Food processing (or processed food) has been demonized for its association with unhealthy dietary patterns and chronic disease, but most of the evidence that drives these associations is based on relatively weak observational studies and relatively arbitrary food processing classification schemes. Moreover, few studies have compared health outcomes following intake of foods with the same nutrient composition that differ only in their processing method.
This narrative review was designed to provide a better understanding of what drives consumer food purchases, how foods are processed, how processing affects nutrient composition, and how food influences eating behavior and energy intake.
The authors of this review argue that the largest drivers of consumer food purchases are palatability (i.e., taste/pleasantness), cost, and convenience, as well as nutrition and sustainability — all of which can be improved by food processing.
|Improved microbial food safety and increased shelf life||Excess fat, sugar, and salt|
|Removal of pesticides and toxins (e.g., aflatoxin)*||Inclusion of additives with unclear health implications*|
|Decrease of toxin formation (e.g., acrylamide)*||Leaching of chemical contaminants|
|Improved digestibility (e.g., gelatinization of starches, denaturation of proteins)||Increased availability of nutrient-poor, energy dense, easily consumable foods*|
|Optimized vitamin retention by specialized processing (e.g., ultrapasteurization)*||Thermal degradation of vitamins|
|Inactivation of antinutritional factors (e.g., lectins, saponins)||Destruction of the food matrix|
|Fortification (addition of micronutrients and certain amino acids in sufficient amounts, but not excessive, amounts)*|
|Decreased food prices and waste (i.e., obtain raw materials at scale and convert waste into new products)*|
|More energy- and water-efficient processing equipment/operations*|
* Likely not possible with at-home processing methods
The biggest concern regarding food processing and its association with noncommunicable disease (e.g., obesity, cancer) is the influence of food processing on eating behavior. Greater degrees of processing are associated with tastier, more energy dense foods due to the addition of excess sugar, salt and fat. These foods can also be consumed quicker than less processed foods, though this is also not always the case.
Digging Deeper: Eating behavior and food processing
Taste-nutrient interactions, food form (solid vs. liquid), eating rate, energy intake, hyperpalatability, and “fat blindness” (our inability to discriminate fat content in a food when it is optimally combined with salt and/or sugar for taste) influence eating behavior and energy intake such that:
- Nutrient- and energy-dense foods tend to taste better.
- Liquid foods have a higher eating rate and lower satiating capacity than solid/semisolid foods.
- Greater eating rates and foods higher in energy density promote greater energy intake.
- Average energy intake tends to increase with the degrees of food processing (e.g., deformation of food structure), although food processing formulation can also sometimes decrease the rate of energy consumption (e.g., cheese vs. milk).
- Portion/serving container sizes can influence energy intake (e.g., 100-calorie snack packs).
- Greater palatability has been associated with an increased intake of both unprocessed and processed foods.
- Food palatability naturally declines during consumption (consider the first bite of a big fast food burger compared to the last bite).
- Fat, sugar, and salt combinations can act synergistically to improve palatability that overcomes physiological (i.e., normal) satiety mechanisms.
The big picture
Food processing is an enormous, complex spectrum. It can be as basic as cooking raw food over an open fire or as complex as transforming milk into whey protein that is then incorporated into a baked good. This spectrum also illustrates the changes food processing has undergone throughout human history. Milk process is a great example of these changes. At first, pasteurization (partial sterilization) was not widely accepted, until its issues were ironed out and it became clear the process could save lives by preventing milkborne diseases. Now, pasteurization can be a quick process and has a smaller effect on vitamins naturally found in milk, as thermal processing time is often proportional to nutrient degradation. Moreover, milk is fortified with vitamin D during processing to promote calcium absorption and makes up 30–60% of vitamin D intake in North America. Innovation in the field of food processing is advancing toward nonthermal, minimal processing techniques, such as hydrostatic pressure, pulsed electric fields, and ultrasound. These techniques are gentler (i.e., retain nutrients) and more efficient (i.e., less energy intensive).
