Microbiome in Weight Management

What we choose to eat is driven largely by taste, likes and dislikes, cultural and perhaps ethical reasons – as well as influenced by images and the latest diet fads we see through our daily newsfeed or social media channels. It also depends on where we live, availability and cost, and of course on hunger and appetite signals. This mix of factors will in turn influence weight. Another important thing to consider is the role of our gut microbiota.

Inflammation and appetite

Firstly, it is important to consider the specific hormones that affect our hunger. These act on the hypothalamus, a small area at the base of the brain, which oversees our daily intake of food and eating behaviour. It has been finely tuned by evolution to monitor the right amount of energy we need to take in through our food.

When the stomach is empty, cells located in its lining secrete a hormone called ghrelin, which is sent to the hypothalamus to signal that it is time to eat. At the end of a meal, when we are full, our gut releases appetite-suppressing hormones such as leptin and peptide YY (PYY). This switches off the need to eat so that we know when enough is enough.

However, research might be suggesting there could be some ‘glitches’ in this appetite system. This could be due to low-grade chronic inflammation (from stress or illness perhaps for example), which can disrupt the microbiota–gut–brain communication. This has the ability to disrupt the hormone response so that the brain doesn’t receive cues that we have had enough to eat, and then we don’t receive the appropriate signal to stop.

It has been proposed that this inflammatory ‘feedback loop’ can be a contributor to overeating and weight gain, and is why obesity is often referred to as a disease of inflammation.

Another crucial part of this inflammatory picture relates to SCFAs (short-chain fatty acids) that are mainly produced by gut microbiota. Studies with mice who were fed a high energy diet alongside supplementation of one SCFA, butyrate, gained much less weight than those that were not.

Therefore, from both an inflammation and a weight management perspective it is important to nourish the gut microbiota appropriately with foods that can encourage the production of SCFAs.

‘Feel good’ food and gut microbiota cravings

Another angle to consider is food cravings. Part of this could be due to the muddled communication between the gut and brain outlined above, but it also relates to the dopamine reward system. Dopamine is one of the so-called ‘feel-good’ neurotransmitters, and is associated with a sense of pleasure – it is this that is activated in addictive behaviours.

The dopamine reward system is also hooked up to our appetite regulation hormones. This makes sense in terms of evolution: when calorie-dense, high-fat and high-sugar foods were scarce our hormones motivated us to find these foods and rewarded us with a feeling of pleasure when we ate them. However, in our modern society, where these foods are available at any time, it is all too easy to end up overconsuming, with a constant ‘reward’ feedback to encourage us to seek out these ‘feel-good’ foods. Chuck in the barrage of advertising to compound the problem and it’s easy to see how temptation can get the better of us. We essentially become conditioned to keep eating high-sugar, high-fat foods.

Furthermore, because our gut microbes produce and influence dopamine, it has been suggested they may have some ability to sway our dopamine reward system towards specific foods they have a preference for eating. This makes sense for their own survival and to give them a superior position in the gut over other microbes.

‘Lean’ gut microbiota…is there such a thing?

It would be entirely misleading to label microbes as having the ability to influence a leaner physique. However, studies on the composition of the gut microbiota have demonstrated that a higher proportion of the Firmicutes group of bacteria is associated with increased inflammation and a higher propensity for obesity. This has born the tongue-in-cheek comment ‘Firmicutes make you fat’ but the reality is that certain groups of gut microbes, like Firmicutes, are particularly adept at extracting energy (calories) from food. In contrast, studies found that gut microbiota profiles with a higher proportion of Bacteroidetes bacteria and a generally more diverse population of microbes were associated with a naturally leaner physique.

Given all this, it doesn’t seem unrealistic to speculate that weight management is not just to do with willpower alone, and it certainly questions the basic ‘calories in versus calories out’ theory. In fact, it is worth considering that our weight and perhaps our penchant for specific foods might have some very significant correlations with the bugs in our gut? These are cutting-edge and somewhat controversial opinions but it does certainly provide food for thought!

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