Evolutionary and neuropsychological perspectives on addictive behaviors and addictive substances: Relevance to the "food addiction" construct

Abstract

It has been argued that food cannot be "addictive", unlike conventional drugs of abuse, because it is an essential part of life. In this paper, evidence is reviewed, largely from an evolutionary psychobiological perspective, that plant-based psychoactive drugs (such as those derived from the opium poppy and the coca leaf) and gambling-related behaviors were once adaptive for human health and survival in a similar manner as energy-based foods were for nourishment. "Evolutionary mismatch" viewpoints contend that certain behaviors were enhanced during the hunter-gatherer lifestyle - from which our genetic endowment had its origins - because they bestowed both survival and reproductive advantages to the species. However, in the context of advanced technology and other rapid environmental changes, these same behaviors have tended to become maladaptive and greatly overexpressed. Similar to the manufactured purification of psychotropic plant-based substances, the reward impact of processed and hyperpalatable foods, with their high levels of sugar, fat, and salt, is much increased from foods produced in nature. It is concluded therefore that what was once beneficial and necessary for our survival has been altered and ultraprocessed into edible products that may be disadvantageous and potentially addictive.

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http://dx.doi.org/10.2147/SAR.S56835
Evolutionary and neuropsychological perspectives
on addictive behaviors and addictive substances:
relevance to the “food addiction” construct
Caroline Davis
Sch ool of Kinesiology and Health
Science, York University, Toronto,
ON, Canada
Correspondence: Caroline Davis
School of Kinesiology and Health Science,
343 Bethune College, York University,
4700 Keele Street, Toronto,
ON M3J 1P3, Canada
Tel +1 416 736 2100 Ext 77 327
Email cdavis@yorku.ca
Abstract: It has been argued that food cannot be “addictive”, unlike conventional drugs
of abuse, because it is an essential part of life. In this paper, evidence is reviewed, largely
from an evolutionary psychobiological perspective, that plant-based psychoactive drugs
(such as those derived from the opium poppy and the coca leaf) and gambling-related
behaviors were once adaptive for human health and survival in a similar manner as energy-
based foods were for nourishment. “Evolutionary mismatch” viewpoints contend that
certain behaviors were enhanced during the hunter-gatherer lifestyle – from which our
genetic endowment had its origins – because they bestowed both survival and reproduc-
tive advantages to the species. However, in the context of advanced technology and other
rapid environmental changes, these same behaviors have tended to become maladaptive
and greatly overexpressed. Similar to the manufactured purification of psychotropic
plant-based substances, the reward impact of processed and hyperpalatable foods, with
their high levels of sugar, fat, and salt, is much increased from foods produced in nature.
It is concluded therefore that what was once beneficial and necessary for our survival has
been altered and ultraprocessed into edible products that may be disadvantageous and
potentially addictive.
Keywords: food addiction, evolution, drugs, gambling
Introduction
Evolutionary psychobiology is a scientif ic perspective that involves the analyses
of inherent neurobiological mechanisms that mediate the behavior of an organ-
ism; in other words, the “hows and whys” of adaptive behavioral responses to
environmental pressures. Darwinian medicine is an extension of this endeavor,
and entails the quest for evolutionary explanations for disease risk.1 A basic tenet
of evolutionary science is that over time, human awareness and motivation has
been shaped by natural selection, which produced biobehavioral characteristics
that bestow a survival or fitness advantage to the species.2 In the broadest sense,
“fitness” refers to an organism’s ability to survive and successfully reproduce in
its current environment, the consequence of which is that the organism contributes
its genes to the next generation.3 Accordingly, humans are born with “innate cogni-
tive blueprints” that are essential for their ability to prosper and produce progeny.2
Importantly, we also have an evolved capacity to experience considerable pleasure
and happiness from these key adaptive pursuits, like eating and drinking, as well
as mating and rearing children.