While food processing does contribute to food and nutrition security (e.g., shelf stability, improved nutrient bioavailability, enrichment/fortification), the nutrition aspect is a bit of a double-edged sword because more and more processing steps are added to processes to reach consumer desired palatability, convenience, and cost. The fat-, sugar-, and salt-driven greater energy density of ultraprocessed foods (UPF) can facilitate overeating by stimulating the release of dopamine in the brain, which is what drives UPF’s association with addictive-like eating behavior (check out this Examine article on food addiction and this Deep Dive on UPF-associated overeating for more context). Beyond the differences in macronutrients and micronutrients, where higher quantities of sugar, salt, and fat from UPFs likely displace the intake of “healthier” foods that include a greater variety of nutrients (e.g., fiber, protein, vitamins, minerals, phytochemicals), UPFs differ from minimally processed foods in three main ways: the food matrix, additives, and contaminants, all of which are associated with cardiometabolic disease.
Food processing tends to alter the cell structure (i.e., food matrix) of food and its components. Think of wheat: a plant in the fields that is processed into flour, that is then baked into white bread. The “processing away” of the food matrix increases the bioavailability of macronutrients that contributes to faster intake and slower satiety signaling that tends to spike glucose and insulin levels. Foods with these characteristics are often referred to as high glycemic foods. This also contributes to a higher risk of cardiometabolic disease, such as diabetes and cardiovascular disease, as well as poor levels of cardiometabolic health markers. Food processing can also increase or decrease the bioavailability of micronutrients, but often degrades them or exposes them to more competition or interactions than they normally would through the body’s own processing via the digestive tract. Some aspects of the food matrix may inhibit absorption of some nutrients, but confer other benefits. For example, fiber can form complexes with some micronutrients, preventing their absorption, but it also slows down the transit of food in the digestive tract, which can reduce spikes in glucose and insulin. Fiber feeds the gut microbiome, stimulates satiety, and may actually end up optimizing the absorption and metabolism of the micronutrients it initially formed a complex with.
Many additives are harmless in the amounts commonly used, and most are monitored by government agencies (such as the FDA in the U.S.) to meet strict cutoffs for safe use, but some may be worse than previously thought. Emulsifiers, which are added to help combine fats and liquids (e.g., oil and vinegar salad dressing) and thicken UPFs (e.g., ice cream), may act like soap in the digestive tract, killing friendly gut bacteria and allowing less friendly ones to take their place. They may also promote gut inflammation and have been associated with disease states (e.g., Crohn’s disease, metabolic syndrome). However, the key here may be dose, as there are natural emulsifiers (e.g., lecithin) present in the diet that come from foods such as eggs, sunflower seeds, and soybeans, the dietary intake of which is estimated to be 14–71 milligrams per kilogram of body weight per day, which is similar to food additive emulsifier regulations. Moreover, most of the available evidence is limited to a few specific additives and mostly in animal and cell models. That said, the European Food Safety Authority’s Emerging Risks report called for urgent research in the area of food emulsifiers, the gut microbiome, and long-term health effects.
One of the telltale aspects of UPFs is the packaging and their constant exposure and re-exposure to plastic and synthetic contaminants. When raw food jumps from container to container throughout processing, coming into contact with harvesting and collection equipment, transport, processing facilities, conveyor belts, rigorous cleaning and sterility procedures for equipment and containers, and more before it reaches its shelf-stable packaging, the potential for chemical contamination is high. While this doesn’t only apply to UPFs (e.g., dairy tends to be high in chemical contaminants likely because of its constant contact with plastic tubing), greater UPF intake has been associated with greater serum levels of chemical contaminants, such as bisphenol A and phthalates. These chemicals can act as endocrine and metabolic disruptors (i.e., they bind to endocrine receptors and can shift hormonal balance) and have been suggested to play a causative role in cardiometabolic diseases. Moreover, dietary fiber, which is removed in many methods of food processing and negatively associated with UPF intake, has been reported to reduce serum concentrations of some chemical contaminants and is known to support detoxification of organs such as the liver and kidneys. While this relationship is far from conclusive, as much of the research is observational or in vitro and in vivo, it may be a minor effect that adds up with other stressors, such as chronic disease and poor lifestyle habits, to contribute to further complications and grave consequences associated with food processing.
Ultimately, it appears that a combined effort from consumers, scientists, and policymakers to demand, understand, and set guidelines for a shift in food processing is needed. Innovative minimal food processing techniques demonstrate the potential to produce nutrient dense, energy adequate and sustainably produced foods, with limited additives and contaminants, that are still tasty, convenient, and don’t break the bank.
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