Ketosis is one way the body can obtain energy from food. Usually, the body breaks down carbohydrates -- foods like bread, fruit, and starchy vegetables -- into glucose, which it uses for energy. Excess energy that comes from consuming more carbs than the body needs becomes fat. If the body does not have sufficient carbohydrates to burn for energy, it will enter ketosis and start burning fat, which is how a person loses weight. The ketogenic or keto diet takes this process one step further by all but removing carbs from the diet so the body begins exclusively burning fat for energy. Many people are adopting this way of eating, but it isn't a lifestyle into which someone should enter uninformed

Ketosis May Cause Bad Breath

Once a person is in full ketosis -- that is, once the body is exclusively burning fat to provide energy instead of carbs -- there will be elevated ketones in the blood. This may cause fruity or acetone-scented breath that will not be alleviated by brushing the teeth. Sugar-free gum can help disguise the smell, but it is important to check that it is acceptable on the keto diet. Most people report that smelly breath disappears within a few weeks.


Weight Loss

Many people turn to the keto diet for weight loss, and some experts back the eating style as a low-carb option that can facilitate this goal. The diet includes plenty of dietary fats for sustenance; followers are instructed to get 70-80% of their calories from fat, 5 to 10 from carbs, and 10-20 from protein. Most of the carbohydrates come from non-starchy vegetables. Diets high in fat can help people feel full longer and eat less with each meal, thus promoting weight loss.


High Ketone Levels in the Blood

In addition to added ketones in the blood, the keto diet also causes decreased and more consistent blood sugar levels. As such, some doctors recommend the diet to people with pre-diabetes and type 2 diabetes. People who are following the keto diet should see a physician regularly to receive blood tests and monitor progress. Keep in mind that the long-term impact of being on a ketogenic diet is still unknown.


Increased Ketones in Breath or Urine

Breath and urine tests can also measure ketones, and both can be done either at home or at a doctor's office. Breathalyzers evaluate the ketones on the breath, while a home urinalysis is similar to a pregnancy test, with a stick that reads the ketones excreted from the body. Although these are good to help monitor ketosis day to day, a blood test at the doctor's office is more accurate.


Reduced Appetite

The keto diet has a similar edict to other diets -- to eat fewer calories than the body burns -- and it seems to have a high success rate for weight loss, especially among those with a substantial amount to lose. Part of the reason is that dietary fats are very satiating, making the body feel full more quickly and leading to a reduction in food intake. Some experts also theorize that ketones themselves reduce appetite and change the number of "hunger hormones" in the blood.


Increased Energy

As the body moves from using mostly carbs for fuel to mostly fat, there's a brief period where dieters feel "off," as their body gets used to the new fuel source. Although many report feeling tired and sluggish at first, after the "keto flu" feeling has worn off, a lot of people find their energy levels increase. The fatigue may last from one to several weeks and is the period during which the body adapts to burning fat. After adaptation, consistent blood sugar levels contribute to more regular energy because the body is not experiencing sugar highs and crashes throughout the day.


Increased Focus

Once the body adjusts to using fats instead of carbs for energy, some people experience increased mental acuity. The brain is composed of primarily fat and can operate quite efficiently with a high-fat diet. In fact, ketones are a potent fuel source for the brain, and some studies show they may have a positive correlation with learning and memory. For those at a higher risk for memory diseases such as Alzheimer's and dementia, a keto diet could help reduce the symptoms, but more research is needed to confirm these preliminary findings.


Short-Term Decrease in Performance

People undertaking moderate to high levels of exercise while converting to the keto diet may see short-term changes in performance abilities. Female athletes especially could experience decreased fitness for the first few weeks, as well as general fatigue. This is generally due to a depletion of the glycogen stores in the muscles -- the stored fuel that comes from consuming dietary carbohydrates. After several weeks, however, performance should return to normal. Many endurance athletes see increased benefits over the long-term by following the keto diet rather than carb-loading before competitions.


Digestive Issues

Not surprisingly, switching to a keto diet affects the digestive system. Many people eat large amounts of carbohydrates, and changing from one main nutrient to another may cause either constipation or diarrhea. The keto diet requires avoiding many starchy fruits and vegetables, leaving mostly high-fiber, low-carbohydrate leafy greens. It often takes the gut time to adjust. Fortunately, these effects should go away after a few weeks.



Many people new to the keto diet report difficulty sleeping, finding themselves waking often throughout the night and tossing restlessly. Insomnia is common when one reduces carbohydrates, at least until the body reacclimates. It must adjust to different blood sugar levels and the presence of increased ketones in the bloodstream. Like many keto side effects, sleep troubles typically improve after a few weeks, especially for those who continue with regular exercise. If insomnia problems persist, taking melatonin may help. Talk to your physician before taking melatonin, especially if you are taking other medications.


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