A small but well-designed study from the National Institutes of Health (NIH) shows how eating processed foods, compared to unprocessed foods, leads you to eat more calories per day and gain more weight (Cell Metabolism, May 16, 2019). Twenty people lived in a lab for a month and alternated between two weeks each on:
• a diet of highly processed foods, or
• a diet of unprocessed or minimally processed foods.
They were allowed to eat as much of the offered food as they wanted, including snacks (up to 5,400 calories per day). On both diets, they were offered the same daily amounts of total calories, sugar, fat, carbohydrates, and fiber. Neither diet was low-carbohydrate, low-fat or high-protein. The difference was in the amount of food processing. In the two weeks on the processed food diet, the subjects ate an average of 500 more calories per day and gained an average of two pounds. On the unprocessed food diet, subjects lost an average of two pounds.
Sample Study Meals
Processed Breakfast: Honey Nut Cheerios, whole milk, packaged muffin with margarine
Unprocessed Breakfast: Greek yogurt or oatmeal with strawberries, bananas, apple slices and walnuts
Processed Lunch: Canned ravioli, white bread and margarine, diet lemonade with fiber, oatmeal cookies
Unprocessed Lunch: Spinach salad with chicken breast, bulgur, sunflower seeds, grapes, and vinaigrette dressing
Processed Dinner: Pre-cooked steak strips and gravy, mashed potatoes, margarine, canned corn, diet lemonade with fiber, low-fat chocolate milk
Unprocessed Dinner: Beef roast, rice seasoned with garlic, onions and green peppers, steamed broccoli, side salad with balsamic vinaigrette, orange slices, pecans
Processed Snacks: Baked potato chips, cheese & peanut butter cracker sandwiches, applesauce, goldfish crackers
Unprocessed Snacks: Fresh fruits and vegetables, nuts and snack seeds
Why So Much Processed Food?
The ever-increasing obesity epidemic in North America parallels the increased supply of processed foods since the 1950s (Annu Rev Public Health, 2014; 35: 83-103). Processed foods have also been associated with increased risk for diabetes and heart attacks (PLoS Med, 2012; 9: e1001235). Reasons for the increase in processed foods include:
• They have longer shelf lives (less spoilage) so they can be sold at lower prices (Public Health Nutr, 2018; 21: 5-17).
• They taste better to many people because they have more added sugars, other refined carbohydrates and various flavorings.
• They take less time and knowledge to prepare than fresh (unprocessed) foods.
• They are widely used in fast food restaurants, which have increasingly replaced home-prepared meals.
Eating processed foods makes you eat faster so that you can eat more before your gut sends messages to your brain to tell you that you are full (Science, 2019; 363: 346-347). It takes far more time to chew up unprocessed foods before you swallow them, and eating more slowly usually means you eat less. Subjects in this study ate the processed foods at an average rate of 37 grams and nearly 50 calories per minute, while they ate unprocessed foods at an average rate of 30 grams and 32 calories per minute.
• Unprocessed foods are those that are recognizable parts of plants (leaves, stems, roots, fruits, seeds) or animals (cuts of meat, poultry or seafood, eggs).
• Minimally-processed foods are parts of plants or animals that have been factory-cleaned and packaged and may have been ground, chopped or otherwise reduced to small particles; blanched or pre-cooked; and/or frozen, canned or dried. Non-flavored dairy products including cheeses and plain yogurt, and simple prepared foods such as pastas or whole grain bread can also be considered to be minimally processed. If the package has a very short list of ingredients (1-4), the food is probably minimally processed, but check for added sugars.
• Highly-processed or ultra-processed foods are “Formulations of several ingredients which, besides salt, sugar, oils, and fats, include flavors, colors, sweeteners, emulsifiers and other additives used to imitate sensorial qualities of unprocessed or minimally processed foods, or to disguise undesirable qualities of the final product” (BMJ Open, March 9, 2016;6(3)). Ultra-processed foods include soft drinks, most dry breakfast cereals, frozen pizzas, frozen meals and entrees, breads, cakes, pies, cookies, snack bars including power bars, diet bars and energy bars, candy, crackers, salty snack foods such as potato chips, corn chips and pretzels, processed meats including those made from poultry or seafood, instant soups and noodle bowls, bottled juices, salad dressings and many others.
The authors of this study recommend cutting way back on highly-processed foods to reduce intake of added sugars and refined carbohydrates, and getting most of your calories from nutrient-rich unprocessed foods including vegetables, fruits, beans, nuts, whole grains and other seeds.
Eat Whole Foods, Not Processed Foods, to Lose Weight