Can I eat fruit during my fast in intermittent fasting?
Sometimes, it depends on the type of IF (intermittent fasting). If is not the same as the keto diet which restricts carbs like fruit and veggies to about 5–10% of daily food intake. A keto diet seems to end up with the same results as calorie restriction (CR) which allows the body to go into a mode of cellular repair, because CR can also cause a state of ketosis.
There are many different forms of IF. EG: You can fast from all food for 18–20 hours everyday. In this case you should try not to eat anything, including fruit. This works for some people but not everyone, and I'm not entirely convinced this type of IF provides the same healthy effects as fasting (autophagy of old or diseased cells and encouraged growth of new stem cells). This is because most of us fast every night anyway for up to 12 hours. 4-5 extras hours might not make that much difference. But I'm not a keto expert so who knows?
I lean toward the form of IF sometimes called the 5-2 Fast Diet (or 4-3). This is 2–3 days each week of calorie restriction (500 calories women/600 men) preferably in succession for greatest results, followed by healthy eating for 4-5 days. 3 days fasting each week will elicit more weight loss and put you in a higher state of ketosis. You can eat fruit if it's part of your calorie allotment. Eating all of your daily allotment in one meal is thought to be preferable because it more closely mimics true water fasting, but eating something in between like a piece of fruit won't hurt to get you over a hump. You could also try half of a avocado, or a cup of bone broth with its natural fat. This might sustain you longer, plus the added fat is great for brain function which can become foggy while fasting.
5-2 fasting can be done every week of your life for some pretty impressive health benefits. If you are loosing too much weight either eat more on eating days (make sure it's healthy, no processed foods) or switch to, or alternate weeks with, a 1-6 program. A 1-6 program could include perhaps a full water-only day with the purpose of stimulating a higher state of ketosis for greatest benefits.
If over age 70 then extra care should be given to eat more protein and fats, and a little extra weight might be protective. Studies are showing the elderly need more weight for longevity. More research is needed here.
Check out Dr. Michael Mosley's book "The Fast Diet". I am not connected with this but so-far, of all the IF and fasting mimicking books I've read, this is the best.
You might also consider a longer fast once or twice a year, especially if you have health issues. But research this so you do it safely. Hope this helpful. Best of luck to you.