“Suddenly and drastically reducing carbohydrates sets your body up for a double whammy of sorts,” says Yawitz. “The brain’s favorite fuel is glucose, which is most easily created from carbohydrates. In very-low-carb diets, the brain has to adjust to using ketones from digested fats for energy. To add to this discomfort, your kidneys release more electrolytes as insulin levels fall.” Additionally, your total body water decreases as carbohydrates become depleted on a keto diet, notes Clark. The result? What’s known as the keto flu, which could cause constipation, nausea, headache, fatigue, irritability, cramps, and other symptoms. Don’t fret, though: Many of these symptoms are short term and should last only a few days to weeks. Make sure to drink plenty of water to help your body cope with these symptoms. And call your doctor if symptoms — especially nausea — are prolonged, advises Yawitz.
Twenty elite ultra-marathoners and ironman distance triathletes performed a maximal graded exercise test and a 180 min submaximal run at 64% VO2max on a treadmill to determine metabolic responses. One group habitually consumed a traditional high-carbohydrate (HC: n = 10, %carbohydrate:protein:fat = 59:14:25) diet, and the other a low-carbohydrate (LC; n = 10, 10:19:70) diet for an average of 20 months (range 9 to 36 months).

As insulin levels plummet from carb-cutting, more water is flushed out, along with excess sodium (in contrast, excess insulin from carbs causes sodium and water retention).4 In some people, dehydration contributes to constipation, which can also result from avoiding fiber-rich carbohydrate foods. While less common, diarrhea or loose bowels can be triggered by a number of factors including too much or too little fat, dairy intolerance, or changes in gut flora. 
A lot of changes are happening in your body and you’re going to feel it! The first five to seven days can be pretty rough, but your body is getting over its dependency on sugar. During this time of transition it is essential that you supplement electrolytes. Your body is flushing out lots of water, and with that goes electrolytes. The Keto Flu can be greatly reduced if you add sodium, potassium and magnesium to your diet. Check out our supplements page for a list of electrolyte supplements we recommend. Stay on course and you’ll start feeling better in no time!
Ketosis is a nutritional process characterised by serum concentrations of ketone bodies over 0.5 mM, with low and stable levels of insulin and blood glucose.[1][2] It is almost always generalized with hyperketonemia, that is, an elevated level of ketone bodies in the blood throughout the body. Ketone bodies are formed by ketogenesis when liver glycogen stores are depleted (or from metabolising medium-chain triglycerides[3]). Ketones can also be consumed in exogenous ketone foods and supplements.
There’s also some evidence that it might help with type 2 diabetes. “An emerging body of research is finding that a keto plan may have some real benefits thanks to its ability to improve the body’s ability to use insulin and also help control appetite, which can result in easier weight loss,” says Karen Ansel, R.D.N., co-author of Healthy in a Hurry.
-Pancreatic Dysfunction: The beta cells in the pancreas that produce the insulin to help control blood sugar become dysfunctional with high blood glucose, raising the risk for type 2 diabetes. Researchers have discovered that beta cell issues are detectable in people whose glucose levels spike two hours after eating, despite those levels staying within the range considered normal and safe by the medical establishment.
There are many ways in which epilepsy occurs. Examples of pathological physiology include: unusual excitatory connections within the neuronal network of the brain; abnormal neuron structure leading to altered current flow; decreased inhibitory neurotransmitter synthesis; ineffective receptors for inhibitory neurotransmitters; insufficient breakdown of excitatory neurotransmitters leading to excess; immature synapse development; and impaired function of ionic channels.[7]
Since originally publishing this article, I’ve been asked whether elevating blood ketones with exogenous sources could trigger a ketone-induced release of insulin that would theoretically reduce hepatic ketogenesis and perhaps slow fat mobilization. This makes sense since you are putting more energy into the system in general (from exogenous ketones), so there would be less need to draw off your own fat stores.

I am not an athlete. I am a mid 30’s male with a sedentary lifestyle. I am 5’10” and 250lbs. I have mild hypertension, high triglycerides, and pre-diabetes. I have eaten whatever I want and as much as I want for years. I have recently started walking/jogging 3-4 times a week, taking fish oil, and eating significantly less carbs plus added fish and steak. Is this diet appropriate and safe for me?
This is an absolutely necessary function for basic survival. As the body can only store carbs for a day or two, the brain would quickly shut down after a couple of days without food. Alternatively it would quickly have to convert our muscle protein into glucose – a very inefficient process – just to keep the brain going. That would make us waste away quickly. It would also ensure that the human race could hardly have survived all those millennia before we had 24-7 food availability.
The thing is, for keto to work, it can’t just be treated like any other diet, which is really confusing considering all the pundits touting the “keto diet.” Eating a balanced diet in daylight hours and night capping with a “keto bar” from Whole Foods is not going to put you in a state of ketosis, nor is eating keto religiously and bingeing the family sized bag of Doritos twice a week. Putting the word “diet” beside “keto” is a bit misleading because it downplays the outrageous restrictions required to put your body in an unnatural fat-burning state. In order to accomplish the “ketosis” most diet plans talk about, you need to radically change your lifestyle -- and, unlike switching to a balanced diet of whole foods, you must be fairly religious about carb restriction in order to reap the benefits.
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