I’ve long been an advocate of eating more “good fat.” But many of my clients are confused about exactly what constitutes good fat these days, especially with headlines like “Butter is Back!” and the resurgence of lard in “healthy” recipe blogs. Now, a new Harvard study published in the Journal of the American Medical Association offers more insight into the healthiest types of fat.

Scientists followed 126,233 adults from two large, long-term studies—the Nurses' Health Study and the Health Professionals Follow-Up Study—for up to 32 years. Every two to four years, participants answered questions regarding their diet, lifestyle, and overall health. At the end of the study, researchers evaluated correlations between the type of fats participants ate and overall death rates.

When compared with eating the same number of calories from carbohydrates, the type of fat consumed made a big difference: a 2% higher intake of trans fat (the type in processed foods) was linked to a 16% percent greater chance of premature death ; and every 5% hike in saturated fat (found in foods like butter and red meat) was associated with an 8% bump in mortality risk.

Conversely, people who had a high intake of unsaturated fats—including both monounsaturated (avocados, nuts, EVOO) and polyunsaturated (fatty fish and sunflower seeds) fats—had an 11-19% lower risk of death.

So, what does all this mean for your daily diet? Below, check out the seven rules of thumb for fat that I share with my clients.

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Include fat in every meal

It's one of the body’s key building blocks. We use dietary fats to make tissue. And certain types are essential for balancing hormones, controlling blood clotting, keeping your brain and arteries healthy, and fighting inflammation. Also, without fat, you wouldn’t be able to absorb certain antioxidants and the fat-soluble vitamins A, D, E and K. Not to mention, fat boosts satiety, so you feel full longer. In fact, for all those reasons, a healthy diet should actually include a higher percentage of calories from fat than from protein.

Sub fat for refined carbs and sugar

One of the best ways to benefit from fat is to use it to displace “bad” carbs. For example, grab a handful of almonds instead of a cookie. Munch on olives instead of refined crackers. And trade half of your usual pasta portion for veggies sautéed in EVOO, garlic, and herbs. Since fats are filling, you should feel just as satisfied (or even more so) when you eat them instead of carb- and sugar-laden foods.

Cut back on saturated animal fats

Recent research on saturated fat has led some people to think butter may be good for you. But that's not exactly what the studies have found. For example, a study from the Journal of the American College of Cardiology found that swapping saturated fat for processed carbs (like white bread and white rice) had zero effect on a person's heart disease risk. While that suggests you aren't any better off eating jelly on your toast instead of butter, it doesn’t necessarily mean butter and other foods high in saturated fat are healthy.

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If you must eat saturated animal fats, choose high quality

Based on all the evidence, I firmly believe it's healthier to have whole grain toast with avocado or almond butter than with dairy butter, and to sauté veggies in EVOO than in butter or lard. However, I do have clients who don’t want to give up certain foods rich in saturated fat. If you feel the same way, look for animal products that are grass-fed and organic. Foods produced this way have been shown to contain healthier types of fats, and higher levels of some nutrients.

Include some plant-based saturated fats

Research shows that saturated fats from plant-based foods, like cocoa butter and coconut oil, don’t act in the same way as saturated fats from animal-based foods. In fact, they may even offer heart-protective benefits. I like to use extra virgin coconut oil in stir-fry meals, baked goods, and smoothies. And I highly recommend making a few squares of dark chocolate (rich in cocoa butter) a daily treat.

Avoid processed fats as much as possible

While trans fats are slowly disappearing from our food supply (check out my previous post about the FDA's ban), it’s still a good idea to be conscious of what's in your food, and limit these processed fats as much as possible. The best strategies are to swap fast food, fried food, and highly processed foods for fresher fare. Plus, when buying any packaged or shelf-stable goods—from salad dressing to frozen food—always read the ingredient list. Good-for-you products should have ingredients that read like a recipe you could make in your own kitchen. They shouldn't have any chemical-sounding words like "hydrogenated" or "interesterified," two terms that signal unhealthy fat.

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Make MUFAs and fatty fish fat staples

On the whole, research suggests that the best fats for health and longevity are monounsaturated fats and omega-3 fatty acids from fish. (Good omega-3 options include salmon, sardines, rainbow trout, mackerel, and tuna.) For a day's worth of healthy fat, start out with a veggie and avocado omelet, or oatmeal with nuts and fruit. For lunch, order an entree salad tossed in EVOO and balsamic vinegar. Snack on nuts, fruit, and a bit of dark chocolate, or veggies with hummus and olives. At dinnertime, oven-roast veggies alongside salmon, or add a generous portion of avocado to black bean and veggie chili.

Each of these meals involves the winning combo of natural fats, lean protein, and plenty of veggies (without processed carbs or added sugar). This kind of meal-building formula is bound to leave you feeling nourished, satisfied, and energized. And you'll be protecting your heart for a long, healthy life.

Do you have a question about nutrition? Chat with us on Twitter by mentioning @goodhealth and @CynthiaSass

Cynthia Sass is a nutritionist and registered dietitian with master’s degrees in both nutrition science and public health. Frequently seen on national TV, she’s Health’s contributing nutrition editor, and privately counsels clients in New York, Los Angeles, and long distance. Cynthia is currently the sports nutrition consultant to the New York Yankees, previously consulted for three other professional sports teams, and is board certified as a specialist in sports dietetics. Sass is a three-time New York Times best-selling author, and her newest book is Slim Down Now: Shed Pounds and Inches with Real Food, Real Fast. Connect with her on FacebookTwitter and Pinterest.