While it's not necessarily dangerous, bad breath is a known side effect of entering ketosis. When you’re taking in a lot of fat, your liver metabolizes it and eventually converts it into smaller ketone bodies. These ketones (including acetone — yep, like nail polish remover acetone) will circulate in your body and diffuse into your lungs. Your body wants balance, so you'll exhale ketones to avoid build-up in your bloodstream. Those compounds are what cause keto breath: a metallic-tasting, somewhat stinky side effect.

This content is strictly the opinion of Dr. Josh Axe and is for informational and educational purposes only. It is not intended to provide medical advice or to take the place of medical advice or treatment from a personal physician. All readers/viewers of this content are advised to consult their doctors or qualified health professionals regarding specific health questions. Neither Dr. Axe nor the publisher of this content takes responsibility for possible health consequences of any person or persons reading or following the information in this educational content. All viewers of this content, especially those taking prescription or over-the-counter medications, should consult their physicians before beginning any nutrition, supplement or lifestyle program.


ME: It is not essential. You can be fully ketogenic without any intermittent fasting. However, most people find it natural to do intermittent fasting as their hunger is reduced to where they don’t need a third meal. Keeping feeding time reduced to a smaller window during the day enables the body to use stored body fat for fuel longer, which benefits weight loss. My husband Craig and I still do intermittent fasting every day as maintenance. It just makes life easier only having to make two meals a day instead of three.

It's really the trans fats that you'll want to avoid completely. "Trans fats are highly processed, and heated to a point where they create free radicals in the body, which increase your risk of cancer.," she says, "Trans fats are found in hydrogenated oils (be on the lookout for this form of fat listed on the ingredients), and these are mostly used in the preparation of processed crackers and packaged foods."

MCTs are natural sources of essential healthy fats for energy. They are easily digestible and absorbed by the body, providing instant but lasting energy. Including MCT oil in the keto diet can stabilize blood sugar levels and enhance the production of ketones. Since that is the goal of your keto diet, optimal blood ketone levels, MCT Oil is a no-brainer.


Abbey, I appreciate all the work you put into this but there are a few things you missed. Not all oils are keto friendly. Vegetable oils are a huge no-no which was not mentioned. Regular mayo usually contains soybean oil which should be avoided. You also missed that foods with preservatives are a no-no which excludes some cheeses (you said enjoy all the cheese you like). Processed sliced cheese or pre-shredded cheese in a bag at the grocery store contains preservatives. Ever notice how shredded cheese in a bag never sticks to itself but when you shred your own cheese it sticks? Preservatives. Most nuts are okay but peanuts are a legume and should be consumed in very small amounts or avoided altogether. Don’t go crazy either, nuts do have carbs. I don’t eat more than a half cup a day of salted almonds. That said, you could have mentioned that getting salted nuts is ideal as you do excrete more salt and other minerals in your urine (eating keto is diuretic so attention must be paid to salt, potassium, magnesium, etc. as you did mention) so finding simple ways to add salt and other minerals is helpful. I also take a multi-vitamin daily. You mentioned you cannot do high intensity workouts. You are not supposed to do high intensity workouts as elevating your heart rate too high actually stops the fat burning process in your body. Your heart rate should be 180 beats minus your age +/- 5 beats depending on fitness level. A 40 year old obese person shouldn’t go over 135 beats/min during a workout as that is the optimal fat burning window. Higher than that and your body reverts to storing fat reserves thinking it will run out if it keeps this pace. Which bring me to metabolism. Its been long believed a high metabolism is good. A high metabolism leads to more hunger (because you’re burning glucose faster), ingesting more food, and typically gaining more weight. Slowing your metabolism down AND teaching your body to consume slow burning ketones instead of quick burning glucose puts less stress on your liver mainly and on your body in general. There’s a lot more but this is getting long so I’ll finish with this. You said this diet focuses on quantity of food and not quality. This is confusing to me….wouldn’t organic and grass-fed meats, be of better quality than non-organic and grain fed meat? (they feed animals grains to fatten them up….shouldn’t that be a huge warning sign for us?). Is food without preservatives not better quality than food with preservatives? Aren’t beverages with no sugar or artificial sweeteners of better quality than sugar/artificial sweetener-filled beverages? I’ve never seen any keto advocate advise ignoring quality foods, in fact its quite the opposite.

