Kao C-C, Wu W-H, Chiou W-B. Exposure to nature may induce lower discounting and lead to healthier dietary choices. J Environ Psychol. 2019;65:101333.
To determine the impact of natural and urban scenery on sugar consumption as mediated by temporal discounting (the tendency to devalue larger future benefits relative to immediate smaller gains, ie, preferring instant gratification over delayed gratification).
The study involved 93 undergraduate students at a Taiwanese university (mean age 20.9 years, 51.6% female) with a self-reported desire to lose weight. The researchers collected information about their motivation to lose weight, time since last meal, and current body mass index (BMI). Exclusion criteria included history of an eating disorder and current participation in a weight-loss regimen (including dietary changes and taking weight-loss supplements).
Participants were randomized into 1 of 3 viewing conditions in which they observed scenes on a laptop computer screen corresponding to 1 of 3 landscape viewing types: natural, urban, or control. Each condition had a sequence of 6 scenes displayed, and each image was displayed for 1 minute. Participants were instructed to “immerse yourself in the environment shown in each picture.”
Participants then completed a measure of temporal discounting (see below) as well as a psychological personality test to mask the purpose of the experiment until after the study’s completion. Lastly, participants received a “participation reward” of bubble tea with an optional amount of sugar added.
- Temporal discounting (TD): An important measure in assessing health behavior choices. TD assesses an individual’s devaluing of future benefits for more immediate rewards, ie, preferring immediate gratification over delayed gratification.1
- In the study, participants answered hypothetical questions about winning the lottery in various dollar amounts—eg, “If you won, would you rather have $2,000 now, or $4,000 a year from now?” Sequential questions of differing amounts identified a preferred “discounting rate” for each participant, from 0 (no discounting) to 1 (total discounting, ie, the participant will always choose instant gratification).
- Sugar amount (SA): Participants were able to self-select how sweet their reward bubble tea was (ie, how much sugar was in it), from 0 (no sugar) to 5 (normal sugar).
Viewing condition had a small but statistically significant impact on both temporal discounting and sugar amount, with further analysis showing the former significantly influencing the latter. Specifically:
- Participants who viewed nature scenes had 17.5% lower mean TD than participants in the urban (P=0.014) and control (P=0.029) groups.
- Similarly, nature-viewing participants had 19.1% lower SA than participants in the urban (P=0.013) and control (P=0.017) groups.
- Mediation analysis demonstrated that:
- Nature viewing was a significant factor in predicting TD (B=−0.18, SE=0.06, t=−2.749, P=0.007);
- TD was a significant predictive factor in determining SA (B=2.83, SE=0.45, t=6.347, P<0.001);
- Nature viewing was a significant predictive factor in determining SA only if TD was included in the analysis (B=−0.95, SE=0.33, t=−2.885, P=0.005).
- Lastly, nature viewing also significantly influenced the sugar-free option (ie, SA=0) but only if TD was included in the analysis (B=1.32, SE=0.50, Z=2.638, P=0.008, Wald=6.956).
All conditions were statistically equivalent regarding motivation to lose weight, time since last meal, and BMI. There was no difference between male and female participants regarding outcomes.
The ability of nature views to influence physiological and psychological state is well established.2–4 This study is one of the first to associate the presence of nature with changes in a health behavior (in this case, sugar consumption), as well as propose an explanatory mechanism (temporal discounting).
Health behaviors (ie, our choices and the actions we take regarding our health) determine 30% to 50% of our health status.5 Some of the most influential “determinants of health” are, by far, our dietary and nutritional consumption choices. This is especially true regarding chronic diseases like cardiovascular disease, diabetes, and obesity, which have well-established and obvious relationships with diet, both calorically and nutritionally.
One of the biggest influences of dietary decisions is the tendency to engage in “temporal discounting,” or the reduced ability to delay gratification.6 It is a common experience to enjoy immediate rewards (eg, eating sugar-filled “junk” food) despite knowing there will be future consequences (such as weight gain). This predilection for unhealthy short-term gains with resultant long-term detrimental effects contributes substantially to individual health conditions and the modern epidemic of many chronic, diet-influenced illnesses.
Environmental surroundings influence every aspect of our health, including conscious and unconscious decision-making that affects health behaviors.