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Davis
‘Food Addiction’
The notion that some individuals can become “addicted” to
food has been widely accepted among the general population
for decades, as shown, for example, by the founding in 1960
of Overeaters Anonymous, a program based on the 12-step
approach first used to treat alcoholism. Despite increasingly
persuasive clinical and scientific support in recent years
for the view that some cases of overeating have striking
behavioral and neurobiological similarities to substance-
(and nonsubstance)-abuse disorders (eg, compulsive intake
in the face of adverse consequences, strong cravings, and
withdrawal symptoms in the abstinent state),4–7 the food-
addiction construct has nevertheless also had its detractors.
In their evaluation of the evidence, however, some critics have
wrongly conflated obesity and binge eating with the notion
of food addiction, a stance that has only served to muddle the
debate.8 Others have, more plausibly, questioned the veracity
of the concept, because “food”, unlike “drugs”, is necessary
for human survival. Therefore, they argue, one cannot develop
strategies to avoid it altogether, as a drug addict could toward
cocaine or heroin or nicotine.9
In the recently published Diagnostic and Statistical
Manual of Mental Disorders (DSM)-5,10 the existence of
behavioral addictions was recognized, for the first time, in
its chapter on substance-related and addictive disorders,
although gambling disorder is currently the only condition
listed in that category. Interestingly, prior to the DSM-5
and since 1980, pathological gambling was classified as
an impulse-control disorder, distinct from substance-abuse
and -dependence disorders. While other excessive behaviors
related to sex, exercise, eating, and shopping had been con-
sidered for inclusion in the behavioral addiction category of
the DSM-5, none was thought to have sufficient (research-
based) validation as a mental health problem at the time of
publication.11
Gambling has always been the least contentious (non-
substance) addictive behavior among members of the
scientific community, as reflected, for example, in the history
of the DSM. By contrast, eating and sex have been viewed
more antagonistically as potentially addictive behaviors.12 This
bias seems to mirror the popular belief that eating and sex are
intrinsic to our well-being, while drug-taking and gambling
are hedonistic, immoral, and supremely unnecessary activities.
It may also be that the nonspecific and abstruse nature of the
food-addiction label is a major impediment to its acceptance
as a valid clinical entity. Indeed, we have argued elsewhere that
this putative syndrome is unsuitably named – perhaps even an
oxymoron – because the word “food” is mostly associated with
positive attributes and connotes the quintessential element
of human existence. “Addiction”, on the other hand, implies
pathology and even antisocial behavior.13 It may be much more
appropriate to use terms like “hyperpalatable processed-food
addiction” or “sweet, fatty, and salty food addiction”, because
the kinds of food that are perpetually craved and eaten to
excess, and that comprise the vast majority of binge episodes,
are not grown or raised in nature. Instead, they are exceed-
ingly dense in calories from added fat, sugar, and salt, and are
perceived by most as irresistibly appetizing.14 Others have also
been critical of the food-addiction terminology and proposed
the terms “eating addiction” or “addictive eating disorder”
to highlight the behavioral disturbances associated with this
compulsive overeating syndrome.15
Several comprehensive review papers have documented
the experimental, preclinical, and clinical evidence that cer-
tain foods can mimic the behavioral and neurophysiological
effects of addictive drugs, and importantly that the data for
these findings come entirely from studies of highly palatable
fare, and show more pronounced effects following periods of
deprivation.4,16–18 Like all creatures, we have a strongly innate
drive to acquire enough food to survive and to sustain our-
selves during lean times; consequently, we have an evolved
proneness to eat beyond caloric need and in the absence of
physiologically driven hunger. There is little dispute, there-
fore, that the many highly processed foods can overwhelm
brain-reward circuitry in a way that natural foods cannot,
because of their sheer density of preferred nutrients.19 In other
words, in the manufacture of these ultraprocessed foods, the
potency of the ingredients that make them so appealing to our
palate (ie, sugar, fat, and salt) has been increased multifold.
In this regard, they display a strong likeness to highly purified
drugs of abuse and contemporary forms of gambling, which
also activate brain-reward pathways beyond their evolved
“safety zone”.
Less often considered in discussions of food addiction and
debates about its conceptual legitimacy is that psychoactive
plant substances and gambling-related activities were once
comparable to natural rewards like food, because they also
conferred a survival and/or reproductive (fitness) advantage.
