Now that you have fasted for quite a long time, you can break your fast at around 4 to 5 pm. Try having some good fat for this purpose, such as coconut oil or MCT oil, butter, or any other healthy fat. MCT oil might come in as a better option in this case since it gets quickly absorbed by the body. It swiftly bypasses the gallbladder and reaches the liver where it is transformed to ketones rapidly.
[1] Shannon L. Kesl, corresponding author Angela M. Poff, Nathan P. Ward, Tina N. Fiorelli, Csilla Ari, Ashley J. Van Putten, Jacob W. Sherwood, Patrick Arnold, and Dominic P. D’Agostino (2016). Effects of exogenous ketone supplementation on blood ketone, glucose, triglyceride, and lipoprotein levels in Sprague–Dawley rats. Nutrition & Metabolism, 13(9)
As for MCT oil (and oil powders), powder formulations tend to cause less digestive distress (e.g. probiotics), but some folks object to the additional ingredients like sunflower lecithin or soluble corn fiber). Even if you’d like to eventually settle on an oil, I’d recommend starting with a powder to see how you respond and to give your body the chance to adapt over time.
Improved cognition: Elevated plasma ketone concentrations divert the brain to utilize ketone bodies for synthesis of phospholipids, which drives growth and myelination. Normally, glucose would be the preferred substrate, which is much less efficient.14 BHB seems to act as a signal for neuronal pathways. These enhance synaptic plasticity, cognition and neuronal stress resistance. 15 In rat studies, ingestion of a ketone ester for 5 days improved their spatial learning and memory. 16.
International Patent # PCT/US2014/031237, University of South Florida, D.P. D’Agostino, S. Kesl, P. Arnold, “Compositions and Methods for Producing Elevated and Sustained Ketosis”. P. Arnold (Savind) has received financial support (ONR N000140610105 and N000140910244) from D.P. D’Agostino (USF) to synthesize ketone esters. The remaining authors have no conflicts of interest.
Exogenous ketones provide the body with another fuel to employ. Think about it like an electric car that runs on both gas and electricity: by consuming ketones along with carbohydrates, the body will preferentially burn the ketones first, saving the carbohydrates for later. Exogenous ketones allow us to enter a metabolic state that wouldn't occur naturally: the state of having full carbohydrate stores, as well as elevated ketones in the blood. This could be advantageous to athletes looking to boost their physical performance. 
This molecule is quite essential if you are using your own fat for fuel, or taking BHB as an exogenous ketone supplement to increase energy production — essentially to be in nutritional ketosis. If you’re not certain about what ketones are or what nutritional ketosis is, you should back up a little bit and read more about that on my company site, Perfect Keto.
Hypoglycemia: why not to be concerned – Taking exogenous ketones can drive blood glucose levels quite low, but you are not likely to feel the typical symptoms of hypoglycemia. This is because when ketone levels are high enough, they dominate as fuel in the brain; hence, you will feel just fine despite having low blood glucose. A highly-cited study by George Cahill, found elevated ketone levels could protect fasted participants when they were administered insulin to induce hypoglycemia.
It’s not clear that the Weir coefficients used to estimate EE are relevant for someone in ketosis, let alone someone ingesting exogenous BHB. (The Weir formula states that EE is approximated by 3.94 * VO2 + 1.11 * VCO2, where VO2 and VCO2 are measured in L/min; 3.94 and 1.11 are the Weir coefficients, and they are derived by tabulating the stoichiometry of lipid synthesis and oxidation of fat and glucose and calculating the amount of oxygen consumed and carbon dioxide generated.) While this doesn’t impact the main observation—less oxygen was consumed with higher ketones—it does impact the estimation of EE and substrate use.
BHB isn’t just an energy source for the brain–it has other effects which promote brain health. BHB can trigger the release of chemicals called neurotrophins, which support neuron function and synapse formation. One of these neurotrophins is called BDNF (brain-derived neurotrophic factor), which is a protein in the brain associated with cognitive enhancement, alleviation of depression and reduction of anxiety.10

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