Photo by Daniel Gois
Recently a reader asked me a simple question that I’m surprised I don’t hear more often, “Why are processed foods so bad?”
She had been having a nutrition debate with her boyfriend. She reads Summer Tomato regularly, but was having trouble describing the health difference between the Real Food I recommend daily and the processed foods I warn against. What exactly is the evidence?
The answer in some ways is just as simple: we don’t know. Unfortunately that isn’t very satisfying intellectually, and our attempts to create theories around the observational fact that obesity and most chronic diseases only appeared after the introduction of processed foods has opened the door to a world of speculation and confusion.
There is no doubt that processed foods are unhealthy. The so-called Diseases of Civilization including heart disease, hypertension, tooth decay, diabetes and some cancers were virtually non-existent before processed foods (usually flour and sugar) were introduced.
We know this because these foods didn’t magically appear in all places at once, but gradually became available to different populations. The longer cultures were shielded from these ingredients, the longer they remained healthy. There is a fascinating account of this phenomenon in Weston Price’s book Nutrition and Physical Degeneration, but he is not the only one who made these kinds of observations.
Still we do not know why processed foods have this effect. There are many hypotheses about what the problem is. Some have blamed “carbs,” others have blamed fats. These days it is fashionable to point fingers at particular kinds of sugars like glucose, fructose or sucrose. People have argued that excess blood glucose and insulin are the issue, while others point to the metabolism of fructose in the liver.
Some say it isn’t the carbs at all, but the gluten protein in wheat that is to blame. If you prefer to pick on animals, there are plenty of people who think animal proteins are the true culprits.
It has also been suggested that the processing method itself is what renders foods unhealthy. Processing food typically removes or destroys nutrients and fiber, which are present in the whole foods that remain healthy. It is possible that these nutrients are required for health, though adding them back in the form of supplements does not seem to solve the problem.
Added preservatives, chemicals and other synthetic substances present in processed foods may also play a role in their unhealthfulness. Or perhaps it is our own biology that has not adapted to quickly digesting foods, or foods that have been processed in a particular way. Trans fats, for instance, are synthesized when oils are hydrogenated by a specific method, and these are almost never found in nature.
Some folks even go so far as to blame pH levels and blood types for our ailing health, though these claims are rarely made by real scientists.
You can find circumstantial evidence to support all these claims, and people do. It’s relatively easy to develop an opinion about nutrition and find a camp that is adamant about its validity. They’ll show you all sorts of data about things that happen in test tubes, in large uncontrolled human populations, or in mice, and insist that you’re a fool for not believing them.
There’s even a good chance they’ll lift their shirt and show you their six-pack as additional evidence of their correctness. And who can argue with abs? I know I can’t.
It’s confusing because a comprehensive scientific explanation of our observation doesn’t yet exist, and probably won’t for a long time. As I explain in chapter 4 of Foodist, nutrition science is very complex and still in its infancy:
“Humans are omnivores, which means we are adapted to eat plants, fungi, and animals. The nutrients in the plant foods we consume depend on the genetics of the individual species, the quality of the soil they are grown in, and the weather conditions during that time. For animal foods, nutrient levels are dependent on what the animals eat throughout their lives and are also affected by their stress and hormone levels. Any toxins or environmental pollutants that the animals and plants are subjected to have the power to impact human health as well.
Nutrient levels of raw foods change depending on the amount of time between harvest and consumption (sometimes going up, sometimes going down), and your cooking method may destroy some nutrients while making others more available. Individual nutrients within a food do not work in isolation, but interact with each other to affect bioavailability (i.e., how our bodies are able to use them). Similarly, the nutrients in one food can interact with the nutrients from another food if they are consumed in combination.
Your metabolism starts responding simply to the smell of food.* How quickly you eat and how much you chew also impact how your body handles it. Your own genetic makeup as well as your fitness level dictate how you respond to different levels and combinations of nutrients, and your digestive tract contains trillions** of microorganisms that affect what you can and cannot absorb. Individuals vary greatly in their sensitivity to different micro and macro nutrients, and all of us have different personal health and fitness goals.
* Amazingly, smell has been shown to significantly impact longevity in some species via the insulin-signaling pathway.
We really have little idea how all these factors work together to impact the health of an individual, and it will likely be several decades before we do. Still the debates will rage over the various theories about what constitutes the healthiest diet, and people will continue to miss the point entirely.
