This depends. If you’re on a time-restricted fast and you’re in no-eating hours, it’s best to stick to no- or low-calorie drinks like water, coffee (with no milk) and tea. If you’re on an alternate day diet or something similar, even during low calorie hours, you can technically drink whatever you’d like — but remember, this will count against your calories. Would you rather spend 100 calories on an apple or a glass of milk? It’s your call.
To keep my energy levels up during strength training, I use a couple of pre-workout supplements: For energy and pump I take Naked Energy (It’s Keto Approved), and for strength and endurance I mix in a scoop of Julian Bakery exogenous ketones. I have found that this really takes my workouts to the next level. I always suggest getting these two supplements to anyone that wants to get into keto.
What if we told you that the answer to losing weight, improving body composition, and feeling better isn’t about dieting, but instead skipping meals every once in a while? For some, intermittent fasting, or going a longer period of time — usually between 14 and 36 hours — with few to no calories, can be a lot easier than you may think. And the benefits might be worth it. If you think about it, all of us “fast” every single day — we just call it sleeping. Intermittent fasting just means extending that fasting period, and being a bit more conscious of your eating schedule overall. But is it right for you? And which method is best?

Still, it's important to note that the results of intermittent fasting are no better than a calorie-restricting diet. A 2017 study in JAMA showed that alternate-day fasting doesn't produce superior benefits for weight loss than daily calorie restriction, and similar conclusions were drawn in a 2018 study published in the American Journal of Clinical Nutrition. So if you don't think fasting is right for you, restricting calories works just as well.
A systematic review of 40 studies found that intermittent fasting was effective for weight loss, with a typical loss of 7-11 pounds over 10 weeks. [2] There was much variability in the studies, ranging in size from 4 to 334 subjects, and followed from 2 to 104 weeks. It is important to note that different study designs and methods of intermittent fasting were used, and participant characteristics differed (lean vs. obese).  Half of the studies were controlled trials comparing the fasting group to a comparison group and/or a control group (either continuous calorie restriction or usual lifestyle), with the other half examining an intermittent fasting group alone. A brief summary of their findings:
Whether you're a speedy eater who overeats before your brain gets the message that you're full or you just never seem to be satisfied, IF might help. “When you're not eating all the time, your hunger hormones don't need to be released that often,” says Jubilee. “The body gets in a better hormonal balance, which enables you to get a grasp on your appetite.”
Fasting is often used as a tool to make a political statement, to protest, or to bring awareness to a cause. A hunger strike is a method of non-violent resistance in which participants fast as an act of political protest, or to provoke feelings of guilt, or to achieve a goal such as a policy change.[citation needed] A spiritual fast incorporates personal spiritual beliefs with the desire to express personal principles, sometimes in the context of a social injustice.[17]