Ketosis can burn fat fast but for some people, this can lead to a potentially fatal condition called ketoacidosis

• Ketosis is a metabolic process that involves the body converting fat to ketones for energy.
• Ketoacidosis is when the body creates an excessive number of ketones, which can be fatal.
• Those at risk of developing ketoacidosis typically have diabetes, alcoholism, or are in starvation mode.

One popular approach to diet is the ketogenic or "keto" diet, which encourages eating high-fat, low-carb foods. Consuming fewer carbohydrates can trigger a process called ketosis, which is when the body uses fat stores for energy instead of sugar, which can result in weight loss.

Ketosis isn't thought to pose any big medical risks, says Jacqueline Yuey Lonier, assistant professor of medicine in endocrinology at Columbia University Irving Medical Center. But in people with diabetes or other medical conditions, ketosis can lead to a dangerous process called ketoacidosis. 

Diabetic ketoacidosis happens when a person's body doesn't have enough insulin to use blood sugar for energy, so it converts fats into acids called ketones. Too many ketones can make the blood acidic, which can cause serious health complications. 

Ahead, a guide to the similarities and differences between ketosis and ketoacidosis, according to medical experts. 

What is ketosis?

Your body prefers to use glucose, or sugar, as fuel. One major source of glucose is carbohydrates. When you don't have enough glucose in your blood or liver, Lonier says the body goes through a series of complex processes that ultimately leads to using fat stores for energy instead of glucose. 

When this happens, your body ramps up production of special compounds called ketones, and when your body starts using those ketones for its primary source of energy, that puts your body in a metabolic state called ketosis. 

Ketosis can happen when people follow a low-carb or ketogenic diet, says Marilyn Tan, clinical associate professor of endocrinology at Stanford School of Medicine. Intermittent fasting, or going long periods without eating, like in the morning after fasting during sleep, can also lead to ketosis. 

Ketosis may have some benefits, such as promoting weight loss and potentially decreasing free radicals in the body. "But we don't have enough data to know whether ketosis is safe for the long-term," says Tan.

While data is mixed about the benefits of the keto diet, ketosis in and of itself usually isn't dangerous, as long as you don't have an underlying condition such as diabetes that can cause medical risks. "It's probably not harmful, but it can cause uncomfortable symptoms," says Lonier.

People who follow the keto diet or practice intermittent fasting sometimes describe these ketosis symptoms as "keto flu." According to the National Library of Medicine, ketosis can cause: 

• Nausea and vomiting
• Headache
• Feeling tired 
• Dizziness
• Difficulty sleeping
• Constipation 

Ketosis may also result in a fruity breath odor that smells like nail polish remover, says Grant Barish, professor of endocrinology at Northwestern University Feinberg School of Medicine. That's because acetone — the chemical in nail polish remover — is a type of ketone.

Ketosis may continue as long as someone's carb intake is exceptionally low, but the above symptoms usually resolve in a few days or weeks as the body gets used to burning fat for energy.

What is ketoacidosis?

Ketoacidosis, which can occur as a side effect of diabetes, starvation, or alcoholism, involves a similar process to ketosis: It occurs when the body doesn't have enough blood sugar, or the body cannot properly use the blood sugar it has access to, so it starts converting fat into ketones for energy. 

Diabetic ketoacidosis occurs because insulin — a chemical that enables your cells to absorb and use glucose for energy — either isn't present or isn't working correctly. This typically occurs in people with diabetes. That said, both starvation and the overuse of alcohol in place of food can cause ketoacidosis regardless of whether you have diabetes. 

"Because there's not enough insulin circulating to allow the glucose to be taken up into the body's tissues, the body perceives it's starving and starts to break down fat cells," says Lonier. 

Ketosis doesn't cause medical problems, but that's because otherwise healthy people have enough insulin to suppress ketone production. 

If there are too many ketones in the body, a person's blood can become acidic, leading to a complication called ketoacidosis.

According to research, the most common symptoms of ketoacidosis include: 

• Nausea and vomiting
• Abdominal pain 
• Dehydration 
• Fast, shallow breathing 
• Weakness 

According to Barish, it's also common for people with ketoacidosis to experience the same fruity breath smell that comes with ketosis, but to a more significant degree due to the higher levels of ketones in their systems.

While ketoacidosis is most commonly seen in people who have diabetes, it can happen in other circumstances — for example, people who drink excessive amounts of alcohol. 

"When the liver metabolizes alcohol, there's a shift toward ketone production," says Lonier. "But you'd have to be drinking excessively for that to happen. Developing ketoacidosis is serious, and it can be life-threatening without treatment. "Your body's tissues and organs can't function in an acidic environment," says Lonier. 

The only treatment for diabetic ketoacidosis is insulin, usually given through an IV at the hospital. 

The treatment for starvation ketoacidosis involves increasing carbohydrate levels, while alcoholic ketoacidosis treatment involves IV fluids and monitoring electrolyte levels. 

If you think you may be experiencing ketoacidosis, seek medical care as soon as you can.

Ketosis vs. ketoacidosis

Ketosis and ketoacidosis involve similar metabolic processes, but ketosis is a regulated process while ketoacidosis is not: Your body doesn't have enough blood sugar to use for energy, so it uses fat stores instead. But experts agree the effects are very different: 

Ketosis

• Occurs as a result of fasting or a low-carb diet
• Isn't usually dangerous for otherwise healthy people
• May cause uncomfortable physical symptoms
• Symptoms resolve when you eat carbs

Ketoacidosis

• Occurs due to insufficient insulin in the body, starvation, or excessive alcohol consumption 
• Can be serious, even life-threatening without medical treatment
• Causes more severe symptoms
• Symptoms only resolve with treatment

The most important takeaway is that while ketosis due to lifestyle factors like fasting or dieting may be uncomfortable, they go away when a person eats carbohydrates that the body can use as fuel. Ketoacidosis is a serious medical condition that needs prompt treatment. 

Insider's takeaway 

Both ketosis and ketoacidosis are processes that happen in the body when there's not enough blood sugar to use as energy, or the body is no longer able to use the blood sugar it has access to. 

Ketoacidosis usually happens in diabetic people who can't produce enough insulin, but it can also happen to people who are excessively starving themselves or drinking high amounts of alcohol. 

While ketosis may have beneficial effects, ketoacidosis can be harmful and needs medical attention ASAP.