One of the most common side effects of starting the ketogenic diet is the “keto flu.” This term describes the often unpleasant, fatigue-inducing symptoms that occur as the body adjusts from a high-carbohydrate to a low-carbohydrate diet. During the keto flu, the body’s stored glucose begins depleting, and the body starts adapting to producing and utilizing ketones as energy. (2)

Some research suggests that ketogenic diets might help lower your risk of heart disease. Other studies show specific very-low-carb diets help people with metabolic syndrome, insulin resistance, and type 2 diabetes. Researchers are also studying the effects of these diets on acne, cancer, polycystic ovary syndrome (PCOS), and nervous system diseases like Alzheimer's, Parkinson's, and Lou Gehrig's disease.
Because some cancer cells are inefficient in processing ketone bodies for energy, the ketogenic diet has also been suggested as a treatment for cancer.[58][59] A 2018 review looked at the evidence from preclinical and clinical studies of ketogenic diets in cancer therapy. The clinical studies in humans are typically very small, with some providing weak evidence for anti-tumour effect, particularly for glioblastoma, but in other cancers and studies, no anti-tumour effect was seen. Taken together, results from preclinical studies, albeit sometimes contradictory, tend to support an anti-tumor effect rather than a pro-tumor effect of the KD for most solid cancers.[60]
A study with an intent-to-treat prospective design was published in 1998 by a team from the Johns Hopkins Hospital[19] and followed-up by a report published in 2001.[20] As with most studies of the ketogenic diet, there was no control group (patients who did not receive the treatment). The study enrolled 150 children. After three months, 83% of them were still on the diet, 26% had experienced a good reduction in seizures, 31% had had an excellent reduction and 3% were seizure-free.[Note 7] At twelve months, 55% were still on the diet, 23% had a good response, 20% had an excellent response and 7% were seizure-free. Those who had discontinued the diet by this stage did so because it was ineffective, too restrictive or due to illness, and most of those who remained were benefiting from it. The percentage of those still on the diet at two, three and four years was 39%, 20% and 12% respectively. During this period the most common reason for discontinuing the diet was because the children had become seizure-free or significantly better. At four years, 16% of the original 150 children had a good reduction in seizure frequency, 14% had an excellent reduction and 13% were seizure-free, though these figures include many who were no longer on the diet. Those remaining on the diet after this duration were typically not seizure-free but had had an excellent response.[20][21]
With grains, most fruits, and many vegetables off the menu, your digestive tract will bog down. “It’s really hard to get adequate fiber eating that way,” says Notte. “A common side effect is significant constipation.” Not only is constipation unpleasant, but it’s also a sign that your gut isn’t happy. “Everything in the keto diet is low in fiber—and that does not support gut health.”
"My suggestion is to start with changing your mindset first and foremost around three very important facts: this is not just another diet, you don’t have to live in Ketosis forever, and you will not be depriving yourself. Having said that, if you are used to eating highly-processed sugary food and refined carbohydrates you’ll need to ease into it," she explains.
I’ve been sugar free for 14 years, but sugar free doesn’t necessarily mean low carb or keto. For me back then it meant no white sugar, white flour or anything white or refined. I still enjoyed sweet potatoes and even honey. As the years went on I discovered even natural sugars caused me to continue to crave and I eventually went low carb back in 2013. I started my blog in 2011 so prior to 2013, some of the recipes are not low carb just sugar free. Here’s a post I wrote about the Differences between a Sugar Free and a Low Carb Diet.
This can be tough for folks who need a "cheat" day, but it can also take a mental toll on the dieter. In a usual diet plan when you go off of it for a day or two, you just get right back in the saddle and start again. With keto it's more than that: You need to start from scratch to get yourself back into ketosis, which can take a few days or weeks. This can really make you feel bad about yourself and take a psychological toll on your well-being and self-worth. (Related: Why You Should Give Up Restrictive Dieting Once and for All)
Thanks for this article. I just started a Keto diet so found it appropriate to my current lifestyle. Though I don’t believe your bottom line is strong enough since you simply stating that the diet is “hard to follow” and food is “notoriously unhealthy” without evidence going deeper into why those “notoriously unhealthy” foods are worse than keeping carbohydrate-heavy food that are addictive and give the body a quick sugar high for energy. I believe “hard to follow” is your opinion only, since acceptable Keto foods are found at all restaurants easily and also all grocery stores. All the foods you mention: “rich in very colorful fruits and vegetables, lean meats, fish, whole grains, nuts, seeds, olive oil, and lots of water” are all Keto-friendly. Many people have been on a Keto-diet for years. A healthy lifestyle is a healthy mindset change and making right choices – it’s not going to be easy.
This is a well-known phenomenon with nearly every type of diet: If you relax the rules even a little bit, you suddenly find yourself overeating. Making entire food groups—such as grains, sugar, and other carbohydrates—off-limits helps make them even more attractive, Macri says. This type of reaction goes beyond a psychological reaction—it can also be physical, she says. “Serotonin is one of the feel-good brain chemicals, and when serotonin decreases, such as it does when you’re on a strict low-carb diet, the brain is on high alert for any kind of reward,” she explains. Let some sugar or bread into your diet, and you could be overcome with a desire for more, Macri warns. “This makes it much more likely that you’ll overeat or even binge on those foods.” 
So people saying that – despite the lack of scientific support – likely have a financial reason to say it. Some of these products are sold under something like a multi-level marketing arrangement, so sales people are entirely paid based on commission. For example, the company Prüvit sells drinkable ketones, called KETO//OS with a multi-level marketing structure.