At the end of the day it really doesn’t matter what the reasons are, since we already know what to do. Simply eliminating or drastically reducing the amount of processed foods you eat vastly improves your health. The scientific mechanisms that explain this are certainly interesting on an intellectual level, but you don’t need to understand them in order to eat well.
This is why my work focuses almost exclusively on behavioral change and psychology. Understanding how to actually eat well (instead of just telling yourself you should and hoping for the best) is far more important than theories about why some foods are healthy and others aren’t.
In fact, if you don’t have a background in science focusing on nutrition theories is likely to be counterproductive, since there is a good chance they will lead you down a path of extreme diet rules, such as avoiding all grains and legumes. Yes it is possible to be healthy without including everything, but it is more work. And more work tends to derail healthy eating.
A more practical approach is to tinker with your behavior until you find a set of habits that make it easy for Real Food to become the majority of what you eat. You know it is working if your new behaviors are easy––essentially automatic––and don’t feel like hard work.
You should also be able to measure the benefits, like being a healthy weight, having lots of energy, normal blood lipids, etc. Maybe you will need to eat fewer grains or more protein, but science can’t tell you that. Only trying it for yourself and seeing how it affects you can. Author Nassim Taleb might call this approach more antifragile.
Nutrition is complicated, but eating is not. Spend your energy discovering what works for you and try not to get too caught up in the science.
Has letting go of nutrition theories helped you get healthier? Let us know in the comments.
Originally published July 30, 2014.
While debates about the relative healthfulness of carbohydrates/type of fat/salt/sweeteners/etc. never cease, there is one nutritional message that can unite (almost) anyone: eat less processed foods. On the surface, this seems obvious; after all, the top sources of calories for adults in the US include grain-based desserts, burgers, sugar-sweetened beverages and chips (1,2), which are certainly not what dietary recommendations are going for. But when we pose “What are the effects of food processing on health?” as a scientific question, things suddenly become very complex. Is there a consensus on what food processing is? Is all food processing unhealthy? What research has been done on processed food?
What is Processed Food?
First, we should start on the tricky subject of definitions.
Jones and Clemens published a nice summary of how various organizations differ in their definitions of “processed food” (3). The United States Department of Agriculture and other government organizations, for example, tend to use a broad definition that includes any changes from a natural state – such as washing, heating, and cooking, to adding preservatives, flavors, additives, etc. The American Institute for Cancer Research uses the term “minimally processed” to denote vegetables, grains, and beans prepared without much added to them, or minimal refining. Then there is the “NOVA” system, an attempt by Dr. Carlos Monteiro and colleagues to categorize food processing into: “unprocessed or minimally processed foods”, which are essentially unmodified from nature or include light processing such as drying, boiling, freezing, etc., “processed culinary ingredients”, “processed foods”, and “ultra-processed foods” as the extreme, which includes foods made with ingredients with limited “unprocessed foods”, such as concentrated energy sources like sugars, oils, fat, salt, extracts like casein, lactose, and whey, or additives like dyes, flavors, sweeteners, etc. (4). There doesn’t appear to be good published data on what the public considers processed food, although the International Food Information Council (IFIC) has developed definitions with input from consumer focus groups, discussed below.
What the Critics Say
Some critiques of definitions push against a broad classification of food processing because it could put washing an apple and baking a cookie in the same basket. To this end, while the NOVA system is an attempt to standardize food processing classification for study, not everyone agrees with it. For instance, Dr. Mike Gibney and colleagues published a commentary last month in AJCN arguing that the system is not superior to using associations of nutrient intakes with disease (5). In essence, they argue that the NOVA definition of “ultra-processed” foods and beverages is too subjective and simplistic; that classifying solely by processing would not be of use to study disease links to specific micronutrients (i.e., goiter, allergies and intolerances, anemia, etc.); that it does not improve upon using already established dietary pattern analysis in research; that analysis of the NOVA system indicates that it does not predict nutrients that are suggested to be increased by processed foods such as fat and salt; that certain nutritional requirements such as folic acid could not be met with solely unprocessed foods; and that there is little evidence to date that processing relates to measures of satiety or “hyper-palatability”/”food addiction”. Further, changes to modern eating that relate to consuming more energy including increased portion sizes and energy density, may not necessarily be related to food processing. (As such, processing can be used to formulate smaller portion sizes and reduce energy density.)
