Are High-Fat Diets As Healthy As They're Cracked Up to Be?
Experts say fat isn't the "superfood" that diets like keto will have you believe.
Celebrities like Kourtney Kardashian, Halle Berry, and Vanessa Hudgens have all touted a high-fat diet as their secret to losing weight and staying fit, all without feeling hungry or deprived. In fact, many of the most popular diets of the past decade included high amounts of fat: the ketogenic diet, Paleo, the Mediterannean diet, the carnivore diet, and the Bulletproof diet.
But it wasn’t too long ago that fat had a bad rap. During the low-fat craze of the '80s and '90s, people looking to lose weight and improve their health opted for a low-fat diet. Then, the pendulum swung the other way. Now, low-carb, high-fat diets are trending for weight loss and better overall health.
That’s probably partially because we’ve learned a lot about fat since the days of low-fat-everything. “Back then, many thought eating fat equaled more body fat,” explains Amanda Baker Lemein, R.D. “Now, we understand that simply is not true.” Instead, we know that if you eat more calories than you burn, you gain weight. And this can happen from overeating any macronutrient — protein, carbs, or fat — not just one alone.
But even if fat isn’t bad for you, does it deserve its current “super nutrient” status? And is it even healthy to eat a high-fat diet long-term? Here, nutrition pros share everything you need to know.
You need fats in your diet to be healthy.
“Fat is the most energy-dense nutrient, containing 9 calories per gram compared to the 4 calories per gram found in carbohydrates or protein,” explains Gabrielle Fundaro, Ph.D., a consultant for Renaissance Periodization. Fat is an essential nutrient, Fundaro says, meaning you have to eat some of it.
While a low-fat diet can be healthy, not getting enough fat in your diet can cause health issues. “Consuming too little fat can result in dry skin, decreased energy or satiety levels in between meals, decreased vitamin absorption for vitamins A, D, E and K, increased risk for depression and other mental or cognitive issues, and hormonal imbalances,” Lindsay says.
So how much fat should you be eating? “Healthy adults should aim to consume between 20 to 35% of their calories from dietary fats,” says Victoria Lindsay, R.D. (So if you’re eating 1,800 calories per day, that would mean eating between 40 and 70 grams of fat.) Of course, those are just general recommendations. How much fat you should eat is really an individual thing, Linsday emphasizes. And if you’re on a true ketogenic diet, your fat intake could be at upwards of 70 percent of your total calories.
In a lot of ways, nutrition experts are enthusiastic about fat’s rise from its previous nutrient non grata status. “I think it is a great thing that we are no longer afraid of fat,” Lemein says. “Fat is incredibly satiating, and because it delays gastric emptying (aka food leaving the stomach), it helps us stay fuller for longer.” Plus, some of the most-nutrient rich foods are high in fat, like avocado, nuts, seeds, and fatty fish like salmon.
But fat isn’t a “superfood.”
With fat bombs, Bulletproof coffee, and other high-fat snacks all over social media, it’s understandable that people get the impression that fat is “better” than other nutrients, or that certain types of fats are “superfoods.”
The truth? “There are no ‘superfoods,’ though there are some foods that are more nutrient-dense than others,” Dr. Fundaro says. There’s some emerging research showing that certain, very specific types of fat might be beneficial (think: MCT oil). But Dr. Fundaro emphasizes that just because something shows potential benefits in a research setting doesn’t mean it’s worth trying as an expensive supplement.
“I find this to be unfortunate, because people may spend time, money, and energy on these ‘biohacks’ that only add extra (and perhaps unneeded) energy to the diet by way of adding fat to their daily intake,” Dr. Fundaro notes. In other words: Eating naturally-occurring fats in whole foods that you enjoy? Great. Adding fat to your diet in the form of supplements or eating high-fat foods you wouldn’t normally eat? Totally unnecessary. Especially if you just end up eating unnecessary calories you’re not enjoying in the name of “health.”
Plus, the pendulum effect is real. “While I’m glad that fat is no longer being vilified, it’s a tradeoff, as carbs are now the trendy nutrient to avoid,” Lindsay points out. But eating carbs is actually better for your health long-term than not eating them.
“It seems as though the pendulum has swung a bit too far in the opposite direction,” Lindsay adds. While keto can be a healthy way to eat, it does carry some worrying side-effects — just like any extreme diet.
What’s more, we don’t know much about the long-term effects of a super high-fat diet. While diets like keto can result in weight loss, it’s usually due to an overall calorie restriction rather than abstinence from or addition of certain foods. “But people don’t see that: all they see is results,” Linsday says. “What they don’t see is one or two years down the road when the person experiencing the dramatic weight loss has gained all if not more of it back. Nor do they see some of the long-term effects of eating in such a restrictive way, mainly because we often don’t know what those are yet. For some diets and eating patterns, only time will tell.”
And not all fats are created equal.
Whether you eat high-fat, low-fat, or somewhere in between, it’s important to know that the types of fat you eat matter. Some types are associated with better health, while others are not.
