You want to hear about a messed-up study? Of course you do.

Here’s how scientists measure the will to live: Separate a young rat from his mother, throw him in a pool of water with no exit, and see how long it takes him to stop optimistically swimming in circles and start sadly treading water as he waits for the inevitable sink to the bottom. It’s a test to measure how long it takes to give up on life.

Don’t worry, the rat lives through it. We’re only bringing this up because in one such experiment in 2010, scientists found if the rat had been consuming probiotics, it was less likely to suffer from that anxiety and despair after being separated from its mother and tossed to its watery doom Effects of the Probiotic Bifidobacterium Infantis in the Maternal Separation Model of Depression. Desbonnet,L., Garrett, L., Clarke, G., et al. Neuroscience, 2010 Nov 10;170(4):1179-88..

That's right: Probiotics—the so-called “good” bacteria that are often found in yogurt and help with digestion—might increase our will to live.

Bring on the Bacteria

How Gut Bacteria Affects Every Aspect of Your Health

One of the most exciting and revolutionary topics in health right now is also one of the least sexy: We’re talking about the bacteria that live in our digestive tracts—what science types often call the gut microbiome. Our bodies play host to trillions of these critters, and they make up a mini-ecosystem that helps us break down the food we eat and absorb its nutrients. At least, that’s all we thought the microbiome did.

Recent research has shown, however, that our belly bacteria have an incredible impact on everything from fat loss to inflammation levels and perhaps even our susceptibility to depression and anxiety Effects of Lactobacillus Acidophilus NCFM on Insulin Sensitivity and the Systemic Inflammatory Response in Human Subjects. Andreasen, A.S., Larse,n N., Pedersen-Skovsgaard T., et al. British Journal of Nutrition, 2010 Dec. 104(12):1831-8.Influence of Gut Microbiota on Subclinical Inflammation and Insulin Resistance. Carvalho, B.M., Saad, M.J.. Mediators Inflamm, 2013. 2013:986734.Regulation of Abdominal Adiposity by Probiotics (Lactobacillus Gasseri SBT2055) in Adults With Obese Tendencies in a Randomized Controlled Trial. Kadooka, Y., Sato, M., Imaizumi, K., et al. European Journal of Clinical Nutrition, 2010 Jun. 64(6):636-43.Prebiotic Intake Reduces the Waking Cortisol Response and Alters Emotional Bias in Healthy Volunteers. Schmidt, K., Cowen, P.J., Harmer, C.J., et al. Psychopharmacology (Berl), 2014 Dec 3..

Diversify Your Infest-ments

Let’s start with the fat loss. Your gut bacteria has a huge effect on your insulin sensitivity, which controls the way your body responds to carbohydrates—specifically how likely it is to turn them into fat The Gut Microbiota as an Environmental Factor That Regulates Fat Storage. Bäckhed, F., Ding, H., Wang, T., et al. Proceedings of the National Academy of Sciences in the USA, 2004 Nov 2;101(44):15718-23.Regulation of Abdominal Adiposity by Probiotics (Lactobacillus Gasseri SBT2055) in Adults With Obese Tendencies in a Randomized Controlled Trial. Kadooka, Y., Sato, M., Imaizumi, K., et al. European Journal of Clinical Nutrition, 2010 Jun. 64(6):636-43.. Essentially, increasing your insulin sensitivity makes it easier to burn carbs. (All hail the muffin gods!)

So how can you manipulate your microbiome into helping you burn more fat? Diversity.

“You’ve got trillions of bacteria that help you digest food,” says Brad Pilon, a nutrition consultant and lead researcher on Flat Belly Forever, a weight-loss system that cuts body fat by optimizing your gut bugs. “But when you don’t have enough kinds of bacteria in there, it can contribute to a lot of issues with your health, and there’s a real correlation with low gut diversity and obesity.”

In one quirky (if, again, kind of messed up) study, scientists pulled the gut bacteria out of obese mice and put ‘em into the bellies of regular mice. Having the gut bacteria of obese mice increased the healthy mice’s body fat even though their diet didn’t change The Intestinal Microbiota and Obesity. Kallus, S.J., Brandt, L.J. Journal of Clinical Gastroenterology, 2012 Jan;46(1):16-24.. And multiple human studies have also shown that crummy gut diversity leads to more fat storage and poor insulin sensitivity. A lack of gut diversity is also a really important marker of inflammation, which is linked to obesity, heart disease, arthritis, and even depression Influence of Gut Microbiota on Subclinical Inflammation and Insulin Resistance. Carvalho, B.M., Saad, M.J. Mediators of Inflammation, 2013. 2013:986734.Effects of Lactobacillus Acidophilus NCFM on Insulin Sensitivity and the Systemic Inflammatory Response in Human Subjects. Andreasen, A.S., Larsen, N., Pedersen-Skovsgaard, T., et al. British Journal of Nutrition, 2010 Dec. 104(12):1831-8.Richness of Human Gut Microbiome Correlates With Metabolic Markers. Le Chatelie,r E., Nielsen, T., Qin, J., et al. Nature, 2013 Aug 29;500(7464):541-6..

Your Mind’s in the Gut

The Mysterious Gut-Brain Axis

That brings us back to our water-logged rodent pal from the beginning and how probiotics can make rats (and even humans) less anxious: the so-called gut-brain axis.

The fact that the brain and belly are linked isn't surprising. (After all, indigestion is a fairly well-known side effect of stress.) But we’re now learning that connection is a two-way street: The mind can affect the gut, and the gut can affect the mind.