Studies found that endurance performance, whether it was anaerobic or aerobic was impaired or maintained with a ketogenic diet. This is still a complicated area to study, since majority of studies used in this review had small sample sizes, no control group or were very short in duration (no more than six weeks). Because of this, it is still unclear whether endurance performance is enhanced or impaired with a ketogenic diet.
We also need to define “reversible”… that’s not easy. But what matters is that a low-carb or ketogenic diet increases metabolic flexibility and decreases pathological insulin resistance. In so doing it decreases cardiovascular risk factors and improves overall health. Many diabetics don’t even need external insulin or other diabetic medications when following a ketogenic diet.
Still, research on the relationship between the keto diet and mental clarity, as well as anxiety and depression, is still in its early stages, and not all people who try the keto diet report noticeable changes in the ways they think. In fact, some people report an increase in brain fog after switching to the keto diet, though this might be explained by the "keto flu", which describes the flu-like symptoms people tend to experience in the first few weeks after beginning the keto diet.

Thank you so much for this article! My husband and I have been following keto for a little over a month now and we love it! I did a lot of research before starting, and am still doing lots of research because I like to be armed with the best information I can have when friends question my choices. Just yesterday I had a friend tell me that our brains need carbs to function (more than what we get from veggies). I hadn’t heard that before so I didn’t know what to answer. Thanks to your article now I know, and I have lots more answers in case more points come up. 😉


A huge concern with the keto diet is the maintenance and potential loss of muscle mass. Many people will just think: hey, dummy, then just eat more protein. However, some research has shown that even if your protein intake remains constant, a low carb diet may promote muscle loss. A study from the Netherlands confirmed these findings. In the study, participants were given three diets (high carb, moderate carb, low carb) and moderate protein. The study found that those following a low carb diet experienced increased muscle breakdown. This is because when we eat carbohydrates, we produce insulin which promotes muscle growth. This is why athletes depend on carbohydrates (along with protein) to fuel their performance. When we eat carbs, the insulin release “unlocks” our muscles to let the protein in so it can do its job at building our muscles. So, when we skip the carbs all together, muscle glycogen stores get depleted, we lose out on those muscle building opportunities. Forget about high intensity training. A depleted glycogen store also means our workouts will suffer because we just don’t have enough oil left in the tank. This was a again suggested in the recent review looking at many ketogenic studies. The studies found that there was greater lean body mass loss in the ketogenic groups compared to the other diets being studied.
Another possible nutrient deficiency: potassium, a mineral important for both electrolyte balance and blood pressure control, notes MedlinePlus. “Inadequate intake of potassium is likely when consumption of fruits and starchy vegetables are decreased,” says Asche. She recommends adding lower-carb sources of potassium to the diet, including avocado and spinach — as well as lower-carb sources of fiber, such as chia seeds and flaxseed (be sure to enjoy ground for the best health benefits).
When you eat foods high in carbohydrates and fat, your body naturally produces glucose. Carbohydrates are the easiest thing for the body to process, and therefore it will use them first – resulting in the excess fats to be stored immediately. In turn, this causes weight gain and health problems that are associated with high fat, high carbohydrate diets (NOT keto).

Heart disease. The connection between the ketogenic diet and cardiovascular disease risk factors is complicated. Many studies have found that the keto diet can lead to significant reductions in total cholesterol, increases in HDL cholesterol levels, decreases in triglycerides levels, and reductions in LDL cholesterol levels, as well as potential improvements in blood pressure levels.

