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expert reaction to impact of sugar on mental health

Using data from the Whitehall II cohort – an interdisciplinary study on ageing – researchers publishing in Scientific Reports analysed people’s sugar intake and the occurrence of common mental disorders.


Ms Catherine Collins, Registered Dietitian, and Spokesperson for the British Dietetic Association, said:

“Depression and mental health issues affect diet in many ways, and researchers have long been keen to determine if a poorer quality diet is a symptom, or a contributor to, mental health problems.

The researchers in this study imply that a sugary diet did indeed contribute to self-reported depression over a five year period (but not two year period) in men. Whilst the food frequency questionnaire used to determine sugar intake was an appropriate tool, ‘translating’ this into daily sugar intake was deeply flawed, and so the findings from this study are interesting, but nothing more.

“This large study of UK men and women employed in the Civil Service reported back only on the men.  Interestingly, 1/3 of the original group were female, which reflects civil service recruitment preferences and not the typical UK population. Women have a far greater emotional engagement with food, yet this study failed to find any correlation between sugar intake and depression short term or longer term in women.

“This survey found no link between total sugar intake and the subjects’ confirmation of ‘doctor diagnosed depression’ within 2 years of the study review. By five years, those men in the reported highest sugar intake had a significantly raised risk of self-reported ‘doctor-diagnosed depression’, even when adjusted for other factors that may contribute to mood, such as marital status, age, alcohol intake and exercise.

“The researchers concluded boldly that ‘their research confirms an adverse effect of sugar intake on long-term psychological health’ and make an unproven recommendation that a lower sugar intake would improve psychological health. Neither of these statements can be justified based on major issues with the diet survey which limits their findings. To be in the highest category of sugar intake required consumption of more than 67g a day. Yet for the average 2500kcal a day recommended for males, this would equal 10.7% of total calories, which is within the recommendations if an assumption was made that half the sugar was from ‘added’ or ‘free’ sources.

“First, although alcohol intake was recorded, its contribution to sugar intake wasn’t qualified – for the heavier drinkers this could have been a significant oversight, especially if the favourite tipple was beer, lager or cider. For heavy drinkers, self-reporting is always inaccurate.

“Second, the use of ‘standard portions’ suggested by the food analysis ‘bible’ (McCance and Widdowsons Composition of Foods (available free online at ) to ‘translate’ the food frequency data into amounts of food and drink consumed are well out of date compared to current estimates, and you can’t ‘scale’ up an intake accordingly. For example, whilst a can of Coke is usually 330ml (but can now also be a downsized 250ml), a muffin or doughnut has almost doubled in size over the last 10 years. Food portion sizes would have distorted the calculated sugar intake significantly. The researchers also failed to separate out the ‘added’ or ‘free’ sugars (such as sugar in tea, chocolate bars, sweets and sugary drinks) from the ‘natural’ or ‘inherent’ sugars present in milk and milk dishes (like custard), which aren’t part of the ‘5% of daily calories from free sugar’ recommendations.

“The group confirmed that sugar intake from foods and drinks correlated with obesity risk. This isn’t surprising, as sugar contributes 4kcal per gram towards daily energy intake. But it can’t be used to predict energy intake overall. For example, a 45g bar of Cadburys Dairy Milk provides 25g of sugar and 240kcals, due to the 14g of fat in the bar, too. But a 330ml can of sugary cola has 35g of sugar. That’s 10g more sugar than the bar of chocolate, but it has fewer calories – 140kcal – because sugar is the only source of calories in this sugary drink.

“Third, the group appear to confuse ‘sugar intake’ from both naturally occurring (e.g. milk) and added (‘free’ sugars, such as sugar added to hot drinks, in sweets and chocolates etc.). This is an oversight.

“Finally, whilst the findings as reported are interesting, the dietary analysis makes it impossible to justify the bold claims made by the researchers about sugar and depression in men. More surprising is the lack of reported effect in women, who have a far more emotional relationship with food. Reducing intake of free sugars is good for your teeth, and may be good for your weight, too. But as protection against depression? It’s not proven.”


