Let me introduce myself. My name is Mark Sisson. I’m 63 years young. I live and work in Malibu, California. In a past life I was a professional marathoner and triathlete. Now my life goal is to help 100 million people get healthy. I started this blog in 2006 to empower people to take full responsibility for their own health and enjoyment of life by investigating, discussing, and critically rethinking everything we’ve assumed to be true about health and wellness...Tell Me More
I’m continuing my crusade of keto mythbusting. Recently, there was keto crotch, then keto bloat, and today I’m returning to one of the O.G. myths—keto body odor. Yes, it seems detractors of the keto diet are hell-bent on making you think your body will become a stinky, bloated mess if you dare to drop your carbs below 50 grams per day…but is it true?
Here’s the spoiler: Yes, people in online keto diet forums occasionally complain about an unpleasant change in body odor when they first go keto. There is no scientific evidence that it actually happens, nor a clear, compelling explanation for why it would. Moreover, the anecdotal (and it’s all anecdotal) evidence suggests that if it does occur, it is rare and temporary. In other words, the whole idea of keto body odor seems to be exaggerated—shocking, I know.
That said, significant dietary changes can result in other physiological changes that may manifest in a variety of ways. Since nobody wants to be the stinky kid, let’s take this opportunity to look at what might be plausible about keto body odor and what to do if you think you’ve been afflicted.
First, let’s clarify what’s meant by “body odor.” In the medical literature, the term is used in reference to aromas associated with breath, urine, feces, vaginal secretions, sweat (usually from the axilla, or armpits), and general bodily essence as it were. Because it’s such a broad term, the causes are also extremely varied. For the purposes of this post, I’m going to use the term “body odor” to mean aromas from sweat and general bodily funk, since that’s what’s usually meant by keto body odor.
Body odor arises when odorless compounds leave the body through glands in the skin and interact with microbes living on the skin’s surface. The microbes then release chemical compounds—what we actually detect as body odor. Typically, commercial deodorants target both pieces of the equation by using antiperspirants to minimize the excretion of the odor precursors and by creating an unfavorable environment for the microbes living on the skin. There is also a genetic component to how much individuals secrete compounds that cause body odor.
Although a huge industry is built around trying to help people mask their natural odors—and suggesting that body odor is always the result of poor hygiene—bodily scents are actually quite important. Just as other animals do, humans use olfactory cues for recognizing kin, making judgments about others’ personality traits and attractiveness, and even for detecting fertility. Although we rarely recognize it, the data suggests that smell probably factors into all our face-to-face social interactions.
Body odor can also result from illness. Before the use of sophisticated modern disease detection techniques, doctors were taught to use their sniffers as a diagnostic tool. Even today, smell can be an important clue that an individual is unwell. Often these odors emanate from the breath or urine, but certain infectious and metabolic diseases can be associated with distinctive body odors. In addition to perceptible body odor, the human olfactory system can detect infection and sense illness in others, presumably an important means of preventing the spread of communicable disease.
The whole notion that a keto diet can cause body odor rests on the assumption that how we smell is affected by what we eat. It turns out that there is scant evidence that that is actually the case.
When I’ve taken up the question of keto diet and body odor previously, I noted that there are really only two human studies that speak to this. One small study found that women judged men’s body odor more negatively when they ate a diet that contained red meat compared to when they abstained from red meat. However, the diets differed in other ways as well. In contrast, a different study found that women rated men’s body odor more positively when the men reported eating more fat, meat, and eggs, and more negatively when they ate more carbs. Hmm.
Nevertheless, the common belief persists that certain foods will make you stinky: garlic, onions, cruciferous vegetables, and spicy foods especially. However, there is no evidence that this is actually the case beyond the obvious bad breath and, ahem, flatus that these foods can cause. In fact, the one study I found on the subject reported that garlic counterintuitively improved body odor.
As you can see, there’s minimal evidence at best linking body odor to diet, and none of it has to do with the keto diet itself. Nevertheless, the belief that keto causes body odor persists…thanks to the few complaints from some in the keto community (and, just maybe, those who have nothing to do with keto but want to cause a stir). While I don’t want to dismiss anecdotal evidence out of hand, I have noticed that once people go keto, their diet is immediately to blame for every weird smell, twitch, or symptom. It’s remarkable really.
In the interest of fairness, let’s look at the explanations that are typically offered for why keto might cause body odor:
The first hypothesis is that keto dieters smell funky because they’re eating a lot more meat. As I already mentioned, there are only two small studies that speak to this, and the findings conflict. The idea at work: protein metabolism yields ammonia as a byproduct (true), which builds up because of eating “too much protein,” resulting in body odor.
