The struggle to resist cravings for unhealthy foods is a part of daily life for countless people. Many people have been led to believe that if they just wrangle a little more self-control, they can overcome their food cravings. However, this approach to managing food cravings only addresses part of the story. Contrary to popular belief, food cravings may not be a primarily brain-based phenomenon that can be overcome by willpower and motivation; in fact, food cravings may originate in an entirely different place – your gut! Gut bacteria have been found to influence the eating behavior of their host to promote their own survival, sometimes at the expense of the host’s health. (1) Read on to learn about how gut bacteria influence eating behavior and food cravings, and why improving your gut health may be the key to kicking your unhealthy cravings to the curb!
The gut-brain axis and eating behavior
The gastrointestinal (GI) tract is not just a series of tubes through which food passes and is digested; the GI tract is actually a highly complex series of organs that is densely innervated. In fact, the prevalence of neurons in the GI tract has led to its nickname, the “second brain.” The gut and the brain in your skull are connected by the gut-brain axis. This axis is a bi-directional communication system that links the nervous system of the gut with the nervous system of your brain. The circulatory system and the vagus nerve serve as links between the gut and brain, along this axis. The circulatory system allows hormones and other signaling molecules to be relayed between the gut and the brain, whereas the vagus nerve allows neurotransmitters to travel between these two locations. Gut bacteria have been found to influence the gut-brain axis of their host through the production of neurotransmitters, substances that mimic human hormones, and short-chain fatty acids, which influence host mood and behavior. (2) These biochemical substances produced by gut bacteria may influence eating behavior in the host by affecting the host’s appetite, satiety, and food cravings.
Gut bacteria generate cravings for their favorite foods
Gut bacteria need to eat to survive, and different types of commensal gut bacteria have different food preferences. Prevotella, one of the primary types of bacteria found in the human gut, thrive on plant-rich diets. Bacteroides, another type of bacteria found in large numbers in the human gut, prefer fat and protein as fuel. (3) Bifidobacteria thrive on dietary fiber, and Roseburia needs polysaccharides (a type of complex carbohydrate) in order to produce the short-chain fatty acid butyrate, which is essential for maintaining gut health. Gut bacteria are highly intelligent and can sense when their desired food is in short supply; this causes them to send biochemical signals to the brain that motivate the host to seek out the desired food. While this may be a beneficial mechanism when induced by commensal bacteria such as those I just mentioned, this mechanism may backfire when induced by potentially pathogenic microorganisms, such as Candida albicans. For example, Candida albicans, an opportunistic yeast that can cause fungal infection, can detect the presence of glucose in its environment. (4) Candida needs simple sugars to survive and increase its virulence, so when it detects that the host’s sugar supplies are low, it may initiate biochemical signals that translate into cravings for sugary foods by the host.
Gut bacteria can hijack the vagus nerve to increase appetite
The vagus nerve is the longest nerve in the human body, and one of its functions is to serve as a link between the gut and brain along the gut-brain axis. The vagus nerve has been found to be important in the regulation of eating behavior and body weight. Vagus nerve activity has been found to provoke excessive eating behavior, beyond the normal point of satiation. (5) Gut microbes that produce adrenergic neurotransmitters, which activate the sympathetic nervous system, may stimulate the vagus nerve and lead to overeating. In addition, an absence of bacteria that produce calming neurotransmitters (see the next section for details) may increase sympathetic vagus nerve activity by default, leading to food cravings and overeating.
Gut bacteria influence hunger and satiety
Approximately 50% of your body’s dopamine and 90% of your body’s serotonin are produced in your gut. Gut bacteria may produce a significant portion of these neurotransmitters. Serotonin and dopamine both influence eating behavior. (6) Lactobacilli and Bifidobacteria, two beneficial genera of gut bacteria, have been found to raise serotonin levels in the body; serotonin is a potent appetite suppressant and may decrease food cravings. (7) Lactobacillus probiotic supplementation has also been found to reduce hunger-inducing hormones in the brain, thus leading to a decreased appetite. (8)
Decreased microbiota diversity may increase food cravings
A more diverse gut microbiota may lead to reduced food cravings for several reasons. First, a highly diverse microbiota is more resistant to pathogenic species that may induce unhealthy food cravings, such as Candida albicans. Secondly, when there is a greater diversity of bacterial species in the gut, it is likely that they will spend more energy interacting and exchanging nutrients with each other, rather than trying to manipulate their host.
Improve your gut health to kick cravings to the curb
If your gut bacteria are continually hijacking your brain, it will be very difficult to wrestle control of your food cravings; in my opinion, this is just one reason why willpower can only go so far when it comes to dieting. However, if gut bacteria are to blame for your cravings, then modulating the health of your gut may be the key to eliminating your cravings for unhealthy foods. While more research is needed to determine specifically what types of bacteria induce unhealthy food cravings, there are some basic modifications you can make to your diet based on the available information we have on this subject. Here are my primary tips for improving gut health that may help reduce or eliminate food cravings:
- Try probiotics. Probiotics may help increase the microbial diversity of your gut, leading to decreased food cravings. I suggest taking a broad-spectrum probiotic that includes Lactobacilli and Bifidobacteria. My favorite line of probiotics are the Ultimate Flora brand (see end of article for a link to one of my favorite Ultimate Flora Probiotic products).
- Take prebiotics. Prebiotics are indigestible carbohydrates that feed the beneficial bacteria in your gut. By fueling the growth of beneficial bacteria, prebiotics may indirectly help reduce cravings. Prebiotics have also independently been found to induce satiety hormones. (9) Prebiotics can be consumed via foods such as garlic, onion, artichoke, and asparagus, or taken in supplement forms such as inulin and fructooligosaccharides (FOS).
- Eat a nutrient-dense diet. Focus on eliminating refined carbohydrates and processed foods from your diet, and instead eat a wide variety of non-starchy vegetables, some starchy vegetables (such as squash and sweet potatoes), properly-prepared grains, nuts, and seeds (as tolerated), healthy fats, and meat, poultry, and fish.