The reasons low-fat diets disappeared

By Howard LeWine, M.D.

Q: Why for so many years was a lowfat diet the craze and now it seems to be gone?

A: For decades, the message was loud and clear: High intake of fat causes weight gain, heart disease and maybe even cancer. The solution? Go low-fat.

Unfortunately, that often meant consuming more carbs and more sugar, and the advice turned out to be misguided.

Nutritionists now suggest people actually need adequate amounts of fat for optimal health — but only the right kind. Good fat gives your body energy and helps your body absorb vital nutrients.

There are two main kinds of fat: saturated and unsaturated. Saturated fat is in animal products like beef and pork, and dairy products like butter, cream and cheese.

Saturated fat is also a staple in most fast, snack and processed foods, such as pizza, dairy desserts, bacon and cookies. If it’s considered junk food, odds are it contains saturated fat.

Unsaturated fat comes in two categories: monounsaturated and polyunsaturated. Monounsaturated fats are found in avocados, peanuts, peanut butter and nuts like almonds, hazelnuts, cashews, pistachios and pecans. High amounts are also in oils, such as olive, peanut, safflower, sunflower and canola oil.

Polyunsaturated fats include omega-6 fatty acids and omega-3 fatty acids. They are also considered “essential” fats because your body can’t make them, and you have to get them from food.

Omega-6s are in oils like soybean, corn, sesame and canola. They’re also abundant in walnuts, peanuts and pumpkin seeds. Omega-3s are in canola oil, soybean oil and walnuts, as well as in fatty fish like salmon, mackerel, herring, tuna and trout.

Good fats, bad fats

How does fat help — and hurt — your health? Too much saturated fat can raise “bad” LDL cholesterol levels. High blood LDL can lead to plaque buildup in arteries throughout the body, which increases the risk of heart attacks and strokes, and also erectile dysfunction and poor leg circulation.

If you cut out saturated fat in your diet, you can lower your risk for all these problems.

In comparison, consuming monounsaturated and polyunsaturated fats helps lower blood pressure and reduce chronic inflammation, which translates to lower cardiovascular risk.

Another benefit of switching fats is that it might help keep your brain healthy. Observational studies suggest that following the MIND diet is linked to a lower risk of memory loss and cognitive decline.

This research-based diet — the name stands for Mediterranean-DASH Intervention for Neurodegenerative Delay — advocates eating more of certain foods that are high in unsaturated fat, like nuts, fatty fish and olive oil.

The diet also stresses cutting down on foods that contain high amounts of saturat- ed fat, such as butter, red meat, pastries, and fried and fast foods.

Howard LeWine, M.D., is an internist at Brigham and Women’s Hospital in Boston and assistant professor at Harvard Medical School. For additional consumer health information, visit health.harvard.edu.

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