The most obvious hurdle with ketogenic diets is that extreme carb restriction makes it very challenging for most people to stick to them, especially long term.
Common adverse effects include fatigue, dizziness, constipation, and sleep problems, which tend to get better within a few weeks. Longer-term adverse effects would depend on the exact composition of the diet and how long it is followed.
Because ketogenic diets eliminate whole grains, most fruits, and many vegetables, they tend to be low in key nutrients, such as folate and potassium, along with fiber, all of which are essential for good health.
LDL cholesterol levels often rise on ketogenic diets, though focusing on foods high in unsaturated rather than saturated fat can help prevent this (more nuts and avocados, less meat and butter, for instance). Overall, the diet’s cardiovascular benefits (notably for triglycerides, HDL, blood sugar, and body weight) may outweigh any increase in LDL, especially for people with diabetes. In any case, research suggests that the increase in LDL is in large, non-dense particles; these are less harmful for cardiovascular health than small, dense particles, which decrease on very low-carb, high-fat diets. Longer, larger clinical trials are needed to better assess these effects.
People with kidney disease (including chronic kidney disease) should steer clear of high-protein versions of the diet because the excess protein, in addition to the increased burden of handling ketones and the associated loss of body water, could worsen their condition. They should consult their doctors before trying a ketogenic diet.
This article first appeared in the UC Berkeley Wellness Letter.