Are Antibiotics Making You Fat?

Are antibiotics making you fat?

Did you know your body is made up of about 100 trillion human cells, but that you are host to 1500 trillion microbes? In fact, two to five pounds of your body weight is nothing but microbes. Most of this microbial life lives in your gut and helps you digest the myriad of foods you eat.

Recent science has revealed that if you have an unhealthy balance of gut microbes — a condition called gut dysbiosis — it affects more than just your digestion. It can cause immune-related disorders including asthma or allergies, lead to mental problems in the form of ADD or bipolar disorder, and even present neurological symptoms like autism or MS.

But did you know that according to a recent study published in Nature, gut dysbiosis brought on my a course of sub-therapeutic antibiotics can also make you fat?

One of the keys here is the word sub-therapeutic. These are the low doses of antibiotics like those routinely fed to factory farmed animals to serve as growth promoters — like the ones we’re routinely subjected to when we eat those same animals.

Tom Philpott summarizes:

In an August study published in Nature, a team of New York University researchers subjected mice to regular low doses of antibiotics—just like cows, pigs, and chickens get on factory farms. The result: After seven weeks, the drugged mice had a different composition of microbiota in their guts than the control group—and they had gained 10 to 15 percent more fat mass.

Why? “Microbes in our gut are able to digest certain carbohydrates that we’re not able to,” says NYU researcher and study coauthor Ilseung Cho. Antibiotics seem to increase those bugs’ ability to break down carbs—and ultimately convert them to body fat. As a result, the antibiotic-fed mice “actually extracted more energy from the same diet” as the control mice, he says. That’s great if you’re trying to fatten a giant barn full of hogs. But what about that two-legged species that’s often exposed to antibiotics?

Good question!

Does this mean antibiotics make us fat?

So what if sub-therapeutic levels of antibiotics make animals fat? Does that automatically mean that normal rounds of antibiotics prescribed by doctors for our illnesses are making us fat?

Does that mean that if we eat meat from animals that have been fed these sub-therapeutic antibiotics, we’ll also get fat?

The answer may just be yes.

First, we find out that research done on the correlation between routine antibiotics and weight gain has been done:

The NYU team has produced another recent paper looking at just that question. They analyzed data from a UK study in the early ’90s to see if they could find a correlation between antibiotic exposure and kids’ weight. The study involved more than 11,000 kids, about a third of whom had been prescribed antibiotics to treat an infection before the age of six months. The results: The babies who had been exposed to antibiotics had a 22 percent higher chance of being overweight at age three than those who hadn’t (though by age seven the effect had worn off).

Next, we find out that even though no one has studied the effect of residual antibiotics in the meat we eat on our own weight gain, they have studied the effects of these residual antibiotics on other micro-organisms:

A recent European study showed that tiny levels of antibiotics could have an effect on microorganisms. The researchers took some meat, subjected it to antibiotic residues near the US limit, and used a traditional technique to turn it into sausage, inoculating it with lactic-acid-producing bacteria. In normal sausage making, the lactic acid from the starter bacteria spreads through the meat and kills pathogens like E. coli. The researchers found, though, that the antibiotic traces were strong enough to impede the starter bacteria, while still letting the E. coli flourish. In other words, even at very low levels, antibiotics can blast “good” bacteria—and promote deadly germs.

If it can do that in naturally-fermented sausage, what do you think it’s doing to your gut?

What can you do about it?

I think the answer is obvious.

1. Avoid any and all unnecessary antibiotic treatment.

I’m not opposed to all antibiotics. I recognize how amazing they are at treating many life-threatening diseases.

As recently as 100 years ago, the world was a much scarier place because of some infections that just couldn’t be combated “naturally” with diet or herbal remedies. Think of all the people who used to have limbs amputated because of gangrene or other infections setting into wounds! Keeping a wound sterilized and clean helps SOME, but it will not prevent some infections from gaining traction. Think of all the people who used to die from bacterial infections like typhoid, syphilis, tetanus, or meningitis — or who used to have to live with terrifying debilitating diseases like leprosy. Antibiotics have made a HUGE, POSITIVE difference in our lives!

That said, I won’t give them to my kids just because they have an ear infection. Mild infections like strep throat or childhood ear infections or sinus infections will often resolve themselves. And, there are safe home remedies that I’ve turned to repeatedly with great success.

But if my kid gets typhoid fever while visiting Mexico, I will most certainly give him an antibiotic.

