The fasting periods were often called ‘cleanses’, ‘detoxifications’, or ‘purifications’, but the idea is similar – e.g. to abstain from eating food for a certain period of time, often for health reasons. People imagined that this period of abstinence from food would clear their bodies’ systems of toxins and rejuvenate them. They may have been more correct than they knew.
Probably, and there are a few reasons why the keto diet usually equals weight-loss gold, says Keatley. For starters, people usually reduce their daily caloric intake to about 1,500 calories a day because healthy fats and lean proteins make you feel fuller sooner—and for a longer period of time. And then there’s the fact that it takes more energy to process and burn fat and protein than carbs, so you're burning slightly more calories than you did before. Over time, this can lead to weight loss.
^ Jump up to: a b c Harris, L; Hamilton, S; Azevedo, LB; Olajide, J; De Brún, C; Waller, G; Whittaker, V; Sharp, T; Lean, M; Hankey, C; Ells, L (February 2018). "Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis". JBI Database of Systematic Reviews and Implementation Reports. 16 (2): 507–547. doi:10.11124/JBISRIR-2016-003248. PMID 29419624.
So how exactly does intermittent fasting work? There are two main approaches. The first method: You limit yourself to 500 calories per day, with alternate days that have no food or calorie restrictions. The second method: You limit the time period of when you can eat to an 8- to 10-hour window. For example, your meals are contained within the hours of 9 am and 7 p.m. Each approach has its pros and cons, so it may take some experimenting to find which way works for you. But no matter which method you choose, periodic fasting is scientifically proven to burn fat effectively without losing too much muscle or dropping your metabolism.
^ Jump up to: a b c d e f g h i j k l m n o p q r s Kossoff EH, Zupec-Kania BA, Amark PE, Ballaban-Gil KR, Bergqvist AG, Blackford R, et al. Optimal clinical management of children receiving the ketogenic diet: recommendations of the International Ketogenic Diet Study Group. Epilepsia. 2009 Feb;50(2):304–17. doi:10.1111/j.1528-1167.2008.01765.x. PMID 18823325
On the other hand, an intermittent fasting-style diet just might feel simpler than trying to follow a more complicated eating plan—and that can count for a lot. “The idea of having a simple rule to follow may make it easier for people to avoid any mindless eating,” Peterson says. “I have had some people tell me that intermittent fasting made it easier for them to eat healthfully.”
The ketogenic diet is calculated by a dietitian for each child. Age, weight, activity levels, culture, and food preferences all affect the meal plan. First, the energy requirements are set at 80–90% of the recommended daily amounts (RDA) for the child's age (the high-fat diet requires less energy to process than a typical high-carbohydrate diet). Highly active children or those with muscle spasticity require more food energy than this; immobile children require less. The ketogenic ratio of the diet compares the weight of fat to the combined weight of carbohydrate and protein. This is typically 4:1, but children who are younger than 18 months, older than 12 years, or who are obese may be started on a 3:1 ratio. Fat is energy-rich, with 9 kcal/g (38 kJ/g) compared to 4 kcal/g (17 kJ/g) for carbohydrate or protein, so portions on the ketogenic diet are smaller than normal. The quantity of fat in the diet can be calculated from the overall energy requirements and the chosen ketogenic ratio. Next, the protein levels are set to allow for growth and body maintenance, and are around 1 g protein for each kg of body weight. Lastly, the amount of carbohydrate is set according to what allowance is left while maintaining the chosen ratio. Any carbohydrate in medications or supplements must be subtracted from this allowance. The total daily amount of fat, protein, and carbohydrate is then evenly divided across the meals.[37]

Intermittent fasting—more an eating pattern than a diet, science says it can help you lose weight (a smaller eating window means less calories consumed), but even better, research has linked it to improved blood sugar levels, decreased risk of heart disease and cancer, and, according to neuroscientist Mark Mattson's research, it might just help your brain ward off neurogenerative diseases like Alzheimer's and Parkinson's while improving mood and memory.