Can antibiotics make you fat?

Fet ko

Can antibiotics make you fat? It’s an interesting idea:

Mother Jones: Can antibiotics make you fat?

Cows regularly get antibiotics in their feed as it helps them put on pounds. The cause may be that it disturbs the gut microbiota and makes the cows absorb more energy from the feed. Mice experience a similar fate when put on antibiotics, adding 10-15 percent of fat mass.

Now, humans aren’t cows or mice. But could we gain weight too by eating antibiotics? It’s still speculative, but it’s another reason not to use antibiotics unless it’t truly necessary. I added this tip to the others about medications on the How to lose weight-page.

What do you think?

Update: I was just told there’s a study showing significant weight gain in people being treated with antibiotics for stomach ulcers. Hard to know if it’s because of the antibiotics or a side effect of curing the ulcer though.


  1. It sure wouldn't surprise me if they did. Cause weight gain, among other potential issues down the line. The microflora in the gut affects health in many ways.

    It's an interesting fact that humans are technically just 10% human. The bacteria in our bodies outnumber human cells 10:1.

  2. No need to wonder:

    "Eradication of Helicobacter pylori increases the incidence of hyperlipidaemia and obesity in peptic ulcer patients"


    "Our findings show that eradication of H. pylori significantly increases the incidence of hyperlipidaemia and obesity in patients with peptic ulcer."

    Reply: #4
  3. I suspect gut flora is a long overlooked metabolic feature. Feed a vegan high fat and they get physically sick; feed a LCHFer lots of grains, we get physically sick. A mismatch of food and gut microbiota fits the model. Vitamin K deficiency fits the model. But I have a harder time fitting obesity unless it stimulates hunger or interferes with fat and protein absorption. Plausible.
  4. Dr. Andreas Eenfeldt, MD Team Diet Doctor
    Thanks, very interesting!
  5. Kim
    @John Most vegans don't physically sick when switching to omnivorous hi fat diet. Human bodies make the necessary enzymes to break down animal protein & fat. It's plant matter we don't digest well.

    To the point of the question posed, I personally have lost weight a couple of times when taking an antibiotic. Could have been the illness for which I was being treated or the drugs. Don't know.

  6. Looks like is an observational study. And what direction did the primary care physician give to these patients with regard to post-procedure diet? Might have been high-carb, low-fat, which of course would raise BMI, etc.
  7. And not just antibiotics. It is very well known among obesity scientists that MANY medications cause weight gain and can disregulate fat cells.

    Disease states themselves can cause weight gain and fat cell disregulation. So can lack of sleep and probably toxins.

  8. You can induce obesity in mice just by transplanting gut microbiota from an obese mouse into a thin sterile mouse with NO CHANGE AT ALL in activity or diet whatsoever.
    Reply: #19
  9. Third Chimp
    I think you will find this blog discussion of a new Chinese intervention study very interesting - regarding the direct effect of diet on gut microbes; the study also makes a good case for microbe *causation* of obesity (but not quite the home run yet, I think).
  10. Alright, that's it. I'm going to the U.S. to find Rich Froning (Crossfit world champion) and make him an offer he can't refuse.
  11. There was an episode of the Nature of Things that dealt with the relationship between chemicals in general and obesity. Very interesting:
  12. It's mainly intensive meat production units (pork & chicken) that are responsible for overuse of antibiotics, however the antibiotic residues in their and human sewerage flows into the sea and contaminates fish, shellfish and shrimps.
    SUPERBUG MARYN MCKENNA has been following the story unfolding.

    Where do UTI's come from?
    Just as well I keep my 25(OH)D at 50ng/ml 125nmol/l

  13. Yes, antibiotics can make you fat. But they can equally make you lean. Combined with diet, antibiotics act as second selective pressure on gut flora. Depending on diet, antibiotics can shift gut flora one way or another. Gut flora affects us in more ways than just gut health, and gut health itself affects the rest of the body.

    For this example, assume antibiotics can kill all bacteria, and assume there's two groups of bacteria; fat-feeding (FFb), and carb-feeding (CFb).

    LCHF + antibiotics. FFb is attacked only by antibiotics. CFb is attacked both by diet and antibiotics. Net result is more FFb, less CFb.

