New evidence shows that changing the amounts of carbohydrates, proteins and fats in breakfast impacts serotonin levels in the brain and the riskiness of people's behavior.

In a study published March 12 in NeuroImage, researchers in Germany varied the macronutrient levels in a carefully measured breakfast to test 32 participants' risk-taking behavior. The authors observed a change in the brain's chemical messaging systems, including the neurotransmitter serotonin, and found that an individual's body fat mass also impacted their willingness to make risky decisions.

Corresponding author Soyoung Q. Park told The Academic Times that the most challenging part of the process was the study's design. People are often less inclined to participate in research that limits their food intake, she explained, as food is such a personal and emotional part of daily life. Park offered participants their favorite lunch after the study in an effort to make the research more appealing, and to provide a normal meal after a breakfast with carefully calculated portions and ingredients. Another possible limiting factor is the participants' fullness, which the researchers first rated to ensure that the results were not driven by what Park refers to as "hanger," or a state of anger from being overly hungry.

The double-blind study featured two different meals, each of which totaled 850 kilocalories. The first had a high carbohydrate-to-protein ratio and included whole-grain bread, strawberry marmalade and two types of fruit along with other simple ingredients. This option was 80% carbohydrates, 10% fats and 10% proteins. The second breakfast, which offered participants sunflower seed bread, Camembert and yogurt, was lower in carbohydrates and higher in protein, with a makeup of 50% carbohydrates, 25% fats and 25% proteins. The makeup of the macronutrients in the second breakfast followed Germany's government recommendation for everyday nutrition.

Participants were asked to make choices between a risky option and a safe alternative 3.5 to 4 hours after the meal. Previous research established this time frame as the period with the biggest difference in neurotransmitters such as serotonin, which is key for the current study. Two risky options offered individuals a 50% gain of large or small numbers, while the safe alternative presented a 100% gain of an intermediate number.

The researchers observed a significant increase in plasma tryptophan in participants who ate a high-carbohydrate breakfast. Tryptophan is a precursor to serotonin in the brain and indicates a higher level of this chemical messenger in the nervous system. Serotonin plays an important role in regulating mood; many people know this chemical may reduce depression and regulate anxiety.

The authors found that serotonin's effect on risk-taking behavior was dependent on a person's body fat mass. After a high-carbohydrate breakfast, individuals with lower body fat had a smaller change in their tryptophan levels, while tryptophan was greatly increased in those with higher body fat. The same meal resulted in people with high body fat being more averse to risk, while low body fat individuals were more prone to make risky decisions. These results suggest that body composition influences one's metabolism of tryptophan, and in turn, the amount of risk one is willing to take.

Park was intrigued to see these changes in tryptophan since the neurotransmitter is often created in the digestive system. One study from the California Institute of Technology estimates that "90 percent of the body's serotonin is made in the digestive tract." As digestive tracts are highly variable between people, Park said that the differences in tryptophan absorption "might be dependent on the gut microbiome composition."

Another key finding from the high-carbohydrate breakfast was increased responses in the parietal lobe, which governs risk-processing in the human brain. The authors found that "individual differences in fat mass were positively correlated with changes" in this brain region, which provides "strong evidence" of macronutrients driving behavioral change. The low-carbohydrate meal resulted in markedly lower changes in both tryptophan levels and risk-taking behavior.

The team notes that more research is needed on how a person's body fat, physical activity or typical eating habits affect their absorption of different nutrients. Park hopes that future research on behavior change will provide a "personalized way to apply nutrition to both physical and brain health."

"What's important to keep in mind is that many people underestimate the impact of nutrition on our health," Park said, though she noted that regulating diet is not a catch-all solution for health problems. In the paper, she and her co-authors provided evidence that macronutrient-driven changes regulate behavior and decisions -- so much so "that it closely mimics pharmacological driven changes." But Park cautions that their findings are just proof of principle and do not necessarily mean that dietary changes should take the place of clinical drugs.

Park and her collaborators are now working on a project that measures how one's body adapts to nutrition over a long period of time. The concept is similar to how antibiotics or other drugs become less effective with repeated use. For example, people who drink coffee every day eventually need more espresso shots for the same effect. Park and her team are curious to see if receptors in human brains and bodies adapt to a certain level of carbohydrates or protein and if this threshold is learned from previous eating habits. 

The study, "Eating to dare - Nutrition impacts human risky decision and related brain function," published March 12 in NeuroImage, was authored by Lu Liu, German Institute of Human Nutrition, University of Lübeck and German Center for Diabetes Research; Sergio Oroz Artigas, Anja Ulrich and Jeremy Tardu, University of Lübeck; Peter N. C. Mohr, Freie Universität Berlin and WZB Berlin Social Science Center; Britta Wilms and Sebastian M. Schmid, German Center for Diabetes Research and University of Lübeck; Berthold Koletzko, University of Munich Medical Center; and Soyoung Q. Park, German Institute of Human Nutrition, University of Lübeck, German Center for Diabetes Research and Charité-Universitätsmedizin Berlin.