Merck Manual

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Processed Foods, Organic Foods, and Bioengineered or Genetically Modified Foods


Shilpa N Bhupathiraju

, PhD, Harvard Medical School and Brigham and Women's Hospital;

Frank Hu

, MD, MPH, PhD, Harvard T.H. Chan School of Public Health

Reviewed/Revised Feb 2023

Processed Foods

The US Department of Agriculture (USDA) defines a processed food as any raw agricultural commodity that been subject to washing, cleaning, milling, cutting, chopping, heating, pasteurising, blanching, cooking, canning, freezing, drying, dehydrating, mixing, packaging, or other procedures that alter the food from its natural state.

Based on this definition, virtually all food is processed to some degree. Some modern food processing, however, strips nutrients from foods. For example, milling removes bran and germ, and thus fiber Fiber Some foods contain fiber, which is a tough complex carbohydrate. Fiber may be Partly soluble: It dissolves in water, and the body may be able to digest some of it. Insoluble: It does not dissolve... read more , iron, and many B vitamins from grains. Processing also often adds additives such as preservatives (eg, benzoates, sorbates, nitrites, sulfites, and citric acid); artificial colors, flavors, and sweeteners; stabilizers; emulsifiers; and synthetic vitamins and minerals and other additives including salt, monosodium glutamate (MSG), sugar, fats, and refined oils. Some food additives can adversely affect children in particular.

Ultra-processed foods (eg, sweets, salty snacks, sugar-sweetened beverages, ready-to-eat meals, and fast food) are increasingly common and make up nearly half of the food supply in many countries. They are made from inexpensive ingredients (including unhealthful fats, refined grains and starches, and added sugar and salt) that are often combined with food additives (including artificial colors, flavors, and preservatives) to make them inexpensive and exceptionally tasty and to prolong shelf life. Most contain little to no whole foods. These foods promote overeating and weight gain and supply a relative dearth of valuable nutrients, increasing risks of insulin resistance and possibly other disorders (eg, coronary artery disease, depression Depression Depression is a feeling of sadness and/or a decreased interest or pleasure in activities that becomes a disorder when it is intense enough to interfere with functioning. It may follow a recent... read more , irritable bowel syndrome Irritable Bowel Syndrome (IBS) Irritable bowel syndrome is a disorder of the digestive tract that causes recurring abdominal pain and constipation or diarrhea. Symptoms vary but often include lower abdominal pain, bloating... read more , cancer, and even early death).

Organic Foods

To be labeled USDA-certified organic, organic foods must be grown and processed according to federal guidelines that address many factors, including soil quality, animal-raising practices, pest and weed control, and the use of additives. For example, for meat to be labeled organic, the animals must be raised in conditions that accommodate their natural behaviors (such as the ability to graze in a pasture), must be fed 100% organic feed and forage, and must not be given antibiotics or hormones. To be labeled with the USDA organic seal, a product must contain 95% organic ingredients.

Although the certainty and extent of health benefits attributed to foods being organic remain unknown, the absence of antibiotics helps prevent antibiotic resistance. Synthetic pesticides may also increase risks of autism Autism Spectrum Disorders Autism spectrum disorders are conditions in which people have difficulty developing normal social relationships, use language abnormally or not at all, and show restricted or repetitive behaviors... read more , attention-deficit/hyperactivity disorder Attention-Deficit/Hyperactivity Disorder (ADHD) Attention-deficit/hyperactivity disorder (ADHD) is poor or short attention span and/or excessive activity and impulsiveness inappropriate for the child’s age that interferes with functioning... read more (ADHD) and impaired cognitive skills in children. One strategy to help contain the increased costs of organic foods is to consider the Environmental Working Group's (EWG) annual lists of pesticide levels that list the dirty dozen (produce that is contaminated with more pesticides than other crops) and the clean fifteen (produce that has the lowest amounts of pesticide residues).

Bioengineered or Genetically Modified Foods

Bioengineered or genetically modified foods are foods containing genetically modified organisms (GMOs).

According to the World Health Organization (WHO), bioengineered or genetically modified foods contain DNA that has been modified through laboratory techniques and that cannot be created through conventional breeding or found in nature. Genetically modified foods have existed in the US food supply since the early 1990s, and their safety in humans and animals is overseen by the U.S. Food and Drug Administration (FDA), the Environmental Protection Agency (EPA), and the USDA.

Beginning in January 2022, foods require labeling that indicates whether they are a bioengineered food. These foods are often common ingredients in other foods and may be difficult to identify.

Although consumption of bioengineered foods poses no risk to human health, food safety advocacy groups have raised concerns such as development of allergies (if the transferred DNA was taken from an allergenic food) and antibiotic resistance resulting from the consumption of herbicide-resistant crops that could theoretically transfer modified antibiotic-resistant genes to the human digestive tract. The WHO has stated that risk of such antibiotic resistance is very small, but not insignificant.

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