For patients who benefit, half achieve a seizure reduction within five days (if the diet starts with an initial fast of one to two days), three-quarters achieve a reduction within two weeks, and 90% achieve a reduction within 23 days. If the diet does not begin with a fast, the time for half of the patients to achieve an improvement is longer (two weeks) but the long-term seizure reduction rates are unaffected.[43] Parents are encouraged to persist with the diet for at least three months before any final consideration is made regarding efficacy.[9]
A ketogenic diet also has been shown to improve blood sugar control for patients with type 2 diabetes, at least in the short term. There is even more controversy when we consider the effect on cholesterol levels. A few studies show some patients have increase in cholesterol levels in the beginning, only to see cholesterol fall a few months later. However, there is no long-term research analyzing its effects over time on diabetes and high cholesterol.

Dr. Campos, it is unfortunate that you retain the medical community’s negative stance on the ketogenic diet, probably picked up in medical school when you studied ketoacidosis, in the midst of an obesity and type II diabetes epidemic that is growing every year, especially among populations who will never see the Harvard Health Letter. The medical community has failed in reversing this trend, especially among children, and the public is picking up the tab, in the form of higher health insurance premiums to treat chronic metabolic diseases which doctors cannot cure. The ketogenic diet does not bid its adherents to eat unhealthy processed meats, and the green leafy vegetables that it emphasizes are important in a number of nutritional deficiencies. People lose weight on the ketogenic diet, they lose their craving for sugar, they feel more satiety, they may become less depressed, their insulin receptors sensitivity is improved, and these are all the good outcomes you fail to mention. There is a growing body of research which demonstrates the neuroprotective effects of the ketogenic diet to slow cancer progression, as well as diseases like Parkinson’s and Alzheimer’s, for which there are no effective medical treatments. Please respect your patients by providing them with evidence-based medical outcomes, not opinions.
Keto is not hard to follow at all. See, this is why I took my diet and nutrition into my own hands. I have PCOS and the ketogenic diet has worked wonders for me. I’m finally pregnant at the age of 32 and after 11 years of marriage because the ketogenic diet made me lose over 100 lbs and brought my insulin resistance under control. I feel better than I’ve ever felt. Sometimes doctors don’t seem to know as much as they should, or as much as they assume they do, and that’s pretty disturbing. Just like they’re still using the old school and very inaccurate BMI charts that are just pure bs. I’ll just take care of myself outside of certain situations involving illness or injury. I’m doing great on my own.
Leftovers will be another thing we will take into consideration. Not only is it easier on you, but why put yourself through the hassle to cook the same food more than once? Breakfast is something I normally do leftover style, where I don’t have to worry about it in the morning and I certainly don’t have to stress about it. Grab some food out the fridge, pre-made for me, and head out the door. It doesn’t get much easier than that, does it?
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Those issues can be part of what's known as the “keto flu,” Warren says. Other side effects of the keto diet, all of which are tied to carb withdrawal, can include lightheadedness, nausea, mental fog, cramps, and headaches, in addition to tiredness. Luckily, the keto flu doesn't usually last more than a week—which is coincidentally about when people start to see the number on the scale go down, says Warren.
If you’re a newbie planning your weekly keto diet plan, make the meals as easy as possible. A keto breakfast, for example, can take advantage of many classic breakfast foods, including eggs, bacon, sausage, and ham. Eggs are real winners in the keto world. They’re extremely versatile, easy to cook, and have just half a gram of carbs but 6 g of protein and 5 g of fat.
You’re transitioning. Your body is equipped to process a high intake of carbs and a lower intake of fat. Your body needs to create enzymes to be able to do this. In the transitional period, the brain may run low on energy which can lead to grogginess, nausea, and headaches. If you’re having a large problem with this, you can choose to reduce carb intake gradually.

