Ask Doctor K: Choose carefully when buying processed foods

DEAR DOCTOR K: Most nutrition advice starts with “avoid processed foods.” What exactly are processed foods? Are they all bad for you?

DEAR READER: A processed food is any food that has been changed in some way from its original state. Processing includes canning, cooking, freezing, dehydration or milling.

As you say, nutrition gurus often urge us to spurn processed foods. I spoke with Stacey Nelson, a registered dietitian and manager of clinical nutrition at Harvard-affiliated Massachusetts General Hospital. She noted that most food needs to go through some degree of processing in order to make it edible and digestible.

The main concern with processing is that it can reduce a food’s nutritional content. It can also add unhealthy things that you should avoid or limit.

In particular, be wary of the following in processed foods:

– REFINED GRAINS. Processed foods may contain refined grains, such as white flour and white rice. Milling whole grains removes the bran (which contains most of the fiber) and the germ (which contains protein, fat, vitamins and minerals). Fortification adds nutrients back after processing, but it may not restore the original nutritional profile.

– ADDED SUGAR. Sweeteners, like table sugar and high-fructose corn syrup, are refined carbohydrates. These are considered unhealthy if they take up too much of your diet. Many processed foods contain added sugar.

– SODIUM. Processed foods often contain a lot of added sodium (mostly table salt). At the top of the list are canned soups, breads, frozen foods and processed meats. Eating too much sodium has been linked to high blood pressure, heart attack and stroke.

– TRANS FATS. Some processed foods contain trans fats, which are associated with a higher risk for clogged arteries. You are most likely to find trans fats in commercial baked goods (crackers, cookies, pastries, pies and doughnuts) and frozen pizza. The “nutrition facts” label lists trans fat levels. Do your best to avoid eating foods with trans fats. They are the “baddest” of the bad fats.

But not all processed foods are unhealthy. Some processed foods offer valuable nutrients as well as convenience. Canned beans and fish, for example, are both healthy processed foods. Frozen fruits and vegetables are also valuable. Producers pick and quickly freeze the produce, which retains its nutrients. (I’ve put a more complete list of healthy processed foods on my website, AskDoctorK.com.)

To check canned and frozen food for overall nutritional value, read the ingredients list. You want something that has minimal ingredients, most or all of which you recognize.

Processed foods are a relatively new thing. Until about 100 years ago, in the developed nations we ate foods (meats, fruits, vegetables) that were grown and raised locally. Industrial-size agriculture, shipping foods long distances and supermarkets were yet to come. As a result, we ate healthier. But preparing meals took longer, and we spent a bigger fraction of our income on food. So there also are advantages to how we eat today. With a little knowledge and attention, we can preserve these advantages while also eating healthier.

Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.