Hagen et al recently posed an important question when they
queried the basis on which neuroscientists tend to classify
drug reward as “abnormal” and food reward as “normal”
when both activate the same mesocorticolimbic dopamine
system, both produce strong approach and consumptive
behaviors, both enhance well-being, and both foster the con-
ditioning of cues that predict their availability.20 Moreover,
these authors dispute the premise that so-called natural

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An evolutionary perspective on addictive substances and behaviors
rewards like food and sex “activate” brain-reward circuitry,
while addictive drugs “hijack” these same pathways. Just
like many highly processed foods, what has made addic-
tive drugs profoundly capable of altering neurobiological
functioning – thereby shifting motivation and behavior toward
compulsion and pathology – is their manufactured potency
and easy availability.
In the following sections of this paper – and largely
from an evolutionary viewpoint – evidence is reviewed that
plant-based drugs and gambling-related behaviors were once
adaptive for human survival in a similar way as nature’s
energy-based foods were for nourishment. Offering this
perspective is intended to challenge the notion that “food”
cannot be addictive in the same way as gambling, inhaling
cocaine, or drinking alcohol, because unlike these activities,
we cannot live without eating. The crux of the issue is that
one is able to have a sufficient diet, with appropriate amounts
of energy, vitamins, and minerals from required macro- and
micronutrients, without consuming ultraprocessed foods, in
the same way as one can live in modern societies without
smoking nicotine or inhaling cocaine.
An evolutionary interpretation of
gambling behavior
Taking chances and wagering on probabilistically uncertain
outcomes are the core components of gambling, a form of
risky behavior that is undertaken, in a myriad of different
ways, to win resources, and that has pervaded all cultures as
far back as prerecorded history.21,22 We have learned that such
activities tend to be favored more by those with a venture-
some predisposition, a proneness to precarious decision mak-
ing, and a high capacity for reward.23–25 Collectively, these
are stable individual-difference traits, with a clear biological
basis in the general population. Undoubtedly, the historic
persistence of gambling-related characteristics strongly
bespeaks their evolutionary significance in the behavioral
repertoire of most animals, including Homo sapiens.
In nonhuman studies, the unpredictability of a valu-
able stimulus seems to be more attractive than the delivery
of a relatively certain reward. Pigeons, for example, will
reliably select the option with a suboptimal probability of
reinforcement (20%) over another that provides a better
(50%) reinforcement, findings that are consistent with other
Pavlovian experiments showing that a seldom-occurring
conditioned stimulus (CS) results in more rapid learning
than when the CS occurs more frequently.26 Interestingly,
it was also found that pigeons reared in a socially enriched
environment were less likely to prefer unpredictability than
those animals reared in isolation.27 These findings mesh
with human-research evidence that pathological gambling
is more likely to develop in people who experience stress-
ful situations and/or a lack of stimulation in their everyday
lives.28 Such findings have been explained by the fact
that poor environments typically resemble unpredictable
environments, which are difficult to comprehend cognitively.
