Few arguments have flip-flopped over the years as much as the one around dietary fat. Back in the ’80s, fat was vilified — experts everywhere warned that eating fat was going to give us all high cholesterol and heart attacks. Soon, store shelves filled with foods labeled “fat-free” and “low-fat.”
Fast-forward a couple of decades, and along with major increases in rates of obesity and heart disease in America came a new dietary enemy: Carbohydrates. Fat-filled bacon, beef, and butter were back on the menu, this time as the unlikely heroes of weight loss.
But more backlash against fat soon followed as experts drilled into different types of fat, and targeted the risks of saturated fat content, not to mention its calorie load. On the flip side, olive oil and salmon — which contain healthy fats like monounsaturated fats and omega-3 fatty acids — soon became the dietary fat darlings that were going to save us all.
More recently, coconut oil and its fatty acids, called medium chain triglycerides, entered the scene. Touted as a health food, it quickly became the oil du jour.
And now? Another kerfuffle after a public health professor from a prominent University claimed coconut oil is “pure poison” because of its high levels of saturated fat. No wonder so many of us are confused about whether fat is good or bad for you, which sources are best, and exactly how much we should be eating.
“There’s a problem of reductionist science here — looking at one facet of the problem instead of the big picture,” says Bill Rawls, M.D., medical director of Vital Plan. “People also tend to go crazy with things, so if they hear, for example, that coconut oil doesn’t raise cholesterol or has a certain benefit, suddenly they want to eat a ton of it.”
Here are some big-picture, simple facts that will help clear up the confusion around fat, plus practical advice to help you eat well and stay healthy.
1. You need fat in your diet — just don’t overdo it.
Fat not only adds flavor to meals, it digests slowly, which helps keep blood sugar levels steady, bellies full longer, and cravings in check. Your cells also need fat since it’s what makes up cell membranes, among other important functions, and your body can use fat for energy.
“Fat is good for a slow, steady burn,” Dr. Rawls says. “It’s really refined sugar and processed carbs that are killing people.” That said, replacing all sugar and grains with fatty foods isn’t the answer. Instead, eating more fruit and vegetables as you cut carbs is a smarter bet, along with consuming moderately more fat plus lean protein (fish, chicken) and whole grains (brown rice, quinoa). Up to 35% of your diet can be fat — 77 grams if you eat 2,000 calories a day, according to the World Health Organization and U.S. government recommendations.
Unfortunately, in reality, when most people cut back on carbs, they eat a lot more fat, and typically in the form of meat and cheese, Dr. Rawls says. Because fat contains 9 calories per gram (compared to the 4 calories per gram of carbohydrate or protein), and because most adults don’t get enough physical activity, it can lead to weight gain, he explains. Those extra pounds then up your risk of heart disease, diabetes, and other health problems.
In fact, people who eat the most meat take in about 700 more calories per day than those who eat the least, and they have a higher risk of obesity, according to a study in the International Journal of Obesity. Iranian researchers who analyzed studies involving a total of more than 1 million subjects also found a direct link between processed and red meat intake and obesity and belly fat, the most dangerous type, reports a separate paper in Obesity Reviews.
The saturated fat in meat and full-fat dairy may be part of the problem (more on that, below). But another factor is that processed and red meat provide relatively few nutrients compared to high-fat plant foods like avocado, nuts, and olive oil. Plant-based fat sources deliver loads of beneficial phytochemicals, fiber, vitamins, and more that not only help keep you healthy, but may also play a role in regulating weight and appetite.
For example, overweight and obese men whose dietary fat came mostly from nuts, avocados, and olive oil lost weight and body fat without making any other changes to their diet, while those who ate foods rich in saturated fat gained weight, according to a study in BMJ. Likewise, women going through a three-month weight loss program who ate 1.7 ounces of almonds a day (a good source of healthy monounsaturated fats) lost more weight and inches than those who followed the same program but didn’t eat the nuts, reports a study in the Journal of Research in Medical Sciences.
2. The fat in olive oil, nuts, avocado, and fish are the healthiest.
There are three main types of dietary fat in food, and, along with your weight, the type of fat you predominately consume impacts other aspects of your health — namely your blood and cell membranes, the dynamic gatekeeper that affects everything coming and going from a cell, Dr. Rawls says. Here’s a rundown of the fats and their effects:
- Monounsaturated fat: Plentiful in olives and olive oil, avocados, and nuts like almonds and peanuts, monounsaturated fat is liquid at room temperature. And thanks to the molecule’s one double bond (the reason it’s called mono), monounsaturated fat is relatively resistant to free-radical damage, Dr. Rawls says. That’s an ideal combo for cell membranes: flexible and fluid but also able to stand up to attack. Research suggests that consuming more olive oil versus sources of saturated fat is linked to lower risk of heart problems, Alzheimer’s, diabetes, cancer, and more.
