Why Does Your Breath Stink on Low-Carb Diets?

Why Does Your Breath Stink on Low-Carb Diets?

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Following a low-carb diet correctly can cause bad breath.

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If you reduce the number of carbohydrates you consume, you -- or those near and dear to you -- might notice an unpleasant side effect -- bad breath. Sometimes the bad breath of low-carb diets can become severe enough to make you rethink your dietary choices. Bad breath on a low-carb diet is actually a good sign; it means that your body is burning fat as a source of energy rather than carbohydrates.

Why It Happens

Carbohydrates normally comprise your body's main source of energy, because carbohydrates break down quickly and easily into glucose and pass into cells, supplying them with the energy they need. When you follow a low-carbohydrate diet, your body doesn't ingest enough carbohydrate to fuel all your cells. So your body begins to break down stored fat as an energy source. During this process, your body creates incompletely burned byproducts called ketones. Ketones pass from your body in urine -- that's why people on low-carb diets often test their urine -- and, less pleasantly, through exhalation. Ketones produce an acetone-like smell, which causes the distinctive breath of ketosis.

Carb Limits

Not all people on a low-carb diet produce ketones. While everyone enters ketosis at their own pace, most people don't until their carbohydrate intake falls below 50 grams of carbohydrate per day, Dr. Peter Attia explains on his website, The Eating Academy. In many cases, you won't enter ketosis unless you take in 20 grams of carbohydrates or less each day, states. Some diets that call themselves low-carbohydrate diets deliberately keep the amount of carbohydrates you ingest well above this level, specifically to keep you from going into ketosis.

Steps to Take

Keto breath means that your diet is working; you're breaking down fat and using it for energy. But that doesn't mean you -- or your closest friends -- have to like it. You can take steps to reduce the smell. Drinking plenty of water washes the ketones out in your urine, leaving fewer to expel via your lungs. Gums, mints and other breath fresheners can help temporarily, but watch out -- many contain carbohydrates. Look for brands that use artificial sugars or you might unwittingly put yourself out of ketosis, which not the way you want to rid yourself of bad breath if you're trying to stick to a low-carb diet.


Very low-carb diets aren't for everyone. If you have kidney disease, your doctor might not want you to consume a large amount of protein, which puts extra stress on your kidneys. Health experts opposed to low-carbohydrate diets state that eating a high-cholesterol diet such as a low-carb diet could raise lipid levels and increase the risk of heart disease. However, a number of studies have shown that lipid levels can also improve on a low-carb diet, a 2004 article in the "Journal of the International Society of Sports Nutrition" reports. In fact, refined carbohydrates might have more of an effect on raising cholesterol levels than low-carb diets, the April 2010 "Scientific American" suggests. Ask your doctor before starting a low-carb diet.