“When you start the keto diet, you lose sodium and other electrolytes in the urine due to reductions in insulin,” says Yawitz. “This is a major contributor to symptoms of keto flu.” So it’s important to replenish sodium through the diet, especially if you exercise or sweat a lot. “This can help ward off more serious side effects that are seen with long-term sodium deficiencies,” says Yawitz. These include lethargy and confusion — and in extreme cases, seizures, coma, and death, according to the Mayo Clinic.
The main limitations of our study are its small sample size, short duration, and lack of control group. That the main outcome, hemoglobin A1c, improved significantly despite the small sample size and short duration of follow-up speaks to the dramatic and consistent effect of the LCKD on glycemia. For other effects, however, such as the rises in serum LDL and HDL cholesterol, the small sample size might be the reason statistical significance was not reached. Future studies of larger samples and containing a control group are needed to better address questions about the effect of the LCKD on serum lipids in patients with type 2 diabetes.
I actually went on a ketogenic diet last year to see if it would help my migraines. I have a history of chronic migraines which would usually last 3 days, sometimes longer. Triptans help a lot but I don’t like having to take them. I stayed in ketosis for about 8 months and experienced a significant reduction in migraines, from feeling some type of headache (mild o r severe) almost everyday to 1 or 2x per month while in ketosis. Although I’m very healthy otherwise, I do think my migraines may have something to do with blood sugar fluctuations (despite previously eating a whole foods diet and no refined carbs), and keto totally stabilized this. I eventually came off of Keto because I’m not really a meat lover. When I came off, but remained low carb, my migraines stayed under control for the most part. When I increase carbs, they do return.
The catch, of course, is that if it sounds too good to be true, it probably is. And that’s exactly what hopeful dieters need to keep in mind when approaching the ketogenic diet (if we're calling it by its formal name). It’s not that this high-fat, moderate-protein, low-carbohydrate approach to eating can’t deliver weight loss in a delicious package, but it’s a restrictive, sometimes complicated affair that isn’t sustainable for most people.
While the science of nerve signaling and genetic mutations is incredibly complex, it makes sense that a therapy, the ketogenic diet, that has been used successfully in epilepsy for 100 years might be helpful in conditions that share some similar features. Could changing the brain’s fuel, help change the malfunctions in its nerve cell firings and neuron excitability?
“constant keto supposedly caused selenium deficiency and stunted growth in epileptic kids on keto diets. As I previously commented large areas of North America & Western Europe have Se-deficient soils with the notable exception of the NA grain-growing regions. Consequently the major source of Se in the SAD is grains and deficiency is a result of eliminating the grains on a Keto or WB diet. Opponents could just as easily use Se-deficiency as an argument against WB. The solution is not eating grains it’s taking a supplement.
But wait, there’s one loophole. Have polycystic ovary syndrome (PCOS)? Then the keto diet may help regulate your periods. “Women with PCOS have high insulin levels, which cause sex hormone imbalances,” notes Yawitz. In a small study published in the journal Nutrition & Metabolism, subjects with PCOS following a ketogenic diet for six months noted improvements in their menstrual cycles — and a small number of women became pregnant, overcoming previous infertility obstacles. “This study was very small, so we can’t make recommendations for all women with PCOS based on its findings,” says Yawitz. “And really, any diet that leads to weight loss should help in PCOS.”
What about fruits and vegetables? All fruits are rich in carbs, but you can have certain fruits (usually berries) in small portions. Vegetables (also rich in carbs) are restricted to leafy greens (such as kale, Swiss chard, spinach), cauliflower, broccoli, Brussels sprouts, asparagus, bell peppers, onions, garlic, mushrooms, cucumber, celery, and summer squashes. A cup of chopped broccoli has about six carbs.
Urine ketone data were missing in a median of 4 participants (range 0–8) at any given visit. The proportion of participants with a urine ketone reading greater than trace was 1 of 17 participants at baseline, 5 of 17 participants at week 2, and similar frequencies at subsequent visits until week 14 when 2 of 18 participants had readings greater than trace and week 16 when 2 of 21 participants had readings greater than trace. During the study, only 27 of 151 urine ketone measurements were greater than trace, with one participant accounting for all 7 occurrences of the highest urine ketone reading (large160).
Protein: A typical recommended keto protein intake is between one and 1.5 grams per kilogram of your ideal body weight. To convert pounds to kilograms, divide your ideal weight by 2.2. It’s important to note that Kidney Disease: Improving Global Outcomes (KDIGO) recommends that adults with diabetes limit their protein intake to less than one gram per kilogram of body weight each day and that adults with chronic kidney disease avoid protein intake greater than 1.3 grams per kilogram per day.
Dirty keto diet: “Dirty” is the apt term, as these version of keto follows the same strict percentages (75/20/5 of fat/protein/carbs) but rather than focusing on healthy versions of fat like coconut oil and wild salmon, you’re free to eat naughty but still keto friendly foods like bacon, sausage, pork rinds, diet sodas and even keto fast food. I do NOT recommend this.
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Certain studies suggest that keto diets may “starve” cancer cells. A highly processed, pro-inflammatory, low-nutrient foods can feed cancer cells causing them to proliferate. What’s the connection between high-sugar consumption and cancer? The regular cells found in our bodies are able to use fat for energy, but it’s believed that cancer cells cannot metabolically shift to use fat rather than glucose. (11)