To which I object… First of all, it’s not necessarily true that going keto means eating more meat. My version of a keto diet certainly isn’t a steak-and-bacon fest—I still eat tons of veggies. If anything, my observation is that keto folks by and large remain fearful of eating “too much” protein lest it kick them out of ketosis. (The issue is not nearly so simple as that, as I’ve explained.) In any case, even if you’re eating a good deal of meat, a healthy liver should be able to convert the amount of ammonia generated into urea and send it off to the kidneys to be excreted as urine.
Toxins such as environmental pollutants accumulate in adipose tissue, a.k.a. fat cells, and these toxins are then released into the bloodstream when people burn fat. Because the keto diet often results in increased burning of body fat, the theory goes that the body is “detoxing” all these pollutants, and that’s what causes body odor. Detoxing is a controversial subject, and while it is true that some of these toxins can be excreted through the skin, the actual amounts are fairly small (the majority get excreted via urine and feces). Plus, it’s not evident that the toxins that are excreted through the skin cause any particular odor. And wouldn’t any diet that actually does what it’s supposed to—i.e. burn fat—be subject to the same “stinky” detox effect? I think we can safely chuck this claim.
Maybe ketones themselves make you smelly? This one has the most potential validity, as it’s well documented that acetone—one of the three ketone bodies—gets excreted when you’re in ketosis. However, it’s the cause of the familiar keto breath, not body odor per se. I’ve seen no evidence linking acetone to actual body odor.
Ok, I hear you saying, “Mark, I see that you’re skeptical, but I’m telling you… I stink!” What can you do about it?
Well, since there isn’t a clearcut cause, I can’t give a clearcut answer, but I’ll tell you what the general wisdom says:
First, you can support your body’s own detoxification pathways as I describe here. Your body should be able to do a fine job taking out the garbage—it’s designed to do so and is efficient at it—but hey, why not drink some coffee and throw some broccoli sprouts on your salad. This is a “can’t hurt, might help” situation.
Same thing goes for taking some nice epsom salt baths, another common recommendation. Whether there is any truth to their detoxifying nature, you’ll get a nice dose of transdermal magnesium with a hefty side of relaxation. Throw in some essential oils and olive oil and soak your cares away… hopefully taking some of the b.o. with it.
You can also experiment with eating less protein and more carbs, but I do see potential downsides to both. You definitely don’t want to eat too little protein, since it serves such a vital role in healthy functioning, and you don’t want to add back too many carbs if being in ketosis is your goal. That said, especially with regard to the protein you probably have room to play around, so feel free to experiment if you want. I’m not overly optimistic that this is the answer, but I’m always a fan of finding what works for you.
Or, take a wait and see approach. Most keto side effects come and go as people become keto-adapted. If your problem is keto breath, not body odor per se, you can try chewing on some fresh herbs or taking chlorophyll supplements, but these will just mask the issue.
Lastly, if it is very noticeable and very bothersome, you can—and probably should—consult your doctor. If you are excreting significant ammonia, which usually happens via the breath, this is a sign of liver or kidney problems that need to be diagnosed asap.
Because switching to a keto diet can initiate a profound metabolic shift, some people might experience side effects. And, sure, it’s conceivable that transient changes to body odor might be one of them. The lack of evidence that body odor is strongly affected by diet (as well as my own experience interacting with the thousands of people in my community who have tried keto) leads me to believe that this is a minor problem at most—and one that most people won’t experience at all. If it’s affecting you, feel free to try to solutions I described above. They might not resolve the problem immediately, but at least they’ll likely have other positive benefits.
Ok, what say you? Are your friends giving you a wide berth now that you’re in ketosis, or are you chalking this up to yet another thing the haters are blowing out of proportion?
Groyecka A, Pisanski K, Sorokowska A, et al. Attractiveness Is Multimodal: Beauty Is Also in the Nose and Ear of the Beholder. Front Psychol. 2017;8:778.
James AG, Austin CJ, Cox DS, Taylor D, Calvert R. Microbiological and biochemical origins of human axillary odour. FEMS Microbiol Ecol. 2013 Mar;83(3):527-40.
Natsch, A. What Makes Us Smell: The Biochemistry of Body Odour and the Design of New Deodorant Ingredients. CHIMIA Intl J Chem. 2015 Aug;69(7-8):414-420.