Therefore, and according to the compensatory hypothesis,
reward seeking is the best behavioral strategy in an unpre-
dictable environment.28
It has also been shown that dopamine activation and
release in reward pathways is sustained during the interval
between the CS and delivery of the reward – a time when
there is maximal uncertainty about its arrival – while the
dopamine-activation level is similar to baseline when the
reward is actually delivered. These findings suggest that
dopamine release is an important learning/teaching signal,
and therefore has a multiple and essential role in the acquisi-
tion of survival behaviors.29 In essence, dopamine is, as well
as other things, a signal of “surprise”, because its release is
triggered by unexpected rewards to a greater degree than
when the reward is perfectly predictable. Thereby, its action
assists the organism in learning the value of a particular
stimulus, and what actions will enhance the likelihood of
acquiring future rewards in a particular circumstance.30 If
reward unpredictability was not a highly motivating event,
important survival behaviors would be extinguished because
of the high failure rate experienced by animals in acquiring
the necessities of life.28 Typically, these behaviors are not
extinguished by failures and losses, but instead the lack of
success tends to arouse and enhance an animal’s interest in
relevant reward-seeking activities. Such motivational pro-
cesses are therefore an evolutionary strategy “that consists
of compensating the difficulty to predict significant objects
and events in a given context”.28
The ability to survive in an uncertain world requires an
innate facility for achieving a successful balance between the
exploitation of known resources (ie, predictable options) and
the exploration of one’s surroundings (ie, riskier choices), in
order to learn about the potential for more valuable options
elsewhere.31 It is the exploration strategy that underlies
behavioral choices in human gambling activities. Not only are
these strategies strongly predisposed in human phylogeny, but
there are pronounced individual differences in preference for
exploration versus exploitation approaches. Take, for example,
the evidence of more variation in reproductive fitness in males
than in females – that is, compared to females whose repro-
ductive success is relatively homogeneous, many males fail

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Davis
to reproduce at all, while some reproduce at relatively high
rates.21 These sex differences have been used to explain in
part why males are inherently more prone to taking chances,
while females tend to be more risk-averse.32
Current gambling addictions, which are increasingly prev-
alent in modern society, can be explained in a manner similar
to the relatively recent emergence of excessive and compul-
sive overeating, and according to “evolutionary mismatch”
viewpoints. The basic tenets of this theory are that certain
behaviors were enhanced during human evolution – and the
hunter-gatherer lifestyle from which our genetic endowment
had its origins – because they conferred both survival and
reproductive advantages to the species. However, in the con-
text of an environment rapidly changed, these same behaviors
have become maladaptive and overexpressed.33 Due to a broad
range of technological advances in agriculture and industry,
environmental changes in the past century or so have occurred
much more rapidly than was observed in prehistoric times.
As noted earlier, the allure of chance is at the heart of
gambling, and can be a highly rewarding stimulus. Especially
when reinforcement is given randomly and intermittently,
interest in the stimulus is aroused and sustained.34 Current
arenas for gambling, such as Las Vegas-style casinos, Internet
sites, and the increasing number of weekly cash lotteries, have
been designed to create intense visual and auditory stimuli,
which are quickly conditioned to signal gains and rewards
to the participants.34 In other words, due to their increased
salience and potency, hyperrewarding stimuli can transform
evolved stratagems for survival into compulsions that com-
promise health and well-being.
Plant substances as medicinal
“food”: a coevolutionary viewpoint
Many botanical materials produce a range of chemicals,
including alkaloids, which have been used historically to
promote health in a variety of ways.35 It is well-established
that humans have frequently and deliberately ingested plant
substances for medicinal purposes.36 In this regard, Hagen
et al have argued compellingly that the human brain evolved
to control and regulate intake of a broad range of psychoactive
plant toxins in order to promote reproductive fitness and to
minimize fitness costs.20 For instance, our genetic ancestors
regularly and knowingly consumed small amounts of poten-
tially lethal substances, which had no macronutrient content,
despite signals of toxicity like their bitter taste or nauseating
effects.20 Indeed, under certain conditions, other mammals
are also known to consume certain plants with low nutritional
value, but which contain highly bioactive compounds.
An important evolutionary question is why animals,
including humans, learned to ignore signs of plant toxicity
like bitter taste and aversive side effects in order to consume
potentially lethal substances that essentially have no energy
content.20 A core premise of evolutionary theory is that a trait
cannot evolve unless it contributes to overall reproductive
success. Therefore, there must have been an advantageous
trade-off for the risk associated with the ingestion of poten-
tially toxic substances. As with modern therapeutic drugs,
when certain plant substances are ingested in small amounts
and below their toxic threshold, they can be helpful in main-
taining health or aiding in disease recovery.37 For instance,
certain plants evolved the ability to synthesize alkaloid
compounds, such as caffeine and nicotine, which on the one
hand served as neurotoxins to deter their consumption by
herbivores, but on the other hand also provided benefits to
those who did ingest them (as discussed in sections to fol-
low).38 Collectively, such behaviors suggest a type of natural
self-medication.37 They also infer an “instrumentalization”
role for certain substances that historically served various
adaptive functions for reproduction and survival.39 It can be
argued therefore that we evolved a genetically determined
predisposition for drug use. It has been the purification of
psychotropic plant ingredients, however, and their ready
availability in many societies globally, that have led to an
increased propensity for problem drug use. The risk for
dependence and abuse is consequently an environmentally
induced fallout of our once-adaptive preferences for these
natural substances.