“I would make broccoli rice or cauliflower rice to at least feel like I was eating some carbs,” she wrote on her blog. “Then I would add protein, so I often ate grilled chicken and fish over broccoli rice, cauliflower rice or spaghetti squash. I mixed in roasted vegetables, fresh salads with homemade dressing, and smoothies made with avocados and bananas.”
A systematic review in 2016 found and analysed seven randomized controlled trials of ketogenic diet in children and young people with epilepsy.[2] The trials were done among children and young people for whom drugs failed to control their seizures, and only one of the trials compared a group assigned to ketogenic diet with a group not assigned to one.[16] The other trials compared types of diets or ways of introducing them to make them more tolerable.[2] Nearly 40% of the children and young people had half or fewer seizures with the diet compared with the group not assigned to the diet. Only about 10% were still on the diet after a few years.[2] Adverse effects such as hunger and loss of energy in that trial were common, with about 30% experiencing constipation.[16]
Dr. Campos, it is unfortunate that you retain the medical community’s negative stance on the ketogenic diet, probably picked up in medical school when you studied ketoacidosis, in the midst of an obesity and type II diabetes epidemic that is growing every year, especially among populations who will never see the Harvard Health Letter. The medical community has failed in reversing this trend, especially among children, and the public is picking up the tab, in the form of higher health insurance premiums to treat chronic metabolic diseases which doctors cannot cure. The ketogenic diet does not bid its adherents to eat unhealthy processed meats, and the green leafy vegetables that it emphasizes are important in a number of nutritional deficiencies. People lose weight on the ketogenic diet, they lose their craving for sugar, they feel more satiety, they may become less depressed, their insulin receptors sensitivity is improved, and these are all the good outcomes you fail to mention. There is a growing body of research which demonstrates the neuroprotective effects of the ketogenic diet to slow cancer progression, as well as diseases like Parkinson’s and Alzheimer’s, for which there are no effective medical treatments. Please respect your patients by providing them with evidence-based medical outcomes, not opinions.
Yes your are totally right, I meant to take off 500 calories a day to lose 1 pound a week (7 days/week x 500 calories/day = 3500 calories/week = 1 pound of fat/week) or take off 1000 calories to lose 2 pounds a week (7 days/week x 1000 calories/day = 7000 calories/week = 2 pounds of fat/week). Thanks to you, I fixed this little typo 🙂 Thanks a lot!
Yes your are totally right, I meant to take off 500 calories a day to lose 1 pound a week (7 days/week x 500 calories/day = 3500 calories/week = 1 pound of fat/week) or take off 1000 calories to lose 2 pounds a week (7 days/week x 1000 calories/day = 7000 calories/week = 2 pounds of fat/week). Thanks to you, I fixed this little typo 🙂 Thanks a lot!