    HCLF + antibiotics. FFb is attacked by both diet and antibiotics. CFb is attacked only by antibiotics. Net result is less FFb, more CFb.

    It's kinda like being hit by a hurricane while there's a famine, but next town over they get hit by the same hurricane while they have abundant food.

    For the entire human, LCHF keeps us lean, HCLF keeps us fat. Combine with the above, and we can see how LCHF + antibiotics can reduce CFb flora even more than either LCHF or antibiotics alone. Combine with the potential effect of gut flora on the rest of the body, and we can see how reducing one group of bacteria through antibiotics + diet can have an effect greater than just with diet alone. With the simplified example above, we can see how the same antibiotics can make us either fat or lean, depending on diet.

    This gives us an interesting take on what's been happening for the last 30 years. We've been taking lots of antibiotics, but we've also shifted our diet toward HCLF. We've been collectively destroying our FFb, while simultaneously cultivating our CFb. Ironically, we can use antibiotics again to reverse all this, but we must go with LCHF first.

    This gives us another interesting possibility. Let's say you go LCHF, and then get an infection, and you have to take antibiotics. Take them, but this time make sure you stick with LCHF strictly, or even outright ZC and all-meat. This way, for the short time you have to take antibiotics, you have a much greater effect on your gut flora than if you just stuck with your regular LCHF, or even if you decided to indulge in some carbs during that short time. After that, return to your regular LCHF.

  14. Francois
    Europeans should know that the use of antibiotics have for all practical reasons been banned in Europe. Some other countries does still use them in animal feed. The reason for the use of the antibiotics is to get rid of unwanted bugs in the intestines of the animal to prevent them from getting sick. There is also a withdrawal period to prevent any antibiotics from being transfered to humans. Producers do adhere to this. However, in dairy cows antibiotics will only be used when the cow are really sick. Antibiotic contaminated milk will be destroyed by the milk buying companies, since they cannot make yogurt with this kind of milk.

    High producing dairy cows consume fairly high levels of starch in their diets, but nutritionists ensure they do not get too much to prevent them from getting over conditioned. Starch makes them fatter. So yes, maybe cows do get fatter when they get antibiotics, simply because bad bugs are removed from their digestive systems and the nutrients are then absorbed better. But let me assure you there is a big move all around the world to reduce the usage of antibiotics in animal feed. Also many animal diets these days actually also contain probiotics.

    In my opinion a similar thing will happen when humans uses antibiotics because they take in too much carbs and they get absorbed better. Thus, the antibiotics should not be blamed, but rather the carbs.

  15. If it was the case that antibiotic overuse in UK farms wasn't occurring there wouldn't be questions raised about the problem in UK parliament.
    Hansard source (Citation: HC Deb, 9 January 2013, c142WH)

    Livestock MRSA Found For First Time In UK Milk

    Big rise recorded in farm antibiotic usage
    It's possible there will be less used this year as the total herd is lower I believe but I'll only believe it when I see some facts to support that idea.

  16. Alan
    Yes antibiotics (and many other drugs and factors) can make you fat. Fluoroquinolones (FQs; such as cipro, levaquin, avelox, etc.) are commonly given to farm animals (illegally) and to humans like candy.

    FQs mutate and deplete mitochondria (a likely major player in obesity and many disease processes). This was published more than 20 years ago.

    FQs dysregulate blood sugar homeostasis--this is a class effect (published).

    All FQ package inserts have a warning that side effects can be delayed and to contact your MD (too late once you have already finished the prescription and you are damaged with no known protocol to fix you). I figured it out before I finished the prescription...

    FQs are toxic to tendons, nerves, muscles, vision, and more.

    FQs produce more oxidative stress than other classes of antibiotics. Perhaps the brain and pancreas get damaged which both can cause dysglycemias.

    FQs are associated with C. difficile. They are big gun antibiotics which can damage and alter the gut microbiome.

    Unfortunately I got hit by FQs and I am still not near normal 3 years later. This is how I ended up eating LC and learning about the DietDocotor.

    Hopefully more people will be aware of the risks of FQs. Getting fat is associated with many more side effects from FQ injury.

