Yogurt, Exercise, and Nature as Mood-Boosting Interventions

Yogurt and Mood: Evaluating the Evidence

The claim that yogurt positively affects mood (Orenstein & Swencionis, 1990) was found, upon closer review, to be based on less solid evidence than initially assumed. Originally extracted from a Daily Mail news article that derived it from an NHS Choices article on health, the NHS had in turn sourced its content from a study detailing research on probiotic bacteria conducted on mice. This chain of secondary and tertiary sources significantly weakens the strength of the original claim.

The Mouse Study: Methods and Results

Researchers in both Canada and Ireland (Bravo et al., 2011) used 36 adult male mice divided into a study group and a control group. Mice in the control group were fed a broth without bacteria, while mice in the experimental group were fed a broth containing Lactobacillus rhamnosus (L. rhamnosus), a bacterium naturally present in yogurt. The experiment was carried out over 28 days, with mice receiving the treatment for one hour each morning.

At the end of the study, the researchers measured corticosterone stress levels in the mice and evaluated their behavior under various conditions. For instance, the behavior of mice was assessed in a maze, in water, and in open space. To address the possibility of confounding effects, the researchers also evaluated the role of the vagus nerve as a potential pathway for the bacteria's effects on the brain. They severed the vagus nerve in a subset of mice and concluded that if those mice no longer appeared less stressed when fed the bacteria-containing broth, the nerve was likely implicated in the effect. Finally, the researchers examined actual brain tissue from the mice to investigate levels of GABA receptor functioning.

Results showed that mice fed L. rhamnosus behaved in less stressful ways compared to mice in the control group. In both the water submersion and maze conditions, treated mice acted less anxiously than control mice. Levels of stress-related corticosterone were significantly lower in the treated mice, as were levels of GABA receptor expression in certain regions of the brain. Behavioral and neurochemical effects also differed in mice that had their vagus nerve severed, suggesting the nerve plays a mediating role.

Bravo et al. (2011) concluded that their findings demonstrated the importance of gut-brain communication and suggested that probiotic bacteria may be helpful for reducing anxiety, stress, and depression.

Limitations of the Probiotic Research

Their findings are, however, inconclusive and should be treated with caution. Most critically, the study was conducted on mice under laboratory conditions and therefore does not demonstrate that probiotic bacteria in yogurt can ease stress in humans. The physiology of mice differs from that of humans, and mice may react differently to the effects of the bacteria.

Second, the amount of bacteria administered to the mice may differ from the amount naturally present in commercially available yogurt. Third, despite efforts to control for confounding variables, the neurochemical changes observed in the mice may have resulted from conditions other than the bacteria themselves. In conclusion, while there is potential for future study in this area, evidence that yogurt reduces stress in humans still requires more rigorous investigation before firm conclusions can be drawn.

Jump Rope, Exercise, and Mood

Jump rope is a form of exercise, and exercise has been shown to have a positive impact on mood through several well-documented mechanisms. These include the release of neurochemicals such as neurotransmitters and endorphins that positively influence mood, the reduction of immune system chemicals that can exacerbate depression, and an increase in body temperature that may produce a calming effect (Mayo Clinic, Depression and anxiety: Exercise eases symptoms).

An interesting recent study adds to the body of evidence by investigating the effects of a rope-skipping program on the physical fitness and mood of elementary school children. The participants were two classes of third-grade students at an elementary school in Pingtung, China (Lee, 2010). Twenty children were randomly divided into an experimental group and a control group, with each group containing ten male and female students. The experimental group jumped rope for five to eight minutes per day, five days a week, for 42 weeks. Body composition, cardiorespiratory endurance, and mood were measured and observed at the end of the program.

Results showed significant differences across all measured variables, with the stamina and energy levels of students in the experimental group significantly higher than those in the control group. Although other conditions may have influenced mood, a substantial body of research supports the conclusion that exercise has a meaningful positive effect on mood. Rope jumping elevates heart rate, which in turn has a positive effect on emotional well-being. As a method of stress reduction, therefore, a curriculum incorporating rope jumping is strongly recommended.

References

Blanchette, I., & Richards, A. (2010). The influence of affect on higher level cognition: A review of research on interpretation, judgement, decision making and reasoning. Cognition & Emotion, 24, 561–595.

Bravo, J. A., Forsythe, P., Chew, M. V., et al. (2011). Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. PNAS, 24, 55–63.

Feldman, V., & Kokinov, B. (2009). Anxiety restricts the analogical search in an analogy generation task. Central and East European Center for Cognitive Science.

Kaplan, R., & Kaplan, S. (1995). The experience of nature: A psychological perspective. Ann Arbor, MI: Ulrich's Bookstore.

Lee, F. (2010). The effects of 4 weeks jumping rope exercise intervention on physical fitness of elementary school students. Etd.npu.edu.tw.

Plante, T. G., Cage, C., Clements, S., & Stover, A. (2006). Psychological benefits of exercise paired with virtual reality: Outdoor exercise energizes while indoor virtual exercise relaxes. International Journal of Stress Management, 13, 108–117.

Ryan, R. M., et al. (2010). Vitalizing effects of being outdoors and in nature. Journal of Environmental Psychology, 30, 159–168.