Note the emphasis on ketosis as a temporary adaptive state. Our ancestors could not be in fasting-induced ketosis permanently because they would eventually exhaust their fat reserves (which were presumably far more limited than ours, owing to the simple fact that they ate less and moved more than we do). They would then progress from fasting to starving, and subsequently die.
Ketoacidosis, on the other hand, is dangerous. But it’s usually limited to people with type 1 diabetes, striking when their glucose levels rise due to illness or a missed insulin dose. Without insulin, cells can’t take in glucose, so they burn fat for fuel instead, producing exceptionally high ketone levels—much higher than the amount generated by the keto diet. That, in combination with high blood glucose levels, essentially poisons the blood. “It’s very easy to tell the difference between nutritional ketosis, which has no negative symptoms [aside from ‘keto breath,’ which can smell like nail polish remover], and dietary ketoacidosis, which is an illness that requires hospitalization and causes lethargy, abdominal pain, nausea, vomiting, rapid breathing, and lack of appetite,” says William Yancy, MD, program director at the Duke Diet and Fitness Center in Durham, North Carolina.
Meanwhile, more than 70 trials have examined the health effects of a low-carb diet. They attest to the benefits64 associated with ketosis and low-carb diets, including a reduction in body weight and body mass index, improved cardiovascular risk factors including blood pressure, and the reversal of Type 2 diabetes. It is virtually impossible to imagine that a diet with so many health improvements in the ‘near term’ (2 years) could ultimately shorten life—and the study authors offer no possible mechanism to explain how this might happen.
Your glycogen stores can still be refilled while on a ketogenic diet. A keto diet is an excellent way to build muscle, but protein intake is crucial here. It’s suggested that if you are looking to gain mass, you should be taking in about 1.0 – 1.2g protein per lean pound of body mass. Putting muscle on may be slower on a ketogenic diet, but that’s because your total body fat is not increasing as much.5Note that in the beginning of a ketogenic diet, both endurance athletes and obese individuals see a physical performance for the first week of transition.
Because it lacks carbohydrates, a ketogenic diet is rich in proteins and fats. It typically includes plenty of meats, eggs, processed meats, sausages, cheeses, fish, nuts, butter, oils, seeds, and fibrous vegetables. Because it is so restrictive, it is really hard to follow over the long run. Carbohydrates normally account for at least 50% of the typical American diet. One of the main criticisms of this diet is that many people tend to eat too much protein and poor-quality fats from processed foods, with very few fruits and vegetables. Patients with kidney disease need to be cautious because this diet could worsen their condition. Additionally, some patients may feel a little tired in the beginning, while some may have bad breath, nausea, vomiting, constipation, and sleep problems.
Sleep enough – for most people at least seven hours per night on average – and keep stress under control. Sleep deprivation and stress hormones raise blood sugar levels, slowing ketosis and weight loss a bit. Plus they might make it harder to stick to a keto diet, and resist temptations. So while handling sleep and stress will not get you into ketosis on it’s own, it’s still worth thinking about.