I’m desperate to find some answers~I have no history of sensitivity to anything, no allergies. I understand allergies can happen at any time. I started the Keto diet and in a one month time I had four separate episodes of my tongue swelling~each episode worse than the one before. I LOVED this diet~felt great, handled it with ease. The last episode almost put me in the hospital~my tongue was so swollen it was coming out of my mouth making it difficult to swollen and breath. I had no choice but to narrow it down to Ketosis. All the foods were the same that I have eaten all my life. No new meds. The last episode I took 2 Benadryl and pulled myself out of Ketosis with consuming a Dr.Pepper, and 2 pieces of white toast. I was terrified. Everyone on Facebook in all these Keto sites tell me it has nothing to do with Ketosis….but I’ve tried literally everything I consumed when a was on that WOE and I’ve had no reaction in days. My body feels horrible, I have no energy, my entire body aches. I want back on the Keto diet because my body was responding really well to it~except for my tongue.

Also, consider supplementing with the amino acid leucine, as it can be broken down directly into acetyl-CoA, making it one of the most important ketogenic amino acids in the body. While most other amino acids are converted into glucose, the acetyl-CoA formed from leucine can be used to make ketone bodies. It’s also present in keto friendly foods like eggs and cottage cheese.
In order to stay in ketosis, you have to limit carbs, but also to some extent protein. This is the predominant difference between keto and traditional lower-carb diets like Atkins. By relying on dietary fat for most of your calories per day, you limit fiber-rich sources (like fruit, veggies, and legumes) and sources of lean protein (like fatty fish) — some of the most nutrient-dense foods on the planet.

To put it roughly, various supporters of the ketogenic diet affirm that it is highly effective in fighting cancer. Although the studies in this area are extensive, one has to note that they have been limited to animals alone. The studies developed on human subjects, however, highlighted that following the ketogenic diet prevents diseases such as gastric, colon and prostate cancer from progressing. Although this diet cannot cure cancer, it could prevent it from further advancing, while having other notable health advantages.
The keto diet is NOT what you seem to picture. I laughed at your description as I was eating lamb chops, cauliflower rice, broccoli, followed by cheesecake. How deprived I was! You should relook at what the diet really is. By the way, my cardiologist highly recommends keto. Most people see a drastic decrease in their triglyceride/HDL ratio. Looking at total cholesterol or LDL alone is 20 years out of date! Even the AHA has caught up, and now says that it’s NOT how heart health should be judged.
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In essence, it is a diet that causes the body to release ketones into the bloodstream. Most cells prefer to use blood sugar, which comes from carbohydrates, as the body’s main source of energy. In the absence of circulating blood sugar from food, we start breaking down stored fat into molecules called ketone bodies (the process is called ketosis). Once you reach ketosis, most cells will use ketone bodies to generate energy until we start eating carbohydrates again. The shift, from using circulating glucose to breaking down stored fat as a source of energy, usually happens over two to four days of eating fewer than 20 to 50 grams of carbohydrates per day. Keep in mind that this is a highly individualized process, and some people need a more restricted diet to start producing enough ketones.

