Your body needs dietary fiber in order to digest food in a regular and healthy manner. Many carbohydrate-rich foods such as whole grains, fruits and vegetables are packed with fiber, so cutting almost all of them out of your diet to remain in ketosis may back things up. The fats and proteins more commonly eaten on the keto diet take longer to digest - potentially causing constipation. "The less fiber you eat, the harder it is for your body to have proper motility," certified nutrition consultant Ariane Resnick tells The Daily Meal. "Keto diets tend to eschew even resistant carbs like fiber, which makes constipation a regular (pun intended!) problem." In a study testing the efficacy of the keto diet to manage epilepsy in children, a majority of patients on the keto diet complained of constipation.
The keto diet may or may not be toxic to you, but it's definitely toxic to your breath. Studies show that people in ketosis can sometimes end up with breath that smells like nail polish remover. Yuck! It has to do with chemical changes that occur inside your body when you enter ketosis. Besides ketosis, other scenarios that may cause this chemical change include fasting, starvation, prolonged and intense exercise, alcoholism and untreated Type 1 diabetes.
Your breath isn't the only place you might notice has an unpleasant smell once you go on the keto diet. Anecdotal reports of, well... potent vaginal odor led to scientific inquiries into what's referred to as "keto crotch." It's thought by some gynecologists and dietitians that the same chemicals that cause "keto breath" cause a pH change in the vagina that results in a different smell, though this theory has never been thoroughly studied.
Advocates of the keto diet claim that once they start eating keto they feel more energized and mentally alert. But the real experience isn't as shiny as it seems. Many who try the keto diet give up after experiencing what's referred to as the "keto flu." In some studies, the keto diet resulted in these symptoms for well over a third of dieters. Symptoms of keto flu vary from person to person, but they generally include nausea, vomiting, constipation, diarrhea, headache, irritability, weakness, muscle cramps and soreness, dizziness, poor concentration, stomach pain, difficulty sleeping and sugar cravings. Reportedly, the symptoms subside after a week or two, but some people don't shake them off as quickly.
Not to be confused with ketosis, ketoacidosis is one of the dangers of the keto diet that's actually life-threatening. Ketoacidosis most commonly occurs in people with diabetes and is one of the reasons people with diabetes should steer clear of this particular weight loss regimen. Ketoacidosis is always a threat for diabetes patients, as it can occur if diabetes is not managed effectively, but ketosis can increase the risk. However, ketoacidosis has also been reported in people without diabetes who were on extremely low-carb diets. Ketosis can trigger ketoacidosis - a condition in which the blood becomes dangerously acidic due to pent-up ketones. Ketones are the acids the body produces when in ketosis as a byproduct of using fat for energy. The high level of acidity from ketones on ketoacidosis can damage the kidneys, liver and brain, and can even result in death.
Lower alcohol tolerance
It's nearly impossible to fit very much booze into the keto diet without breaking ketosis, since most types of alcohol have a lot of carbs. But if you do find a way to drink on keto, you're going to feel a buzz much more easily. Anecdotal accounts seem to support this, and there are a few factors as to why. One reason is because every carb you consume from alcohol must be restricted from the rest of your diet to maintain ketosis. Therefore, your food-to-booze ratio is going to fall in booze's favor. Additionally, studies show that high-carb meals eaten before drinking can reduce blood alcohol content. Fewer carbs means more alcohol flowing through your veins. Some also say that since your liver is preoccupied with producing glycogen and ketones when you're in ketosis, its ability to process alcohol is impaired. Of course, having a lower alcohol tolerance isn't always dangerous - but it can be.
Lower energy levels
The body's main source of energy is carbohydrates. That's why in order to use fat cells for energy, you must restrict your carbohydrate intake so extremely. "It takes your brain and other organs some time to adapt to using this new fuel," says registered dietitian Katherine Brooking. "The sudden decrease in carbohydrate intake on the keto diet can lead to a drop in energy levels, with some dieters reporting fatigue, confusion or brain fog."