Ethanol and ripened fruit
The human preference for sweet taste is an innate character-
istic that has evolved to activate pleasure-generating brain
mechanisms that are phylogenetically very well preserved.40
Prehistorically, sugars provided various evolutionary
advantages. For instance, they have been shown to have
natural analgesic properties in infants and children, they
signal the likely absence of toxicity in the food source, and
they provide a prompt source of energy to the organism,
since the mammalian brain uses only glucose as a source of
energy.41,42 It is believed that in turn fruits evolved a richness
of sugar to promote their consumption by herbivores as a
way of dispersing seeds.43
Ethanol is a naturally occurring substance that is produced
in ripe and overripe fruits where the sugar and starch compo-
nents of the plant undergo yeast fermentation. Therefore, our
preference for selectively consuming ripe over unripe fruits
demonstrates another evolutionary adaptation, because the

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alcohol plumes radiating from ripe fruit help in the localization
of this food source.44 There are also antibacterial properties
associated with eating fermenting fruits.45 Furthermore,
consumption of small traces of ethanol acts as an appetite
stimulant: another beneficial adaptation given the valuable
nutritional resources found in ripe fruit. In addition, it can
facilitate social behavior, which is conducive to reproduction
and safety. Even small amounts of alcohol have the ability
to reduce social inhibition, anxiety, and discomfort, and to
increase communication and intimacy.39
The presence of ethanol in ripe fruit suggests that
chronic albeit low-level exposure to this substance must
have occurred in all frugivore species, which in turn would
have favored the evolution of physiological advantages of
alcohol ingestion while minimizing related costs.46 It has
been suggested therefore that modern humans have almost
certainly evolved a preference for alcohol because our his-
torical ancestors derived from frugivorous primates who
had a sensory bias associating fruit-derived alcohol with
nutritional reward.46
The availability of alcohol at concentrations higher than
those achieved by yeast fermentation alone has occurred only
relatively recently in human history as a result of distillation
and purification processes.44 These changes in potency have
clearly increased the population odds of alcohol misuse and
dependence. Other factors have also contributed importantly
to the increased prevalence of hazardous drinking and alco-
holism. For instance, the powerful alcohol industry has played
a key role in promoting alcohol use through its lobby against
tax increases, against restrictions on availability, and against
advertising regulations.47 On the other hand – and in order to
try and enhance its status as a good corporate citizen – the
alcohol industry has also provided support for educational
interventions, despite compelling evidence that educational
approaches are largely ineffective in changing drinking
behaviors.48 In many countries, the public sale of alcohol
is not restricted to just bars and restaurants, but occurs at a
host of community venues like sporting arenas, fairgrounds,
and centers for the performing arts. Such liberal access to
alcohol at relatively low cost with full legal sanction makes
this drug more available than all illicit substances and other
legal drugs like nicotine.
