Does your gut need a reset?

Yes, I'm Ready

Do you want to start feeling better?

Yes, Where Do I Start?

Do you want to start feeling better?

Yes, Where Do I Start?

Do Antibiotics Cause Weight Gain

Antibiotics are often criticized and purported to damage to metabolism.  The theory suggests that by negatively altering bacteria in your gut, antibiotics then damage your metabolism and cause weight gain, high blood sugar, etc.. But is this actually true? Lets discuss.

Do Antibiotics Cause Weight Gain

Dr. Michael Ruscio: Hey, everyone. This is Dr. Ruscio. Let’s talk about if antibiotics actually damage your metabolism. Now, if you haven’t heard much about this argument, there is a concern, a hypothesis, that antibiotics, by damaging or altering the bacteria in your gut, can have a negative impact on your metabolism. And as you’ve been learning more about the world of bacteria in your gut called the microbiota, we are seeing associations between diabetes and obesity and alterations in these gut bacteria.

So it’s understandable to think that an antibiotic, something that alters and may cause the loss of some bacteria in the gut, may have a negative impact on those bacteria, which may then translate to a negative impact on diabetes, obesity, weight gain, what-have-you.

So it’s one thing to have a theory or a hypothesis or to show observation or correlation, it’s another thing to show cause. And there was a study done that looked into and tried to answer the question of: “Does the administration of antibiotic therapy affect the bacteria in the gut and does that cause impairments in metabolism?”

So, I want to read you a few quotes from the study. The name of the study, “Effects of Gut Microbiota Manipulation by Antibiotics on Host Metabolism in Obese Humans: A Randomized Double-Blind Placebo-Controlled Trial.” So this trial, being placebo-controlled, controls for bias, controls for placebo effect, and gives us a much more true and representative answer to this question. It was also performed in obese subjects, so these are people who already have a predilection toward becoming overweight. So there’s a very intelligent design of this study.

And I want to read you a few quotes, and we’ll put these quotes up here on the screen. “We investigated how gut microbiota manipulations by antibiotics—a seven-day administration of amoxicillin, vancomycin, or placebo—affects host metabolism in 57 obese and prediabetic, meaning having high blood sugar, men. Vancomycin, but not amoxicillin, decreased bacterial diversity and reduced Firmicutes.” Firmicutes is a broad group of bacteria. So we do see an effect. So first thing we’ve seen, the antibiotics do cause an effect, more so, the vancomycin, so we do see an effect.

Second thing, “Adipose tissue,” meaning fat tissue, “gene expression of oxidative pathways was upregulated by antibiotics, whereas immune-related pathways were downregulated by vancomycin.” So what this means is we’re seeing some mechanisms involved with fat cells, fat cell metabolism, and the immune system be affected.

Okay, so we’ve seen bacteria be affected, we’ve seen some pathways be affected. But now here’s the most important thing, do these skewing of bacteria or skewing of certain pathways actually cause effect in human subjects? And this is a key thing as a healthcare consumer or as a doctor to be aware of. It’s one thing to show stuff happens in the body. Stuff happens in the body all the time, right?

If you open a postcard that says, “Hey, I love you, from your mother and all your cousins,” you’re going to have a flood of happy hormones in your body that will cause an effect in your body. It doesn’t necessarily mean that something is going to be super clinically relevant. Will that make you lose 4 pounds of weight? Probably not, right. So, it’s one thing to show there’s an effect in the body, something measurable. But does that effect translate to something meaningful?

This is the next quote, “Antibiotics did not affect tissue-specific insulin sensitivity, energy/substrate metabolism, postprandial hormones or metabolites, systemic inflammation, gut permeability, or fat cell size.” So this is important. When we look at more clinical end-point measures, true meaningful effects, we don’t see much in the way of an effect.

And the last point here, “Importantly, energy harvest, fat cell or adipocyte size, and whole-body insulin sensitivity were not altered at the eighth-week follow-up despite there being an alteration in some of the gut bacteria, indicating that interference with adult microbiota by a seven-day course of antibiotics had no clinically relevant impact on metabolic health in obese humans.”

So what I’m trying to illustrate here and what’s important to bear in mind is that you can have a theory that something is bad, and you can show that the something bad, in this case antibiotics, causes changes in the body, as we saw there being some changes in the bacteria or the microbiota and also some changes in certain pathways.

But it’s another thing to connect that all the way to the end-point of this having a measurable, meaningful impact on a human and on their health. And in this case, a short course of antibiotics in obese and pre-diabetic men did not have a measurable negative impact on fat cell size insulin sensitivity, even though we saw alterations in some pathways in the body.

So what this means is—at least according to this study—antibiotics don’t tend to have a major negative or any clinically relevant negative impact on metabolism. Why this is important is because while the overuse of antibiotics is certainly not doing anyone any favors and is a practice that needs to stop. Using antibiotics for people who have legitimate infections that require care, it’s important to undergo that treatment and not to be fearful and thinking that, if you’re an adult and antibiotic is going to cause a significant amount of weight gain.

Now, that being said, there is definitely literature showing that antibiotic use, especially early in life, in infants, does put them at higher risk for negative metabolic consequences for the rest of their life.

So this comes back to a theme of trying to use antibiotics discerningly and only when absolutely necessary. Now, if the child has a life-threatening infection, of course, that’s going to be a safe play. If a child has a head cold or the flu and you’re thinking about just taking antibiotics even though they’re not indicated, because you think it may help your child recover more quickly, then that’s not intelligent. Because the flu is caused by a virus, not a bacteria, so antibiotics will not help. Now, if the flu becomes prolonged and you end up with a secondary bacterial infection, then the antibiotic may make sense. So these are things that you want to discuss with your doctor for children.

Coming back to the point at hand in adults that tend to have well-formed gut microbiota and immune system, there tends to be less of a deleterious or a negative effect from antibiotics across the board. And this study quantified and showed that, that effect on metabolism is not present. Meaning, there’s no clinically relevant negative impact on metabolism in adults from antibiotics.

I’m not saying that antibiotics should be used indiscriminately. They should be used when needed. But we should remain open to the use of antibiotics and not be feared into thinking that antibiotics are going to be a bad idea no matter what. Because that is a bit of an overinflated statement and we want to take from medicine what works, leave what doesn’t. So let’s leave using antibiotics because you have a head cold. Let’s use antibiotics when they’re clinically indicated and use them discerningly.

So this is Dr. Ruscio. And I hope this helps you get healthy and get back to your life. Thanks. Bye.

What do you think? I would like to hear your thoughts or experience with this.

Dr. Ruscio is your leading functional and integrative doctor specializing in gut related disorders such as SIBO, leaky gut, Celiac, IBS and in thyroid disorders such as hypothyroid and hyperthyroid. For more information on how to become a patient, please contact our office. Serving the San Francisco bay area and distance patients via phone and Skype.


I care about answering your questions and sharing my knowledge with you. Leave a comment or connect with me on social media asking any health question you may have and I just might incorporate it into our next listener questions podcast episode just for you!