Losing weight has previously been seen to improve the psychological state of overweight and obese individuals, including mood. But when it comes to the effects of low carb diets, the researchers from CSIRO noted that previous research has looked at weight loss, but not the psychological implications.
To investigate this, the team designed a one year study involving 106 overweight and obese individuals with an average age was 50 years. Fifty five of these were randomly assigned to follow a very low-carb and high fat diet, and 51 followed a high-carb, low fat diet.
Throughout the year and afterwards the participants’ total mood disturbance, anger-hostility, confusion-bewilderment, and depression-dejection were measured.
The weight loss of participants on both diets was around the same, averaging at 13.7kg (30.2lbs). In the first eight weeks, both groups also experienced an improvement in mood.
After that, however, only those on the low fat diet kept their improved mood; those in the low-carb group were seen to revert to an initial, more negative baseline mood.
“This outcome suggests that some aspects of the low-carbohydrate diet may have had detrimental effects on mood that, over the term of one year, negated any positive effects of weight loss,” the authors wrote.
The study itself was unable to provide a firm explanation for the observation, but the researchers suggested a number of possible reasons.
The low-carb dieters may have experienced greater food preoccupation, social eating impairment and dysphoria than their low-fat counterparts because the Western diet is so geared towards high carb food like bread, pasta and rice.
Another suggestion is that highly prescriptive diet plan, which set out specific quantities of food and regular advice and counselling had an impact on mood.
However the low fat dieters, too, were on a prescriptive plan, and their mood improvement remained. Something about the low carb diet may therefore have interacted with the physiological discomfort of a prescriptive regime.
The researchers suggested that the low carb diet had some effect on serotogenic functions in the brain, especially since such functions have been linked to depression and anxiety in the past. A high carb intake can increase serotonin synthesis, whereas fat and protein intakes reduce serotonin concentrations in the brain.
“Further studies evaluating the psychophysiological effects of low carb diets on serotonin and neurotrophic factors are required,” they wrote.
The low carbohydrate diet was designed to provide 4 per cent of total energy as carbohydrate, 35 per cent as protein, and 61 per cent as fat (of which 20 per cent saturated fat).
The low fat diet gave 46 per cent of energy as carbohydrates, 24 per cent as protein, and 30 per cent as total fat (less than 8g saturated fat).
Archives of Internal Medicine, 2009; 169(20):1873-1880
“Long-term effects if a very-low-carbohydrate diet and a low fat diet on mood and cognitive function.”
Authors: Brinkworth, G; Buckley, J; Noakes, M; Clifton, P; Wilson, C.