Is it unhealthy to be in ketosis for more than 6 months on a low carb diet? I would like to be in ketosis for a year if healthy.
Long-term ketogenic diet can have various side effects.
The most common adverse effects included gastrointestinal disturbances (40.6%), hyperlipidemia (12.8%), hyperuricemia (4.4%), lethargy (4.1%), infectious diseases (3.8%) and hypoproteinemia (3.8%).
Side effects include constipation, dyslipidemia, growth slowing, acidosis, and kidney stones.
Impaired physical performance is a common but not obligate result of a low carbohydrate diet.
The moderate adverse effects comprised of...mineral deficiencies...
Ketovale mentions many side effects from a mixture of anecdotal and study reports: the side effects mentioned above plus keto flu (headache, weakness, brain fog, increased hunger and fatigue), acetone-like breath, muscle cramps, insomnia, reduced bone mineral density, keto rash...
A low-carbohydrate diet based on animal sources was associated with higher all-cause mortality in both men and women, whereas a vegetable-based low-carbohydrate diet was associated with lower all-cause and cardiovascular disease mortality rates.
You might be interested in this study: Long-term effects of a ketogenic diet in obese patients.
Specifically, for 83 obese study participants on a ketogenic (<30g carb/day) diet for 24 weeks:
The weight and body mass index of the patients decreased significantly (P<0.0001). The level of total cholesterol decreased from week 1 to week 24. HDL cholesterol levels significantly increased, whereas LDL cholesterol levels significantly decreased after treatment. The level of triglycerides decreased significantly following 24 weeks of treatment. The level of blood glucose significantly decreased. The changes in the level of urea and creatinine were not statistically significant.
All of these changes (weight and BMI decreased, total cholesterol decreased, LDL decreased, triglycerides decreased, HDL increased, blood glucose decreased) are normally considered to be indications of improved health.