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This is a common saying that refers to mainly shopping and purchasing foods from the sections the line a grocery store's walls.  This may help you avoid some preservatives.  Many health professionals recommend shopping the perimeter of the store as many of these foods are less processed and are typically considered "whole foods." The main sections on the perimeter include:  the produce section with fruits and vegetables, the meat/deli counter, the seafood counter, the dairy case and also eggs and the frozen sections. Most foods in the aisles are much more processed and will also most likely have varying amounts of additives. The produce section will have the most whole foods that are minimally processed.  Typically fresh fruits and vegetables do not contain.  Stock up on these foods to help decrease or avoid additives. Note that not all items in the produce section will be preservative-free.  Items like pre-washed, pre-cut fruits and vegetables may have some additives to maintain freshness or color. Raw nuts and seeds are also good options for avoiding preservatives. These may be available in bulk bins near the produce or in a separate bulk section of your store. The meat, deli, and seafood counter will have a bigger range of processed items compared to the produce section.  Try to stick to meats that are uncooked and in their more natural state, such as raw, whole chicken, raw beef or raw fish. For example, instead of pre-cooked chicken breasts, purchase an entire chicken or chicken breasts raw and prepare them yourself.  Or instead of buying turkey deli meat, purchase a turkey breast to roast and slice yourself. Also, don't always forego frozen items.  Many times frozen meats and seafood do not contain additives because the freezing keeps them fresh and prevents spoilage. The dairy and egg case is another area that has a wide range of processing and amounts of additives.  Eggs typically will be preservative and additive free as you cannot add anything to shelled eggs.  They do range in what the chickens are fed and how they were raised.  Also, liquid eggs and liquid egg whites may contain additives. You may want to consider avoiding dairy foods with added sugars or flavorings and buy plain or unflavored items.  For example, buy plain yogurt instead of fruited yogurts. Cheeses like sliced or shredded cheese may have some additives to prevent the cheese from sticking to itself.  Try buying blocks of cheese and slicing or grating cheese yourself. Also, watch out for highly processed cheeses, such as American cheese and Velveeta. The freezer aisles can contain very processed foods and minimally processed items.  Be smart on what you choose.  Many frozen fruits and vegetables are minimally processed and contain little to no additives or preservatives.  Make sure you read the label to double check. Frozen fruits and vegetables that come with a sauce or gravy will have additives.  Avoid these if you don't want to consume preservatives. Most other frozen foods will be processed and contain additives.  Minimize these in your diet or avoid them all together if desired. It will be difficult to purchase only foods from the perimeter to the store.  When purchasing items from the inner aisles, be careful about what you choose.  Try to avoid the aisles that contain candy, chips, crackers, cereals or cookies.  These foods are guaranteed to be processed and contain a significant amount of additives. If you're going to buy canned vegetables or meats, choose those with no salt added.  Canning does a great job at preserving foods and therefore many of these items contain minimal additives. For items like salad dressing, condiments or sauces, read the labels for those that contain more natural ingredients and less additives.  This is a popular request by consumers, so with a little extra time with the labels, you should be able to find appropriate substitutes.
Shop the perimeter of the grocery store. Choose whole, unprocessed fruits and vegetables. Purchase meat and seafood that is minimally processed. Be wary of the dairy case. Stick to minimally processed items in the freezer aisles. Be mindful when shopping in the aisles.