On the 21st Nov 2015, the “New Scientist” published an article called “Gut Thinking”. We have summarised the main points here and hope you enjoy it!
There are two main systems that motivate us to eat food: the hunger system and the reward system. Hunger is primarily mediated by chemical hormones. Hormones send messages to the brain from the gut and from fat cells, as discussed in the blog on hunger a few weeks ago. Examples of these hormones are ghrelin, insulin and neuropeptide-Y
The reward system is driven by the chemical dopamine. Its production is triggered more strongly by foods high in sugar and fat; hence the reward associated with eating such foods is higher than for low-calorie foods. This provided an evolutionary advantage to our ancestors because food was not always readily available. Hence, when they found sweet or fatty foods, they would be inclined to consume more because of the associated pleasurable feeling. This enabled them to store food in the form of fat for times of famine. However, today food is plentiful and this system may no longer play to our advantage!
Recent genetic work has demonstrated there is a connection between the reward and hunger systems. There is a gene called alpha-ketoglutarate-dependent dioxygenase, or, more simply FTO. One variant of the gene FTO is associated with a 70% increased risk of obesity: the particular variant that has been studied causes the body to produce higher levels of the hunger chemical ghrelin. It is also associated with a weaker reward response to sugary and fatty foods; hence people with the FTO variant are driven to consume more foods to satisfy themselves sufficiently.
Surgical techniques have also been shown to influence the relationship between the body and hunger. Patients who have undergone gastric bypass surgery become fuller more quickly and are less attracted to high-calorie foods. Patients that have gastric bands inserted, also become fuller more quickly but are still attracted to high-calorie foods. One proposed reason for the different responses is that following gastric band insertion, food enters the small intestine more quickly so the hormone response is quicker. With gastric bypass surgery, there is no associated change in the rate at which hormones are released. This suggests that gut hormones influence the reward system of the brain: in other words, the two systems are not mutually exclusive.
The response of the brain to different food types can be tricked. In a study carried out by Susan Roberts of Tufts University, participants were given low-calorie foods that mimicked higher-calorie foods (e.g: a low calorie pizza). By the end of the trial, the participants were attracted more to low-calorie food options than they were before the trial started. This study demonstrated that we may not have as much control over the foods we choose as we might think!
Recently it was shown that the microbes within our gut can also influence our food preferences. One of the ways they achieve this is by altering the receptors on our tongue. Another way is by producing chemicals that are very similar to naturally produced hormones, mimicking their action. This suggests that food supplements such as probiotics may actually be helpful in limiting food cravings, as they alter the bacteria content of the gut. This finding may also explain why people are more likely to be fat if they have a close friend or relative who is fat: because individuals who spend more time together are more likely to transmit their gut bacteria one-to-the other.
If you are interested to read this article in full, you can purchase the “New Scientist” online or from most newsagents. If you are interested to speak to a health professional about using probiotics for your gut problems, why not book a session with one of the consultants at the London Gastroenterology centre. Our specialists are very knowledgeable about gastrointestinal problems and conditions and offer a large variety of services including endoscopy, colonoscopy and life-style advice.