Was reading an article about the effects of drinking tea with sugar versus tea with stevia, tea with sucralose (sold here in the US as Splenda, for example), and tea without sweetener, on stress reactions.*
Fifty people of a wide range of ages participated in the experiment. On the test days the participants first filled out a questionnaire about their level of stress, then after either the no-stress or the stress condition drank teas. In the no-stress situation, participants simply filled out a questionnaire about their mood state; in the stress situation they had 10 minutes in which to solve math and logic problems, which they were told was going to tell the researchers whether they had high, medium, or low IQ. This test has been shown to reliably induce stress (no surprise there!)
Here is the tea-drinking methodology as described in the article:
“Participants were then seated in individual sensory booths to taste the tea samples. A total of four samples were presented in a sequential monadic fashion based on William Latin Square Design31. Approximately 90-mL of each sample was provided in a 112-mL cup with a three-digit code. Participants were asked to rate on a 9-point scale how calm (1: extremely stressed; 9: extremely calm) and pleasant (1: extremely unpleasant; 9: extremely pleasant) they felt before drinking the tea samples. Participants were then asked to drink the entire cup of tea and rate only its sweetness intensity on a 15-cm anchored line scale (0: extremely weak; 15: extremely strong). Participants also rated their overall liking of the tea sample on a 9-point hedonic scale (1: dislike extremely; 9: like extremely). Participants also rated how calm and pleasant they felt after drinking the tea sample similar to how they did before drinking the sample.”
The order in which they drank the teas varied from person to person. From reading the methodology, the authors did not take into account this order in the data analysis. I assume that they felt they didn’t need to do so, because they felt that the results clearly favored the calming effect of tea with sugar compared to tea with the other sweeteners. Here is the graph:
[BTW, wondering why the calmness was negative for both stevia and unsweetened, rather than neutral...no explanation for this in the paper, and of course we don't have any idea about the order of presentation of the teas and whether this order may have led to any outliers, not to mention whether there were people who were outliers to begin with.]
The authors speculate that the reason that the sugar was more calming was because it provided the brain with the calories it needed to deal with the stress. As they noted, the brain needs glucose to function—in fact it uses more glucose than any other organ of the body, and takes up about 3% of the calories we need each day.
At the same time, they point to literature that suggests that sucrose activates many more brain pathways than do artificial sweeteners.** Therefore another possible explanation for the effect may be that the reward circuits in the brain are activated more readily by sucrose than by other sweeteners.
I would like to point to another possibility: that theanine and caffeine in tea crosses the blood-brain barrier and enters the brain more quickly and easily in the presence of sucrose. Theanine has a calming effect that is pretty well established, at least when taken by itself. When taken with caffeine, it may be even more effective.*** (See my blogpost http://virginiaspairteas.blogspot.com/2016/01/caffeine-l-theanine-and-egcg-and-timing.html).
When sugar is added, caffeine and theanine may go into effect more quickly. Here’s why:
There is a transport system for neutral amino acids into the brain that works when the system can also transport glucose (sucrose is made up of two molecules of glucose). Caffeine also enters the brain more easily with a dollop of sucrose. In this study, theanine and caffeine entered the participants’ bloodstreams throughout the tea drinking process, no matter what sweetener was. But when sucrose was available, theanine and caffeine could zip right into the brain. The result would be a focussing effect!
You can try this experiment for yourself. Assign yourself something somewhat stressful to do — for me it was writing this blogpost. Then use either a sweetener or sucrose and see what the effect is. Repeat on some other occasion, with the other compound—if you started with the sweetener then sucrose, or vice versa. And let me know what happened.
For me the sucrose was indeed more effective…
But here is a catch: if you use artificial sweeteners regularly (I don’t), your brain will light up the reward circuits in the same way as sucrose…and maybe act as if you had taken sucrose with your theanine and caffeine.****
Let me know what results you get with the experiment I suggest, and when you do, let me know whether you take artificial sweeteners regularly.
* Samant, S. S. et al. Tea-induced calmness: Sugar-sweetened tea calms consumers exposed to acute stressor. Sci. Rep. 6, 36537; doi: 10.1038/srep36537 (2016).
** Guido K.W. Frank, Tyson A. Oberndorfer, Alan N. Simmons, Martin P. Paulus, Julie L. Fudge, Tony T. Yang, Walter H. Kaye. Sucrose activates human taste pathways differently from artificial sweetener. NeuroImage, Volume 39, Issue 4, 15 February 2008, Pages 1559–1569.
*** Camfield, David A; Stough, Con; Farrimond, Jonathon; Scholey, Andrew B. Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis. Nutrition Reviews, ISSN 0029-6643, 08/2014, Volume 72, Issue 8, pp. 507 - 522
**** Erin Green, Claire Murphy. Altered processing of sweet taste in the brain of diet soda drinkers. Physiology & Behavior, Volume 107, Issue 4, 5 November 2012, Pages 560–567
As an aside: remember Jolt, the cola drink “with all the sugar and twice the caffeine?” One afternoon many years ago was working on a project with a student when we both started to flag, and thinking had become absurdly difficult. I then remembered that another student had given me a bottle of Jolt, so I unearthed it and we each took a swig. About 10 minutes later we both looked up…the Jolt had jolted us! The caffeine was mainlined into our brains by the sugar, and we could finish the job.
That said, I am not recommending Jolt, just present this story to illustrate how sugar can make caffeine move more quickly into the brain.