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Study: Processed Food Diet Can Put on the Pounds

A new study has found that following a diet that consists of processed foods can quickly result in weight gain.

The study by a team of researchers at the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, MD, was the first of its kind conducted on humans – and with astonishing results.

In the study, 20 participants lived in a lab for four weeks, spending two weeks each on two types of diet:

One rich in highly processed foods (like food out of a box or canned prepared food).
One rich in whole foods, like whole grains, Greek yogurt, nuts, fruit and vegetables.

Both diets offered the same number of daily calories, and comparable amounts of sugar, fat, carbohydrates and fiber. But because the processed food diet generally lacked enough fiber, the participants were given supplemented fiber beverages.


The subjects were allowed to eat as much of the offered food as they wanted, and they had access to snacks and water. But when they ate mostly processed foods, they consumed on average 500 more calories per day and gained on average 2 pounds, mostly in the form of fat.

When they ate whole foods, they lost the same amount of weight and saw increases in a gut hormone that suppresses hunger and decreases in a hunger hormone called ghrelin.

The researchers surmised that one of the reasons the study subjects consumed more when on the processed-food diet was that they seemed to eat faster when they ate such foods. Whole foods typically require more chewing and people eat more slowly when consuming these types of foods.

When people eat quickly, by the time the stomach signals to the brain that it is full, it may be too late. Other studies have found that it takes about 20 minutes for the gut to signal to the brain we are full.

While other studies on processed foods have shown similar results in mice, research on humans has found links between processed foods and higher risks of developing obesity and cancer – and an increased risk of death.

Despite that, ultra-processed foods account for nearly 60% of food-energy consumption in the U.S.

What the study participants ate

Processed diet

Breakfasts included:

  • A bowl of sweetened breakfast cereal (including Honey Nut Cheerios) and a pre-packaged muffin with margarine, or
  • Pre-packaged croissant with margarine, turkey sausage and sweetened blueberry yogurt and added fiber.

Dinner was usually:

  • Packaged ravioli with processed cheese and white bread; or
  • Canned chili with tortilla chips and salsa.

Whole-food diet

Breakfast was usually:

  • Greek yogurt or oatmeal with fresh fruit and nuts, or
  • Eggs with hash browns made from fresh potatoes.

Dinner was usually:

  • Shrimp scampi with spaghetti, olive oil, garlic, cream, tomatoes, parsley, basil and fresh-squeezed lemon juice with a green leaf salad, or
  • Grilled chicken breast, farro, apples, grapes and vinaigrette dressing.

The takeaway

If you are eating pre-packaged, processed foods you should make a concerted effort to cook more food for yourself using raw ingredients.

Try to avoid processed foods like macaroni and cheese, canned pasta, frozen meals, chips and candy, donuts, and sweetened breakfast cereals, as well as non-sweetened ones like Cheerios – even Multigrain Cheerios contain 6 grams of sugar per serving.

Try to include vegetables and fruits in your diet for fiber, eat healthy carbs like rice, quinoa and potatoes, and any meats like fish, chicken, beef, turkey and pork (sausage is processed, so try to avoid it).