Nothing to see here, folks, this is the usual 'system I is cheap and reasonably accurate' vs 'system II is expensive and highly accurate'; from http://whywereason.wordpress.com/2012/03/05/why-the-future-of-neuroscience-will-be-emotionless/

After waiting a few minutes to let the sugar reach the brain the students assessed four cars and four jobs, each with 12 key aspects that made them more or less appealing (Bos designed the study so an optimal choice was clear so he could measure of how well they decided). Next, half of the subjects in each group spent four minutes either thinking about the jobs and cars (the conscious thought condition) or watching a wildlife film (to prevent them from consciously thinking about the jobs and cars). Here’s the BPS Research Digest on the results:

For the participants with low sugar, their ratings were more astute if they were in the unconscious thought condition, distracted by the second nature film. By contrast, the participants who’d had the benefit of the sugar hit showed more astute ratings if they were in the conscious thought condition and had had the chance to think deliberately for four minutes. ‘We found that when we have enough energy, conscious deliberation enables us to make good decisions,’ the researchers said. ‘The unconscious on the other hand seems to operate fine with low energy.’

So go with your gut if your energy is low. Otherwise, listen to your rational horse.