Diets require discipline, and it is not always easy for people to follow them without indulging in a "cheat day." One day may not make a big difference in the long-term, but a recent study from the University of British Columbia in Okanagan, Canada (UBCO), found that when it comes to the keto diet, a single dose of carbohydrates may have dangerous side effects.
Lower carbohydrate diets (varying amount of carbohydrates in each study) have shown promise in improving A1c and weight management in Type 2 diabetes, is shown to be better than low-fat diets in improving blood pressure and lipid levels, and more. Along with that, more ketosis studies on different disease states are out there and growing. Ketosis has also been explored for its promise, at least in the short term, for metabolic disease, Alzheimer’s disease, and diabetes.

The ketogenic diet is a high-fat, low-carbohydrate, and moderate-protein diet that has been proved to be an effective treatment among patients with epileptic conditions such as glucose transporter 1 deficiency, pyruvate dehydrogenase deficiency, tuberous sclerosis complex, Rett syndrome, Dravet syndrome, and specific mitochondrial disorders (1, 2).

Also, be aware that, while diet can be an extremely powerful tool to regain control over many aspects of health, diet by itself remains insufficient for full health. Just as filling up the gas tank of your car with quality gasoline helps your car run well, but other aspects of your car need attention over time (change the oil, tune-ups, new tires on occasion, etc.), so it goes with diet. We must also pay attention to vitamin D and iodine status, the potential for common endocrine disruptions such as thyroid dysfunction, efforts to cultivate bowel flora, and other issues. Focus on diet as a start, not as an end.
But what does the science say? Results are mixed. In one Spanish study of 20 obese adults, participants were put on a low-calorie keto diet and lost an average of 40 pounds over four months. Another small experiment had a similar outcome. In a six-month Experimental & Clinical Cardiology study of 83 obese adults, those on the keto diet lost an average of 33 pounds, while lowering their bad (LDL) cholesterol levels and increasing their good (HDL) cholesterol.
In one study they were testing the endurance of the Mice by giving on group MCTs in their daily food, and the other group of mice LCTs. The study lasted for 6 weeks. The total swimming time until exhaustion was measured, and at first there was no difference. As the weeks went by, those fed MCTs quickly began to out-perform the others and continued to improve throughout the testing period.

Second point, I have never tried ketogenic dieting and also I did my calculations based on a 4:1 ratio and I was amazed at how much fat I would need to consume even at my size and the foods I would have to 1. Get rid of to achieve that and 2. Add in my diet to get there and , no thank you. My heart goes out to the families with children who do have to be on this diet.
While the science of nerve signaling and genetic mutations is incredibly complex, it makes sense that a therapy, the ketogenic diet, that has been used successfully in epilepsy for 100 years might be helpful in conditions that share some similar features. Could changing the brain’s fuel, help change the malfunctions in its nerve cell firings and neuron excitability?
The New York Times pieces also points out that studies are disproving this concern and making a case for both children and adults with type 1 diabetes to consider a ketogenic diet. Specifically, a 2018 study published in the journal, Pediatrics, which took a look at glycemic control among children and adults with type 1 diabetes who followed a very low-carbohydrate, high-protein diet. The researchers found that both the adults and children who consumed this diet along with smaller doses of insulin than typically required exhibited “exceptional” blood sugar control without high rates of complications. In addition, the study data did not show an adverse effect of a very low-carbohydrate diet on children’s growth, although more research may still be a good idea, according to researchers.

One reason it's hard to determine the exact health effects of diets is that it's often unclear whether any observed effects come from the diet or from a combination of other factors, like stress, environment or genetics. Still, that doesn't mean all the bold claims about the keto diet are wrong, but rather that you should approach them with a healthy degree of skepticism.

For people with Type 1 Diabetes, you probably have heard of their diabetic emergency, diabetic ketoacidosis, also referred to as DKA. This can be life threatening condition for people with Type 1 diabetes and Certified Diabetes Educators spend many hours teaching preventive care for DKA. This condition should not be confused with nutritional ketosis, the fat burning state reached when following the Ketogenic diet. The two conditions are quite different.
The good news is, it is not necessary to stay on a ketogenic diet at all times to reap this benefit. Our ancestors went through fast and feast cycles and the body is designed for flexibility. We may be able to reduce cancer risk, prolong life, improve brain function, and benefit from ketosis otherwise by being in ketosis or fasting a few days a week.

