The sweet stuff, you see, can offer us feelings of pleasure as can fat. So when fat is removed, sugar subs in to keep us momentarily satisfied (and it is quite the affordable fat substitute for manufacturers).
However, high added sugar intake can result in rapid blood glucose and insulin rise and crash as the sugars are quickly absorbed into the blood – especially in the absence of fat or fibre. Or excess refined sugar can impact the intestinal microbiome, encouraging the flourish of not-so-helpful gut bugs over the helpful ones.
And either of these scenarios or a poor diet high in added sugar may contribute to issues with mood.
So, when recent research out of Spain found that regular, daily intake of full-fat yoghurt was associated with a 22% reduced risk of depression than those who barely enjoyed a ½ a serve a week, and those that consumed low-fat were more likely to be depressed, the question is raised as to why.
Could it be because of increased added sugar intake?
Well, it may be a factor, but is likely to be more complex than that.
14,539 participants were assessed for depression at baseline, and by follow-up – an average of 9.3-years later – there were 727 cases of depression.1
Additionally, food frequency questionnaires were taken at baseline and follow-up, which included assessment of prebiotic food and yoghurt intake.
The researchers found intake of 125g of full-fat yoghurt seven or more times a week was associated with reduced depression risk compared with the lowest intake, and low-fat yoghurt consumption was associated with a higher incidence of depression (at least in the first two years after follow-up). Interestingly, when stratified by sex, this association was significant only in women, and researchers found no significant correlation between mood and prebiotic consumption.
While the findings are preliminary and observational, they reflect past research noting a similar relationship between full-fat yoghurt consumption and improved mood.
It raises questions, and many ideas, as to why such a correlation is being seen. Here are few to consider:
Low-fat yoghurts are often higher in sugar
Flavoured yoghurts are often low-fat and high added sugar. And as mentioned above, too much of the sweet stuff can have deleterious effects on mood. This can be due to the relationship between blood glucose, cortisol and reproductive hormones.
Too much sugar creates a surge in blood glucose, a surge in insulin, and a dramatic drop in each. This is a stressful event, where the body can produce the stress hormone cortisol in response to stabilise the blood glucose rollercoaster.
The pre-cursor to cortisol is shared with reproductive hormone progesterone. If you are in a stressed state – whether through what you eat or otherwise – cortisol production is prioritised over the reproductive hormones to get you through the stressful experience (and the body thinks it is a bad time to make babies, as it seems dangerous out there!).
Cortisol is our friend in acute moments of stress (i.e. when you have a car accident or are being chased by a grizzly bear). But when cortisol is produced consistently and chronically, progesterone production can be compromised; a hormone that when not produced in adequate amounts or becomes out of balance with the other reproductive hormones can influence our mood.
Granted, there are low-fat plain yoghurts that haven’t any added sugar, containing only naturally occurring lactose (which is about 4g per 100g of dairy). And as the study above did not differentiate between plain or flavoured yoghurts, the sugar-thing may not be the whole picture here.
There are some nutrients that low-fat yoghurt provide a little of but exist in abundance in full-fat dairy.
These include conjugated linoleic acid (CLA), and vitamin B6.
Vitamin B6 is a co-factor in pathways to form happy neurotransmitters such as GABA and dopamine.
CLA is thought to reduce inflammation, in the gut and more broadly. This could impact mood through implications on gut health, as well as inflammation in the brain itself, which has been associated with depression.
It is thought that those non-responsive to anti-depressants but exhibit high markers of inflammation may improve their mental health with anti-inflammatory treatment.2-3
Interestingly, the study above only found the significant relationship between full-fat consumption and reduced incidence of depression in women. Here may be why:
- Women are more likely to experience low mood, or at least report it;
- Women may have been more astute in measuring intake;
- CLA may exert anti-estrogenic activity.4 As progesterone can exert anti-anxiety and anti-depressant effects, by reducing excess oestrogen in the body and finding balance with progesterone, mood may be stabilised in women.
However, as mentioned above, stress generally causes the body to limit progesterone production. This can mean an excess of oestrogen, resulting in irritability, sadness and all manner of things associated with premenstrual syndrome.
So! By moderating oestrogen, and also exerting anti-inflammatory activity, CLA may help moderate mood.
In addition, good healthy fats are often satiating, don’t cause a massive spike and crash in blood glucose, and leave us feeling fuller for longer. So in the end, we eat less and less inclined to reach for the sugary snacks to get us through the day.
Feeding gut bugs
Those that ate more full-fat yoghurt had less risk of depression, and this could be due to increased consumption of probiotics contained within the yoghurt.
A healthy microbiome and probiotic consumption have been implicated in improved mental health, perhaps due to the gut-brain axis.2;5 And consistent consumption of 1x 125g yoghurt a day containing more than 1x 107 CFUs/g (the number of bacteria) could be enough to produce benefits to health.1
But this prospective study did not directly account for the probiotic content. A shame, really, but a good thing to include in a food frequency questionnaire in future.
A whole diet and lifestyle
As with any study, there are many confounding factors! Analysing a relationship between one food or nutrient and correlating a health outcome should also take into account an individual’s entire diet and lifestyle.
And the researchers acknowledged this. Those that ate the full-fat yoghurt were more like to eat a whole food diet typical of the Mediterranean style and exercise more. Two factors are very beneficial for mental health.
Moderate physical activity has been shown to boost endorphins, and a typical Mediterranean way of eating includes nutrient-dense real food high in antioxidants and anti-inflammatory properties, including phytochemicals and omega-3 fatty acids which are great for our brain and mood. And fibre to keep our gut bugs happy.
Moreover, and possibly most importantly, the diet really lacks the heavily refined and processed stuff.
Boost mood with real food
No doubt, there are plenty of other ideas as to the underlying mechanisms at play – and something the researchers are hoping future controlled intervention studies may be able to answer.
For now, as with much in the great world of science, watch this space. But understand that eating foods as close to their original form as possible, or with little added or heavily processed ingredients we are going to be doing ourselves a big mood-boosting favour.
By Angela Johnson (BHSc Nut. Med.)
- Perez-Cornago, A, Sanchez-Villegas, A, Bes-Rastrollo, M, Gea, A, Molero, P, Lahortiga-Ramos, F, & Martínez-González, MA 2016, ‘Intake of High-Fat Yogurt, but Not of Low-Fat Yogurt or Prebiotics, Is Related to Lower Risk of Depression in Women of the SUN Cohort Study’, The Journal Of Nutrition, vol. 146, no. 9, pp. 1731-1739
- Hayley, S, Audet, M, & Anisman, H 2016, ‘Inflammation and the microbiome: implications for depressive disorders’, Current Opinion in Pharmacology, vol. 29, no. Cancer * Immunomodulation, pp. 42-46
- Miller, AH, & Raison, CL 2016, ‘The role of inflammation in depression: from evolutionary imperative to modern treatment target’, Nature Reviews Immunology, no. 1, p. 22.
- Liu, J, & Sidell, N 2005, ‘Anti-estrogenic effects of conjugated linoleic acid through modulation of estrogen receptor phosphorylation’, Breast Cancer Research And Treatment, vol. 94, no. 2, pp. 161-169.
Foster, JA, & Neufeld, KM 2013, ‘Gut-brain axis: how the microbiome influences anxiety and depression’, Trends in Neurosciences, no. 5, p. 305