Nicotine
In the coevolution between flora and fauna, some plants
developed the capacity to synthesize neurotoxic alkaloids like
nicotine in order to deter their own consumption by humans
and other animals.38 In a relationship that was essentially
antagonistic, but also mutually beneficial, herbivores in turn
regularly used such plant toxins to improve their health and
well-being: a process that has been variously called “self-
medication” or “pharmacophagy”.36 Contrary to public
opinion, however, nicotine consumption is not a modern
invention, but was widely used by hunter-gathers in the
Americas for millennia.49
Alkaloids like nicotine not only tend to improve perfor-
mance and concentration and enhance mood50 but are also
known to have effective antiparasitic properties,51 and were
ingested by our herbivore ancestors as a defense against their
own helminth infections.52 Helminthiasis is the infestation of
intestinal parasitic worms (eg, roundworms or hookworms)
whose eggs are secreted via human feces and in turn con-
taminate the soil in areas with poor sanitation. This condi-
tion was historically, and continues to be, a pressing global
health problem, because it compromises nutritional status
and can also impair cognitive processes.53 Indeed, it has been
proposed that the human propensity to consume neurotoxic
plant substances may have evolved in large part as a type
of chemoprophylaxis and/or as a form of chemotherapy to
combat dangerous parasite infections.36
In a recent and innovative study designed to test the
self-medication hypothesis regarding the recreational use
of tobacco, the Aka – a group of Central African foragers
who regularly smoke tobacco and who also have very high
rates of helminth infections – were studied longitudinally.36
Importantly for the purposes of this study, the Aka are not
aware of the medicinal benefits associated with nicotine use.
Findings indicated that higher nicotine exposure was associated
with a significantly lower “worm burden” among the adults
tested. Moreover, in a subset of the sample who were treated
with an effective commercial antiparasitic drug (albendazole),
those with higher cotinine (a metabolite of nicotine and bio-
marker for exposure to nicotine) concentrations in the blood
in the first year after treatment had lower reinfection rates in
the second year. Together, these results provide support for
the chemoprophylaxis hypothesis of nicotine use.
Nicotine is a notable example of a plant-based substance
whose use was not problematic and did not lead to tobacco
addiction until dramatic production and processing changes
took place during the middle of the nineteenth century,
events that increased the potency of tobacco and led to the
greatly increased manufacturing capacity of cigarettes. In an
interesting treatise on the history of tobacco, Slade describes
the industrial innovations that caused the “greatest epidemic
of the twentieth century”.54 For instance, the development of
flue-curing at very high temperatures reduced the nitrogenous

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material and increased the sugar content in the tobacco leaf,
thereby making its smoke easier to inhale. Early mecha-
nized cigarette rollers were still labor-intensive until the
invention in 1884 of a machine that increased production
from approximately 3,000 cigarettes a day to 120,000, caus-
ing availability to increase and prices to fall. And finally, the
perfection of the friction match ensured that smoking could
take place virtually anywhere.
Other plant alkaloids
The opium poppy (Papaver somniferum) is an ancient but still
heavily used medicinal plant, which has been cultivated in
eastern Mediterranean countries like Turkey since prehistoric
times, and was profoundly important in the culture and diets
of people in these regions for its important role in counteract-
ing the deleterious effects of pain.55 Archaeological findings
have also revealed the widespread use of opium for cult
rituals and for its healing and soporific properties.56 Opium
is the dried “milk” of the poppy capsule, which comprises
approximately 12% morphine with lesser amounts of codeine,
and is the sole source of these key pharmaceuticals.57 In other
words, the opium poppy is the only commercial source of
morphine and codeine, because this type of alkaloid precludes
chemical synthesis as a marketable and affordable option.58
Historically, benzylisoquinoline alkaloids like morphine and
codeine from the opium poppy were typically obtained by
manual extraction, but harvests were generally small because
these compounds accumulate in relatively low levels in plant
cells.35 Therefore, our genetic ancestors would only have
received trace levels of these chemicals.