Similarly, the 2014 American Society for Nutrition scientific statement on the nutritional role of processed foods by Dr. Connie Weaver and colleagues (6) takes issue with using the NOVA classification based on subjectivity, favoring instead IFIC definitions of processed foods as described below:
|Type of Food||Examples|
|Foods that require little processing or production (also called “minimally processed”).||Washed and packaged fruits and vegetables; bagged salads; roasted and ground nuts and coffee beans|
|Foods processed to help preserve and enhance nutrients and freshness of foods at their peak.||Canned tuna, beans and tomatoes; frozen fruits and vegetables; pureed and jarred baby foods|
|Foods that combine ingredients such as sweeteners, spices, oils, flavors, colors, and preservatives to improve safety and taste and/or add visual appeal. (Does not include “ready-to-eat” foods listed below.)||Some packaged foods, such as instant potato mix, rice, cake mix, jarred tomato sauce, spice mixes, dressings and sauces, and gelatin|
|“Ready-to-eat” foods needing minimal or no preparation.||Breakfast cereal, flavored oatmeal, crackers, jams and jellies, nut butters, ice cream, yogurt, garlic bread, granola bars, cookies, fruit chews, rotisserie chicken, luncheon meats, honey-baked ham, cheese spreads, fruit drinks and carbonated beverages|
|Foods packaged to stay fresh and save time||Prepared deli foods and frozen meals, entrées, pot pies and pizzas|
Republished from http://www.foodinsight.org/sites/default/files/IFIC_Handout1_high_res.pdf
The statement addressed how processed foods contribute to the health and nutrition of populations, stakeholders in improving diet, and research still needed. Analysis of foods that provide nutrient enrichment and fortification (added by processing) indicates that much of the population would fall below adequate intakes for several nutrients. On the other hand, on average they contribute to nutrients that are recommended to be limited such as added sugar, sodium, saturated fat, and calories. They critique the term “ultra-processed” because the degree of processing does not necessarily reflect nutrient content of a food. The paper also summarizes what the future of processed food should look like to better address nutritional and food security around the world, including more cross-discipline collaboration to improve upon processed products and better communication between consumers and relevant stakeholders (6). It also remains to be seen whether the NOVA classification system would lead consumers to choose better diets compared to healthy diet patterns developed by nutrient epidemiology such as MyPlate, DASH, or Mediterranean-style diets, which can include foods with various levels of processing (7).
Thus, depending on how you define it, food processing can contribute necessary nutrients but also nutrients that should be reduced, and how different forms of processing may affect health is understudied.
Research on Processed Foods
Most research on “processed foods” as a whole-diet approach has come from epidemiological studies or animal experiments. Many challenges exist that may prohibit effective research from being done, including defining and classifying processed foods, accurate recalling of foods in dietary surveys, utilizing suitable comparisons, getting study subjects to stay on an assigned diet for the necessary period of time, etc.
Instead of looking at processing, per se, as predictive of health effects, much research currently looks at individual aspects of food processing that may contribute to increased (or decreased) health risks. For example, my dissertation research focuses on dietary phosphorus, which is widely utilized as a food additive (8). Growing evidence suggests that excess phosphorus in the diet, particularly in the form that is added for processing purposes, may increase risks for cardiovascular and bone disease, particularly in those who have kidney disease. For example, a human trial directly compared foods with elevated levels of phosphorus additives vs. those that do not have additives and measured surrogate outcomes for bone and mineral metabolism, and observed changes that would predict long-term bone loss (9). For more, see recent reviews from our group (10,11). It is, however, difficult to definitively tease out the effect of individual components like phosphorus additives to long-term health from the whole food packages that they accompany.
An upcoming trial by Dr. Kevin Hall and others will test the effect of “ultra-processed foods” (based on the NOVA definition) in a highly controlled setting to see what effect on insulin sensitivity and other outcomes such foods have that should prove very interesting and continue the discussion on the utility of such classification schemes (12).
Like any nutrition guidance, we must rely on imperfect evidence to communicate dietary recommendations. Which is why telling the public to choose alternatives to “processed foods” when possible is likely an appropriate message despite scientific disagreement on classifications and health implications. Indeed, the 2015-2020 Dietary Guidelines for Americans contain 25 instances and the scientific report 67 instances of the word “processed” (13,14), in context implying that we should limit processed food, mostly focusing on processed meats where more research has been done. This is because processed foods tend to contribute nutrients that Americans already consume high amounts of, such as sodium and saturated fat. At the same time, it will be interesting to see the results of natural experiments such as Brazil’s Dietary Guidelines, which put the focus on food processing instead of nutrient levels (15). It is an area ripe for research and cross-disciplinary collaborations.