In recent years, researchers have become more and more interested in how our gut microbiome impacts our health, including our body weight. While the verdict is still out on exactly how and why, there are many studies to suggest there is indeed a link between those trillions of microorganisms living in our gut and the number on the scale. We are also learning more about how antibiotics can have significant and long-term effects on our gut microbiome. Given the influence of our microbiome on our weight and antibiotics on our microbiome, it’s reasonable to ask the question - do antibiotics make you gain weight? In this article we’ll look to the research for answers to that question and provide guidance on what you can do about it. 

Our microbiome and our weight - What’s the connection?

It’s hard to imagine, but trillions of microorganisms of varying species live on and within the human body; with the majority of them residing in our intestines. These microbes perform a variety of physiological functions that are essential to our health. More specifically, those located in the intestines (collectively known as the gut microbiome) appear to play important roles in the energy we absorb/harvest from food, fat storage, and metabolism, all factors that can influence our weight. 

But how changes to the gut microbiome influence our weight is still somewhat unclear. Interestingly, there are studies showing differences in the microbiome composition of persons with excess body weight versus those who are lean. But is this causation or association? We don’t yet know for sure. One really fascinating thing is that there are multiple studies where we take the microbiome from mice with obesity and transplant it into other mice and these mice then go on to develop obesity. But human studies are less convincing and more research is needed. 

One thing that we have seen consistently in humans is that various diets can change our microbiome. For example a high fiber diet can increase the diversity of the microbiome and the number of healthy gut bacteria. Additionally, a recent study showed that persons consuming a high fiber diet actually absorb fewer calories versus those eating a diet that is high in processed foods. These researchers concluded that high fiber intake helps to feed the gut bacteria so they absorb some of that energy rather than all of it going to the human host to be stored as fat.

Do antibiotics cause weight gain?

Antibiotics are one of the most important medical discoveries of our time and are necessary for the treatment and prevention of many life-threatening illnesses. Their ability to kill microbes in our body may have some drawbacks, though, as they can also negatively influence the good microorganisms that are important to our health. Studies have shown mixed results as far as how long these changes to the microbiome last after antibiotic use with some studies suggesting that the microbiome returns to its pretreatment state within a few weeks, while others suggest that even short-courses of antibiotics can influence the composition of our gut microbiome for years. It’s likely that the type of antibiotic and duration of use play a role in how long it takes for the microbiome to return to its pretreatment state. 

What role this has on our long-term health is still being investigated, but given what we know about the gut microbiome and metabolism, it’s understandable to hypothesize that antibiotics may cause a change in our gut microbiome that adversely affects our weight. But the verdict is still out. A small study from 2010 showed significant and persistent weight gain after the use of high dose antibiotics (vancomycin) for the treatment of infective endocarditis (an infection of the lining of the heart). Other observational studies have been done, primarily looking at antibiotic use in infancy (and even in utero), and while there seems to be an association between antibiotics and higher body weight, we can’t say for certain that antibiotics cause weight gain. 

How to support your gut microbiome and prevent weight gain while taking antibiotics

Until we know more about whether antibiotics actually cause weight gain, and because they can be life-saving when needed, you should not avoid the use of antibiotics when a medical professional prescribes them. But you can consider these strategies to support your gut microbiome:

Avoid unnecessary use of antibiotics

The CDC estimates that at least 28% of antibiotics are prescribed unnecessarily in the US.  This can lead to unwanted side effects, unnecessary long-term changes in the gut microbiome, and the growing problem of antibiotic resistance. Patients and healthcare providers should partner to use antibiotics judiciously for the treatment of bacterial infections and avoid their use when it isn’t necessary.  

Take probiotics 

There is some research to suggest that probiotics can help to restore the good bacteria killed off by antibiotics. You can get these in the form of a supplement from a number of retail stores or online, but know that the quality can vary greatly. Also, supplements are not regulated by the FDA for safety, so it’s a good idea to first discuss their use with your healthcare provider.

Eat fermented foods 

These foods may be a better way to incorporate probiotics to help restore the microbiome more naturally. Fermented foods include yogurt, kefir, kombucha, tempeh, miso, sauerkraut, and kimchi. 

Increase intake of dietary fiber 

We have understood for quite some time that fiber is an important component of a healthy diet. It turns out this may be in part because dietary fiber (such as that found in whole grains, fruits, and vegetables) increases the diversity of our gut microbiome. If you’re struggling to get more fiber in your diet, start by changing up breakfast. Once you’re doing that consistently, you can continue making changes one meal at a time. 

Participate in regular physical activity 

Though further research is really needed to understand the mechanisms behind it, studies show that exercise can alter the composition of the gut microbiome in ways that improve many aspects of our health. It’s just one more reason to get moving! 

Trust your gut 

While the effects of antibiotics and the gut microbiome on body weight are still being investigated, we do know that a number of factors can make losing weight difficult. If you’ve struggled to lose weight with diet and exercise alone, it may be time to take the next step with a medical weight loss program. The Board Certified Doctors at Form Health will conduct a thorough evaluation to identify various factors that may be affecting your weight. Your Doctor and Registered Dietitian will work with you to create a personalized weight loss plan that addresses nutrition, physical activity, and mindset shifts, and if appropriate, includes a prescription for FDA-approved medicine. Take our quiz to find out if you’re a candidate today.