On the ketogenic diet, carbohydrates are restricted and so cannot provide for all the metabolic needs of the body. Instead, fatty acids are used as the major source of fuel. These are used through fatty-acid oxidation in the cell's mitochondria (the energy-producing parts of the cell). Humans can convert some amino acids into glucose by a process called gluconeogenesis, but cannot do this by using fatty acids.[57] Since amino acids are needed to make proteins, which are essential for growth and repair of body tissues, these cannot be used only to produce glucose. This could pose a problem for the brain, since it is normally fuelled solely by glucose, and most fatty acids do not cross the blood–brain barrier. However, the liver can use long-chain fatty acids to synthesise the three ketone bodies β-hydroxybutyrate, acetoacetate and acetone. These ketone bodies enter the brain and partially substitute for blood glucose as a source of energy.[56]

Restricting your calories may be important for some individuals depending on their goals. Additionally, it may aid in the initiation of ketosis; however, not everyone will require calorie tracking to maintain a deficit. It is not uncommon for caloric-restriction to occur inadvertently as a ketogenic diet tends to be satiating, leaving individuals satisfied with fewer calories.
Appetite Control: The high-fat nature of the ketogenic diet along with elevated ketone and stable blood glucose levels have been shown to have a profound effect on appetite. This may give individuals who have a difficult time controlling the amount of food they eat “freedom” in knowing that they won’t be as hungry and thus less likely to consume excess calories.
There are theoretically no restrictions on where the ketogenic diet might be used, and it can cost less than modern anticonvulsants. However, fasting and dietary changes are affected by religious and cultural issues. A culture where food is often prepared by grandparents or hired help means more people must be educated about the diet. When families dine together, sharing the same meal, it can be difficult to separate the child's meal. In many countries, food labelling is not mandatory so calculating the proportions of fat, protein and carbohydrate is difficult. In some countries, it may be hard to find sugar-free forms of medicines and supplements, to purchase an accurate electronic scale, or to afford MCT oils.[54]
Try Googling “TDEE Calculator”. Once you plug in your stats, the site will calculate your total daily energy expenditure. This is a useful guide in determining how many calories to eat. From there, if you are trying to lose weight, just reduce your caloric intake, increase your expenditure (through exercising more), or use a combination of the two.
“Combining a super restrictive diet with long periods of non-eating is not good,” says Keatley. “The body will cannibalize its own muscle for energy if intake from food is too low but the body does not differentiate between something like a calf muscle or a heart muscle. Keep in mind all your important organs are made of smooth muscle and going on a diet like this may harm something like your bladder or lungs just as much as provide fat loss.”
I eat relatively healthy and fairly low carb (I am already gluten free). I am interested in getting into Ketosis for the the health benefits, but am quite thin for a guy and don’t want to lose any weight. I look at the sample diet above and am pretty sure I would drop weight quickly (I consume about 2,500+ calories daily now). I eat 3 meals plus 2-3 snacks (snacks mostly of nuts (with raisins that would have to go), greek yogurt (would switch to plain), peanut butter, cheese and fruit (would need to reduce qty)). Would eating straight up butter be ok for additional calories also once I am in Ketosis?