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