Opium and other poppy-derived opiates, such as heroin,
have now become major drugs of abuse, with a global pro-
duction of illicit manufacture. Through purification processes
using chemical extraction, morphine was first produced in
the early nineteenth century by Friedrich Sertürner, and is
believed to be the first isolation of a plant alkaloid in his-
tory.59 Since then, advanced technology has produced greater
supplies and more purified end products, while metabolic
engineering and selective breeding have been used to increase
the content of alkaloid levels like morphine in the latex of the
plant. Morphine is now easily turned into heroin by chemical
production, a process that effectively increases its potency
to twice that of morphine. The opium poppy is indeed a
poignant example of a plant-based compound that through
human ingenuity has provided both great positive and great
negative value to humankind.58
Cocaine is another psychotropic plant substance, which
derives from the Erythroxylum coca leaf and has been
consumed in many regions of South and Central America
since prehistory. It has been noted that for millennia,
people have sought out as food plant species that contained
disproportionate amounts of secondary chemicals that
provided benefits beyond being a source of calories and
macro/micronutrients. The ancient practice of chewing the
coca leaf exploited the cocaine content in this plant for use as
a local anesthetic, and to combat the deleterious consequences
of high altitude.60 The behavioral effects of this medicinal
alkaloid also importantly include increases in stamina and
attentional focus and the suppression of appetite, outcomes
that were clearly adaptive during periods of hunting and for-
aging, in times of food scarcity, and during long migrations
to suppress fatigue and cravings when food was scarce.45 In
addition, plants like the coca leaf provided neurotransmitter
precursors like tryptophan and tyrosine when high-quality
food (eg, meat) was not available.61 Moreover, the coca leaf
also functioned as food, in that it is rich in many essential min-
erals (eg, calcium and iron) and vitamins (eg, A, B2, and E).61
Once again, through the ingenuity of mankind, this psychotro-
pic substance has been condensed and significantly purified
into powder and crystals that are magnitudes stronger and
more potent than the substance used beneficially – albeit in
trace amounts – by our ancestral forbears.
In conclusion, it should also be noted that historically
both cocaine and opium were generally only problematic to
localized immigrant groups until each of these products was
processed and transformed into more transportable, longer-
lasting, and more potent products. In other words, it was
essentially the development of highly processed drugs that
led to the addiction problem as we think of it today.
Processed foods as modern “drugs”
The popular press, as well as the scientific and medical
community, has often vilified processed foods for their role
in providing a poor-quality diet and for their contribution to
rapidly increasing health problems like diabetes and cardio-
vascular disease. In discussing these issues, however, it is
important to be specific about the impugned “culprit” and the
criticisms levied at it. Simply stated, food processing refers
to the mechanical or chemical alteration of a particular food
from the state in which it was grown or raised, by means of
some preserving technique to avoid spoilage. It is also an age-
old technology that has existed since prehistoric times, and
whose original purpose was to enable access to energy stores
during times of scarcity.62 As such, it has helped to ensure
that sufficient food is available to feed global communities.
In other ways, food processing has also contributed to the

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health of global populations. For example, if not for the
fortification and enrichment of such foods as bread and milk,
large proportions of the population would have deficien-
cies of vitamins like A, C, D, and E, and minerals like iron,
calcium, magnesium, and folate.62 It is clear, therefore, that
it is the kind of alterations made to the food that determine
their merits and demerits.
Until relatively recently, most preserving and processing
of food took place in the home. However, with the advent
of large-scale industrial food processing and the capitalist
enterprise, technologies changed dramatically to accom-
modate the quest for commercial success and to gain the
“competitive edge”. Enhancing the palatability of foods is
at the heart of food marketers’ strategies to increase revenue
at the retail level. Consumption of sugar, for example, has
tripled worldwide in the last half century, largely because it
has been added to nearly all processed foods.63 Over the past
3 to 4 decades, the proportion of household consumption of
ultraprocessed foods – those products that are ready to eat or
ready to heat – has steadily replaced unprocessed/minimally
processed foods.64 The former are typically characterized by
greater energy density, and contain significantly more added
sugar, saturated fat, and sodium than the latter. Carbonated
soft drinks and commercial baked goods appear to be the
most significant vectors for sugar and salt, while added oils
contribute to the high fat content in much of the ultrapro-
cessed and highly palatable foods we consume today.65 Of
all these added ingredients, many believe that sugar – ie,
any sweetener containing fructose that is supplemented via
