Are salads healthy? Here’s what you should add and avoid.

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Q: How do I know if my salad is actually healthy? Which ingredients should I add to my salads, and which should I avoid?

A: Salad is usually a healthy food, but only if you add the right combination of ingredients and stay away from store-bought bottled dressing.

To build a great salad, start with lettuce or leafy greens. It may surprise you to learn that the type of greens you choose doesn’t really matter that much. Compared to other greens, iceberg lettuce probably has the fewest nutrients, but pretty much all lettuces are low in vitamins and minerals. Dark leafy greens like spinach have more micronutrients, but the type of iron in spinach is poorly absorbed, and there’s plenty of oxalate, so be careful if you’re prone to kidney stones.

The main health benefit of lettuce and other greens in a salad is the fiber. Salads are usually packed with fiber, which is a nutrient — just not for you! Fiber is really food for the microbiome, the trillions of bacteria that live in your gut. Fiber is also the key to metabolic health. Bacteria in your gut turn fiber into short-chain fatty acids, which can regulate immune function and keep inflammation in check.

To increase the fiber in your leafy green salad, add assorted vegetables, like broccoli and green peppers, and add beans and lentils.

But the healthiest salads include plenty of other good-for-you ingredients, such as antioxidants. Antioxidants are chemicals that are essential for your liver, which detoxify virtually all the environmental poisons that enter the body. To perform this magic trick, your liver needs these antioxidants.

For antioxidants, try chopped colorful vegetables (the darker, the better), chopped fresh fruits, herbs (fresh or dried) and spices. Then add proteins, like free-range eggs, pastured beef, fish, chicken, tofu, beans or lentils.

Add fats and fermented foods to your salad

Now layer on some whole-food fats — including avocado, olives, nuts, and seeds. Nuts and seeds (like chia seeds and walnuts) are replete with the anti-inflammatory alpha-linolenic acid (ALA), an omega-3 fatty acid shown to reduce risk for heart disease.

For other sources of omega-3s, try small fish, such as anchovies (commonly found in Caesar salads). You can also include other wild-caught fish (sardines, salmon, mackerel) or chicken (free-range, pasture-raised chicken has fewer antibiotics).

Cheeses are a fantastic addition because they contain odd-chain fatty acids, which are protective against diabetes and heart disease. We’ve all been taught to avoid fats because they have more calories, but dairy fatty acids are unique in that they have a specific phospholipid on their end which prevents inflammation. Just don’t use American cheese, which is not actually cheese. Instead, try varieties such as feta, cotija, parmesan and mozzarella.

Bonus points go to kale, cabbage, and Brussels sprouts — cruciferous vegetables that can increase your body’s own natural production of antioxidants and stimulate the production of liver detoxification enzymes. Another bonus: fresh tomatoes contain lycopene, an antioxidant that supports ocular function and prevents cataracts.

Adding fermented foods such as kimchi and sauerkraut can give you a gut-friendly boost, as can homemade dressings made with natural, unsweetened yogurt. And fermented foods already have short-chain fatty acids in them.

Avoid store-bought salad dressings

Okay. Now let’s talk about salad dressings. To make a great homemade dressing, focus on ingredients such as extra virgin olive oil, avocado oil, tahini, vinegar, Dijon, herbs, spices and citrus juices low in sugar (lemon, lime, grapefruit).

The oleic acid in olive oil activates the liver to produce a factor that speeds up metabolism. The acetic acid in vinegar inhibits an enzyme that breaks down starches in the mouth, thus reducing the rate of glucose that appears in your bloodstream. Some homemade dressings get extra antioxidants from spices and seasonings such as ginger, garlic, turmeric, thyme and oregano.

But the same can’t be said about most store-bought dressings. Store-bought versions are often made with canola and soybean oils, which are chock full of linoleic acid, an inflammatory omega-6 fatty acid.

They can also sneak in large amounts of fructose (the sugar molecule), in the form of cane sugar, high-fructose corn syrup or honey — which harm mitochondria, the energy-producing factories that power each of your cells. When your mitochondria don’t work right, your blood glucose and insulin spike, and your liver has no choice but to turn the fructose into fat — driving fatty liver and insulin resistance and potentially furthering your risk of developing heart disease, cancer and diabetes.

You might be surprised at how common it is for sugar to sneak into bottled dressings. For example, high-fructose corn syrup is the second ingredient in Kraft’s Creamy French dressing, which has five grams of added sugar. And watch out for fat-free dressings — for instance, Ken’s Sundried Tomato Vinaigrette has 12 grams of added sugar.

Store-bought dressings can also contain ingredients that are bad for your gut and the trillions of bacteria that reside there. These bacteria send chemical signals to your brain asking to be fed. If you don’t feed your bacteria, they actually start to feed on you — stripping the mucin, a protective layer, right off your intestinal cells. Over time, this can lead to irritable bowel syndrome, inflammatory bowel disease and altered intestinal permeability, which some people call “leaky gut.” It can also cause systemic inflammation.

Store-bought dressings often contain emulsifiers, such as carboxymethylcellulose, polysorbate-80 or carrageenan, which keep the fat and water from separating — and can dissolve that protective mucin layer in your gut. Those pesky added sugars can also cause bad microbiome bacteria to proliferate, potentially leading to gastrointestinal distress, gas, bloating, diarrhea and inflammation.

Croutons and crispy things

But that doesn’t mean you should skip the dressing. Studies have shown that fats — such as in avocados — actually help your body absorb the nutrients from some vegetables. The key is to choose the right ingredients and, ideally, make your own dressing at home.

It’s also a good idea to steer away from “crispy” things (such as fried onions and tortilla strips), which are often fried in seed oils at high temperatures, risking the formation of trans fats and acrylamide, a known carcinogen. I’d also suggest being cautious about dried fruits; some varieties and brands cover them in sugar to make them sweeter and more palatable.

And lastly, beware of processed breads. A Caesar salad is not a Caesar salad without croutons — but commercial croutons are typically packed with preservatives, sodium and vegetable oils. Bake your own croutons, or pair your salad with a slice of sourdough bread. But please, don’t eat the fried tortilla bowl.

Robert H. Lustig is an emeritus professor of pediatrics at the University of California at San Francisco and the author of “Metabolical: The Lure and the Lies of Processed Food, Nutrition and Modern Medicine.”

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