It's that time of year again.
Christmas carols blaring from the stores tell us that "It's the most wonderful time of the year", but most of the people maxing out their credit cards inside those stores don't look like they're taking the advice to "be of good cheer".
According to a comprehensive review of the depression-inducing effects of added sugars published in Medical Hypotheses, maybe they would feel better if they weren't fuelling their Christmas gift-buying/Boxing Day sale marathon with sugary foods and beverages.
(Come to think of it, they would probably feel a lot better if they chose not to stress themselves to the eyeballs and bury themselves in debt in the first place, but that's an article for another day. Oh and by the way, if you know anyone who would rather receive valuable information on health and well-being than yet another pair of socks or Christmas sweater, you could always…)
The review, titled The depressogenic potential of added dietary sugars, summarises the current state of scientific knowledge on the effects of the ubiquitous sweet stuff on our mood, and the mechanisms by which those effects occur.
First, what is the evidence that added sweeteners sour our mood? There are three types of study designs that can shed light on the sugar-mood connection:
For example, a meta-analysis of ten cross-sectional studies found that those who consumed the most sugar-sweetened beverages (such as soft drinks, sweetened iced tea, juice drinks and energy drinks) had a 30 per cent higher risk of being depressed than those who drank the least.
Prospective cohort studies find a roughly 20 per cent higher risk of becoming depressed in those with the highest consumption of added sugars compared with the lowest, and once again, consumption of sugar-sweetened beverages is a particular culprit.
And experimental studies show that added sugars do not have any beneficial effect on mood (contrary to the popular belief in the 'sugar rush' effect), and in fact have deleterious effects on components of mood, including alertness and fatigue.
So now we come to the second question: how does the consumption of added sugars affect our mood and depression risk?
The review proposes 6 primary mechanisms: inflammation, gut dysbiosis, dysregulation of dopamine pathways, oxidative stress, insulin resistance and formation of advanced glycation end-products (AGEs). These mechanisms interact with each other in complex ways:
I've written many articles about the role that our resident gut bacteria play in health and disease, including mental health (see, for example, Gut bugs and human health: A tale of two evolutionary trajectories, Fat chance of having a healthy gut, Anxiety and the gut microbiome: How your gut bugs can chill you out or stress you out, and Of bugs and brains - how your gut microbiome affects mental health, for starters).
I've also covered the inflammation-depression connection (see Inflammation: why you're fat, sick, tired, depressed and in pain... and what to do about it and Rumination inflammation), and as you can see from the above diagram, inflammation is inextricably linked with oxidative stress, insulin resistance and AGE formation.
So in this article, I'm going to hone in on the effect of sugar consumption on dopamine signalling in the brain.
Dopamine is a neurotransmitter - a chemical messenger that allows nerve cells to talk to each other, and to muscle and gland cells - associated with reward, learning and motivation. In my previous article, Reprogramming your stone age brain for health and happiness, I explained how the dopamine system gets 'hijacked' by supernormal stimuli such as hyperpalatable foods (those rich in calories, fat, refined carbohydrates and/or salt).
Research on sugar in particular indicates that it stimulates the dopamine system, in a dose-dependent fashion; that is, the higher the intake of sugar, the greater the release of dopamine. In the short term, this results in an intense sensation of reward, which prompts us to reach for more sugar... and THAT'S why it's so hard to stop at one slice of cake or one doughnut!
However, continual high intake of sugar causes maladaptive changes in the structure and function of dopamine pathways. Over time, the brain reduces the number of dopamine receptors in an attempt to protect itself against continual overstimulation of dopamine pathways (much like people develop 'tolerance' to addictive drugs, requiring higher and higher doses to get high).
Interestingly, reduced dopamine activity has been observed in the brains of depressed people. This is associated with the decreased ability to experience pleasure (anhedonia), and the enormous difficulty in motivating themselves to take any actions that might improve their lives, that depressed people experience.
Or in science-speak,
"A substantial body of evidence suggests that chronic added sugar ingestion can interfere with intrinsic reward systems in a manner capable of inducing anhedonia and motivational deficits. Both are hallmark symptoms and maintenance factors of depression."
The depressogenic potential of added dietary sugars
Put plainly, over time, eating too much sugar makes you feel like all the joy has been sucked out of life, and causes you to feel like you couldn't be bothered doing anything - what's the point, when nothing you do brings you any enjoyment? And the more unmotivated you become, the less you engage in any activities that could make you feel better about yourself, and life in general. It's quite literally a depressing downward spiral.
Reversing this spiral is not easy. As a person's dopamine system adapts to a constant barrage of excessive sugar, higher and higher degrees of sweetness are required for them to experience any sensation of reward from eating.
If this person suddenly drops all added sugars and attempts to follow a wholefood plant-based diet, he or she will at first experience no enjoyment from the new way of eating, and will be tempted to abandon it without a clear understanding that this is a temporary state, which will correct itself over time.
How long does it take? The very unsatisfactory answer is, it depends. Genetic variations in dopamine receptor activity, the amount of added sugar the person was previously consuming, the length of time they've been overconsuming sugar, and the level of stress in their life will all impact on how quickly their dopamine system recovers its equilibrium to the point where they can once again perceive the natural level of sweetness in whole, natural foods as rewarding.
And there's an additional complication: in the early stages of this recalibration process, added sugar becomes even more reinforcing. That is, if you cut out all added sugars for 1 week and then eat something with an added sweetener, you'll find it even more rewarding than previously, when you were eating sugar all the time.
I see this pattern frequently in my clients: they stick to a healthy diet with no added sugar for a couple of days, weeks or even months, notice how great they're feeling and how much sweeter natural foods such as fruits and starchy vegetables taste to them... then they let down their guard, eat just one slice of cake, piece of chocolate or scoop of ice cream, and find themselves bingeing uncontrollably. Back to square one.
How do you escape this dietary Pleasure Trap?
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