  17. Sue
    The antibiotics shouldnt be blamed its the poor old carbs again????
  18. @ "The antibiotics shouldnt be blamed its the poor old carbs again????"
    While it's true the refined, over processed carbohydrates provide an ideal base for the proliferation of pathogenic gut microbia see Comparison with ancestral diets suggests dense acellular carbohydrates promote an inflammatory microbiota, and may be the primary dietary cause of leptin resistance and obesity we cannot, and should not, overlook the fact that regular antibiotic use disrupts the formation and composition of our gut microbiome and promotes the proliferation of pathogenic antibiotic resistant forms that make maintaining weight equilibrium difficult.

    For many people reducing refined carbohydrates is the complete solution but others reach a weight plateux and others find, even with carb restriction, their blood glucose levels remain obstinately high. For these people a low carbohydrate regime, combined with improvements to gut flora via Bitter Melon, Chinese Yam (to reduce pathogenic gut flora ) and prebiotics, probiotics, fermented foods (to establish commensal flora) and improvement in immune function to reduce reliance on antibiotics (Vit D 50ng/ml 125nmol/l, melatonin, lactoferrin etc) is required to address the underlying problem with gut flora that many years of antibiotic and refined carbohydrate exposure has created.

  19. Indeed! Tell us more.
  20. I am currently on a round of antibiotics for a dental problem, so this topic gives me pause. In general I have avoided antibiotics for all the reasons we know about. One has to be thoughtful about when to take them, but this kind of information is certainly confusing.

  21. TJ
    I have been steadily gaining weight for the last 6 months and I am exercising and watching what I eat. I can't seem to lose or even stop the gain. It is driving me nuts. Then a thought occured to me and that is that I have been on long term antibiotic treatment for this period of time. I am now on week 24 of Zimax. Thank you for this website, now at least I know why. I am almost at the end of the treatment so hopefully I will start to lose it all again.
  22. rosy
    it's the mobile phone which is playing havoc with the cells in our body and causing diseases that didn't exist ten years back
  23. anaa
    I do not understand about antibiotics, but it is necessary for us to know the elements that are good for our consumption. Where healthy foods so we need both animal and vegetable materials. Thanks for the information removed. let's get together to discuss it.
  24. Me
    Well here to tell you that in my experience they have made me fatter and unhealthy. All my life I've been fit and in optimal health; I exercise regularly and eat a very clean diet. Three years ago a stupid doctor gave me antibiotics for a viral ear infection. I didn't know they shouldn't be given for viruses, I trusted the so-called expert. Ever since I've had digestive issues and weight gain. My clothes don't fit any more, I've gained inches around my thighs and I look like I'm five months pregnant. Prior to antibiotics my tummy was the one area I never had a problem with in 42 years, I never needed to do sit ups I always had abs. Now no matter how much I starve myself and work out I cannot shift the weight, I have a permanent pot belly. I had a stool test and found I had blastosystis hominus. No freakin way was I going back on the suggested antibiotics that don't even kill it. I've been taking alternative treatments. I knew the weight gain was the antibiotics because it was instant and out of the ordinary for me. I have been trying to regain my health since and don't think I ever will. After my experience I wouldn't touch antibiotics again unless I was dying.
    Reply: #25
  25. Bjarte Bakke Team Diet Doctor
    Me, I'm sorry to hear that. Are you eating LCHF now? And if yes, have you added a fasting regiment? LCHF + fasting is the single most powerful weight loss formula I know of. Learn more about fasting.
  26. Ben
    Spent about 2 hours of searching the web and reading through studies on antibiotics and weight gain. I'm a long time subscriber of DietDoctor so I was happy to find this post on here. Should have started my search on here, to begin with, oh well.

    Anyway, I have been eating LCHF for the past year and have lost around 20 pounds "Woop Woop" however, recently I was put on antibiotics for a bad case of epididymitis "Ouch!!!" To my surprise, I gained about 7 pounds in a week! You can imagine my dismay and perplection when the scale frazzled my mind with what it showed me :) My eating regime for anyone interested is:

    Morning - Nothing
    Lunch - Nothing
    Dinner - Good old LCHF something!

    Yeah, I eat once a day :)

    Thanks for posting this article, it has put my mind at rest to some extent. I'll report back when I get off my course of antibiotics (1 week to go tomorrow) Tell me about it, most people need 7 days! I got 2 weeks of Doxy prescribed.

Leave a reply

Reply to comment #0 by

Older posts