Saturated fat isn’t inherently unhealthy, but high intakes are associated with increased risk of cardiovascular disease, Dr. Fundaro says. “Animal fats (with the exception of fish oils) are common sources of saturated fats. Coconut oil is high in saturated fat, as well. Replacing saturated fat with polyunsaturated fat may reduce the risk of cardiovascular disease.” There’s some debate over whether saturated fat really is detrimental to health or not, but for now, it’s recommended that saturated fat make up no more than 10% of your daily calories.
“Monounsaturated is a beneficial fat that is associated with improved cardiovascular health,” says Allison Knott, MS, RDN, CSSD.” It’s found in vegetable oils (like olive and canola oil) and other common foods like peanuts, avocado, and various nuts and seeds.
These are generally found in plant foods and fish, and there are several different types. The most notable are:
- Omega-3 fats: These are probably the most buzzed-about “healthy fat.” There are two kinds of omega-3 fatty acids in fish: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA),” Lindsay explains. “The form of omega-3 in plants is called alpha-linolenic (ALA).” Ideally, you want to get all three in your diet. “Good sources of omega-3 fats include fatty fish like salmon or mackerel and some nuts and seeds like flax seeds and walnuts.”
- Omega-6 fats: These are found in leafy green vegetables, nuts, seeds, and vegetable oils like sunflower oil, safflower oil, canola oil, and soybean oil. “While omega-6 fats were once vilified as it was worried that excessive amounts could lead to inflammation and chronic disease, recent studies have shown that omega-6 fats may actually have a heart protective effect,” Linsday explains. That’s why the most recent nutrition guidelines call for consuming unsaturated fats (including omega-6s) in place of saturated fats. An expert’s advice? “Prioritize omega-3 fats, and consume — but not excessively — nutrient dense foods high in omega-6 fats to ensure the right balance.”
You probably know that these are the fats you want to stay away from, as even small amounts can increase your risk of cardiovascular disease, Linsday says. “Thankfully, artificial trans fats are being phased out by food manufacturers. They usually come in the form of partially hydrogenated oils in fast food or pre-packaged snack and convenience foods. Trans fats are also naturally found in beef fat and dairy fat in very small amounts.”
How to decide how much fat to include in your diet:
When figuring out how much fat you should include in your diet, it can be helpful to know that based on the latest research, low-carb and low-fat diets perform equally in terms of weight loss and improving metabolic health. So how do you choose a fat intake that makes sense for you?
Do what you can stick with.
“The most healthful diets include a variety of foods that an individual enjoys in amounts that promote health and well-being,” Dr. Fundaro says. The Mediterranean Diet, DASH Diet, and Flexitarian diets are all often rated as the “best” diets by U.S. News and World Report, she points out. None of them are particularly low in carbohydrates or fat, nor do they recommend cutting out any food groups. “They are simply easy to follow, nutrient-dense, appropriate to use for weight loss (within a caloric deficit), and generally cardioprotective,” she adds.
On the other hand, low-fat and low-carb diets can be really hard to follow, which means lasting weight loss is not likely — if that’s your goal. For that reason, it’s best to choose a diet that you can envision yourself continuing with long-term. Even if you’re not concerned with your weight, Dr. Fundaro says getting a healthy variety in your diet is key. That means eating a wide array of plants (veggies, fruits, and whole grains) while limiting processed foods, saturated fats, trans fats, added sugars, and sodium.
Choose low-fat foods for the right reasons, if at all.
Despite the popularity of high-fat diets, low-fat foods are still widely available in grocery stores. Whether or not you should choose them, Lindsay says, is mostly up to personal preference. “I know plenty of people who, for example, prefer 2% or skim milk in their cereal versus whole milk, and I’d never disapprove of that choice if that’s what they like.” Some people are also advised by their doctor to use low-fat products because of a health condition, such as heart disease.
“The issue for me is when people choose low-fat foods because they’re too afraid to choose the full-fat counterpart for fear of eating too many calories or eating something they feel might be too ‘unhealthy,’” Lindsay explains. This may indicate an issue like orthorexia, or another non-sustainable eating pattern.
Lindsay also recommends avoiding processed low-fat snack foods like crackers, chips, and cookies. “The problem with these products is that as a substitute for fat, manufacturers will usually compensate with added salt and/or sugar, not to mention that the taste is usually inferior to the full-fat version anyway.” If you want to have one of these foods, in most cases, you might as well go for the real thing.
Keep things balanced.
At the end of the day, it’s about finding balance in your day-to-day food choices — and in your overall approach to eating.
For example, if someone is consuming a breakfast that includes nuts (aka another fat source), maybe a low-fat yogurt is the right choice for them to balance out their overall intake, Lemein says. But, if they are just eating fruit and yogurt, the extra fat might add some staying power to the meal and help keep them fuller for longer, she adds.
“As a dietitian, what I’d love to see is this: balance,” Lindsay says. The most nutritious diets are diverse. “Have your carbs, have your protein, and yes, have your fat, but keep it balanced by eating a variety of foods.”