Impact of nutrition on social decision making

Abstract

Food intake is essential for maintaining homeostasis, which is necessary for survival in all species. However, food intake also impacts multiple biochemical processes that influence our behavior. Here, we investigate the causal relationship between macronutrient composition, its bodily biochemical impact, and a modulation of human social decision making. Across two studies, we show that breakfasts with different macronutrient compositions modulated human social behavior. Breakfasts with a high-carbohydrate/protein ratio increased social punishment behavior in response to norm violations compared with that in response to a low carbohydrate/protein meal. We show that these macronutrient-induced behavioral changes in social decision making are causally related to a lowering of plasma tyrosine levels. The findings indicate that, in a limited sense, "we are what we eat" and provide a perspective on a nutrition-driven modulation of cognition. The findings have implications for education, economics, and public policy, and emphasize that the importance of a balanced diet may extend beyond the mere physical benefits of adequate nutrition.

Keywords: decision making; nutrition; social decision; tyrosine; ultimatum game.

Fig. 1.

Decision making depends on breakfast carb/protein ratio. (A) In study 1, subjects were grouped in low- vs. high-carb/protein groups depending on the macronutrient composition of their breakfast on that morning. Yellow bars indicate the fraction of subjects who decided to reject. Subjects with high-carb/protein ratio breakfasts showed significantly more rejection behavior (*P < 0.05). (B) Differences (high-carb/protein minus low-carb/protein condition) in rejection rates separated for fairness categories (fair, medium, unfair) during the UG in the intervention experiment (study 2). Subjects showed an increase in rejection rates after a high-carb/protein ratio breakfast compared with after a low-carb/protein ratio breakfast. The values indicated are mean changes (±SEM, *P < 0.05).

Fig. 2.

Macronutrient composition-dependent changes in postprandial tryptophan, tyrosine, and glucose and the correlation of tyrosine with rejection rates. Blue lines indicate low- and yellow lines indicate high-carb/protein condition for (A) tryptophan/LNAA, (B) tyrosine/LNAA, and (C) glucose values (±SEM in shadowed area, *P < 0.05 and **P < 0.001). For visualization purposes, the data points were interpolated. (C) Shadowed area represents the time window of glucose decline, which significantly differs between the conditions. (D) Triangles indicate single data points for change in rejection rates and change in tyrosine/LNAA values od high- vs. low-carb/protein conditions.

Fig. S1.

UG procedure. A picture of the proposer is shown for 1,500 ms, subsequently the endowment of the corresponding proposer is presented (1,000 ms), and then his or her offer (3,000 ms). Subjects can decide whether they accept or to reject the offer within 5,000 ms and their decision is highlighted on the screen.

Fig. S2.

Breakfast study 2. According to the experimental condition, either a high-carb/protein breakfast (Left) or low-carb/protein breakfast (Right) was served.

Fig. S3.

Timeline study 2. Subjects attended the research unit at 0800 hours and were prepared for the experiments. At 0845 hours subjects received breakfast according to the respective experimental condition. Blood was drawn at 11 time points with a 15-min interval between 0845 hours and 1045 hours, with additional samples at 1130 and 1315 hours. T1–T4 indicates blood samples used for measurement of tryptophan and tyrosine and G1–G9 indicates blood samples used for measurement of glucose, cortisol, ACTH, insulin, testosterone, and SHBG.