- Polyunsaturated fats: These fat molecules have multiple double bonds (thus the prefix poly), which make them liquid at room temperature like monounsaturated fats, but also more susceptible to damage from free radicals, Dr. Rawls says. Omega-3 fatty acids and omega-6 fatty acids are two types of polyunsaturated fat that are essential for cell growth, brain function, and immunity. Omega-3 fatty acids are plentiful in salmon, sardines, flax, and walnuts; omega-6 fatty acids are found in corn and soybean oils, plus poultry, eggs, and grains.
“Your body uses omegas to create prostaglandins, chemical messengers that are involved in immune response,” Dr. Rawls says. Omega-6s are pro-inflammatory, while omega-3s are anti-inflammatory — so they balance each other to help ensure a normal and healthy immune response.
The problem is, most people consume too few omega-3s and way too many omega-6s, thanks to the modern American diet that’s heavy in grains and highly processed vegetable oils (found in fried and packaged foods), and low in fish. The result: excess inflammation. That’s a convincing reason to up your intake of omega-3s, either in your diet or by supplementing with krill oil or fish oil.
- Saturated fat: Found in red meat, butter, full-fat dairy, and coconut and palm oils, saturated fat is solid at room temperature and stands up well to heat and free-radical damage. A little can be good for cell membranes, helping to keep them strong, Dr. Rawls says. But too much may make membranes overly stiff like lard and keep them from functioning optimally, he says.
“Dumping a lot of saturated fat into your system also makes blood really thick, which can increase friction in blood vessels,” Dr. Rawls says. So while saturated fat may not raise your LDL “bad” cholesterol (too much sugar does that), eating a lot, even in the form of coconut oil, isn’t a good idea, he says. A general guideline: Only cook with coconut oil when it makes sense for flavor. Nutritional guidelines also suggest limiting saturated fat to less than 10% of your daily calories.
3. Trans fats and fatty fried foods are truly toxic.
There is a fourth type of fat called trans fats. These partially hydrogenated oils start as unsaturated oils, which food manufacturers then tweak so they’re solid at room temperature. That extends shelf life, which is why they’ve historically been used widely in packaged breads and pastries.
But research eventually revealed their dangerous dark side: For one, trans fats increase both LDL “bad” cholesterol and lower HDL “good” cholesterol. A research review published in the journal BMJ involving data from more than 200,000 participants found that eating foods with trans fats is associated with coronary heart disease and all-cause mortality. Trans fats also enter brain cell membranes, changing the ability of the neurons to communicate; that could play a role in Alzheimer’s disease and cognitive decline, reports a paper in Slovakia’s Bratislava Medical Journal.
Thankfully, the FDA banned trans fats, and as of this past summer, food companies can no longer put partially hydrogenated oils in products. But the rules did allow time for food already on shelves to cycle out, so some may still lurk in stores.
Fried foods aren’t much better than trans fats, especially if you eat out, where they’re typically soaked in oils high in pro-inflammatory omega-6s, says Dr. Rawls. “Cooking with such extreme, high heat also damages the fat and creates free radicals,” he says. “Putting that into your body installs the fat and free radicals into cell membranes, which triggers a chain reaction that messes with your health.” (Fry oil at restaurants, which is often reheated multiple times, is more degraded and more readily absorbed by food, making it riskier.)
A review of research in the journal Nutrients found strong evidence that consuming fried foods four or more times per week increases risk of developing chronic disease. Those who eat fried foods seven or more times a week had a 55% jump in the risk of developing diabetes and heart disease, according to a separate study in the American Journal of Clinical Nutrition.
4. A few simple tricks can make fat even healthier.
As with so many things in life, the old adage “everything in moderation” rings true with dietary fat. These simple guidelines can help you enjoy your fat and reap the benefits, too.
- Always choose cold-pressed, extra virgin oils: Olive oil is the perfect go-to for cooking and dressing salads thanks to its phytonutrients and monounsaturated fat, but use other oils for flavor only as needed. When possible, choose oils whose labels include the terms cold-pressed and extra virgin, which have the highest levels of antioxidants and other phytonutrients, as well as better flavor.
- Use low heat when cooking: Whether sautéing vegetables or cooking meat, be sure to use low heat to avoid altering or degrading the fat and generating free radicals, Dr. Rawls says.
- Choose grass-fed beef and omega-3, organic eggs: These options are the healthiest when you do consume animal sources of saturated fat, as they contain higher levels of healthy omega-3 fatty acids.
- Opt for wild salmon: Compared to farmed, wild salmon tends to be lower in contaminants; sardines, however, are even lower.
- Check ingredients lists on nut butters: Whether you like almond butter, peanut butter, or another nut butter, choose one whose ingredients list only nuts and possibly salt. Many brands contain palm oil, a saturated fat, to prevent the separation of oils from the nut solids, as well as sugar or another sweetener such as agave or cane syrup.
One final bit of advice: When you do eat fat, let go of the guilt and enjoy it! Sharing the occasional cheese plate or spooning up a scoop of ice cream are part of what makes life so sweet.
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