Here is a study in a rat model about lactic acid causing anxiety and aggression, and some other studies regarding carb malabsorption and depression
Anxiety and Aggression Associated with the Fermentation of Carbohydrates in the Hindgut of Rat
Authors: Hanstock TL, Clayton EH, Li KM, Mallet PE.
Institution: School of Psychology, University of New England, Armidale, NSW 2351, Australia.
Summary:Lactic acid accumulation in the caecum and colon resulting from the fermentation of carbohydrates can lead to deleterious effects in ruminant and monogastric animals, including humans.
In the present study, we examined the behavioural effects of two types of commonly consumed foods: soluble and fermentable carbohydrates (FCs). Thirty-six male Wistar rats were fed either a commercial rat and mouse chow, a soluble carbohydrate (SC)-based diet or an FC-based diet. Social interaction, anxiety, aggression and locomotor activity were examined by employing a social interaction test and a light/dark emergence test, while physical parameters of hindgut fermentation were examined after sacrifice, either 3 or 21 h after feeding.
Results showed that anxiety (spending less time in the light compartment during the light/dark emergence test) and aggression (increased fighting during the social interaction test) were increased following raised concentrations of fermentation end products, such as lactic acid and volatile fatty acids (VFAs) in the caecum of rats.
These associations occurred regardless of dopamine and 5-HT concentrations in the prefrontal cortex (PFC) and provide evidence supporting a general effect of FCs on behaviour. Possible mechanisms of action along with similarities between a rat and human model of acidosis are discussed.
Study link:
http://www.ncbi.nlm.nih.gov/entrez/...dopt=Abstract&list_uids=15276799&query_hl=143
Anxiety Following Increased Hind-Gut Fermentation
Authors: Hanstock TL, Claytons EH, Mallet PE.
Institution: School of Psychology, University of New England, Armidale NSW 2351.
Background: Previous investigations into the effects of carbohydrate on behaviour have focussed on behavioural changes 2-4 hrs after consumption of the diet and have not considered the effect of site of digestion. Fermentation and lactic acid production in the caecum and colon can lead to detrimental effects in several animal models, including adverse behaviour in horses.
Objective: To determine changes in anxiety promoted by the consumption of fermentable carbohydrate and increased fermentation in the hind-gut of rats. Design - Randomised control trial with 3 iso-energetic dietary treatment groups, a soluble carbohydrate diet containing wheat (n=12), a fermentable carbohydrate diet based on cooked and cooled rice (n=12) and a basal control rat and mouse Chow diet (n= 12). Behaviour was assessed 3 and 21 hrs after dietary consumption by the light dark emergence test.
Outcomes: The 3 diets promoted different fermentation patterns in terms of pH and lactic acid concentrations in the caecum of rats 3 or 21 hrs after consumption. The length of time spent in the dark compartment of the light dark emergence test, indicating increased anxiety, was associated with increased concentrations of D- and L-lactic acid in the caecum (r(2)= 0.97 and 0.96 respectively; P <0.01) irrespective of dietary group.
Conclusions: Fermentation of carbohydrate leading to increased concentrations of lactic acid in the caecum of rats was associated with increased anxiety in rats. This has important implications in terms of those diets promoting increased fermentation (eg. with a high intake of resistant starch) without considering any possible detrimental effects.
Study link:
http://www.ncbi.nlm.nih.gov/entrez/...dopt=Abstract&list_uids=15023601&query_hl=141
Malabsorption of Carbohydrates and Depression in Children and Adolescents
Authors: Varea V, de Carpi JM, Puig C, Alda JA, Camacho E, Ormazabal A, Artuch R, Gomez L.
Institution: Department of Pediatric Gastroenterology, Hepatology and Nutrition, Hospital Sant Joan de Deu, Barcelona, Spain.
varea@hsjdbcn.org
Background: Previous studies have shown an association between sugar malabsorption and depressive symptoms in adult women. Incompletely absorbed sugars may form nonabsorbable complexes with tryptophan, an amino acid precursor of serotonin, decreasing its availability. As serotonin is the most important neurotransmitter involved in depressive disorders, its depletion could lead to the onset of depression.
Results: In the group with sugar malabsorption, there was a 28.5% prevalence of depressive symptoms that was higher than expected in our population. In the group with depression, the authors found a higher than expected prevalence of sugar intolerance (71.42% versus 15% in controls).
Conclusions: The unexpected prevalences obtained for the groups studied suggest that there may be an association between sugar intolerance and depressive symptoms during adolescence.
Study link:
http://www.ncbi.nlm.nih.gov/entrez/...&dopt=Abstract&list_uids=15861016&query_hl=72
Carbohydrate Malabsorption Syndromes and Early Signs of Mental Depression in Females
Authors: Ledochowski M, Widner B, Sperner-Unterweger B, Propst T, Vogel W, Fuchs D.