Here’s a good example: In 2011, British scientists gave probiotics to both rats and human subjects. After a month, they noted a significant decrease in both the rats’ anxiety-like symptoms and in the humans’ levels of anger, distress, hostility, and depression Assessment of Psychotropic-like Properties of a Probiotic Formulation (Lactobacillus Helveticus R0052 and Bifidobacterium Longum R0175) in Rats and Human Subjects. Messaoud,i M., Lalonde, R., Violle, N, et al. British Journal of Nutrition, 2011 Mar;105(5):755-64.. More recent research out of Oxford showed that supplements designed to boost the numbers of healthy gastrointestinal bacteria may improve anxiety levels by changing the way we process emotional information. The study participants were actually found to pay less attention to negative words and more attention to positive words after three weeks of supplementing Prebiotic Intake Reduces the Waking Cortisol Response and Alters Emotional Bias in Healthy Volunteers. Schmidt, K., Cowen P.J., Harmer, C.J., et al. Psychopharmacology (Berl), 2014 Dec 3..

“Some people think this is a little out there," Pilon says. "But after all, we accept that your kidneys affect brain function, and there’s evidence the liver might be involved with multiple sclerosis. If you start viewing the microbiome as another organ, it makes a lot of sense.”

What You Can Do

How to Increase Gut Bacteria

Taking advantage of the many benefits of diverse, healthy gut bacteria isn't as easy as eating yogurt every single day—but it's not much harder, either. Follow these five steps.

1. Fill up on fiber.

Soluble fiber (which is found in oatmeal, lentils, beans, and fruit) ferments in the colon and feeds the bacteria that live there, which keeps ‘em happy and may improve their ability to prevent weight gain A Systematic Review and Meta-analysis of the Prebiotics and Synbiotics Effects on Glycaemia, Insulin Concentrations and Lipid Parameters in Adult Patients With Overweight or Obesity. Beserra, B.T., Fernandes, R., do Rosario, V.A., et al. Clinical Nutrition, 2014 Oct 20. pii: S0261-5614(14)00256-8.Microbiota-Generated Metabolites Promote Metabolic Benefits Via Gut-Brain Neural Circuits. De Vadder, F., Kovatcheva-Datchary, P., Goncalves, D., et al. Cell, 2014 Jan 16;156(1-2):84-96..

2. Keep your weight down.

Obesity damages gut diversity, which is one more reason to try to maintain a healthy weight Differential Adaptation of Human Gut Microbiota to Bariatric Surgery–Induced Weight Loss. Furet, J.P., Kong, L.C., Tap, J., et al. Diabetes, 2010 Dec;59(12):3049-57..

3. Be careful about antibiotics.

Downing antibiotics can be a doctor’s first response to conditions as common as bronchitis, sinus infections, and sore throats. But these pills kill off massive amounts of both “good” and “bad” gut bacteria (“anti-biotic” is literally the opposite of “pro-biotic”). Worst of all, exposure to antibiotics at a young age may even influence whether a person will develop diabetes or Crohn’s disease later in life Molecular Analysis of the Gut Microbiota of Identical Twins With Crohn's Disease. Dicksved, J., Halfvarson, J., Rosenquist, M., et al. The ISME Journal, 2008 Jul;2(7):716-27.Aberrant Gut Microbiota Composition at the Onset of Type 1 Diabetes in Young Children. de Goffau, M.C., Fuentes, S., van den Bogert, B., et al. Diabetologia, 2014 Aug;57(8):1569-77.. Try to explore alternatives whenever possible.

4. Get plenty of sleep.

A healthy sleep cycle helps the body produce the hormones melatonin and prolactin, which have been found to improve the bacteria balance and help with digestion A Protective Effect of Melatonin on Intestinal Permeability Is Induced by Diclofenac Via Regulation of Mitochondrial Function in Mice. Mei, Q., Diao, L., Xu, J.M., et al. Acta Pharmacologica Sinca, 2011 Apr;32(4):495-502. Melatonin Improves Bowel Symptoms in Female Patients With Irritable Bowel Syndrome: A Double-blind Placebo-controlled Study. Lu, W.Z., Gwee, K.A., Moochhalla, S., et al. Alimentary Pharmacology and Therapeutics, 2005 Nov 15;22(10):927-34.Prolactin Is an Important Regulator of Intestinal Calcium Transport. Charoenphandhu, N., Krishnamra, N.. Canadian Journal of Physiology and Pharmacology. 2007 Jun;85(6):569-81..

5. Eat lots of fermented foods.

This is super important. Foods like yogurt, kefir, sauerkraut, and kimchi are jam-packed with beneficial bacteria—just make sure the jars say they contain live cultures. If you’re not wild about these traditional sources, try making your own fermented food with this recipe, and play with the spices and veggies until you find something you like. If you can’t stand the slightly sour taste of fermented foods (or even if you can), probiotic pills are also a source of gut bugs.

The Takeaway

We weren’t kidding when we said practically every facet of your health is affected by an invisible alien ecosystem in your gut that you’ve probably never given much thought to. It’s kind of crazy, but it’s also important: At a time where there are rising rates of obesity and type 2 diabetes across America, we need to start thinking more about the microbiome and the role it can play in managing those health issues. Luckily, tending to your gut bugs doesn’t have to be complicated: Eat fermented foods, sleep a lot, fill up on fiber, and maintain a healthy weight. Your belly and your brain will thank you.

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