Weight loss is big business. Some authorities estimate that 45 million Americans are trying to lose weight each year and spend upwards of $33 billion annually to do so. It has been suggested that overweight and obese people experience significant improvements on a range of subjective symptoms after weight loss, regardless of diet composition.
However, dieting is also common in healthy-weight people looking to improve body composition and/or athletic performance. Consuming high-protein diets has become a popular method to aid in weight loss, as research has shown high-protein diets suppress hunger and preserve lean body mass during energy restriction in sedentary and athletic populations. These benefits are important for dietary adherence and long-term success, but they are only a piece of the puzzle.
Dieting can be psychologically complex. The brain and nervous system communicate through small chemicals called neurotransmitters. Collectively, these neurotransmitters are what allow us to be aware, have emotion, remember things, move our body, regulate body temperature, sleep, and do or feel anything that our brain allows for. In fact, many diseases like Parkinson's, Alzheimer’s, depression, insomnia, ADHD, and anxiety have been linked to neurotransmitter imbalances.
There are many ways to classify neurotransmitters, but for our purposes it’s especially important to understand the role that amino acids play in different neurotransmitters. Some amino acids, such as glycine, taurine, and glutamate, serve directly as neurotransmitters, whereas other amino acids like tyrosine and tryptophan serve as precursors for neurotransmitter synthesis. Tyrosine is the precursor for the synthesis of the catecholamines: dopamine, adrenaline (epinephrine), and noradrenaline (norepinephrine). These neurotransmitters play a central role in attention, learning, motivation, and alertness. Tryptophan serves as the precursor for serotonin, which can have an indirect effect on well-being and happiness, and plays a variety of other roles as well.
There is some controversy surrounding high-protein diets because the consumption of a lot of large neutral amino acids – tyrosine, tryptophan, and the branch-chained amino acids (BCAAs) – has been shown to alter brain neurochemistry through basic competition. That is, these amino acids all share the same transporters that allow access into the brain, and thus they all compete for entry. Since the transporters are not specific to any one of the amino acids, the largest determinant of which enters the brain is their concentrations. Thus, if the plasma level of the BCAAs increases, then brain concentrations of tryptophan, tyrosine, and their respective neurotransmitters is reduced. Theoretically, this may have negative consequences for mood, sleep, hunger, and overall liveliness.
On the other hand, carbohydrate intake has been observed to increase serotonin production secondary to insulin promoting tryptophan uptake in the brain. Theoretically, this may benefit mood. > The study under review aimed to compare the effects of different dietary protein-to-carbohydrate ratios on cognitive performance, mood, and sleep quality during short-term energy restriction.