In the context of this article the Sugar-Brain refers to neural correlates regarding
sugar consumption. Firstly, information is given on the classification of
sugar, a brief mention of different categories of sugar, and the properties underpinning
different sugars. Secondly, a concise
overview of brain reward mechanisms is appropriate.
The term sugar, in everyday discussion, generally
refers to sweets or highly processed sweet tasting food. The term is
excessively ambiguous, so when discussing in everyday conversation it is not always
clear what one is referring to. I
usually assume the referent is highly
processed, calorie dense, sweet food, in most cases.
Sugar, in the context of science,
is defined precisely and is dependent on various properties. Sugar (of all
types ) is a carbohydrate. The term
carbohydrate was originally used to describe compounds that were hydrates of carbon;
they have an empirical formula of CH2O. In my book- The Carbohydrate Files 2nd
editon (2007)- I presented two classification
systems: Basic
Carbohydrate Classification System
(BCCS) and the Advanced Carbohydrate Classification System (ACCS). A concise
overview of the ACCS is presented here.
Carbohydrates are polyhydroxy
aldehydes, ketones, alcohols, acids, their simple derivatives and
their polymers having linkages of
the acetal (any organic compound formed by adding alcohol
molecules to aldehyde molecules)
type. They may be classified according to their degree of
polymerization ((Polymerization
is a chemical process that combines several monomers to form a polymer or polymeric
compound.) and may be divided into three principal groups: sugars,
oligosaccharides and polysaccharides. Sugars are the focus in the current
article.
Monosaccharides, the basic units
of a carbohydrate, are white crystalline solids that may be divided into
aldoses, which have an aldehyde group on the first carbon atom, and ketoses,
which typically have a ketone group on the second carbon atom. They may also be
divided according to the number of carbon atoms that they contain. The suffix “-ose”
is used to identify these molecules as sugars.
Triose: monosaccharide with three
carbons
Tetrose: monosaccharide with four
carbons
Pentose: monosaccharide with five
carbons
Hexose: monosaccharide with six
carbons
Heptose: monosaccharide with
seven carbons
Sugars include monosaccharides,
disaccharides, and polyols (sugar alcohols). The
monosaccharides are categorized
as glucose, fructose, and galactose (formula C6H12O6). The disaccharides are composed
of two monosaccharide units. The binding between the two
sugars results in the loss of a
hydrogen atom (H) from one molecule and a hydroxyl group (OH)
from the other. The disaccharides
are categorized as sucrose, lactose, trehalose, and maltose
(formula C12H22O11). Sugar
alcohols, technically called polyols, are are found in numerous sports drinks,
bars, and various other types of sweets. Polyols are generally known as
sugar-free
sweeteners. They are
carbohydrates, but they aren’t sugars. Chemically, polyols are considered
polyhydric alcohols or sugar alcohols because part of their structure resembles
sugar and part is similar to alcohols. However, these sugar-free sweeteners are
neither sugars nor alcohols. The most widely used polyols are sorbitol,
mannitol, and maltitol.
Proponents of the Sugar-Brain claim that consumption of sugar can activate the same
brain reward mechanisms (dopamine pathway referred to as mesolimbic dopamine
system) as the consumption of addictive drugs. This is true; so it is not a
myth? You have probably seen photos
comparing the sugar-brain with the drug addiction-brain. Hold on before jumping
to conclusions. The problem with the claim is the way it is presented
(implications) and inferences made regarding the claim. The claim is a rhetorical
device used to convince people that sugar consumption is bad, like drug
consumption.
What is the mesolimbic dopamine system? Drug
researchers have traditionally identified the mesolimbic dopamine system as the
brain system mostly involved with drug addiction. This system may be extended
to include cortical areas (in PFC)- mesolimbic cortical dopamine system
(Kandel, 2012). Some sources refer to these systems as being the same; however,
the mesolimbic dopamine system can be more accurately described as projecting
from the ventral tegmental area to the nucleus accumbens (NA, often referred to
as the major pleasure center in the brain), while the mesolimbic cortical
dopamine system projects from the ventral tegmental area and extends to areas
in the PFC. Their distinction is not important in the context of this article
(either are involved with drug consumption and brain reward mechanisms-
reward/pleasure circuitry). These circuits are rich in dopaminergic neurons. Dopamine
cell bodies are located in the ventral tegmental area and substantia nigra. The
focus here, is on the projection from the ventral tegmental area.
Objects, stimuli, activities or internal physical
states can serve as rewards for humans and non-human animals. Rewards have
positive value and facilitate feelings of pleasure and positive emotion; they
act as positive reinforcers. Not only do rewards lead to the activation of
dopaminergic activity, but so does expectations or anticipation of rewards. "[T]he
flow of dopamine is set off by the simplest expectation of pleasure, even
though the pleasure may not materialize" (Kandel, 2012, p.428).
The brain's reward mechanisms are activated when we
enjoy art, experience beautiful scenery, are exposed to attractive faces,
listen to pleasant music, are exposed to humor or novelty, drive a sports car
and experience romantic love. The Sugar-Brain could easily be called the
Love-Brain.
Evaluating brain imaging is complicated, and there
is often disagreement among those highly qualified regarding implications of
imaging. If sugar consumption is not a rewarding act what can we expect
regarding activity of brain reward circuitry? It is a drastic
over-simplification to suggest that - because, consuming sugar may lead to
activation (reiterating- the variability in activation is large) of brain reward
mechanisms- it should be held in the same regards as drug use. "Dopamineric neurons in the striatum
respond to all kinds of pleasure." Eric Kandel- Nobel Laureate
Science sounding information is often inserted to
enhance persuasive value.
References available upon request