A metabolic process called ketogenesis and a body state called ketosis are responsible. Ketosis is simply a normal metabolic pathway in which body and brain cells utilize ketones to make energy, instead of relying on only sugar (i.e., carbohydrate). In fact, humans developed an evolutionary ability to burn ketones as an adaptation to periods of food scarcity. 
When you lose weight, fat cells shrink. In a fat cell, there are triglycerides and cholesterol. Now, as that fat cell shrinks, you can burn triglycerides, but you cannot burn cholesterol. So it will go into the blood, go to the liver, and come out through the bile. But you’ll be totally fine as long as your triglycerides are low. (If you’re not using those as fuel, then you’re eating too much sugar.)

When you get to one meal a day, just make sure the meal is a robust one, containing all the needed nutrients to fortify your body with vitamins, minerals, amino acids, those important fatty acids, trace minerals—all of it. (This can be aided with green drink powders and high-quality electrolyte supplements that will help you get your daily requirements for potassium.)
Meal prepping is the secret to eating on a tight budget. It allows you to buy the items that are on sale, in bulk, and prepare them for quick access throughout the week. The meal prep detailed here took us about 2 hours of “active time” and another 3 hours of “passive time”. The passive time was mostly waiting for the chicken to cook/cool. The items we prepped for this meal plan are:
The wildly popular Crack Chicken is actually pretty simple in its ingredient list: chicken, cream cheese, cheddar cheese, bacon, scallion, and Ranch seasoning! The end result is creamy and rich, and packed with flavor. It’s proof that a recipe doesn’t have to be complicated to taste great. Crack Chicken is deliciously addictive, which is where the name comes from.
I LOVE Urban Remedy, but as another review said, this plan is my least favorite and I will not order again. First of all, the stevia in the drinks makes me super bloated and they just taste sickly sweet and like stevia. I feel like a cleanse should train your palate away from sweetness. In addition, the meals are just too repetitive, and I found the salmon and chicken to be very bland and unappetizing. Could this not be more varied? Maybe some sardines, tuna? Finally, through NO fault of Urban Remedy, this plan made me realize I had an egg allergy.
Low Carb Bars — There are a plethora of “keto-friendly” on-the-go bars that have hit the store online and on the shelves. Before you fall for their marketing scheme, check the ingredients and calculate the net carbs per bar. Make sure the bar will fit within your calorie and net carb limits for the day. The two most common bars that can be eaten on keto, albeit sparingly, are Quest Bars and NuGo Smarte Carb Bars. Use these as a last resort if you have no other keto snacks available.
There are vegetables that are high in carbs and others low in carbs. The keto diet recommends sticking to the ones low on carbs but encourages you to eat a lot of them. Best vegetables are all green ones to make it easy. And vegetables that grow above the ground (e.g. lettuce) are always better than the ones that grow below the ground (e.g. potatoes)
Con: Results can vary depending on how much fluid you drink. By drinking more water, you dilute the concentration of ketones in the urine and thus a lower level of ketones will be detected on the strips. The strips don’t show a precise ketone level. Finally, and most importantly, as you become increasingly keto-adapted and your body reabsorbs ketones from the urine, urine strips may become unreliable, even if you’re in ketosis.
Lemon juice contains citrates (the substance that gives citrus fruits their sour taste). When you’re low on citrates, you’re at risk for kidney stones. Add the lemon juice to your kale shake or drink it in water. Try to consume at least one lemon per day (lemon juice or the fruit of the lemon).34 I also recommend taking my electrolyte mix because it contains minerals in their citric form, as in potassium citrate, helping to bind oxalate stones and neutralize uric-acid stones.35,36
In the first week, many people report headaches, mental fogginess, dizziness, and aggravation. Most of the time, this is the result of your electrolytes being flushed out, as ketosis has a diuretic effect. Make sure you drink plenty of water and keep your sodium intake up.6One of the fathers of keto, Dr. Phinney, shows that electrolyte levels (especially sodium) can become unbalanced with low carb intake.