"My suggestion is to start with changing your mindset first and foremost around three very important facts: this is not just another diet, you don’t have to live in Ketosis forever, and you will not be depriving yourself. Having said that, if you are used to eating highly-processed sugary food and refined carbohydrates you’ll need to ease into it," she explains.
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.
Sharon M. Nickols-Richardson, PhD, RD, , Mary Dean Coleman, PhD, RD, Joanne J. Volpe, Kathy W. Hosig, PhD, MPH, RD, “Perceived Hunger Is Lower and Weight Loss Is Greater in Overweight Premenopausal Women Consuming a Low-Carbohydrate/High-Protein vs High-Carbohydrate/Low-Fat Diet,” The Journal of Pediatrics: Vol 105, Issue 9: 1433–1437; September 2005. http://www.sciencedirect.com/science/article/pii/S000282230501151X.
Following a ketogenic diet, your food intake would be roughly 5 to 10 percent carbohydrates, 15 percent protein, and 75 to 80 percent fat. This would be a pretty seismic shift for most people who follow a standard American diet; according to a 2016 report by the CDC, the average American adult’s diet is 50 percent carbohydrates, 16 percent protein, and 34 percent fat. Your average day on a ketogenic diet might include eggs, cheese, assorted meats and small amounts of nuts and avocados, and modest amounts of vegetables that are low in carbs, like spinach and lettuce.
To me, food is fuel but it should also be enjoyed. I just can't get past the fact that many keto recipes (and I've developed many) don't leave me satisfied—and all the substitutes and high-fat ingredients tend to give me (and clients) a stomachache. The keto diet is more like feeding the body "medicine" to trigger a process (ketosis—using fat as fuel instead of carbs) than it is about the enjoyment of it.
All carbs turn to sugar in your body but some people can handle eating sweet potatoes or regular potatoes and not have any craving issues. I just look at them and I gain weight and I crave more and more. I am very carb intolerant. The more I indulge in carbohydrates the more I want and on and on and on it goes. It’s a vicious cycle and I finally stopped the cycle. Know how? By eating keto!

Also, when you eliminate sugar and high-carb foods from your daily diet, "your body is able to heal itself and detox from the accumulated inflammation that it is constantly fighting," That means less brain fog, improved cognition and brain health. Consequently, the improved mental clarity makes it easier for you to make smart food choices, adds the nutritionist.
When ketosis kicks in, the body switches from stealing protein for fuel to burning fat. “The body starts to rely more heavily on fat stores,” Notte explains. Molecules called ketones are released when body fat is metabolized, and some cells in the brain can use ketones for fuel. However, your brain needs more than 100 grams of carbohydrates a day, according to research, and while your body makes the switch to relying on fat—ketones—for energy, your brain can suffer.
Stats: female, 31, 5'5" 169 lbs. Down from 221 since March 2018. Would like to keep the weight loss going, but in a sustainable way. I just got hired on as a seasonal worker in a warehouse. I am spending 5 hrs a day moving boxes up to 70 lbs. I walk about 1500 steps in my shift according to my fitbit, and have 250-300 minutes of what it thinks of as "activity." The fitbit says I am burning 4000 kcal daily. Which i know can be overestimated. The last week i have logged 11+ miles per day between work and my usual life stuff. Prior to this, i was eating about 1300 kcal daily and averaging about 9k steps daily, with roughly 30-60 minutes of activity (fitbit recognizes activity as anything that elevates heart rate above 120 bpm--I was doing cardio and weight lifting 5 days a week for 60-90 mins. Cardio counts towards this, weight lifting does not) So clearly 1300 kcal in ratio of 90/90/20 is not enough food to sustain the kind of activity I am currently doing, but I have no idea how to recalculate my macros for this!

Another difference between older and newer studies is that the type of patients treated with the ketogenic diet has changed over time. When first developed and used, the ketogenic diet was not a treatment of last resort; in contrast, the children in modern studies have already tried and failed a number of anticonvulsant drugs, so may be assumed to have more difficult-to-treat epilepsy. Early and modern studies also differ because the treatment protocol has changed. In older protocols, the diet was initiated with a prolonged fast, designed to lose 5–10% body weight, and heavily restricted the calorie intake. Concerns over child health and growth led to a relaxation of the diet's restrictions.[18] Fluid restriction was once a feature of the diet, but this led to increased risk of constipation and kidney stones, and is no longer considered beneficial.[3]

Here are a few of the most common side effects that I come across when people first start keto. Frequently the issues relate to dehydration or lack of micronutrients (vitamins) in the body. Make sure that you’re drinking enough water (close to a gallon a day) and eating foods with good sources of micronutrients. To read more on micronutrients, click here >


To get the most benefit from the Keto diet, you should stay physically active. You might need to take it easier during the early ketosis period, especially if you feel fatigued or lightheaded. Walking, running, doing aerobics, weightlifting, training with kettlebells or whatever workout you prefer will boost your energy further. You can find books and online resources on how to adapt Keto meals or snacks for athletic training.
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