Pros: The most consistently beneficial of all diets here, study after study shows that upping your protein intake can help significantly reduce body fat and build lean muscle. For example: Guys who ran sprint intervals, did resistance training, and ate a diet of 2.4g of protein per kg of bodyweight per day (roughly 1g per lb of bodyweight) gained 1.2kg of lean muscle and lost almost 5kg of fat in just four weeks, according to a study in the American Journal of Clinical Nutrition. If you cut calories but eat high protein, the macro can help prevent your metabolism from plummeting and help keep hunger at bay, since protein is so satiating. The study analysis also confirmed that eating a ton of protein stuff doesn’t cause you to gain weight or harm any internal systems, despite myths.
Ketoacidosis (KA) is a life-threatening condition in which your body doesn’t make enough insulin. This causes you to have dangerously high levels of ketones (substances occurring when the body uses fat stores for energy) and blood sugar. The combination of both makes your blood incredibly acidic, and this can, in turn, change the normal functioning of your internal organs such as your liver and kidneys. Patients suffering from ketoacidosis must get treatment immediately or they could slip into a coma and even die.

About 20% of children on the ketogenic diet achieve freedom from seizures, and many are able to reduce the use of anticonvulsant drugs or eliminate them altogether.[3] Commonly, at around two years on the diet, or after six months of being seizure-free, the diet may be gradually discontinued over two or three months. This is done by lowering the ketogenic ratio until urinary ketosis is no longer detected, and then lifting all calorie restrictions.[45] This timing and method of discontinuation mimics that of anticonvulsant drug therapy in children, where the child has become seizure free. When the diet is required to treat certain metabolic diseases, the duration will be longer. The total diet duration is up to the treating ketogenic diet team and parents; durations up to 12 years have been studied and found beneficial.[9]

"What I don't like about any commercial diet is that the focus is not on your actual food choices," Hogan said. "It's about calories or points or numbers, and that really takes away from your ability to be in tune with your hunger cues and your fullness cues and what you're really craving. If we become more in tune with those things, we naturally consume how much the body needs. Paying too much attention to numbers takes away from that."
"Those with type 1 diabetes should avoid a ketogenic diet," warns Joseph Galati, MD, a hepatologist at the Liver Specialists of Texas in Houston, "Many patients with type 1 diabetes have some degree of renal impairment, and handling the build-up of ketones and acids in the body may cause too much stress on the kidneys. Of course, any pregnant women with diabetes, especially those requiring insulin should avoid such an extreme diet given the low glucose levels will be a constant [health] threat."
Several comprehensive studies and meta-analyses have demonstrated that after a few months or even a year of a low carb diet versus a moderate/high carb diet, there are no significant differences in the amount of weight lost (2,3,4,5).  I will say, however, most of these diets are NOT keto and are simply lower carb (i.e. 20%).  Also, long-term effects (beyond 1 year) are not often studied due to budgetary constraints, so interpret results as you wish.
If it all feels a little bit 90s, that’ll be because this was basically the diet that kept Rachel from Friends looking, well, like Rachel from Friends. Think of it as the 20th-century version of no carbs before Marbs. Thankfully though, the old premise of each as much as you want, as long as you don’t go near a carb, has had a makeover. The New Atkins diet reintroduces carbs in phases.
6. Longer life. A recent meta-analysis in the British Medical Journal found the diet significantly improved health and led to a 9 percent reduction in death from heart disease, cancer, Parkinson's, and Alzheimer's. Other studies have found that the diet's healthy fats may lessen the inflammation and pain of rheumatoid arthritis and cut the risk of getting amyotrophic lateral sclerosis (Lou Gehrig's disease) by 60 percent.
When you’re eating the foods that get you there (more on that in a minute), your body can enter a state of ketosis in one to three days, she adds. During the diet, the majority of calories you consume come from fat, with a little protein and very little carbohydrates. Ketosis also happens if you eat a very low-calorie diet — think doctor-supervised, only when medically recommended diets of 600 to 800 total calories.
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