In the same way, if a farm animal is truly sick, I’ve got no problem removing them from the herd and giving them a therapeutic dose of antibiotics to treat the infection and save their life. It’s the humane thing to do.

The key here is to avoid unnecessary antibiotics.

2. Avoid buying food made from animals that have been treated with antibiotics.

You can do this by knowing your farmer. Buy directly from them and know how they treat their animals. Ask what they do when animals get sick. Ask how they prevent infection.

You can also do this by buying organic, as organic standards forbid the use of antibiotics. A rancher raising a certified organic herd of cattle will still treat his animals with antibiotics, but the treated animal will be culled from the herd and not sold to you as organic beef.


(photo by thejavorac)


  1. Esteban says

    This is such a distortion of the facts it’s a joke. It’s all about causing fear. There is not one study that has shown any residual anti biotics in any meat whatsoever. This is all assumed and not based on science. If don’t want to get fat, just quit the carbs and sugar. The fatty meat is good for you. Try reading Gary Taubes.

  2. Mary B says

    Absolutely agree with your article. We are very careful about where we buy our meats, dairy, eggs, etc. Either direct from trusted farms or small, local meat store that guarantees no hormones, antibiotics, etc. The interesting thing is that the local meat store products usually are very reasonable when compared with the big grocery or box store. One of the perks of living in Amish country!

  3. says

    Unfortunately, it’s not just antibiotics that destroy beneficial bacteria. So do:
    Chlorine and fluoride in water
    Antibacterial soap
    Protein deficiency
    Heavy metal exposure

  4. says

    Holy cow – what a great article! I never thought about antibiotics that way. I work behind the scenes in the medical industry doing medical coding yet I am a firm believer in what makes people healthy is bone broth, CLO, sleep, and eating nourishing foods.

    I see the trends in our society…obesity, hypertension, depression (to just name a few) and I hope some day a doc will pick up Nourishing Traditions and think, “Hey, there might be something to this!”.

    I haven’t been sick at all since my hubby and I switched to real food. I am shocked by how easily prescriptions are handed out; while I am grateful that we have made so many strides in Western Medicine, I do believe that it can sometimes do more harm than good.

    I hope that everyone gets all the information so they can make educated decisions for themselves. I sometimes think “If I knew then what I know now”, I believe I would’ve made a lot of different choices when it comes to my health.

    Thanks for posting!

  5. says

    Let me tell you…. I have experienced the negative side affects of antibiotics first hand. I used to get strep throat all the time and abused antibiotics. This caused a major gut imbalance and damage to my gut lining that I am still trying to heal today. It caused severe depression, brain fog, joint deterioration, and malnutrition. The worst of it was that it damaged my immune system so badly I had to have thoracic surgery from fluid in my lungs due to an underlying infection. All this at 32 years of age and have been healthy otherwise. If you can find other ways to recover from minor infections or illnesses, I highly reccommend only using antibiotics as a last resort.

    • says

      I used to get sinus infections all the time and always went on antibiotics for them. I never thought that the severe depression I experienced in my teens might have been connected to this antibiotic use until I read your comment. Thanks that’s something for me to consider.

  6. says

    Antibiotics can be pretty scary. I know firsthand how they can completely mess up your digestive system, and it’s interesting that they can lead to obesity as well! I think that understanding and treating gut bacteria is truly the medicine of the future. Your gut flora affects so many things, and I hope that doctors will soon take notice!

    I also like your stance on treating disease with antibiotics, and I agree completely. They can be lifesaving miracles under the right circumstances, but they are so overused. I’m glad you take a moderate, reasonable stance on them!

  7. Erik Olsen says

    And what about probiotics as a supplement? We take Culturelle regularly and I’ve heard probiotics should be taken before and during any period where you need to take antibiotics.

  8. Madi says

    I’m on antibiotics right now because I have contracted MRSA. This is my second time. Once the antibiotics stop, will I be able to take control of my weight? I eat clean. Grain-free and no processed foods. Organic. I get myself so upset because I just don’t get why my body is the way that it is. This makes sense.

  9. Ann Holloway via Facebook says

    they should bring back penicillin if they’re allergic to them give them ampicillin its the same damn thing

  10. Tina Fogg via Facebook says

    Other countries don’t even treat some of the things Drs. treat with antibiotics here. I haven’t used them in years…to me it’s kind of like antibacterial soap. That is why there are super bugs…overuse.

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