Bugs: Coming soon in an ice-cream near you!

'Nanners and Rummy Raisin
Ice Cream"' by ulterior epicure
under a CC license

Within a few days after our birth our intestines get populated by numerous bacteria. Such bacteria will, normally, keep us company until the end of our lives. With them, we are connected by a bit more than a mere co-existence. Current knowledge describes our relationship with plenty of the gut flora microorganisms as "symbiotic": we feed them, provide warmth and shelter to them and in return the keep our guts safe from pathogens, train our immune systems and release metabolites of theirs, some of which are necessary for us. Well, that relationship does go pear-shaped occasionally, but life is full of messy stuff, isn't it?

The interesting thing is that the more we look into our intestinal population the more links we find between their existence and our lives. Yesterday, the New Scientist was highlighting research findings on rats, which suggest that the composition of the gut flora has an effect on appetite, initially, and, later on, changes in the body weight: Changing the gut flora of obesity-resistant rats to that of the obesity-inclined one increased the appetite, firstly, and the weight, secondly, of the former.

Weight changes and the composition of the gut flora is nothing new. In 2006, the New Scientist featured a corresponding article. It was based again on research carried out on mice. That time they compared normal μmice with ones that had been living in sterile conditions and, thus, had no microorganisms within their digestive track. Those mice tended to stay slim. Having their gut populated by the flora of the normal mice lead to a body weight increase of about 25%. If the flora used was similar to that of obese mice, the weight gain was much higher. That observation was attributed to the effect of the gut flora on the food that passes via the intestines; the microorganisms living there help metabolize it more efficiently, thus producing more energy the mass unit than without their intervention. The more efficient the microorganisms are, the higher the weight gain for mice.

Combining the two observations there are several questions that come to mind:

• Let's assume that gut flora that is more efficient in processing the food we normally eat leads to us getting more calories out the food. Temporarily, that will lead to weight increase unless we either reduce our food intake or increase our physical activity. However, it is suggested in the 2012 article that the appetite (of rats) is enhanced. Does this mean that the flora microorganisms mess with the energy intake - appetite mechanism of the host? And if yes, is that a temporary effect? What pathway does it messes up with?
• Since the gut flora lives on what food we consume and on the metabolites secreted by our cells, locally, do they have any mechanism to "encourage" us to eat the food that is most nutritious to them? I don't necessarily refer to "mind-control" but to any pleasant or unpleasant symptom that may encourage or discourage us from eating stuff that "tastes" nice or not-so nice, respectively, to our intestinal guests.
• Is it possible to sustainably change one's gut flora in such a way that it will lead to better weight control? Can this be done in a safe way? What will be the catches (because, surely, there will be at least one downside!)?

The last point carries particular weight for the food industry. Foodstuffs with probiotic content have been consumed practically since the beginning of civilisation; fermented dairy products being a common example. Recently, the trend has expanded and, for some time, probiotics (and prebiotics) became central to what is typically referred to as "functional food".

'Strawberry Panna Cotta'
by Matthew S. Cain under
a CC license

If probiotic microorganisms can indeed help maintain a healthy body weight, without negative side effects, they could become particularly interesting for foods that tend to be tempting and are often responsible for making a weight-loss diet feel particularly punishing.

Ice-cream is a good example. The idea has been explored a few years ago and there seems to be little concern for technological limitations. Household-oriented recipes have also been available for - say - yoghurt ice-cream or more exotic stuff, such as kefir-based chocolate ice-cream.

Having said that, I find the path of "slimming" foods to be a potentially slippery one. Regardless of how pleasant the thought is of devouring tons of yummy ice-cream and, still, lose weight, the wise thing to do is seek for a healthy, balanced diet and live a life with plenty of physical activity. And then, why not, enjoy the occasional scoop or two of our favourite dairy vice....