The predominant mechanism that connects viewing of the environment with health effects, potentially including sugar consumption, invokes an evolutionary perspective. Natural scenes are known to promote psychophysiological relaxation via evolutionarily derived “biophilic” responses.7,8 Across millennia, our species has evolved to relax in body and mind when encountering the natural “baseline” environments of our prehistoric ancestors.9,10
In this study, the presence of nature vs urban or control views may have shifted autonomic nervous system (ANS) activity into a parasympathetic state away from more sympathetic dominance, thereby decreasing energy metabolism and the (unconscious) desire to have available “quick energy” in case fight or flight became necessary. Multiple studies have demonstrated ANS responses to similarly designed interventions.11,12 Though the short duration of this study makes detecting hormonal changes impractical, it is possible that interest in metabolically available sugar was also influenced by neuroendocrine changes as shown in other studies.13–15 These mechanisms could explain the relationship between nature viewing, temporal discounting, and sugar consumption by modulating feelings of hunger and satiety, as well as cognitive function and decision-making regarding health behaviors. More research in this area is needed to establish causative pathways.
This study did have its limitations. The researchers conducted no pre-post comparison of the outcome measures, so while no between-group differences in time since last meal, BMI, or motivation for weight loss were present, it cannot be ruled out that individuals in the nature group had a priori tendencies for lesser TD and/or SA. Future studies may want to standardize these factors between groups before the experimental exposure, to best determine if the variable is responsible for the measured effects.
In addition, the researchers did not ask participants why they chose their amount of sugar reward, so it may be that TD was unrelated. Future studies could address this, though it is also possible that nature-mediated TD is an unconscious process, as it is with other nature-based mental-emotional effects, such as mood, attention, memory, etc. Lastly, this was a pilot study of 93 Taiwanese undergraduates; larger studies with more diverse sample populations would increase the generalizability of the findings.
Environmental surroundings influence every aspect of our health, including conscious and unconscious decision-making that affects health behaviors. In particular, this study suggests that exposure to nature-based scenery may be helpful for reducing sugar intake in adolescent populations at risk for obesity, diabetes, cardiovascular disease, and other diet-related conditions. Combined with existing research demonstrating measurable effects on physiological and psychological state, it is becoming more apparent that contact with stimuli from natural environments may be a fundamental contributor to human health.
- Green L, Myerson J. A discounting framework for choice with delayed and probabilistic rewards. Psychol Bull. 2004;130(5):769-792.
- Twohig-Bennett C, Jones A. The health benefits of the great outdoors: A systematic review and meta-analysis of greenspace exposure and health outcomes. Environ Res. 2018;166:628-637.
- Kondo MC, Jacoby SF, South EC. Does spending time outdoors reduce stress? A review of real-time stress response to outdoor environments. Health Place. 2018;51:136-150.
- Vanaken G-J, Danckaerts M. Impact of green space exposure on children’s and adolescents’ mental health: a systematic review. Int J Environ Res Public Health. 2018;15(12):2668.
- Magnan S. Social determinants of health 101 for health care: five plus five. Natl Acad Med Perspect. 2017;7(10):1-9.
- Plazola MCC, Castillo LHS. Temporal discounting and health behavior: a review. MOJ Public Health. 2017;6(6):437-440.
- Grinde B, Patil GG. Biophilia: does visual contact with nature impact on health and well-being? Int J Environ Res Public Health. 2009;6:2332-2343.
- Wilson EO. Biophilia. Cambridge, MA: Harvard University Press; 1984.
- Ulrich RS. Human responses to vegetation and landscapes. Landsc Urban Plan. 1986;13:29-44.
- Kaplan S. The restorative benefits of nature: toward an integrative framework. J Environ Psychol. 1995;15(3):169-182.
- van den Berg MMHE, Maas J, Muller R, et al. Autonomic nervous system responses to viewing green and built settings: differentiating between sympathetic and parasympathetic activity. Int J Environ Res Public Health. 2015;12(12):15860-15874.
- Gladwell VF, Brown DK, Barton J, et al. The effects of views of nature on autonomic control. Eur J Appl Physiol. 2012;112(9):3379-3386.
- Antonelli M, Barbieri G, Donelli D. Effects of forest bathing (shinrin-yoku) on levels of cortisol as a stress biomarker: a systematic review and meta-analysis. Int J Biometeorol. 2019;63(8):1117-1134.
- Roe JJ, Ward Thompson C, Aspinall PA, et al. Green space and stress: evidence from cortisol measures in deprived urban communities. Int J Environ Res Public Health. 2013;10(9):4086-4103.
- Lin B, Yen Y, Qian X, Chen Y, Chan T. Association between neighborhood greenspace and fasting plasma glucose from a large cohort study in Taiwan. Urban For Urban Green. 2019;44:126439.