It’s only dangerous to not get enough carbs at each meal if one is taking too much meds or insulin for the amount of carbs they are eating! Restricting carbohydrates doesn’t lead to hypoglycemia unawareness, but having lots of lows and lots of highs will (and decreasing insulin and carbs leads to way fewer highs and fewer lows, or at least it can). On the other hand, being in ketosis does make low blood sugars less negative as an experience. I still feel my lows just fine, but they are less of an emergency because my brain still works (feeding on ketones) and by body doesn’t freak out and release tons of adrenaline that then makes me want to eat a house. Mind you, I still wake up and know immediately if I’m low, I know from experience and how it feels in my head and body but without the crazy shakes. This is not unawareness but it is less reactive.


One of the most basic and most profound benefits of a ketogenic diet is that it drastically lowers inflammation (1). This is mainly due to the reduced amount of free radical production that occurs when burning ketones for energy instead of glucose. Less inflammation allows for more energy production and an overall more efficiently functioning body. This allows for a heightened ability of the body to heal in many different aspects.
The keto diet gained most of its attention for its role in the nutritional management of epilepsy and Alzheimers. More recently, science has shown positive clinical outcomes for a number of types of cancers through its ability to minimize tumor growth. In the case of all three of these diseases, ketones are therapeutic through providing an alternative substrate to glucose.
In addition, recent papers within the last few years investigating the effect of ketogenic dieting on obesity conclude that it’s an extremely effective way to not only lose fat, but spare muscle loss while curbing many disorders related to obesity as well (many of which have been discussed above), including the set of symptoms and risk factors known as Metabolic Syndrome (i.e. abdominal obesity, diabetes, hypertension, and elevated cholesterol)
This is a helpful article. But there are some inaccurate things too. I have type two diabetes and use a keto genie diet to lose weight (45# so far). I was able to get my cholesterol down, Triggs down, and my A1C to 6! I went off and followed a Mediterranean diet for a year. I gained back 15# and my diabetes got worse. So I am back on keto. I am using a closer to Mediterranean keto both then and now.
I’ve been doing low-carb-high-fat (LCHF) for more than nine years. I’m not diabetic and never was so far as I know, nor was I particularly overweight. I simply became convinced over time that this way of eating is the best way to limit the damage which can be done by a lifetime of exposure to the standard American high-carb, starchy, sugary diet. I love my fatty meat, egg yolks, butter, sour cream, and more. I suppose I am fortunate I never had “carb-cravings”.

In a 2016 meta-analysis and systematic review, the researchers found that the low carbohydrate diet decreased fat in the liver significantly, but liver function tests did not improve significantly. When we look closely at the studies in the meta-analysis, they either found no effect on liver enzyme levels or a significant effect. In other words, the liver function of some people stayed the same on the low-carbohydrate diet while others improved significantly. Why the difference?
There is a reason why we store hundreds of thousands of calories in the form of fat in our body and only about 2000 calories in the form of glucose (with only a small amount of this useable by the brain). The reason is simple - The body prefers fat as its fuel source. Mark Sisson explains this in his article ‘A metabolic Paradigm Shift, or Why Fat is the Preferred Fuel for Human Consumption’.
Over the past century, ketogenic diets have also been used as natural remedies to treat and even help reverse neurological disorders and cognitive impairments, including epilepsy, Alzheimer’s symptoms, manic depression and anxiety. Research shows that cutting off glucose levels with a very low-carb diet makes your body produce ketones for fuel. This change can help to reverse neurological disorders and cognitive impairment, including inducing seizure control. The brain is able to use this alternative source of energy instead of the cellular energy pathways that aren’t functioning normally in patients with brain disorders.

The research on how diet affects PCOS is minimal, but there is one compelling study on the ketogenic diet and women with PCOS. In this study, five overweight women ate a ketogenic diet (20 grams of carbohydrates or less per day) for 24 weeks. The results were astounding — average weight loss was 12%, free testosterone decreased by 22%, and fasting insulin levels dropped by 54%. What’s even more impressive is that two of the women became pregnant despite previous infertility problems.
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