food processing – is the primary component contributing
to the addictive potential of some foods. For instance, in
an examination of the components of a typical “fast food”
meal, it was concluded that while added fat and salt tend to
increase the salience of the food, it is the sugar and caffeine
that foster its compulsive intake.66
The most problematic sugar seems to be fructose, which
has increased globally, at least threefold in the last century.67
Evidence suggests that dietary fructose is not required for
any human biochemical reaction; moreover, in the quantities
we consume it, there are various negative effects on human
metabolism, such as an undermining of normal satiety
signals.68 There are also compelling arguments that fructose
is simply “alcohol without the buzz”, because the latter is
produced by the fermentation of fructose.68 In fact, the simi-
larities between sugar and alcohol are particularly strong,
because both have a strong potential for abuse. Interestingly,
although comparative data are very limited, population
prevalence rates of “food addiction” (as diagnosed by the
frequently used Yale Food Addiction Scale)69 and alcoholism
appear to be approximately the same: between 5% and 10%
of the population.70,71 It has also been found that a hedonic
responsiveness to sweet taste is positively correlated with a
propensity to drink alcohol excessively and with the genetic
risk for alcoholism.72
Although ultraprocessed foods do not produce the
inebriation caused by alcohol or the euphoria some experi-
ence from stimulant drugs like cocaine, they nevertheless
have pronounced parallels with conventional addictive
drugs. For instance, both have the capacity for triggering
cravings, and are associated with compulsive consumption
and the inability to cut down, even when the consequences
are knowingly dire.73 Similarly to the downwardly spiral-
ing process of drug addiction, excessive stimulation of the
brain’s common reward pathway – a core mechanism of
human survival – by foods made highly palatable by the
addition of sugar, fat, and salt contributes to increasingly
compulsive consumption. In turn, the effects of tolerance
and reduced inhibitory control may prompt even more
frequent and more prodigious intake, contributing to an
interdependent series of behaviors that tend to become
more severe over time.
Conclusion
In summary, there is good evidence that humans have shared
a 200 million-year coevolutionary relationship with psycho-
tropic plant chemicals,61 and that most popular addictive drugs
are derived from plant neurotoxins or their close chemical ana-
logs.20 As reviewed in this paper, there is considerable historical
evidence of the deliberate use by humans of plant materials for
medicinal/self-medication purposes. In our ancestral environ-
ment, “drugs” were simply plants and therefore were consumed
alongside other more energy-rich foods.61 Unlike current times,
the biologically active compounds found in plants would
have been scarce in hunter-gatherer environments. Through
cultivation, purification, and chemical modification, however,
these same substances have increased in concentration, and
are now plentiful and highly potent.45 In addition, there are
many “novel psychoactive compounds” that are manufactured
as substitutes for plant-based compounds like cocaine,74 or
as synthetic alternatives, such as the dozens and dozens of
manmade cannabinoids.75 Consequently, pharmacophagic
qualities that would once have conferred a survival advan-
tage in our “environment of evolutionary adaptation” appear
to diminish reproductive fitness in our current surroundings
through excessive and sometimes compulsive use.45 In other
words, even if substance-seeking from medicinal plants was a

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Davis
process of adaptive self-medication for our hominid ancestors,
it is not necessarily so in our contemporary environment for
the reasons stated earlier.61
Over time, and via cultivation, manufacturing, and
advanced technology, certain processed foods have also
acquired the strength to sabotage healthy brain function and
override well-regulated and adaptive behaviors. In other words,
they can overpower normal brain mechanisms and divert them
from guiding human behaviors in advantageous directions.76
What has happened to the foods that comprise much of our
current diet is directly parallel to the transformation of other
once-adaptive substances and behaviors to forms that are
highly addictive and potentially dangerous. In a similar feat
of insidious contrivance, the reward impact of food has been
magnified multifold by the addition of sugars, fats, and salt, as
well as other taste enhancers like monosodium glutamate.
Therefore – and in the context of the rise in global rates
of obesity, for instance – genetically-based predispositions
that were once beneficial have become disadvantageous in
environments that provide ad libitum and superfluous access
to nutritional substances. As Lustig et al stated poignantly
about sugar, “… nature made [it] hard to get; man made it
easy”:63 so can the same be said of all potentially addictive
substances derived from plant materials.
Acknowledgments
The author wishes to thank very much the two anonymous
reviewers who reviewed and offered exceedingly insightful
suggestions on an earlier draft of this paper. I am indebted
to them for their very helpful comments.
Disclosure
The author reports no conflicts of interest in this work.
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