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Sugar's Effect on Neurotransmitters

By Jeffrey Traister

Carbohydrates contain sugar your body metabolizes for energy. Carbohydrates also influence the blood levels of certain amino acids and the synthesis of neurotransmitters, substances in your brain that communicate messages between nerve cells and affect your mood, appetite and sleep. Consult your doctor about specific concerns regarding your diet and the effect sugars have on neurotransmitters.

Amino Acids and Neurotransmitters

Tryptophan and tyrosine are dietary amino acids vital for synthesis of neurotransmitters, also called monoamines. Tryptophan is the precursor to serotonin and tyrosine is the precursor to dopamine and norepinephrine. Scientists at the University of Pittsburgh School of Medicine in Pennsylvania report the rate of synthesis of neurotransmitters in the brain depend on concentrations of the monoamine precursors, according to research published in the "Journal of Nutrition" in 2007. The scientists explain that diet influences brain pools of these amino acids and the rate of synthesis of neurotransmitters.


Sugars in your body come from dietary carbohydrates, including polysaccharides that contain ten or more units of glucose, oligosaccharides that contain three to nine units of glucose, disaccharides, such as lactose, sucrose and maltose and monosaccharides. Lactose, the sugar in milk, contains glucose and galactose that your body converts into glucose. Sucrose, a common sweetener, contains glucose and fructose that your body converts to fat or glucose. Maltose from the processing of barley contains two molecules of glucose.

Sugar Metabolism and Insulin

The absorption of glucose, the sugar your cells utilize for energy, stimulates secretion of insulin into blood. Insulin is a hormone that transports glucose from your blood into your cells. Insulin also increases transfer of amino acids from your blood into your skeletal muscle cells, particularly large neutral amino acids, including branched-chain amino acids such as leucine, isoleucine and valine. Branched-chain amino acids produce muscle protein. As a result of insulin’s effect on amino acids, increasing carbohydrate consumption reduces the amount of large neutral amino acids in the blood and increases the ratio of amino acid precursors to neurotransmitters, enabling higher concentrations of these precursors to pass through the blood-brain barrier and enter the brain.

Carbohydrate Meals and Neurotransmitters

Increasing your consumption of sugars increases the production of neurotransmitters in the brain. Scientists at Massachusetts Institute of Technology in Cambridge found that a carbohydrate-rich meal induces increases blood levels of insulin and increases ratios of tryptophan to large neutral amino acids and tyrosine to large neutral amino acids, according to research they published in the "American Journal of Clinical Nutrition" in January 2003. The scientists report that carbohydrate consumption increases tryptophan greater than it increases tyrosine. This suggests carbohydrates have a bigger effect on serotonin production in the brain than it has on neurotransmitters dopamine and norepinephrine production in the brain.

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