Low-carb diets take advantage of the body's ability to burn fat and feel less hungry when in a state called ketosis. While many people try these diets, they are particularly beneficial to those with type 2 diabetes, metabolic syndrome, and insulin resistance. Even if a person with these health concerns is not trying to lose weight, they might benefit from a doctor-recommended keto diet.

For this diet to work properly, you need to be in a state of ketosis, where the body burns fat as fuel because it does not have access to enough carbohydrates. While some people rely on urine testing strips to determine if they are in ketosis, there are several signs and symptoms — essentially the side effects of this bodily state — to look for as well.

Bad breath

Bad breath is probably the complaint that most people hear about when talking about ketosis. Elevated ketone levels are responsible for the fruity smell that develops on the breath of people in ketosis. The same process can also give the urine a distinctive odor.

Fortunately, the bad breath that comes along with a ketogenic diet isn't an indication that anything is wrong; in fact, it means your body is responding to the diet.

young man smelling his breath against his hand


Loss of appetite

If you are hoping for weight loss, this is a welcome symptom that your body is in ketosis. Researchers aren't sure exactly why reduced appetite comes along with ketosis. They think perhaps the ketones provide signals to the brain, reducing hunger. The high levels of protein and vegetables required for a ketogenic diet may also help regulate hormones that signal hunger.

woman refusing plate of pancakes being offered



Also known as keto flu, it can be difficult to push through symptom this unless you understand it is temporary. The body needs some time to adjust to this new way of eating and learn how to fuel itself without carbs. It makes sense to experience fatigue during this time.

Adding electrolytes or even just potassium and magnesium to the diet can help make this adjustment period easier to push through.

man fallen asleep at his desk at work


Improved energy and concentration

If they tough it out through the initial stage of keto flu, many people are rewarded with an improvement in overall energy levels, as well as an increased ability to focus. Once the brain switches from using glucose to ketones for fuel, energy and clarity get a boost. Ketones are an easy-to-use and powerful source of fuel for the brain, so it makes sense that once the brain becomes adept at using ketones rather than glucose, these benefits appear.

woman focusing on notebook and laptop screen


Increased thirst

People new to ketosis should expect to be thirstier than they used to be. In addition to some early water weight loss from a ketogenic diet, elevated ketone levels can also cause dehydration. Offset this concern by setting reminders to drink water frequently and supplement with electrolytes. Always keep an eye on other indicators — for example, if the urine remains too dark despite drinking a good amount of water, see a healthcare provider.

woman drinking a glass of water


Upset stomach

The switch to a ketogenic diet is a big change for most people eating the standard American diet. It makes sense that the shift can lead to an upset stomach. To avoid this as much as possible, people on the diet should stay hydrated and make sure they are eating enough fiber to minimize discomfort. Some people find relief by taking probiotics. The good news is, the body will adjust to this way of eating after the initial learning phase.

young man holding his stomach, in pain


Sleep issues

During the first few days of sticking to a ketogenic diet, many people find themselves tossing and turning during the night or waking up in the early morning hours and struggling to fall back asleep. This has less to do with the high levels of ketones and more to do with lower carb levels. Just like carbs make us drowsy after a big meal, they help us sleep at night. Like other symptoms of ketosis, the body should adjust to the change.

woman awake at 3:41 am, insomnia concept



While headaches can occur alongside the keto flu, developing headaches without other symptoms is common as well. There are a few reasons why headaches are common with ketosis, including the reduction of sugar in the diet and dehydration Many people also cut back on caffeine by reducing soft drink or coffee consumption when making these dietary changes, so headaches for the first little while are to be expected. If they continue longer or become overwhelming, see a doctor.

older man with headache pinching his nose


Weight loss

The side effect that many people look forward to when eating a ketogenic diet is weight loss. For a long time, it was thought that calories were calories and any weight loss was the result of eating fewer calories. Now researchers are finding that ketogenic diets provide better weight loss results than low fat and low-calorie options.

woman standing on bathroom scale


No symptoms

Some people experience few, if any, side effects of going on the ketogenic diet. That's great, and they are lucky, but how can they be sure they are in ketosis without experiencing symptoms? Urine test strips are very accurate for determining whether ketosis has kicked in. There are also monitors that use the breath, but these are generally considered less reliable.

Testing the urine isn't strictly necessary, though. It is generally accepted that people who limit their carbohydrate intake to 50 grams or less and eat 1.5 grams of protein for each kilogram of body weight will go into ketosis. Anyone who was instructed to begin the ketogenic diet but thinks they are not going into ketosis should talk to their doctor.

smiling woman holding bowl of cauliflower and broccoli


Nausea and digestive issues

Transitioning to a ketogenic diet can be a shock to the system, especially for your digestive tract. As your body adapts to a higher fat intake and lower carbohydrate levels, you might experience nausea, diarrhea, or constipation. Usually temporary, these symptoms can be mitigated by including more fiber-rich vegetables to your diet and staying hydrated. Remember, your digestive system is getting used to a new fuel source, and like any change, it might take some time to adjust.

Young man having nausea at home. Feeling sick


Difficulty sleeping

For many, the initial stages of ketosis come with a notable shift in sleep patterns. You might find yourself lying awake at night, struggling to fall asleep, or waking more often during the night. This is due to the body's adjustment to a lower carb intake, which can temporarily upset natural sleep rhythms. To combat this, consider incorporating relaxation techniques into your bedtime routine, such as meditation or reading, to help ease the transition. Over time, as your body becomes more accustomed to ketosis, sleep quality should improve.

Sleepless woman suffering from insomnia, sleep apnea or stress. Tired and exhausted lady. Headache or migraine. Awake in the middle of the night. Frustrated person with problem.


Mental clarity

Once past the initial hurdles of adapting to a ketogenic diet, many report a significant boost in mental clarity and cognitive function. This phenomenon, sometimes referred to as "ketone brain," is attributed to the brain's efficient use of ketones as a fuel source. Unlike glucose, ketones provide a consistent energy supply to the brain, which enhances focus, concentration, and overall cognitive performance. This new level of mental clarity can be one of the most rewarding aspects of the ketogenic lifestyle.

During yoga class women do Alternate Nostril powerful breathing practice energizing third eye chakra, close up focus on African female, improve mental clarity, enhances ability to concentrate


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