Institution: Department of Clinical Nutrition, Institute of Medical Chemistry and Biochemistry, University of Innsbruck, Austria.
Summary: Fructose and lactose malabsorption are characterized by impaired duodenal fructose transport or by the deficiency of mucosal lactase, respectively. As a consequence, the nonabsorbed saccharides reach the colon, where they are broken down by bacteria to short fatty acids, CO2, and H2.
Bloating, cramps, osmotic diarrhea, and other symptoms of irritable bowel syndrome are the consequence and can be seen in about 50% of carbohydrate malabsorbers. We have previously shown that fructose as well as lactose malabsorption were associated with signs of mental depression. It was therefore of interest to investigate possible interactions between fructose and lactose malabsorption and their influence on the development of signs of depression. In all, 111 otherwise healthy volunteers (81 females and 30 males) with gastrointestinal complaints were analyzed by measuring breath H2 concentrations after an oral dose of 50 g lactose and of 50 g fructose one week apart…
Further analysis of the data show that this association was strong in females (P < 0.01), but there was no such association between carbohydrate malabsorption and early signs of depression in males. In conclusion, the data confirm that fructose malabsorption may play a role in the development of mental depression in females and additional lactose malabsorption seems to further increase the risk for development of mental depression.
Study link:
http://www.ncbi.nlm.nih.gov/entrez/...&dopt=Abstract&list_uids=10961700&query_hl=61
Fructose Malabsorption is Associated with Early Signs of Mental Depression
Authors: Ledochowski M, Sperner-Unterweger B, Widner B, Fuchs D.
Institution: Universitatsklinik Innsbruck, Arztliche Direktion, Anichstrasse 35, A-6020 Innsbruck, Austria.
Summary: Fructose malabsorption is characterized by the inability to absorb fructose efficiently. As a consequence fructose reaches the colon were it is broken down by bacteria to short fatty acids, CO2 and H2.
Bloating, cramps, osmotic diarrhea and other symptoms of irritable bowel syndrome are the consequence and can be seen in about 50% of fructose malabsorbers. Having made the observation that persons with fructose malabsorption very often seem to present not only with signs of irritable bowel syndrome but also with signs of pre-menstrual syndrome and mental depression, it was of interest to establish whether such an association could be demonstrated in patients.
Fifty-five adults with gastrointestinal complaints of unknown origin (12 males, 43 females) were analyzed by measuring breath hydrogen concentrations after an oral dose of 50 g fructose and were classified as normals or fructose malabsorbers according to their breath H2 concentrations.
All patients filled out a Beck s depression inventory - questionnaire. Fructose malabsorption was detected in 36 of 55 individuals (65.5%). Subjects with fructose malabsorption (DeltaH2 concentrations >10 p.p.m. after fructose load) showed a significantly higher score in the Beck s depression inventory than normal fructose absorbers. This was true especially for females. Fructose malabsorption may play a role in the development of depressed mood.
Fructose malabsorption should be considered in patients with symptoms of major depression or pre-menstrual syndrome. Further studies are needed to clarify the background of this association.
Study link:
http://www.ncbi.nlm.nih.gov/entrez/...d&dopt=Abstract&list_uids=9620891&query_hl=61
Fructose- and Sorbitol-Reduced Diet Improves Mood and Gastrointestinal Disturbances in Fructose Malabsorbers
Authors: Ledochowski M, Widner B, Bair H, Probst T, Fuchs D.
Institution: Dept. of Clinical Nutrition, Institute of Medical Chemistry and Biochemistry, University of Innsbruck, Austria.
Background: Fructose malabsorption is characterized by the inability to absorb fructose efficiently. As a consequence fructose reaches the colon where it is broken down by bacteria to short fatty acids, CO2 and H2. Bloating, cramps, osmotic diarrhea and other symptoms of irritable bowel syndrome are the consequences and can be seen in about 50% of fructose malabsorbers. We have previously shown that fructose malabsorption is associated with early signs of mental depression and low serum tryptophan concentrations.
Results: Depression scores were reduced by 65.2% after 4 weeks of diet (P < 0.0001), and there was a significant reduction of meteorism (P < 0.0001) and stool frequency (P < 0.01). Improvement of signs of depression and of meteorism was more pronounced in females than in males.
Conclusion: Fructose- and sorbitol-reduced diet in subjects with fructose malabsorption does not only reduce gastrointestinal symptoms but also improves mood and early signs of depression.
Study link:
http://www.ncbi.nlm.nih.gov/entrez/...ubmed&dopt=Abstract&list_uids=11099057&query_
Glynis