Nutrient deficiencies can occur on any diet if the dieter does not make sure to eat foods with all of the nutrients they need. The keto diet is no exception. "To maintain a very low carbohydrate keto diet, one would need to almost completely restrict grains, beans, dairy and fruits, as well as many vegetables," says registered dietitian Rachael Hartley. "Eliminating entire groups of food can put one at risk for a nutritional deficiency. As a dietitian, I would be concerned about B-vitamins, which are commonly found in grains, calcium, as well as potassium and vitamin C, which are found in many fruits." If you do become deficient in a certain nutrient, you may start to feel sluggish or experience one of these other symptoms of vitamin or mineral deficiency.
Poor mental health
While children who are put on the keto diet for epilepsy are closely monitored to ensure they are actually in ketosis, this is not true of the average dieting adult. "Most people on keto aren't actually in ketosis," says Hartley. "It is very challenging to maintain ketosis. Instead, most adults attempting keto are basically just starving their brains - and that's obviously not so great for mental health." Hartley says that in addition to fatigue, keto dieters may experience mood swings and symptoms of anxiety and depression. "Your mental health is best when your brain and body are being adequately fueled!"
Reduced athletic performance
If you're a pro athlete, or just get competitive with yourself at the gym, the keto diet may not be for you. According to some studies, people who went on the keto diet suffered a decline in athletic performance. There's a reason marathoners carb-load before a big race! Without those carbs, your body may not perform as efficiently when it's time to kick up the intensity.
Risk of heart disease and stroke
When you look at the list of foods that are good for your heart, you might notice: Lots of them have carbs. Additionally, some foods of greater concern to your heart health when eaten in excess are totally allowed on the diet, such as processed meat and cheese. Experts are concerned that eating these foods in excess is more likely on the keto diet, since keto dieters rely on fats and proteins for calories. So despite some research that suggests keto could improve cholesterol in the short term, it's hard to say whether eating this way is hurting your heart. The type of low-carb food that dieters choose to eat also matters. In a study published in the Annals of Internal Medicine, people who consumed mostly unsaturated fats and vegetables showed better markers for heart health than people who consumed mostly saturated fats and animal proteins. However, both groups still showed an increased mortality risk.
Unhealthy gut bacteria
Take all the probiotics you want - your diet still matters when it comes to the bacteria in your gut. Using a simulated version of a human digestive system, a team of researchers recently tried to gain more insight on how low-carb diets high in animal protein and fats affect the gut microbiota. They discovered that switching from a balanced diet to one deprived of carbs resulted in a change in gut bacteria that decreased the amount of disease-fighting antioxidants that were produced. On the other hand, when gut bacteria metabolize carbs, they produce more antioxidants. The gut bacteria you end up with on keto might not be healthiest for your body overall.
Before you try keto, ask yourself: Am I really going to eat this way for the rest of my life? If the answer is no, it's probably healthier just to skip the diet altogether. "Yo-yo dieting" is a term for trying diet after diet, resulting in a cycle of weight loss and regain. The dangers of yo-yo dieting are well documented. A study published in the journal Circulation used data from over 6 million people to show that fluctuations in factors like blood sugar, blood pressure, cholesterol and weight (all of which are influenced by weight loss diets) result in a huge increase of mortality risk. In fact, people with the most variability over their lifetimes were 2.3 times more likely to die of any cause and over 40 percent more likely to suffer a heart attack or stroke than those who remained relatively stable in these markers. That means that dieting and quitting, dieting and quitting, etc., can actually put your health at much higher risk than many other "unhealthy" habits your diet aims to break. The risk of yo-yo dieting isn't only reserved for trying keto - it applies to most of these other wellness fads, too.
More from The Daily Meal:
Ways You Didn't Know You Were Sabotaging Your Diet
20 Surprising Reasons You're Not Losing Weight
19 Health Myths You Should Stop Believing Right Now