Prof. Tom Sanders, Professor Emeritus of Nutrition and Dietetics, King’s College London, said:

“This is an observational study not a clinical trial and its interpretation needs to be treated with caution.

“The authors report that poor mental health was more common in women under 50, in lower employment grades, current smokers, who were leaner rather than fatter as might be expected with a high sugar intake, and who had other life-style influences (e.g. divorce, sleep deprivation). Sugar intake was greater in those with low socioeconomic status and was associated adverse health related behaviours such as smoking and low physical activity.

“There was no significant gender interaction meaning that males followed the same pattern. However, I note that if individuals with clinical depression at baseline are excluded there is no significant effect.

“While the authors have tried to adjust for the effects of social factors there still is a risk of residual confounding. There is also a major problem in that sugar intake is under-reported in the overweight and obese which the authors acknowledge. From a scientific standpoint it is difficult to see how sugar in food would differ from other sources of carbohydrate on mental health as both are broken down to simple sugars in the gut before absorption and the glycemic index of sugar is less than refined starchy foods such as white bread and rice.

“A further limitation is that the association with sugar intake and poorer mental health was only seen with the measurements of intake at baseline and not with the follow up measurements. When individuals reduced there sugar intake in the later follow up phases there was no change in risk of poorer mental health. To be a convincing results, I would expect to see the association with high sugar intake to persist with long-term follow-up which was not the case.”


Prof. Rob Howard, Professor of Old Age Psychiatry, UCL, said:

“This study is important because it is the first to be able to show that an increase in risk of about a quarter in common mental disorders, mostly mild anxiety and depression, in men who eat the most sugar cannot be explained by those who were already anxious or depressed using sugar as a form of comfort.

“Failure of the data to reveal an uncomplicated association between high sugar intake and subsequent development of more serious depression is also important. Study of larger and more representative participant samples, with better capture of the development of mental health symptoms, will be needed before we can add depression and anxiety to the long list of physical health conditions that we already know are linked to high dietary sugar intake.”


* ‘Sugar intake from sweet food and beverages, common mental disorder and depression: prospective findings from the Whitehall II study’ by Knuppel et al. published in Scientific Reports on Thursday 27th July.


Declared interests

Ms. Collins: “No conflict of interest to declare”

Prof. Tom Sanders: “Prof Tom Sanders is a Scientific Governor of the charity British Nutrition Foundation, member of the scientific advisory committee of the Natural Hydration Council (which promotes the drinking of water), and honorary Nutritional Director of the charity HEART UK. He is now emeritus but when he was doing research at King’s College London, the following applied:

“Tom does not hold any grants or have any consultancies with companies involved in the production or marketing of sugar-sweetened drinks. In reference to previous funding to Tom’s institution: £4.5 million was donated to King’s College London by Tate & Lyle in 2006; this funding finished in 2011. This money was given to the College and was in recognition of the discovery of the artificial sweetener sucralose by Prof Hough at the Queen Elizabeth College (QEC), which merged with King’s College London. The Tate & Lyle grant paid for the Clinical Research Centre at St Thomas’ that is run by the Guy’s & St Thomas’ Trust, it was not used to fund research on sugar. Tate & Lyle sold their sugar interests to American Sugar so the brand Tate & Lyle still exists but it is no longer linked to the company Tate & Lyle PLC, which gave the money to King’s College London in 2006.

“Tom also used to work for Ajinomoto on aspartame about 8 years ago.

“Tom was a member of the FAO/WHO Joint Expert Committee that recommended that trans fatty acids be removed from the human food chain. Tom has previously acted as a member of the Global Dairy Platform Scientific Advisory Panel and Tom is a member of the Programme Advisory Committee of the Malaysian Palm Oil Board. In the past Tom has acted as a consultant to Archer Daniel Midland Company and received honoraria for meetings sponsored by Unilever PLC. Tom’s research on fats was funded by Public Health England/Food Standards Agency.”

Prof. Howard: “Although I work at UCL, I have no connection with any of the authors of this study.”

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