many athletes must at some point—it’s best not to banish carbs from the dining table.
The Myth: Saturated Fat Is Off The Hook
The reality: For years we’ve heard that eating saturated fat is like pouring superglue into our arteries. That made crispy bacon, cheese-laden pizza and frosty ice cream universally considered bad news for our health. So when the media picked up on recent research questioning the role that the oft-maligned fat plays in heart health and hailed that “butter is back,” some people used it as a license to welcome lard back into their kitchen (De Souza et al. 2015; Malhortra, Redberg & Meier 2017; Pimpin et al. 2016). Not so fast.
“Lack of harm is not the same thing as being good for you,” says David Katz, MD, MPH, director of the Yale University Prevention Research Center and founder of True Health Initiative. “All these studies show is that there is more than one way to eat badly. While high intakes of saturated fat can be a marker of a poor overall diet, when saturated fat calories are supplanted by refined carbs or added sugars, things are equally detrimental.” Katz says these studies shouldn’t be construed to suggest that raising saturated fat intake does not raise the risk for heart disease. “Getting your fill of saturated fat from the usual sources like pizza and cheeseburgers is still not a wise move.”
Indeed, there is still solid evidence that saturated fat is not an innocent bystander (Sacks et al. 2017). A rigorous review of randomized controlled studies (considered the gold standard of nutrition research) published in the Cochrane Database concluded that a reduction in saturated fat intake does result in a drop in cardiovascular disease risk, and replacing this type of fat with polyunsaturated fats like those in walnuts, flax and fatty fish is heart protective (Hooper et al. 2015). Further, Harvard researchers found that among nearly 130,000 people, those who ate more unsaturated fat (mono and poly) instead of saturated fat had a lower risk for heart conditions (Li et al. 2015). But when people cut saturated fat from their diet and replaced it with refined carbohydrates, any benefits were canceled out.
Complicating matters further is that not all saturated fats are created equal. Katz says that certain saturated fats like stearic acid in chocolate and lauric acid in coconut oil might be more innocuous than types found in foods like beef and dairy. “Still, that doesn’t mean they are beneficial for you in the way that unsaturated fats found in nuts, seeds, avocado and olive oil have proven to be.” And, importantly, people eat foods, not isolated fatty acids. So certain compounds in items like fermented cheese and yogurt may lessen the negative impacts of their saturated fat.
Bottom line: Despite the viral news headlines, no one should think that eating loads of saturated fat is healthy. For the record, the Dietary Guidelines for Americans 2015–2020 advises limiting saturated fat to less than 10% of total daily calories. Most experts—including Katz—still recommend focusing your fat-eating efforts on the unsaturated variety, as modeled in the tried-and-true Mediterranean diet. But as long as your diet is dominated by whole foods, an occasional taste of bacon, cheesecake and yes, even butter, won’t do much harm.
The Myth: High-Fat Is Healthier Than High-Carb
The reality: If you take a recent study published in The Lancet at face value, you might think that trading in beans for bacon will help you enjoy more birthdays. After analyzing the dietary data of 135,335 individuals from 18 countries, higher carb intake was associated with an increased risk of total mortality, whereas total fat intake was not found to raise death risk (Dehghan et al. 2017). But context is key: The typical American diet is roughly 49% carbs, 34% fat and 16% protein, so it cannot be considered especially high in carbs or low in fat. In turn, we shouldn’t use research like this as permission to greatly fatten up our diets.
But that’s beside the point: Katz feels strongly that we need to stop paying attention to such studies, as they do the public a major disservice. “Depending on the foods you choose, you can eat a low-fat, high-carb diet full of jelly beans and soda that’s terribly unhealthy and raises your disease risk, or you can eat a high-fat diet rich in fried foods that does the same.” So if the diets in the aforementioned study were skewed toward higher intakes of processed carbs like white bread and white rice and higher intakes of beneficial fats like olive oil and nuts, it’s not surprising fat came out on top.
“It’s time to stop obsessing about macronutrient numbers and instead look at the actual foods we are eating,” says Katz. “The longest-living populations on the planet vary widely in their intakes of total carbs and fat, but what doesn’t vary is their focus on wholesome foods.”
Bottom line: People should look past simplified recommendations (i.e., reduce carbohydrates and increase fat) and instead look at their diets in the context of what they are eating overall. In other words, choose mostly healthful foods and the healthful fats and healthful carbs will take care of themselves in whatever percentages suit a person’s tastes.
The Myth: Vegetable Oil Is A Killer
The reality: If you believe the internet hype, you should approach soybean, corn, sunflower and other vegetable oils as if they are sprayed with cyanide. Apart from GMO concerns, their abundance of omega-6 fats is blamed for firing up inflammation in the body and setting the stage for poor health. But as so often is the case with the science of fat, things are much more nuanced.
Omega-6 fat is not inherently unhealthy. The omega-6 fat linoleic acid is deemed essential because we must obtain it from our diets, so including some foods rich in omega-6 (e.g., grapeseed oil or sesame seeds) helps us get what we need. But Katz says the problem is that the typical modern diet—thanks largely to the prevalence of processed package and restaurant foods, which are often made with cheap vegetable oils—contains much higher amounts of omega-6 fats compared with omega-3s. The ratio has increased from perhaps 1:1 during evolutionary times to upward of 20:1 today (Simopoulos 2016).
“This skewed balance can interfere with omega-3 metabolism, leading to health problems, including autoimmune diseases,” says Katz. It may also be contributing to our obesity crisis (Simopoulos 2016). So instead of simply demonizing omega-6 fat, Katz says, we need to pay more attention to increasing our omega-3 fat intake. Omega-3s can come from plant foods like walnuts, flax, chia, hemp seeds and canola oil or from fatty fish such as salmon, sardines and mackerel. Grass-fed beef and dairy provide small amounts as well.
Bottom line: People should fret less about adding some vegetable oil to their frying pan and instead focus efforts on getting back in omega balance by reining in consumption of processed foods rich in omega-6 while simultaneously eating more fare rich in omega-3.
After 2018, you can say goodbye to margarines and packaged snack foods (at least as you remember them). In response to overwhelming evidence linking trans fat intake to heart disease—along with resulting pressure from health organizations—the FDA has taken measures to remove manmade trans fat from the food supply, which is usually found in the form of partially hydrogenated oil, citing that it’s “no longer generally recognized as safe.” But that doesn’t mean all trans fats will go away. They also occur naturally in small amounts in certain meat and dairy products. The jury is still out on whether natural trans fat is anywhere near as harmful as the kind made in a lab.
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