My mom told me that avocados are full of fat, and I know fat makes you gain weight. Should I skip the guac this semester?

Don’t fear fat. Your mom’s fat-free diet obsession is simply a continuation of the “low-fat” craze of the 1980s.

Fat-free diet foods may actually be less healthful in the long run, according to Katherine Hall, a registered dietitian with Optimal RD and a certified LEAP therapist. 

“When food companies take the fat out of products, they often add in more sugar, preservatives and chemicals to make the food product stable,” Hall said. “My recommendation to clients is to enjoy the product for what it is — in its whole form. So if you are going to eat a piece of chocolate, to enjoy the chocolate in moderation and not binge on something low-fat, fat-free, or reduced sugar.”

Fats have a bad rap because of their caloric density. Carbohydrates and proteins contain four calories per gram, whereas fats have nine, meaning foods with a higher percentage of fat will have a higher calorie count, which scares dieters and the health conscious.

Despite its high calorie content, fat is crucial to your health. Fats absorb vitamins, build hormones and keep your brain and nervous system functioning properly, according to the American Heart Association. The 2015–2020 Dietary Guidelines state that your diet should be 20–35 percent fat.  

But not all fats are created equally. Before you order a side of fries,or slather more butter on your pancakes, you should know that there are different types of dietary fat. 

Unsaturated fats are the good fats. These are found in avocados, nuts, fish and plant-based oils. Their molecular chains bend, which keeps them from stacking on top of each other. Since they don’t easily fit together, most unsaturated fats are liquid at room temperature.

When you eat them in moderation, unsaturated fats can lower cholesterol levels, reduce inflammation and decrease heart disease risk, according to the Harvard School of Public Health. You can find a food’s unsaturated fat content on its nutrition label. 

Saturated fats are made up of tightly packed molecules that have no gaps in between them. Hall said saturated fats are rigid and solid at room temperature.

“Typically, I think of animal fats, like the marbling in steaks, butter and cream,” she said. 

Saturated fats raise cholesterol levels, and high consumption can increase the risk of heart disease, according to the American Heart Association. To reduce saturated fat intake, Hall suggests that her clients consume lean meats like turkey, chicken and fish. She also encourages them to buy cuts of meat that include the words “loin” and “roast,” as these are lower in saturated fat.

Last, and most definitely least, are trans fats. Manufacturers synthetically produce trans fats by altering the chemical structure of vegetable oils. Industries remove the natural molecular branching of vegetable oils by adding hydrogen atoms. This straightens out the molecules and causes them to tightly stack together instead. The change in structure dramatically modifies the way these substances behave. 

Food items containing trans fat last longer and taste better — think fast foods, baked goods, heavily processed snacks and stick margarines. Your body also metabolizes these fats differently. The FDA encourages individuals to keep trans fat intake as low as possible, as consumption can raise cholesterol levels and increase the risk of heart disease. If that isn’t scary enough, a 2 percent increase in trans fat calories is associated with a 23 percent increase in heart disease, according to a meta-analysis published in The New England Journal of Medicine.

You can check nutrition labels for trans fat content. However, food companies are allowed to say their product is trans fat free as long as there is less than 0.5 grams of trans fat present. As a backup, check the ingredients for “partially hydrogenated oil.” If this is listed in the ingredients panel, ring the alarms — the food probably contains trans fat.

To combat bad fats in a world of processed foods, Hall suggests incorporating meatless Mondays into your week. Plants don’t have saturated fats but can still provide a lot of protein. 

Hall also stresses the importance of food preparation methods. By baking, broiling or steaming foods instead of frying, you can dramatically decrease the saturated fat content.

So don’t fend off fats completely, just choose the right kinds. Forgo the potato chips for a handful of walnuts. Dress your sandwich with two to three thin avocado slices instead of mayo. Order a grilled chicken sandwich in lieu of a cheeseburger. And those fat-free packaged snacks? Leave those in the ’80s with side ponytails and shoulder pads.